I am trying to find a simple example where the enums are shown as is. All examples I have seen tries to add nice looking display strings but I don't want that complexity.
Basically I have a class that holds all the properties that I bind, by first setting the DataContext to this class, and then specifying the binding like this in the xaml file:
<ComboBox ItemsSource="{Binding Path=EffectStyle}"/>
But this doesn't show the enum values in the ComboBox as items.
You can do it from code by placing the following code in Window Loaded event handler, for example:
yourComboBox.ItemsSource = Enum.GetValues(typeof(EffectStyle)).Cast<EffectStyle>();
If you need to bind it in XAML you need to use ObjectDataProvider to create object available as binding source:
<Window x:Class="YourNamespace.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:System="clr-namespace:System;assembly=mscorlib"
xmlns:StyleAlias="clr-namespace:Motion.VideoEffects">
<Window.Resources>
<ObjectDataProvider x:Key="dataFromEnum" MethodName="GetValues"
ObjectType="{x:Type System:Enum}">
<ObjectDataProvider.MethodParameters>
<x:Type TypeName="StyleAlias:EffectStyle"/>
</ObjectDataProvider.MethodParameters>
</ObjectDataProvider>
</Window.Resources>
<Grid>
<ComboBox ItemsSource="{Binding Source={StaticResource dataFromEnum}}"
SelectedItem="{Binding Path=CurrentEffectStyle}" />
</Grid>
</Window>
Draw attention on the next code:
xmlns:System="clr-namespace:System;assembly=mscorlib"
xmlns:StyleAlias="clr-namespace:Motion.VideoEffects"
Guide how to map namespace and assembly you can read on MSDN.
I like for all objects that I'm binding to be defined in my ViewModel, so I try to avoid using <ObjectDataProvider> in the xaml when possible.
My solution uses no data defined in the View and no code-behind. Only a DataBinding, a reusable ValueConverter, a method to get a collection of descriptions for any Enum type, and a single property in the ViewModel to bind to.
When I want to bind an Enum to a ComboBox the text I want to display never matches the values of the Enum, so I use the [Description()] attribute (from System.ComponentModel) to give it the text that I actually want to see in the ComboBox. If I had an enum of days of the week, it would look something like this:
public enum DayOfWeek
{
// add an optional blank value for default/no selection
[Description("")]
NOT_SET = 0,
[Description("Sunday")]
SUNDAY,
[Description("Monday")]
MONDAY,
...
}
First I created helper class with a couple methods to deal with enums. One method gets a description for a specific value, the other method gets all values and their descriptions for a type.
public static class EnumHelper
{
public static string Description(this Enum value)
{
var attributes = value.GetType().GetField(value.ToString()).GetCustomAttributes(typeof(DescriptionAttribute), false);
if (attributes.Any())
return (attributes.First() as DescriptionAttribute).Description;
// If no description is found, the least we can do is replace underscores with spaces
// You can add your own custom default formatting logic here
TextInfo ti = CultureInfo.CurrentCulture.TextInfo;
return ti.ToTitleCase(ti.ToLower(value.ToString().Replace("_", " ")));
}
public static IEnumerable<ValueDescription> GetAllValuesAndDescriptions(Type t)
{
if (!t.IsEnum)
throw new ArgumentException($"{nameof(t)} must be an enum type");
return Enum.GetValues(t).Cast<Enum>().Select((e) => new ValueDescription() { Value = e, Description = e.Description() }).ToList();
}
}
Next, we create a ValueConverter. Inheriting from MarkupExtension makes it easier to use in XAML so we don't have to declare it as a resource.
[ValueConversion(typeof(Enum), typeof(IEnumerable<ValueDescription>))]
public class EnumToCollectionConverter : MarkupExtension, IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
return EnumHelper.GetAllValuesAndDescriptions(value.GetType());
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
return null;
}
public override object ProvideValue(IServiceProvider serviceProvider)
{
return this;
}
}
My ViewModel only needs 1 property that my View can bind to for both the SelectedValue and ItemsSource of the combobox:
private DayOfWeek dayOfWeek;
public DayOfWeek SelectedDay
{
get { return dayOfWeek; }
set
{
if (dayOfWeek != value)
{
dayOfWeek = value;
OnPropertyChanged(nameof(SelectedDay));
}
}
}
And finally to bind the ComboBox view (using the ValueConverter in the ItemsSource binding)...
<ComboBox ItemsSource="{Binding Path=SelectedDay, Converter={x:EnumToCollectionConverter}, Mode=OneTime}"
SelectedValuePath="Value"
DisplayMemberPath="Description"
SelectedValue="{Binding Path=SelectedDay, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
To implement this solution you only need to copy my EnumHelper class and EnumToCollectionConverter class. They will work with any enums. Also, I didn't include it here, but the ValueDescription class is just a simple class with 2 public object properties, one called Value, one called Description. You can create that yourself or you can change the code to use a Tuple<object, object> or KeyValuePair<object, object>
For those who wanted to see the ValueDescription class:
public class ValueDescription
{
public object Value {get; set};
public object Description {get; set};
}
I used another solution using MarkupExtension.
I made class which provides items source:
public class EnumToItemsSource : MarkupExtension
{
private readonly Type _type;
public EnumToItemsSource(Type type)
{
_type = type;
}
public override object ProvideValue(IServiceProvider serviceProvider)
{
return Enum.GetValues(_type)
.Cast<object>()
.Select(e => new { Value = (int)e, DisplayName = e.ToString() });
}
}
That's almost all... Now use it in XAML:
<ComboBox DisplayMemberPath="DisplayName"
ItemsSource="{persons:EnumToItemsSource {x:Type enums:States}}"
SelectedValue="{Binding Path=WhereEverYouWant}"
SelectedValuePath="Value" />
Change 'enums:States' to your enum
Use ObjectDataProvider:
<ObjectDataProvider x:Key="enumValues"
MethodName="GetValues" ObjectType="{x:Type System:Enum}">
<ObjectDataProvider.MethodParameters>
<x:Type TypeName="local:ExampleEnum"/>
</ObjectDataProvider.MethodParameters>
</ObjectDataProvider>
and then bind to static resource:
ItemsSource="{Binding Source={StaticResource enumValues}}"
based on this article
Nick's answer has really helped me, but I realised it could be tweaked slightly, to avoid an extra class, ValueDescription.
I remembered that there exists a KeyValuePair class already in the framework, so this can be used instead.
The code changes only slightly :
public static IEnumerable<KeyValuePair<string, string>> GetAllValuesAndDescriptions<TEnum>() where TEnum : struct, IConvertible, IComparable, IFormattable
{
if (!typeof(TEnum).IsEnum)
{
throw new ArgumentException("TEnum must be an Enumeration type");
}
return from e in Enum.GetValues(typeof(TEnum)).Cast<Enum>()
select new KeyValuePair<string, string>(e.ToString(), e.Description());
}
public IEnumerable<KeyValuePair<string, string>> PlayerClassList
{
get
{
return EnumHelper.GetAllValuesAndDescriptions<PlayerClass>();
}
}
and finally the XAML :
<ComboBox ItemSource="{Binding Path=PlayerClassList}"
DisplayMemberPath="Value"
SelectedValuePath="Key"
SelectedValue="{Binding Path=SelectedClass}" />
I hope this is helpful to others.
You'll need to create an array of the values in the enum, which can be created by calling System.Enum.GetValues(), passing it the Type of the enum that you want the items of.
If you specify this for the ItemsSource property, then it should be populated with all of the enum's values. You probably want to bind SelectedItem to EffectStyle (assuming it is a property of the same enum, and contains the current value).
There are many excellent answers to this question and I humbly submit mine. I find that mine is somewhat simpler and more elegant. It requires only a value converter.
Given an enum...
public enum ImageFormat
{
[Description("Windows Bitmap")]
BMP,
[Description("Graphics Interchange Format")]
GIF,
[Description("Joint Photographic Experts Group Format")]
JPG,
[Description("Portable Network Graphics Format")]
PNG,
[Description("Tagged Image Format")]
TIFF,
[Description("Windows Media Photo Format")]
WDP
}
and a value converter...
public class ImageFormatValueConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value is ImageFormat format)
{
return GetString(format);
}
return null;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value is string s)
{
return Enum.Parse(typeof(ImageFormat), s.Substring(0, s.IndexOf(':')));
}
return null;
}
public string[] Strings => GetStrings();
public static string GetString(ImageFormat format)
{
return format.ToString() + ": " + GetDescription(format);
}
public static string GetDescription(ImageFormat format)
{
return format.GetType().GetMember(format.ToString())[0].GetCustomAttribute<DescriptionAttribute>().Description;
}
public static string[] GetStrings()
{
List<string> list = new List<string>();
foreach (ImageFormat format in Enum.GetValues(typeof(ImageFormat)))
{
list.Add(GetString(format));
}
return list.ToArray();
}
}
resources...
<local:ImageFormatValueConverter x:Key="ImageFormatValueConverter"/>
XAML declaration...
<ComboBox Grid.Row="9" ItemsSource="{Binding Source={StaticResource ImageFormatValueConverter}, Path=Strings}"
SelectedItem="{Binding Format, Converter={StaticResource ImageFormatValueConverter}}"/>
View model...
private ImageFormat _imageFormat = ImageFormat.JPG;
public ImageFormat Format
{
get => _imageFormat;
set
{
if (_imageFormat != value)
{
_imageFormat = value;
OnPropertyChanged();
}
}
}
Resulting combobox...
It works very nice and simple.
xaml
<ComboBox ItemsSource="{Binding MyEnumArray}">
.cs
public Array MyEnumArray
{
get { return Enum.GetValues(typeof(MyEnum)); }
}
All the above posts have missed a simple trick. It is possible from the binding of SelectedValue to find out how to populate the ItemsSource AUTOMAGICALLY so that your XAML markup is just.
<Controls:EnumComboBox SelectedValue="{Binding Fool}"/>
For example in my ViewModel I have
public enum FoolEnum
{
AAA, BBB, CCC, DDD
};
FoolEnum _Fool;
public FoolEnum Fool
{
get { return _Fool; }
set { ValidateRaiseAndSetIfChanged(ref _Fool, value); }
}
ValidateRaiseAndSetIfChanged is my INPC hook. Yours may differ.
The implementation of EnumComboBox is as follows but first I'll need a little helper to get my enumeration strings and values
public static List<Tuple<object, string, int>> EnumToList(Type t)
{
return Enum
.GetValues(t)
.Cast<object>()
.Select(x=>Tuple.Create(x, x.ToString(), (int)x))
.ToList();
}
and the main class ( Note I'm using ReactiveUI for hooking property changes via WhenAny )
using ReactiveUI;
using ReactiveUI.Utils;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Reactive.Linq;
using System.Windows;
using System.Windows.Documents;
namespace My.Controls
{
public class EnumComboBox : System.Windows.Controls.ComboBox
{
static EnumComboBox()
{
DefaultStyleKeyProperty.OverrideMetadata(typeof(EnumComboBox), new FrameworkPropertyMetadata(typeof(EnumComboBox)));
}
protected override void OnInitialized( EventArgs e )
{
base.OnInitialized(e);
this.WhenAnyValue(p => p.SelectedValue)
.Where(p => p != null)
.Select(o => o.GetType())
.Where(t => t.IsEnum)
.DistinctUntilChanged()
.ObserveOn(RxApp.MainThreadScheduler)
.Subscribe(FillItems);
}
private void FillItems(Type enumType)
{
List<KeyValuePair<object, string>> values = new List<KeyValuePair<object,string>>();
foreach (var idx in EnumUtils.EnumToList(enumType))
{
values.Add(new KeyValuePair<object, string>(idx.Item1, idx.Item2));
}
this.ItemsSource = values.Select(o=>o.Key.ToString()).ToList();
UpdateLayout();
this.ItemsSource = values;
this.DisplayMemberPath = "Value";
this.SelectedValuePath = "Key";
}
}
}
You also need to set the style correctly in Generic.XAML or your box won't render anything and you will pull your hair out.
<Style TargetType="{x:Type local:EnumComboBox}" BasedOn="{StaticResource {x:Type ComboBox}}">
</Style>
and that is that. This could obviously be extended to support i18n but would make the post longer.
Universal apps seem to work a bit differently; it doesn't have all the power of full-featured XAML. What worked for me is:
I created a list of the enum values as the enums (not converted to
strings or to integers) and bound the ComboBox ItemsSource to that
Then I could bind the ComboBox ItemSelected to my public property
whose type is the enum in question
Just for fun I whipped up a little templated class to help with this and published it to the MSDN Samples pages. The extra bits let me optionally override the names of the enums and to let me hide some of the enums. My code looks an awful like like Nick's (above), which I wish I had seen earlier.
If you are binding to an actual enum property on your ViewModel, not a int representation of an enum, things get tricky. I found it is necessary to bind to the string representation, NOT the int value as is expected in all of the above examples.
You can tell if this is the case by binding a simple textbox to the property you want to bind to on your ViewModel. If it shows text, bind to the string. If it shows a number, bind to the value. Note I have used Display twice which would normally be an error, but it's the only way it works.
<ComboBox SelectedValue="{Binding ElementMap.EdiDataType, Mode=TwoWay}"
DisplayMemberPath="Display"
SelectedValuePath="Display"
ItemsSource="{Binding Source={core:EnumToItemsSource {x:Type edi:EdiDataType}}}" />
Greg
public class EnumItemsConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (!value.GetType().IsEnum)
return false;
var enumName = value.GetType();
var obj = Enum.Parse(enumName, value.ToString());
return System.Convert.ToInt32(obj);
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
return Enum.ToObject(targetType, System.Convert.ToInt32(value));
}
}
You should extend Rogers and Greg's answer with such kind of Enum value converter, if you're binding straight to enum object model properties.
I liked tom.maruska's answer, but I needed to support any enum type which my template might encounter at runtime. For that, I had to use a binding to specify the type to the markup extension. I was able to work in this answer from nicolay.anykienko to come up with a very flexible markup extension which would work in any case I can think of. It is consumed like this:
<ComboBox SelectedValue="{Binding MyEnumProperty}"
SelectedValuePath="Value"
ItemsSource="{local:EnumToObjectArray SourceEnum={Binding MyEnumProperty}}"
DisplayMemberPath="DisplayName" />
The source for the mashed up markup extension referenced above:
class EnumToObjectArray : MarkupExtension
{
public BindingBase SourceEnum { get; set; }
public override object ProvideValue(IServiceProvider serviceProvider)
{
IProvideValueTarget target = serviceProvider.GetService(typeof(IProvideValueTarget)) as IProvideValueTarget;
DependencyObject targetObject;
DependencyProperty targetProperty;
if (target != null && target.TargetObject is DependencyObject && target.TargetProperty is DependencyProperty)
{
targetObject = (DependencyObject)target.TargetObject;
targetProperty = (DependencyProperty)target.TargetProperty;
}
else
{
return this;
}
BindingOperations.SetBinding(targetObject, EnumToObjectArray.SourceEnumBindingSinkProperty, SourceEnum);
var type = targetObject.GetValue(SourceEnumBindingSinkProperty).GetType();
if (type.BaseType != typeof(System.Enum)) return this;
return Enum.GetValues(type)
.Cast<Enum>()
.Select(e => new { Value=e, Name = e.ToString(), DisplayName = Description(e) });
}
private static DependencyProperty SourceEnumBindingSinkProperty = DependencyProperty.RegisterAttached("SourceEnumBindingSink", typeof(Enum)
, typeof(EnumToObjectArray), new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.Inherits));
/// <summary>
/// Extension method which returns the string specified in the Description attribute, if any. Oherwise, name is returned.
/// </summary>
/// <param name="value">The enum value.</param>
/// <returns></returns>
public static string Description(Enum value)
{
var attrs = value.GetType().GetField(value.ToString()).GetCustomAttributes(typeof(DescriptionAttribute), false);
if (attrs.Any())
return (attrs.First() as DescriptionAttribute).Description;
//Fallback
return value.ToString().Replace("_", " ");
}
}
Simple and clear explanation:
http://brianlagunas.com/a-better-way-to-data-bind-enums-in-wpf/
xmlns:local="clr-namespace:BindingEnums"
xmlns:sys="clr-namespace:System;assembly=mscorlib"
...
<Window.Resources>
<ObjectDataProvider x:Key="dataFromEnum" MethodName="GetValues"
ObjectType="{x:Type sys:Enum}">
<ObjectDataProvider.MethodParameters>
<x:Type TypeName="local:Status"/>
</ObjectDataProvider.MethodParameters>
</ObjectDataProvider>
</Window.Resources>
...
<Grid>
<ComboBox HorizontalAlignment="Center" VerticalAlignment="Center" MinWidth="150"
ItemsSource="{Binding Source={StaticResource dataFromEnum}}"/>
</Grid>
Using ReactiveUI, I've created the following alternate solution. It's not an elegant all-in-one solution, but I think at the very least it's readable.
In my case, binding a list of enum to a control is a rare case, so I don't need to scale the solution across the code base. However, the code can be made more generic by changing EffectStyleLookup.Item into an Object. I tested it with my code, no other modifications are necessary. Which means the one helper class could be applied to any enum list. Though that would reduce its readability - ReactiveList<EnumLookupHelper> doesn't have a great ring to it.
Using the following helper class:
public class EffectStyleLookup
{
public EffectStyle Item { get; set; }
public string Display { get; set; }
}
In the ViewModel, convert the list of enums and expose it as a property:
public ViewModel : ReactiveObject
{
private ReactiveList<EffectStyleLookup> _effectStyles;
public ReactiveList<EffectStyleLookup> EffectStyles
{
get { return _effectStyles; }
set { this.RaiseAndSetIfChanged(ref _effectStyles, value); }
}
// See below for more on this
private EffectStyle _selectedEffectStyle;
public EffectStyle SelectedEffectStyle
{
get { return _selectedEffectStyle; }
set { this.RaiseAndSetIfChanged(ref _selectedEffectStyle, value); }
}
public ViewModel()
{
// Convert a list of enums into a ReactiveList
var list = (IList<EffectStyle>)Enum.GetValues(typeof(EffectStyle))
.Select( x => new EffectStyleLookup() {
Item = x,
Display = x.ToString()
});
EffectStyles = new ReactiveList<EffectStyle>( list );
}
}
In the ComboBox, utilise the SelectedValuePath property, to bind to the original enum value:
<ComboBox Name="EffectStyle" DisplayMemberPath="Display" SelectedValuePath="Item" />
In the View, this allows us to bind the original enum to the SelectedEffectStyle in the ViewModel, but display the ToString() value in the ComboBox:
this.WhenActivated( d =>
{
d( this.OneWayBind(ViewModel, vm => vm.EffectStyles, v => v.EffectStyle.ItemsSource) );
d( this.Bind(ViewModel, vm => vm.SelectedEffectStyle, v => v.EffectStyle.SelectedValue) );
});
I'm adding my comment (in VB, sadly, but the concept can be easily replicated over to C# in a heartbeat), because I just had to reference this and didn't like any of the answers as they were too complex. It shouldn't have to be this difficult.
So I came up with an easier way. Bind the Enumerators to a Dictionary. Bind that dictionary to the Combobox.
My combobox:
<ComboBox x:Name="cmbRole" VerticalAlignment="Stretch" IsEditable="False" Padding="2"
Margin="0" FontSize="11" HorizontalAlignment="Stretch" TabIndex="104"
SelectedValuePath="Key" DisplayMemberPath="Value" />
My code-behind. Hopefully, this helps someone else out.
Dim tDict As New Dictionary(Of Integer, String)
Dim types = [Enum].GetValues(GetType(Helper.Enumerators.AllowedType))
For Each x As Helper.Enumerators.AllowedType In types
Dim z = x.ToString()
Dim y = CInt(x)
tDict.Add(y, z)
Next
cmbRole.ClearValue(ItemsControl.ItemsSourceProperty)
cmbRole.ItemsSource = tDict
I wouldn't recommend implementing this as it is but hopefully this can inspire a good solution.
Let's say your enum is Foo. Then you can do something like this.
public class FooViewModel : ViewModel
{
private int _fooValue;
public int FooValue
{
get => _fooValue;
set
{
_fooValue = value;
OnPropertyChange();
OnPropertyChange(nameof(Foo));
OnPropertyChange(nameof(FooName));
}
}
public Foo Foo
{
get => (Foo)FooValue;
set
{
_fooValue = (int)value;
OnPropertyChange();
OnPropertyChange(nameof(FooValue));
OnPropertyChange(nameof(FooName));
}
}
public string FooName { get => Enum.GetName(typeof(Foo), Foo); }
public FooViewModel(Foo foo)
{
Foo = foo;
}
}
Then on Window.Load method you can load all enums to an ObservableCollection<FooViewModel> which you can set as the DataContext of the combobox.
I just kept it simple. I created a list of items with the enum values in my ViewModel:
public enum InputsOutputsBoth
{
Inputs,
Outputs,
Both
}
private IList<InputsOutputsBoth> _ioTypes = new List<InputsOutputsBoth>()
{
InputsOutputsBoth.Both,
InputsOutputsBoth.Inputs,
InputsOutputsBoth.Outputs
};
public IEnumerable<InputsOutputsBoth> IoTypes
{
get { return _ioTypes; }
set { }
}
private InputsOutputsBoth _selectedIoType;
public InputsOutputsBoth SelectedIoType
{
get { return _selectedIoType; }
set
{
_selectedIoType = value;
OnPropertyChanged("SelectedIoType");
OnSelectionChanged();
}
}
In my xaml code I just need this:
<ComboBox ItemsSource="{Binding IoTypes}" SelectedItem="{Binding SelectedIoType, Mode=TwoWay}">
<Window.Resources>
<ObjectDataProvider x:Key="DiaryTypeEnum"
MethodName="GetValues" ObjectType="{x:Type System:Enum}">
<ObjectDataProvider.MethodParameters>
<x:Type TypeName="z:Enums+DiaryType"/>
</ObjectDataProvider.MethodParameters>
</ObjectDataProvider>
</Window.Resources>
...
<ComboBox ItemsSource="{Binding Source={StaticResource DiaryTypeEnum}}" SelectedItem="{x:Static z:Enums+DiaryType.Defect}" />
Where z its xmlns:z="clr-namespace:ProjName.Helpers"
My Enum into static class
public static class Enums
{
public enum DiaryType
{
State,
Defect,
Service,
Other
}
public enum OtherEnumOrMethods
{
//TODO
}
}
Nick's solution can be simplified more, with nothing fancy, you would only need a single converter:
[ValueConversion(typeof(Enum), typeof(IEnumerable<Enum>))]
public class EnumToCollectionConverter : MarkupExtension, IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
var r = Enum.GetValues(value.GetType());
return r;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
return null;
}
public override object ProvideValue(IServiceProvider serviceProvider)
{
return this;
}
}
You then use this wherever you want your combo box to appear:
<ComboBox ItemsSource="{Binding PagePosition, Converter={converter:EnumToCollectionConverter}, Mode=OneTime}" SelectedItem="{Binding PagePosition}" />
here is my short answer.
public enum Direction { Left, Right, Up, Down };
public class Program
{
public Direction ScrollingDirection { get; set; }
public List<string> Directions { get; } = new List<string>();
public Program()
{
loadListDirection();
}
private void loadListDirection()
{
Directions.AddRange(Enum.GetNames(typeof(Direction)));
}
}
And Xaml:
<ComboBox SelectedIndex="0" ItemsSource="{Binding Path=Directions, Mode=OneWay}" SelectedItem="{Binding Path=ScrollingDirection, Mode=TwoWay}"/>
Good Luck!
I have several Tiles (TileLayoutControl Class) in my xaml (only shown 2 in this example) whose Visibility are binded to Boolean Properties and converted through BooleanToVisibilityConverter.
This works just fine. My question is
Can I bind the visibility to the Command instead so that I can remove the need of those several Boolean Properties?
Something like binding the Visibility to Command.CanExecute
If Yes, How can I achieve that? Any help will be really appreciated! Thanks.
<dxlc:Tile Command="{Binding Tile1Command}"
Visibility="{Binding Path=IsTile1Visible , Converter={StaticResource BooleanToVisibilityConverter}}"/>
<dxlc:Tile Command="{Binding Tile2Command}"
Visibility="{Binding Path=IsTile2Visible , Converter={StaticResource BooleanToVisibilityConverter}}"/>
ViewModel
private bool _isTile1Visible;
public bool IsTile1Visible
{
get { return _isTile1Visible; }
set { this.RaiseAndSetIfChanged(ref _isTile1Visible, value); }
}
public ReactiveCommand Tile1Command { get; private set; }
Tile1Command = new ReactiveCommand();
Tile1Command.Subscribe(p => PerformTile1Operation());
Yes, just use RxUI bindings:
<dxlc:Tile x:Name="Tile1" />
Then in your View constructor (make sure to implement IViewFor<Tile1ViewModel> to get this extension):
this.BindCommand(ViewModel, x => x.Tile1Command);
this.WhenAnyObservable(x => x.ViewModel.Tile1Command.CanExecuteObservable)
.BindTo(this, x => x.Tile1.Visibility);
You could also solve this in the ViewModel level, though that's not what I would do - in the ViewModel ctor:
Tile1Command = new ReactiveCommand(/* ... */);
Tile1Command
.Select(x => x ? Visibility.Visible : Visibility.Collapsed)
.ToProperty(this, x => x.Tile1Visibility, out tile1Visibility);
ReactiveCommand is an ICommand implementation that is simultaneously a RelayCommand implementation...
Assume that the ReactiveCommand has been declared like this...
public ReactiveCommand FileCommand { get; private set; }
...and has been instantiated in a View Model like this...
SomeText = "";
FileCommand = new ReactiveCommand(this.WhenAny(vm => vm.SomeText, s => !string.IsNullOrWhiteSpace(s.Value)));
FileCommand.Subscribe(param => MessageBox.Show("Processing"));
... which means if the property SomeText is empty, then the command cannot be executed, otherwise the command can be executed. And if the command is executed, a message box will get displayed.
If your objective is to simply eliminate the boolean IsTile1Visible, you can make a Xaml declaration like this...
<Button Content="File"
Command="{Binding FileCommand}"
Visibility="{Binding FileCommand, Converter={genericMvvm1:CommandToVisibilityConverter}}" />
where the visibility is bound to the same command and uses a value converter...
and the value converter looks like this...
public class CommandToVisibilityConverter : MarkupExtension, IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
try
{
ICommand iCommand = value as ICommand;
if (iCommand != null)
{
if (iCommand.CanExecute(parameter))
{
return Visibility.Visible;
}
return Visibility.Collapsed;
}
}
catch
{
}
return value;
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
return null;
}
public override object ProvideValue(IServiceProvider serviceProvider)
{
return this;
}
}
The value converter simply dereferences the command into a basic ICommand and converts it into a visibility. Note that since this converter inherits from Markup Extension, there's no need to declare it as a static resource in the Xaml's object graph.
NOTE: the same functionality can be achieved by using 'code-behind' available in ReactiveUI, but the Xaml/ValueConverter appeals to developers who do not want their View Models to deal explicitly with the 'Visibility' property.
You could potentially do that, but it would require subclassing the command so that it also implements INotifyPropertyChanged, and the underlying condition would need to raise PropertyChange for the CanExecute property whenever it changes.
It won't work without that, as ICommand doesn't implement INotifyPropertyChanged - it uses CanExecuteChanged instead.
Note that you could simplify the property, however, by just handling it yourself in the constructor:
// In constructor:
Tile1Command = new ReactiveCommand();
Tile1Command.Subscribe(p => PerformTile1Operation());
IReactiveObject self = this as IReactiveObject;
Tile1Command.CanExecuteChanged += (o,e) => self.RaisePropertyChanged(new PropertyChangedEventArgs("IsTile1Visible"));
Then your property becomes:
// Use command directly here...
public bool IsTile1Visible
{
get { return Tile1Command.CanExecute; }
}
My ViewModel class has a child property of type 'Messages' that has an indexed property, like:
public class ViewModel
{
// ...
public Messages Messages
{
get
{
if (_messages == null)
{
LoadMessagesAsync();
_messages = new Messages();
}
return _messages;
}
set
{
_messages = values;
PropertyChanged(new PropertyChangedArgs("Messages");
}
}
// ...
private void LoadMessagesAsync()
{
// Do the service call
Messages = theResult;
}
}
public class Messages
{
// ...
public String this[String name]
{
get { return _innerDictionary[name]; }
}
// ...
}
I don't think I need to fill in the rest of the gaps as it is all straight-forward.
The problem I am having is that the binding is not updating when I set the Messages property to a new object. Here is how I am referencing the property in XAML (with ViewModel as the DataContext):
<TextBlock Text="{Binding Messages[HelloWorld]}" />
It was my assumption that the binding would update when the PropertyChanged event was raised for the "Messages" property.
I've read elsewhere that my Messages class should raise a PropertyChanged event with either an empty string (""), "Item[]" or "Item["+name+"]" for the property name. However, since I am completely replacing the Messages object, this won't work as I never actually change the contents.
How do I make this work?
UPDATE
So I've done some digging into the behavior and into the BCL source code to see what's expected as a way to figure out how to make my code work. What I've learned is two-fold:
First, Silverlight data-binding is actually looking at the return object from the Messages property as the source of the binding. So raising PropertyChanged from ViewModel (sender is ViewModel) is not handled by the binding. I actually have to raise the event from the Messages class.
This is no different than using the following: Text={Binding Messages.HelloWorld}"
The reason that Myles' code work is that 'Data' returns 'this' so the binding is fooled into treating the parent class as the binding source.
That said, even if I make it so my child object raises the event, it still won't work. This is because the binding uses the System.Windows.IndexerListener as the binding target. In the SourcePropertyChanged method, the listener checks if the property name is "Item[]" but takes no action. The next statement delegates to the PropertyListener which checks the property name and only handles the event if it is equal to "Item[HelloWorld]".
So, unless I explicitly raise the event for each possible value within my collection, the UI will never update. This is disappointing because other articles and posts indicate that "Item[]" should work but looking at the source proves otherwise.
Nevertheless, I still hold out hope that there is a way to accomplish my goals.
OK the underlying problem here is that the Binding does not have a Path specified, therefore, the binding framework does not know which property name to look out for when handling PropertyChanged events. So I have fabricated a Path for the binding in order for change notification to work.
I have wrote the following code that proves the indexer binding is refreshed when the actual underlying dictionary changes:
ViewModel
public class BindingTestViewModel : AppViewModelBase, IBindingTestViewModel
{
private Dictionary<string, object> _data = new Dictionary<string, object>();
public BindingTestViewModel()
{
_data.Add("test","1");
_data.Add("test2", "21");
}
public object this[string index]
{
get
{
return _data[index];
}
set
{
_data[index] = value;
NotifyOfPropertyChange(() => Data);
}
}
public object Data
{
get
{
return this;
}
}
public void Refresh()
{
_data = new Dictionary<string, object>
{
{"test", "2"}, {"test2", "22"}
};
NotifyOfPropertyChange(() => Data);
}
}
My XAML:
<navigation:Page.Resources>
<Converters:IndexConverter x:Name="IndexConverter"></Converters:IndexConverter>
</navigation:Page.Resources>
<Grid x:Name="LayoutRoot">
<TextBox Height="23"
HorizontalAlignment="Left"
Margin="288,206,0,0"
Name="textBox1"
Text="{Binding Path=Data,Converter={StaticResource IndexConverter},ConverterParameter=test}"
VerticalAlignment="Top" Width="120" />
<Button x:Name="ReloadDict" Click="ReloadDict_Click" Width="50" Height="30" Content="Refresh" VerticalAlignment="Top"></Button>
</Grid>
The converter:
public class IndexConverter : IValueConverter
{
public object Convert(object value, Type targetType,
object parameter, CultureInfo culture)
{
var vm = value as BindingTestViewModel;
var index = parameter as string;
return vm[index];
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
I don't necessarily like answering my own questions but I have found a solution to my problem. I've been able to keep my original flow and address the idiosyncrocies of SL4 data-binding. And the code seems a bit cleaner, too.
What it boils down to is that I don't replace the child object anymore. That seems to be the key. Instead, I create a single instance and let that instance manage changing the internal list of items as needed. The child object notifies the parent when it has changed so the parent can raise the PropertyChanged event. The following is a brief example how I've gotten it to work:
public class ViewModel
{
// ...
public Messages Messages
{
get
{
if (_messages == null)
{
lock (_messagesLock)
{
if (_messages == null)
{
_messages = new Messages();
_messages.ListChanged += (s, e) =>
{
NotifyPropertyChanged("Messages");
};
}
}
}
return _messages;
}
}
}
public class Messages
{
// ...
public String this[String name]
{
get
{
if (_innerDictionary == null)
{
_innerDictionary = new Dictionary<String, String>();
LoadMessagesAsync();
}
return _innerDictionary[name];
}
}
// ...
private void LoadMessagesAsync()
{
// Do the service call
_innerDictionary = theResult;
NotifyListChanged();
}
// ...
public event EventHandler ListChanged;
}
For brevity, I've left out the obvious parts.
Silverlight 3 app with a TabControl bound to an ObservableCollection using an IValueConverter. Initial the binding works (converter called) on app startup. Changes, Clear() or Add(), to the bound collection are not reflected in the TabControl... converter not called.
note: the bound ListBox reflects the changes to the bound collection while the TabControl does not.
Ideas?
/jhd
The XAML binding...
<UserControl.Resources>
<local:ViewModel x:Key="TheViewModel"/>
<local:TabConverter x:Key="TabConverter" />
</UserControl.Resources>
<StackPanel DataContext="{StaticResource TheViewModel}">
<ListBox ItemsSource="{Binding Classnames}" />
<controls:TabControl x:Name="TheTabControl"
ItemsSource="{Binding Classnames, Converter={StaticResource TabConverter}, ConverterParameter=SomeParameter}"/>
<Button Click="Button_Click" Content="Change ObservableCollection" />
</StackPanel>
The ViewModel...
namespace DatabindingSpike
{
public class ViewModel
{
private ObservableCollection<string> _classnames = new ObservableCollection<string>();
public ViewModel()
{
_classnames.Add("default 1 of 2");
_classnames.Add("default 2 of 2");
}
public ObservableCollection<string> Classnames
{
get { return _classnames; }
set { _classnames = value; }
}
}
}
The converter (for completeness)...
namespace DatabindingSpike
{
public class TabConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
var source = value as ObservableCollection<string>;
if (source == null)
return null;
var param = parameter as string;
if (string.IsNullOrEmpty(param) || param != "SomeParameter")
throw new NotImplementedException("Null or unknow parameter pasased to the tab converter");
var tabItems = new List<TabItem>();
foreach (string classname in source)
{
var tabItem = new TabItem
{
Header = classname,
Content = new Button {Content = classname}
};
tabItems.Add(tabItem);
}
return tabItems;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
}
Update 8/19
The concise answer is you have to implement INotifyPropertyChanged on the view model and notify listeners when the Property/Collection is changed.
Implement INotifyPropertyChanged on the ViewModel
* implement the interface INotifyPropertyChanged
* define the event (public event PropertyChangedEventHandler PropertyChanged)
* subscribe to the CollectionChanged event (Classnames.CollectionChanged += ...)
* fire the event for listeners
Best,
/jhd
ViewModel update per above... ValueConverter now called on all changes to the Property/Collection
public class ViewModel : INotifyPropertyChanged
{
private readonly ObservableCollection<string> _classnames = new ObservableCollection<string>();
public ViewModel()
{
Classnames.CollectionChanged += Classnames_CollectionChanged;
}
public event PropertyChangedEventHandler PropertyChanged;
private void Classnames_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
NotifyPropertyChanged("Classnames");
}
private void NotifyPropertyChanged(string info)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
foreach (PropertyChangedEventHandler d in handler.GetInvocationList())
{
d(this, new PropertyChangedEventArgs(info));
}
}
}
public ObservableCollection<string> Classnames
{
get { return _classnames; }
}
}
The XAML binding...
<UserControl.Resources>
<local:ViewModel x:Key="TheViewModel"/>
<local:TabConverter x:Key="TabConverter" />
</UserControl.Resources>
<StackPanel DataContext="{StaticResource TheViewModel}">
<ListBox ItemsSource="{Binding Classnames}" />
<controls:TabControl x:Name="TheTabControl"
ItemsSource="{Binding Classnames, Converter={StaticResource TabConverter}, ConverterParameter={StaticResource TheViewModel}}"/>
<Button Click="Button_Click" Content="Change Classnames" />
</StackPanel>
The ValueConverter (basically unchanged
public class TabConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
var source = value as ObservableCollection<string>;
if (source == null)
return null;
//also sorted out the binding syntax to pass the ViewModel as a parameter
var viewModel = parameter as ViewModel;
if (viewModel == null)
throw new ArgumentException("ConverterParameter must be ViewModel (e.g. ConverterParameter={StaticResource TheViewModel}");
var tabItems = new List<TabItem>();
foreach (string classname in source)
{
// real code dynamically loads controls by name
var tabItem = new TabItem
{
Header = "Tab " + classname,
Content = new Button {Content = "Content " + classname}
};
tabItems.Add(tabItem);
}
return tabItems;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
I realize this is a slightly old question at this point, but I don't know that anyone has explained why you need to do the INotifyPropertyChanged on the bound property on your view model.
The ItemsControl itself needs to be bound to an ObservableCollection for the collection change events to cause the ItemsControl to re-evaluate. Your converter is returning a distinct List (or Observable) collection each time it is called rather than holding on to a single ObservableCollection and adding items to it. Therefore, these collections never have any of the collection changed events raised on them... they're always new, each time the binding is re-done.
Raising PropertyChanged forces the binding to be re-evaluated and re-runs your converter, returning a distinct collection and reflecting your changes.
I feel a better approach may be to do the conversion in your ViewModel rather than in a Converter. Expose an ObservableCollection of TabItem that you bind directly to and that you modify in place. The TabControl should then see changes made directly to your collection without the need to raise PropertyChanged and re-evaluate the entire binding.
[Edit - Added my approach]
ViewModel:
public class TabSampleViewModel
{
private ObservableCollection _tabItems = new ObservableCollection();
public TabSampleViewModel()
{
AddTabItem("Alpba");
AddTabItem("Beta");
}
public ObservableCollection<TabItem> TabItems
{
get
{
return _tabItems;
}
}
public void AddTabItem( string newTabItemName )
{
TabItem newTabItem = new TabItem();
newTabItem.Header = newTabItemName;
newTabItem.Content = newTabItemName;
TabItems.Add( newTabItem );
}
}
View:
<controls:TabControl ItemsSource="{Binding TabItems}"/>
Expose
public ObservableCollection<TabItem> Classnames
{
get { return _classnames; }
set { _classnames = value; }
}
If you debug the valueconverter you'll see it's not being called as often as you think it is.
The problem could be that your ValueConverter returns a List<TabItem> instead of an ObservableCollection<TabItem>. Try that one line change and see if it helps.
Well the problem is that I have this enum, BUT I don't want the combobox to show the values of the enum. This is the enum:
public enum Mode
{
[Description("Display active only")]
Active,
[Description("Display selected only")]
Selected,
[Description("Display active and selected")]
ActiveAndSelected
}
So in the ComboBox instead of displaying Active, Selected or ActiveAndSelected, I want to display the DescriptionProperty for each value of the enum. I do have an extension method called GetDescription() for the enum:
public static string GetDescription(this Enum enumObj)
{
FieldInfo fieldInfo =
enumObj.GetType().GetField(enumObj.ToString());
object[] attribArray = fieldInfo.GetCustomAttributes(false);
if (attribArray.Length == 0)
{
return enumObj.ToString();
}
else
{
DescriptionAttribute attrib =
attribArray[0] as DescriptionAttribute;
return attrib.Description;
}
}
So is there a way I can bind the enum to the ComboBox AND show it's content with the GetDescription extension method?
Thanks!
I would suggest a DataTemplate and a ValueConverter. That will let you customize the way it's displayed, but you would still be able to read the combobox's SelectedItem property and get the actual enum value.
ValueConverters require a lot of boilerplate code, but there's nothing too complicated here. First you create the ValueConverter class:
public class ModeConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter,
CultureInfo culture)
{
return ((Mode) value).GetDescription();
}
public object ConvertBack(object value, Type targetType, object parameter,
CultureInfo culture)
{
throw new NotSupportedException();
}
}
Since you're only converting enum values to strings (for display), you don't need ConvertBack -- that's just for two-way binding scenarios.
Then you put an instance of the ValueConverter into your resources, with something like this:
<Window ... xmlns:WpfApplication1="clr-namespace:WpfApplication1">
<Window.Resources>
<WpfApplication1:ModeConverter x:Key="modeConverter"/>
</Window.Resources>
....
</Window>
Then you're ready to give the ComboBox a DisplayTemplate that formats its items using the ModeConverter:
<ComboBox Name="comboBox" ...>
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Converter={StaticResource modeConverter}}"/>
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
To test this, I threw in a Label too, that would show me the actual SelectedItem value, and it did indeed show that SelectedItem is the enum instead of the display text, which is what I would want:
<Label Content="{Binding ElementName=comboBox, Path=SelectedItem}"/>
I like the way you think. But GetCustomAttributes uses reflection. What is that going to do to your performance?
Check out this post:
WPF - Displaying enums in ComboBox control
http://www.infosysblogs.com/microsoft/2008/09/wpf_displaying_enums_in_combob.html
This is how I am doing it with MVVM. On my model I would have defined my enum:
public enum VelocityUnitOfMeasure
{
[Description("Miles per Hour")]
MilesPerHour,
[Description("Kilometers per Hour")]
KilometersPerHour
}
On my ViewModel I expose a property that provides possible selections as string as well as a property to get/set the model's value. This is useful if we don't want to use every enum value in the type:
//UI Helper
public IEnumerable<string> VelocityUnitOfMeasureSelections
{
get
{
var units = new []
{
VelocityUnitOfMeasure.MilesPerHour.Description(),
VelocityUnitOfMeasure.KilometersPerHour.Description()
};
return units;
}
}
//VM property
public VelocityUnitOfMeasure UnitOfMeasure
{
get { return model.UnitOfMeasure; }
set { model.UnitOfMeasure = value; }
}
Furthermore, I use a generic EnumDescriptionCoverter:
public class EnumDescriptionConverter : IValueConverter
{
//From Binding Source
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (!(value is Enum)) throw new ArgumentException("Value is not an Enum");
return (value as Enum).Description();
}
//From Binding Target
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
if (!(value is string)) throw new ArgumentException("Value is not a string");
foreach(var item in Enum.GetValues(targetType))
{
var asString = (item as Enum).Description();
if (asString == (string) value)
{
return item;
}
}
throw new ArgumentException("Unable to match string to Enum description");
}
}
And finally, with the view I can do the following:
<Window.Resources>
<ValueConverters:EnumDescriptionConverter x:Key="enumDescriptionConverter" />
</Window.Resources>
...
<ComboBox SelectedItem="{Binding UnitOfMeasure, Converter={StaticResource enumDescriptionConverter}}"
ItemsSource="{Binding VelocityUnitOfMeasureSelections, Mode=OneWay}" />
I suggest you use a markup extension I had already posted here, with just a little modification :
[MarkupExtensionReturnType(typeof(IEnumerable))]
public class EnumValuesExtension : MarkupExtension
{
public EnumValuesExtension()
{
}
public EnumValuesExtension(Type enumType)
{
this.EnumType = enumType;
}
[ConstructorArgument("enumType")]
public Type EnumType { get; set; }
public override object ProvideValue(IServiceProvider serviceProvider)
{
if (this.EnumType == null)
throw new ArgumentException("The enum type is not set");
return Enum.GetValues(this.EnumType).Select(o => GetDescription(o));
}
}
You can then use it like that :
<ComboBox ItemsSource="{local:EnumValues local:Mode}"/>
EDIT: the method I suggested will bind to a list of string, which is not desirable since we want the SelectedItem to be of type Mode. It would be better to remove the .Select(...) part, and use a binding with a custom converter in the ItemTemplate.
Questions of using reflection and attributes aside, there are a few ways you could do this, but I think the best way is to just create a little view model class that wraps the enumeration value:
public class ModeViewModel : ViewModel
{
private readonly Mode _mode;
public ModeViewModel(Mode mode)
{
...
}
public Mode Mode
{
get { ... }
}
public string Description
{
get { return _mode.GetDescription(); }
}
}
Alternatively, you could look into using ObjectDataProvider.
I've done it like this :
<ComboBox x:Name="CurrencyCodeComboBox" Grid.Column="4" DisplayMemberPath="." HorizontalAlignment="Left" Height="22" Margin="11,6.2,0,10.2" VerticalAlignment="Center" Width="81" Grid.Row="1" SelectedValue="{Binding currencyCode}" >
<ComboBox.ItemsPanel>
<ItemsPanelTemplate>
<VirtualizingStackPanel/>
</ItemsPanelTemplate>
</ComboBox.ItemsPanel>
</ComboBox>
in code I set itemSource :
CurrencyCodeComboBox.ItemsSource = [Enum].GetValues(GetType(currencyCode))