WPF bound ComboBox with CompositeCollection - setting SelectedItem - wpf

I have a bound WPF comboBox that has an ItemsSource set to a CompositeCollection. I'm trying this to try and accomodate adding <Select> and <Add New...> selections to precede an ObservableCollection of 'regular' objects. What I can't figure out is how to, in code-behind, select one of these added choices.
This is how I'm building the CompositeCollection:
private CompositeCollection CreateItemsSource(ObservableCollection<T> source)
{
CompositeCollection cmpc = new CompositeCollection();
cmpc.Add(new ComboBoxItem { Content = "<Select>" });
cmpc.Add(new ComboBoxItem { Content = "<Add New...>" });
var cc1 = new CollectionContainer { Collection = source };
cmpc.Add(cc1);
return cmpc;
}
This is what the ComboBox looks like:
<DataTemplate x:Key="LookupComboTemplate">
<TextBlock Text="{Binding}"/>
</DataTemplate>
<ComboBox ItemsSource="{Binding SubCategories.ItemsSource}"
ItemTemplate="{StaticResource LookupComboTemplate}">
<ComboBox.SelectedItem>
<Binding Path="SourceData.SubCategoryObj" Mode="TwoWay"></Binding>
</ComboBox.SelectedItem>
</ComboBox>
I've got a situation where SelectedItem SourceData.SubCategoryObj is null (it's an optional property). In this case, I want to manually select and display the <Select> choice. But no matter what I do (setting SelectedIndex is ignored, setting SelectedValue to the ComboBoxItem in the CompositeCollection is ignored) I get a blank ComboBox when it renders.
I'd appreciate any advice on how I can do this.
Thanks!
Corey.

You should be able to fix this with a custom valueconverter for your SelectedItem binding. http://wpftutorial.net/ValueConverters.html should give you some pointers.
I'm not sure if combox wants a simple string or some composite object but you can check that. Something like
public class ComboConverter: IValueConverter
{
public object Convert(object value, Type targetType,
object parameter, System.Globalization.CultureInfo culture)
{
if (value == null)
return "<Select>";
return value;
}
public object ConvertBack(object value, Type targetType,
object parameter, System.Globalization.CultureInfo culture)
{
if (value.toString().Equals("<Select>")
return null;
return value;
}
should give you the "<Select>" entry if the selected item is null.

Related

Wpf combobox selected item not working

I have two object: UserDto and RoleDto. User has a property which is the RoleDto.
In my viewmodel I have the following:
public UserDto User
{
get { return _user; }
set
{
if (_user == value) return;
_user = value;
User.PropertyChanged += UserPropertyChanged;
OnPropertyChanged("User");
}
}
private UserDto _user;
public IEnumerable<RoleDto> Roles { get; set; } //I load all available roles in here
In the view, I want to select the role that the user belongs. This is how I define the combobox in the view:
<ComboBox Grid.Row="3" Grid.Column="1" Margin="5" ItemsSource="{Binding Roles}" SelectedItem="{Binding User.Role, Mode=TwoWay, ValidatesOnDataErrors=True, UpdateSourceTrigger=PropertyChanged}" DisplayMemberPath="Description" />
If I try to create a new user and select a role from the combobox, it is correctly binded to the user. The problem is that when I load a user that already exists, the role is not displayed in the combobox (even the user has a role defined).
Any help please?
Thanks in advance
This is because the reference of RoleDTO that your UserDTO has, does not match any of the RoleDTOs in Roles collection which you set as ItemsSource of ComboBox.
Better define a property on your ViewModel like
public RoleDTO SelectedRole
{
get { return Roles.FirstOrDefault(role => role.Role == User.RoleDto.Role); }
set { User.RoleDto = value; OnPropertyChanged("SelectedRole"); }
}
and set it as SelectedItem of you combobox
ItemsSource="{Binding Roles}" SelectedItem="{Binding SelectedRole, Mode=TwoWay, ValidatesOnDataErrors=True, UpdateSourceTrigger=PropertyChanged}" DisplayMemberPath="Description" />
In my opinion the second option on this page is the easiest way.
https://rachel53461.wordpress.com/2011/08/20/comboboxs-selecteditem-not-displaying/
You can override the equals property on your object so that it returns true if the items have the same data. Then when the combo box box goes to check to make sure your item is in the selection it will find a match.
The other way to solve this problem is using Converter on Binding. when you use binding to bind SelectedItem, WPF will check the reference of SelectedItem against all objects inside ItemsSource property and of course if there was no match, SelectedItem will be empty. using Converter you can tell WPF that how it should match SelectedItem.
In this case you just need find SelectedItem among ItemsSource and return it to Binding. so follow these steps:
1- Create a class and implement IValueConverter. It has two methods: Convert and ConvertBack
2- for Convert method do something like this:
public class MySelecteItemBindingConverter : IValueConverter
{
public object Convert(object value, Type targetType,
object parameter, CultureInfo culture)
{
var mySelectedItem = value as MySelectedItemType;
var myItemsSource = parameter as List<MySelectedItemType>;
var matchedItem = myItemsSource.FirstOrDefault(i=>i.Id == mySelectedItem.Id);
return matchedItem;
}
public object ConvertBack(object value, Type targetType,
object parameter, CultureInfo culture)
{
// Do just like Convert method
}
}
3- Use this Converter on your Binding like this:
var myBinding = new Binding("YourBindingPath");
myBinding.Converter = new MySelectedItemBindingConverter();
myBinding.ConverterParameter = myItemsSource; //this is List<MySelectedItemType> in this example
myCombo.SetBinding(ComboBox.SelectedItemProperty, myBinding);
Note: if you want to do binding from XAML you can not pass ConverterParameter like this, instead you should create a static list and use that as ItemsSource or use MultiBinding to pass your ConverterParameter using a trick. here there is a good and simple explanation about it: Binding ConverterParameter

How can I switch out one UserControl for another during runtime within a Window in WPF?

I have a portion of a Window that should display one of several UserControls. Each UserControl presents the same data, only in a different format, arrangement, and style. The particular UserControl that will be presented in this section of the Window should be determined by a single setting that is stored in the ViewModel of the Window.
How can I make it so that the program end user can change the UserControl that is displayed in the Window at run-time?
I figured it out. In my ViewModel, I have a UserControl property called SelectedUC, and another property, called Style, that is an enum type, which enumerates the different UserControls that I am using. In the set part of the Style property I have OnPropertyChanged("SelectedUC"); The get part of the SelectedUC property has a switch-case statement that sets the field of the SelectedUC to a new instance of the corresponding type of UserControl and passes the ViewModel (this) as a parameter.
private MyStyleEnum _style = MyStyleEnum.OneStyle;
public MyStyleEnum Style
{
get { return _style; }
set
{
if (value != _style)
{
_style = value;
OnPropertyChanged("Style");
OnPropertyChanged("SelectedUC");
}
}
}
private UserControl _selectedUC;
public UserControl SelectedUC
{
get
{
switch (Style)
{
case MyStyleEnum.OneStyle:
_selectedUC = new ucOneControl(this);
break;
case MyStyleEnum.AnotherStyle:
_selectedUC = new ucAnotherControl(this);
break;
}
return _selectedUC;
}
set { _selectedUC = value; }
}
In my MainView's xaml, I have a ContentPresenter with the Content property bound to the SelectedUC property in the ViewModel.
<ContentPresenter Content="{Binding SelectedUC}" />
In my SettingsView's xaml, I have a group of RadioButtons that are all bound to the Style property and use a Converter and ConverterParameter.
<Window x:Class="MyProject.View.SettingsView"
xmlns:cv="clr-namespace:MyProject.Converters"
xmlns:vm="clr-namespace:MyProject.ViewModel">
<Window.Resources>
<cv:EnumToBoolConverter x:Key="EBConverter"/>
</Window.Resources>
<RadioButton Content="One" IsChecked="{Binding Path=Style, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged, Converter={StaticResource ResourceKey=EBConverter}, ConverterParameter={x:Static Member=vm:MyStyleEnum.SingleLine}}"/>
</Window>
EnumToBoolConverter.cs:
public class EnumToBoolConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
if (parameter.Equals(value))
return true;
else
return false;
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
return parameter;
}
}
One (quick but not necessarily best) way is to add a ContentControl to your window
<ContentControl Name="cc" />
Then set the content of it however you like. Eg. set it in code-behind
cc.Content = new UserControl1();

WPF - Button IsEnabled Binding Converter

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}}"/>

Silverlight Change Content Based on Control CheckState (Toggle multiple ContentPresenters)

I would like to change the content of a control based on its current CheckState (checked, unchecked, indeterminate). If possible I would like the solution to use only XAML and require no code behind.
I am wondering which control to use and how to define the multiple sets of content.
Example: A "ToggleContent" control that displays UserControl1 when the checked state is Unchecked and UserControl2 when the checked state is Checked.
The XAML might look something like this:
<ToggleContent>
<ToggleContent.ContentUnchecked>
<local:UserControl1></local:UserControl1>
</ToggleContent.ContentUnchecked>
<ToggleContent.ContentChecked>
<local:UserControl2></local:UserControl2>
</ToggleContent.ContentChecked>
</ToggleContent>
I'm not sure what "no code behind" means, but this sounds like a perfect example for using a ValueConverter and changing visibility based on the check state.
It would look something like this:
<StackPanel>
<CheckBox x:Name="MyCheckBox"/>
<local:UserControl1 Visibility="{Binding IsChecked, ElementName=MyCheckBox, Converter={StaticResource BoolToVis}, ConverterParameter=False">
<local:UserControl2 Visibility="{Binding IsChecked, ElementName=MyCheckBox, Converter={StaticResource BoolToVis}, ConverterParameter=True">
The Converter:
public class BooleanToVisibilityConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
if (value == null) return Visibility.Collapsed;
bool comparer = true;
if(parameter != null)
{
comparer = System.Convert.ToBoolean(parameter);
}
return System.Convert.ToBoolean(value) == comparer ? Visibility.Visible : Visibility.Collapsed;
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}
Here's a nice post from Jeff Wilcox on value converters
You can create a style to CheckBox or ToggleButton, replace the ContentPresenter inside the style by your UserControls and change them visibility in the CheckStates.
id create a user control based on the checkbox and use the visualstatemanager to load your controls.

Bind a Wpf HierarchicalDataTemplate ItemsSource to a CollectionViewSource in a dictionary?

I'm trying to display a Wpf Treeview with items sorted by a CollectionViewSource.
Currently, everything is working except sorting using this code in my resource dictionary:
<HierarchicalDataTemplate DataType="{x:Type books:Container}" ItemsSource="{Binding Path=Items}">
<nav:ContainerControl />
</HierarchicalDataTemplate>
What would be the syntax for changing the HierarchicalDataTemplate to bind to a CollectionViewSource that in turn pulls from the Items property?
I've tried variations of the code posted on Bea Stollnitz's blog with no success. I can't figure out how to set the source of the CollectionViewSource.
Well let me just say that I hate my proposed solution, but it does work. Perhaps a WPF guru will enlighten us both with a better alternative. Of course if you were using a ViewModel behind your view, you could simply wrap the Items property of the model with a CollectionView in the ViewModel and be done with it.
But here's another solution. Basically, your HierarchicalDataTemplate can stay as is except you would add a Converter to the Binding. I implemented the following converter and changed the XAML accordingly.
<HierarchicalDataTemplate DataType="{x:Type books:Container}"
ItemsSource="{Binding Items, Converter={x:Static local:CollectionViewConverter.Instance}}">
<nav:ContainerControl />
</HierarchicalDataTemplate>
CollectionViewConverter.cs
public class CollectionViewConverter : IValueConverter
{
public CollectionViewConverter() {}
static CollectionViewConverter(){
Instance = new CollectionViewConverter();
}
public static CollectionViewConverter Instance {
get;
set;
}
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
var view = new ListCollectionView((System.Collections.IList)value);
view.SortDescriptions.Add(new SortDescription("Name", ListSortDirection.Ascending));
return view;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
// not really necessary could just throw notsupportedexception
var view = (CollectionView)value;
return view.SourceCollection;
}
}
I did as you suggested and wrapped the Items collection with a ListCollectionView:
private SortDescription _ItemsLcvSortDesc;
private SortDescription ItemsLcvSortDesc
{
get
{
if (_ItemsLcvSortDesc == null)
_ItemsLcvSortDesc = new SortDescription("SortOrder", ListSortDirection.Ascending);
return _ItemsLcvSortDesc;
}
}
private ListCollectionView _ItemsLcv;
public ListCollectionView ItemsLcv
{
get
{
if (_ItemsLcv == null)
_ItemsLcv = CollectionViewSource.GetDefaultView(Items) as ListCollectionView;
_ItemsLcv.SortDescriptions.Add(ItemsLcvSortDesc);
return _ItemsLcv;
}
}
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