Combobox manually setting Text property doesn't work
Since xceed wpf toolkit doesnt work for me, I am trying to create a custom multi selection ComboBox using C# and WPF, by populating a ComboBox with Checkboxes and setting their width property so that the dropdown wont close, and using the Content property for the label.
Given the selection is multiple and not for one item, I want to set the text of the ComboBox to be something like "X selected" where X represents the number of checked items in the ComboBox.
Before even getting to the stage where I figure out how many items are checked, I tried to manually set the text of the ComboBox programmatically using event handlers (CheckBoxClosed & SelectionChanged) but the text of the Checkbox remains empty.
The code is part of a bigger project, so I cant really paste all of it here, but the bindings work properly as you can see in the image.
Can anybody tell me if there is something I'm missing on how to change the text of the ComboBox?
I even tried:
following the
ComboBox.ItemTemplatestructure as you can see in the .xaml.cs below.setting the
SelectedValueandSelectedItemproperties.
xaml:
<ComboBox ItemsSource="{Binding ParameterValueList, UpdateSourceTrigger=LostFocus}"
DropDownClosed="ComboBox_DropDownClosed"
LostFocus="ComboBox_DropDownClosed"
SelectionChanged="ComboBox_SelectionChanged"
>
<ComboBox.ItemTemplate>
<DataTemplate>
<CheckBox
Content="{Binding ValueToString}"
Width="250"
IsChecked="{Binding IsChecked, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}" />
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
xaml.cs
public partial class MainView : Window
{
private IEventAggregator \_eventAggregator;
public MainView(MainViewViewModel vm, IEventAggregator eventAggregator)
{
InitializeComponent();
_eventAggregator = eventAggregator;
vm.OnRequestClose += (s, e) => this.Close();
DataContext = vm;
}
private void ComboBox_DropDownClosed(object sender, System.EventArgs e)
{
(sender as ComboBox).Text = "test closed";
//(sender as ComboBox).SelectedValue = new CheckBox()
//{
// IsChecked = true,
// Content = "test closed"
//};
//string text = (sender as ComboBox).Text;
}
private void ComboBox_SelectionChanged(object sender, System.Windows.Controls.SelectionChangedEventArgs e)
{
(sender as ComboBox).Text = "test changed";
//(sender as ComboBox).SelectedItem = new CheckBox()
//{
// IsChecked = true,
// Content = "test Selected"
//};
//(sender as ComboBox).IsDropDownOpen = true;
//string text = (sender as ComboBox).Text;
}
}
As I understand it, you want your custom combo box to display something different that the string representation of the selected item, and in particular to show some indication of the items that are checked. As one approach, something like this might be easier if you just make an actual CustomComboBox subclass and do all of this internally. But regardless of whether you make a custom control, one way to achieve your objective is to set the ComboBox properties to IsEditable, IsReadOnly, !Focusable and (very importantly) !IsTextSearchEnabled.
Depending on your implementation, the IsTextSearchEnabled value could explain why you're getting a blank, because by default the ComboBox will attempt to match the displayed text with an existing item. With the default value of true if the display is something like for example "[2] Dogs;Cats" then the selection will get reset to -1 and the text will disappear.
Here's the kind of thing I mean, where the check box data template is internal to the control and being checked and being selected are separate. In the list of checked items, an item that is also selected (by clicking the text portion of the combo) then it appears in [brackets]. This might not be "exactly" what you intend, but hopefully will serve as a starting point for what you're doing.
C#
class CustomComboBox : ComboBox
{
public CustomComboBox()
{
Height = 30;
Width = 150;
BorderBrush = new SolidColorBrush(Colors.Teal);
BorderThickness = new Thickness(2);
IsEditable = true;
IsReadOnly = true;
Focusable = false;
IsTextSearchEnabled = false;
ItemTemplate = CreateCheckboxTemplate();
CheckedItems.CollectionChanged += (sender, e) => Refresh(sender, null);
}
SemaphoreSlim IsRefreshing = new SemaphoreSlim(1,1);
void Refresh(object? sender, RoutedEventArgs? e)
{
if (IsRefreshing.Wait(0))
{
try
{
var countDisplay = CheckedItems.Count == 0
? string.Empty
: $"[{CheckedItems.Count}] ";
if (CheckedItems.Count == 0)
{
Text = SelectedItem?.ToString() ?? string.Empty;
}
else
{
var selectedNotChecked = string.Empty;
if (SelectedItem is not null && !CheckedItems.Contains(SelectedItem))
{
selectedNotChecked = $" : [{SelectedItem}]";
}
Text = $"{countDisplay} {string.Join(";", CheckedItems.Select(_ => localFormatItem(_)))}{selectedNotChecked}";
string localFormatItem(object item)
{
if (SelectedItem == item)
{
return $"[{item?.ToString() ?? " "}]";
}
else
{
return item?.ToString() ?? string.Empty;
}
}
}
}
finally
{
IsRefreshing.Release();
}
}
}
private DataTemplate CreateCheckboxTemplate()
{
var dataTemplate = new DataTemplate(typeof(string));
var checkBoxFactory = new FrameworkElementFactory(typeof(CheckBox));
checkBoxFactory.SetBinding(ContentControl.ContentProperty, new Binding("."));
checkBoxFactory.SetValue(CheckBox.FontSizeProperty, 14.0);
checkBoxFactory.SetValue(CheckBox.ForegroundProperty, Brushes.DarkSlateBlue);
checkBoxFactory.AddHandler(CheckBox.CheckedEvent, new RoutedEventHandler(OnCheckBoxChecked));
checkBoxFactory.AddHandler(CheckBox.UncheckedEvent, new RoutedEventHandler(OnCheckBoxUnchecked));
dataTemplate.VisualTree = checkBoxFactory;
return dataTemplate;
}
private void OnCheckBoxChecked(object sender, RoutedEventArgs e)
{
if (sender is CheckBox checkbox) CheckedItems.Add(checkbox.DataContext);
}
private void OnCheckBoxUnchecked(object sender, RoutedEventArgs e)
{
if (sender is CheckBox checkbox) CheckedItems.Remove(checkbox.DataContext);
}
protected override void OnSelectionChanged(SelectionChangedEventArgs e)
{
base.OnSelectionChanged(e);
Refresh(this, new RoutedEventArgs());
}
public ObservableCollection<object> CheckedItems { get; } = new ObservableCollection<object>();
}
XAML
Since the DataTemplate is now baked into the control, all that needs to be done here is to bind the data source.
<Window x:Class="custom_combo_box.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:custom_combo_box"
mc:Ignorable="d"
Title="MainWindow" Height="300" Width="500">
<Window.DataContext>
<local:MainWindowDataContext>
</local:MainWindowDataContext>
</Window.DataContext>
<Grid>
<local:CustomComboBox x:Name="comboBox" ItemsSource="{Binding ParameterValueList}"/>
</Grid>
</Window>
Initialize with Test Values
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
comboBox.SelectionChanged += (sender, e) => Title = $"Main Window {comboBox.SelectedItem}";
#region I N I T I A L I Z E T E S T V A L U E S
// DataContext.ParameterValueList = new[] { 1, 2, 3 }; // Just testing...
DataContext.ParameterValueList = new[] { "Dogs", "Cats", "Pets"};
#endregion I N I T I A L I Z E T E S T V A L U E S
}
new MainWindowDataContext DataContext => (MainWindowDataContext)base.DataContext;
}