# .NET and More > WPF, WCF, WF >  [WPF] Checkboxes in ComboBox - display number of checked items when closed

## NickThissen

Hi,

I need to have a ComboBox that displays a list of CheckBoxes when dropped down so the user can check the relevant ones and then close it again. When closed, I want the ComboBox (the 'Text' area) to display the number of checked items (for example "Checked items: 3").

I cannot seem to figure this out... I can get the CheckBoxes in the ComboBox, that's easy enough using a DataTemplate, but then it also uses the same template for the 'selected item' and thus shows the last clicked ("selected") CheckBox in the text area. Selecting an item is actually not really defined for this ComboBox, I just need the user to check some items and be done with it, he doesn't need to select any items.

I've tried looking for solutions, and there seem to be a few different solutions to having a different template for the selected item as for the dropdown items, but none seem to work for me...

The code-behind for all of my attempts is:

vb.net Code:
Imports System.Collections.ObjectModel
 Class MainWindow
     Private items As ObservableCollection(Of ComboBoxItem)
     Public Sub New()
         ' This call is required by the designer.
        InitializeComponent()
         ' Add any initialization after the InitializeComponent() call.
         items = New ObservableCollection(Of ComboBoxItem)
        For i As Integer = 1 To 5
            items.Add(New ComboBoxItem() With {.Text = "Item " & i})
        Next
         comboBox.ItemsSource = items
     End Sub
     Private ReadOnly Property CheckedItems As Integer
        Get
            Return items.Where(Function(cbi) cbi.IsChecked).Count()
        End Get
    End Property
 End Class
 Public Class ComboBoxItem
     Private _Text As String
    Public Property Text() As String
        Get
            Return _Text
        End Get
        Set(ByVal value As String)
            _Text = value
        End Set
    End Property
     Private _IsChecked As Boolean
    Public Property IsChecked() As Boolean
        Get
            Return _IsChecked
        End Get
        Set(ByVal value As Boolean)
            _IsChecked = value
        End Set
    End Property
 End Class

*Attempt 1:*
Source
My XAML code:


```
    <Window.Resources>   
        <ControlTemplate x:Key="X" TargetType="{x:Type ContentControl}">
            <CheckBox Content="{Binding Text}" IsChecked="{Binding IsChecked}" />
        </ControlTemplate>
    </Window.Resources>
    
    <Grid>
        <ComboBox Name="comboBox" VerticalAlignment="Top" Margin="10">                  
            <ComboBox.ItemTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}, Path=CheckedItems}" />
                </DataTemplate>
            </ComboBox.ItemTemplate>
            <ComboBox.ItemContainerStyle>
                <Style TargetType="{x:Type ComboBoxItem}">
                    <Setter Property="Margin" Value="5"/>
                    <Setter Property="Template" Value="{StaticResource X}" />
                </Style>
            </ComboBox.ItemContainerStyle>
        </ComboBox>
    </Grid>
```

I am trying to bind the TextBlock Text property to the 'CheckedItems' property in my Window, I hope I'm not screwing that up...

Anyway, the result is a dropdown containing CheckBox items which I can check (correct), but after closing, the 'text area' remains empty. Even if I select an item (which isn't really defined for me) it displays nothing.



(Text too long, see post 2...)

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## NickThissen

*Attempt 2:*
Source
My XAML:


```
    <Window.Resources>   
        <DataTemplate x:Key="ComplexTemplate">
            <CheckBox Content="{Binding Text}" IsChecked="{Binding IsChecked}" />
        </DataTemplate>
        <ControlTemplate x:Key="SimpleTemplate">
            <TextBlock Text="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}, Path=CheckedItems}" />
        </ControlTemplate>
    </Window.Resources>
    
    <Grid>
        <ComboBox Name="comboBox" VerticalAlignment="Top" Margin="10">
            <ComboBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel>
                        <ContentControl x:Name="content" Content="{Binding}" ContentTemplate="{StaticResource ComplexTemplate}"/>
                    </StackPanel>
                    <DataTemplate.Triggers>
                        <DataTrigger Binding="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType=ComboBoxItem}}" Value="{x:Null}">
                            <Setter TargetName="content" Property="ContentTemplate" Value="{StaticResource SimpleTemplate}"/>
                        </DataTrigger>
                    </DataTemplate.Triggers>
                </DataTemplate>
            </ComboBox.ItemTemplate>
        </ComboBox>
    </Grid>
```

This produces an error as soon as I start, saying it cannot convert a ControlTemplate to a DataTemplate...


*Attempt 3:*
Finally I simply tried to bind the Text property of the ComboBox to the property in my Window (same as before), but nothing... The text area stays empty.



I'm kinda out of ideas... What else can I do? This can't be so hard?

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## Evil_Giraffe

Sounds to me like you don't actually want a ComboBox, but rather an Expander.  What you're describing is really strange behaviour for a ComboBox.  The Expander control will give you that "hiding" behaviour that you're after, without the strangeness of the ComboBox implementation.

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## Evil_Giraffe

To fix your issue with the Count of items.

First off, I took your code and removed the code behind into its own class, MainWindowViewModel.

In the constructor of the Window, I instantiated one of them and set it as the DataContext of the Window:


vbnet Code:
Class MainWindow     Public Sub New()         ' This call is required by the designer.        InitializeComponent()         Me.DataContext = New MainWindowViewModel()     End Sub End Class

Normally, you'd set the DataContext from outside the Window, but this'll do for now.

Now, our XAML looks a bit like this:



```
<Window x:Class="MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">
    <StackPanel>
        <Expander>
            <ListView ItemsSource="{Binding Items}">
                <ListView.ItemTemplate>
                    <DataTemplate>
                        <CheckBox Content="{Binding Text}" IsChecked="{Binding IsChecked}" />
                    </DataTemplate>
                </ListView.ItemTemplate>
            </ListView>
        </Expander>
        <TextBlock Text="{Binding CheckedCount}" />
    </StackPanel>
</Window>
```

(I've changed some of the property names slightly)

Now, the problem with the Binding for CheckedCount is that it needs to know when the CheckedCount property changes.  Which it can't at the moment.  So, get that ViewModel class implementing INotifyPropertyChanged so it can raise the PropertyChanged event when the items are checked on/off. But we don't yet know _that_ so let's add an event to the ComboBoxItem class that lets us know when it gets checked:


vbnet Code:
Public Class ComboBoxItem    ' ...    Private _IsChecked As Boolean    Public Property IsChecked() As Boolean        Get            Return _IsChecked        End Get        Set(ByVal value As Boolean)            _IsChecked = value            RaiseEvent IsCheckedChanged(Me, EventArgs.Empty)        End Set    End Property     Public Event IsCheckedChanged(sender As Object, eventArgs As EventArgs) End Class

That lets us hook on to the event, and raise our own event in the ViewModel:


vbnet Code:
Imports System.Collections.ObjectModelImports System.ComponentModel Public Class MainWindowViewModel    Implements INotifyPropertyChanged     Private m_items As ObservableCollection(Of ComboBoxItem)     Public Sub New()         m_items = New ObservableCollection(Of ComboBoxItem)        For i As Integer = 1 To 5            Dim comboBoxItem As New ComboBoxItem() With {.Text = "Item " & i}            AddHandler comboBoxItem.IsCheckedChanged, AddressOf Me.ComboBoxItemIsCheckedChanged             m_items.Add(comboBoxItem)        Next     End Sub     Public ReadOnly Property Items As ObservableCollection(Of ComboBoxItem)        Get            Return m_items        End Get    End Property     Public ReadOnly Property CheckedCount As Integer        Get            Return m_items.Where(Function(cbi) cbi.IsChecked).Count()        End Get    End Property     Public Event PropertyChanged(ByVal sender As Object, ByVal e As System.ComponentModel.PropertyChangedEventArgs) Implements System.ComponentModel.INotifyPropertyChanged.PropertyChanged     Private Sub ComboBoxItemIsCheckedChanged(ByVal sender As Object, ByVal eventArgs As EventArgs)        RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs("CheckedCount"))     End Sub End Class

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