I have a combo which is bound to a list of statuses:
public enum Status
{
[Description(#"Ready")]
Ready,
[Description(#"Not Ready")]
NotReady
}
I am using a converter to display the the description of the enum in the combo box, which is based on the example here: https://stackoverflow.com/a/3987099/283787
public class EnumConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value == null)
{
return DependencyProperty.UnsetValue;
}
var description = GetDescription((Enum)value);
return description;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
var enumValue = GetValueFromDescription(value.ToString(), targetType);
return enumValue;
}
...
I am binding to the combox box in the view:
<ComboBox
ItemsSource="{Binding Statuses}"
SelectedItem="{Binding SelectedStatus, Converter={StaticResource EnumConverter}}">
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Path=., Converter={StaticResource EnumConverter}}" />
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
My view model contains the following:
public ObservableCollection<Status> Statuses { get; set; } = new ObservableCollection<Status>(new List<Status> { Status.Ready, Status.NotReady });
private Status selectedStatus = Status.Ready;
public Status SelectedStatus
{
get
{
return this.selectedStatus;
}
set
{
this.selectedStatus = value;
this.NotifyPropertyChanged(nameof(this.SelectedStatus));
}
}
Problem
The combo is empty when the view model displays.
I am unable to set the SelectedStatus from view model, even if I set the binding Mode=TwoWay.
How do I successfully selected an item in the combo on start up and from the view model?
Don't use a converter for the SelectedItem binding:
<ComboBox
ItemsSource="{Binding Statuses}"
SelectedItem="{Binding SelectedStatus}">
...
The SelectedItem property should be bound to a Status source property provided that the ItemsSource property is bound to an ObservableCollection<Status>.
Related
I have a binding list of Models and a DataGrid. Value can be of couple of data types (bool, double).
public class Model
{
public object Value { get; set; }
}
public void Initialize()
{
var models = new BindingList<Model>();
models.Add(new Model(){ Value = "hello"});
models.Add(new Model(){Value=true});
signals.ItemsSource = models;
}
I want to display the data in the data grid and I want to use textbox for numbers, but combo(true/false) for boolean values.So I implemented bool2string converter and DataTemplateSelector. In my example I have one text column and one template column displaying the same data. When I start the application the combo values are not initialized (nothing is selected). Once I start playing with values, everything works,the values are properly synchronized (if I change value in one column, it will propagate to the other column). Do you have any idea, what mistake I'm doing?
public class BoolToStringConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
return ((bool)value == true) ? "true" : "false";
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
var comboValue = (value as ComboBoxItem).Content.ToString();
return (String.Compare(comboValue, "true", StringComparison.InvariantCultureIgnoreCase) == 0);
}
}
public class DynamicDataTemplateSelector : DataTemplateSelector
{
public override DataTemplate SelectTemplate(object item, DependencyObject container)
{
var element = container as FrameworkElement;
var signal = item as Model;
if (element != null && signal != null)
{
if (signal.Value is bool)
return element.FindResource("BoolTemplate") as DataTemplate;
else
return element.FindResource("TextTemplate") as DataTemplate;
}
return null;
}
}
My xaml looks like following:
<Window.Resources>
<comboQuestion:DynamicDataTemplateSelector x:Key="DataTemplateSelector"/>
<comboQuestion:BoolToStringConverter x:Key="BoolToStringConverter"/>
</Window.Resources>
<Grid>
<DataGrid Grid.Row="1" Name="signals" AutoGenerateColumns="False" ItemsSource="{Binding}" >
<DataGrid.Resources>
<DataTemplate x:Key="BoolTemplate">
<ComboBox SelectedItem="{Binding Value, Converter={StaticResource BoolToStringConverter}, Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}">
<ComboBoxItem>true</ComboBoxItem>
<ComboBoxItem>false</ComboBoxItem>
</ComboBox>
</DataTemplate>
<DataTemplate x:Key="TextTemplate">
<TextBox Text="{Binding Value, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
</DataTemplate>
</DataGrid.Resources>
<DataGrid.Columns>
<DataGridTextColumn Header="TextValue" Binding="{Binding Value}"/>
<DataGridTemplateColumn Header="DynamicValue" CellTemplateSelector="{StaticResource DataTemplateSelector}"/>
</DataGrid.Columns>
</DataGrid>
</Grid>
EDIT:
I tried to change the SelectedItem to SelectedValue and I also tried to change the Convert part of the converter to:
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
var cbi = new ComboBoxItem();
cbi.Content = ((bool)value == true) ? "true" : "false";
return cbi;
}
however, the behavior remains the same.
You can convert a boolean to an index number using the following converter:
public class BooleanToIndexConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
return ((bool)value == true) ? 0 : 1;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
return ((int)value == 0) ? true : false;
}
}
Then bind to SelectedIndex on the ComboBox:
SelectedIndex="{Binding Value, Converter={StaticResource BooleanToIndexConverter}}
I have the following scenario
1- A combobox in xaml
<ComboBox
x:Name="PublishableCbo" Width="150" IsEnabled="True" HorizontalAlignment="Left" Height="20"
SelectedValue="{Binding Path=Published, Mode=TwoWay}"
Grid.Column="6" Grid.Row="0">
<ComboBox.Items>
<ComboBoxItem Content="All" IsSelected="True" />
<ComboBoxItem Content="Yes" />
<ComboBoxItem Content="No" />
</ComboBox.Items>
2- In a model class, I defined a property and bind to the selectedvalue in combobox
public bool Published
{
get
{
return _published;
}
set
{
_published = value;
OnPropertyChanged("Published");
}
}
I know I have to implement a converter, but don't know exactly how. What I want is when a select Yes/No, in the model get a True/false value, when "all" is selected, to get null value.
In order to be able to assign null to the Published property, you would have to change its type to Nullable< bool > (you can write bool? in C#).
public bool? Published
{
...
}
The Converter could be implemented so that it converts from string to bool and vice versa, perhaps like shown below. Note that the converter uses bool, not bool? since the value is passed to and from the converter as object, and hence boxed anyway.
public class YesNoAllConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
object result = "All";
if (value is bool)
{
result = (bool)value ? "Yes" : "No";
}
return result;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
object result = null;
switch ((string)value)
{
case "Yes":
result = true;
break;
case "No":
result = false;
break;
}
return result;
}
}
To enable the use of this converter, you have to change your ComboBox item type to string, and bind to the SelectedItem property, not SelectedValue.
<ComboBox SelectedItem="{Binding Path=Published, Mode=TwoWay,
Converter={StaticResource YesNoAllConverter}}">
<sys:String>All</sys:String>
<sys:String>Yes</sys:String>
<sys:String>No</sys:String>
</ComboBox>
where sys is the following xml namespace declaration:
xmlns:sys="clr-namespace:System;assembly=mscorlib"
I have an ObservableCollection<MyEntity> and MyEntity has a IsChecked property with a PropertyChanged event.
I have a Button and I would like to change IsEnabled property to true when at least one of MyEntity of the MyObservableCollection is checked.
I created a converter which takes the ObservableCollection and return true when a MyEntity is checked at least.
But the return "null" is returned.
What is wrong ? Thank you for your help.
XAML
<Window.Resources>
<CollectionViewSource x:Key="MyObservableCollection"/>
<src:MyConverter x:Key="MyConverter"/>
</Window.Resources>
<Button IsEnabled="{Binding Converter={StaticResource MyConverter}, Source={StaticResource MyObservableCollection}}"/>
C# Converter
class MyConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (null == value)
return "null";
ReadOnlyObservableCollection<object> items = (ReadOnlyObservableCollection<object>)value;
List<MyEntity> myEntities = (from i in items select (MyEntity)i).ToList();
foreach (MyEntity entity in myEntities)
{
if (entity.IsChecked)
{
return true;
}
}
return false;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new System.NotImplementedException();
}
}
I think your Binding is wrong. The Converter want's the underlying collection not the CollectionView. And set the CollectionViewSource.Source after InitializeComponent(), the Binding will be refreshed.
<Button IsEnabled="{Binding Path=SourceCollection,
Converter={StaticResource MyConverter},
Source={StaticResource MyObservableCollection}}" />
Since StaticResources are resolved at the time of intializing itself i.e. at the time of InitializeComponent() but till that time your collection is yet not intialized that's why null value is passed to the converter.
So, better choice would be to move that property in your code behind and bind to that property since binding will be resloved after InitializeComponent(). Create property in your code-behind-
public CollectionViewSource MyObservableCollection { get; set; }
and bind to your button -
<Button IsEnabled="{Binding MyObservableCollection, RelativeSource=
{RelativeSource AncestorType=Window}, Converter={StaticResource MyConverter}}"/>
Well I was wondering how to bind a boolean property to a combobox.Combobox will be a yes/no combobox.
You could use a ValueConverter to convert the boolean value to a ComboBox index and back. Like this:
public class BoolToIndexConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
return ((bool)value == true) ? 0 : 1;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
return ((int)value == 0) ? true : false;
}
}
}
Assuming Yes is on index 0 and No on index 1. Then you'd have to use that converter in binding to the SelectedIndex property. For this, you declare your converter in your resources section:
<Window.Resources>
<local:BoolToIndexConverter x:Key="boolToIndexConverter" />
</Window.Resources>
Then you use it in your binding:
<ComboBox SelectedIndex="{Binding YourBooleanProperty, Converter={StaticResource boolToIndexConverter}}"/>
I have found myself using the IsSelected property of the ComboBox items for this in the past. This method is entirely in xaml.
<ComboBox>
<ComboBoxItem Content="No" />
<ComboBoxItem Content="Yes" IsSelected="{Binding YourBooleanProperty, Mode=OneWayToSource}" />
</ComboBox>
First solution is to replace your 'Yes/No' combobox with a checkbox because, well, checkbox exists for a reason.
Second solution is to fill your combobox with true and false objects and then bind the 'SelectedItem' of your combobox to your Boolean property.
Here is an example (replace enabled/disabled with yes/no):
<ComboBox SelectedValue="{Binding IsEnabled}">
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Converter={x:Static converters:EnabledDisabledToBooleanConverter.Instance}}"/>
</DataTemplate>
</ComboBox.ItemTemplate>
<ComboBox.Items>
<system:Boolean>True</system:Boolean>
<system:Boolean>False</system:Boolean>
</ComboBox.Items>
</ComboBox>
Here is Converter:
public class EnabledDisabledToBooleanConverter : IValueConverter
{
private const string EnabledText = "Enabled";
private const string DisabledText = "Disabled";
public static readonly EnabledDisabledToBooleanConverter Instance = new EnabledDisabledToBooleanConverter();
private EnabledDisabledToBooleanConverter()
{
}
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
return Equals(true, value)
? EnabledText
: DisabledText;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
//Actually won't be used, but in case you need that
return Equals(value, EnabledText);
}
}
And no need to play with indices.
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))