WPF Drag n drop doesn't fire CommanBinding.CanExecute - wpf

Question

Yes, I know it sounds weird, but it doesn't, the question is why, and if there's a work around. It works with everything, even when you hit PrintScreen or Pause keys, CanExecute fires. So after doing a drag drop, in order to make it fire, you have to do "something" else, like a mouse click, focus, hit a key, anything. That'll make the event fire, and allow Execute to happen. Anyway, here's my code, I know it's long, but it'll help you help me.
I found this bug in our large main project, so I simplified it to this little app to isolate the problem.
XAML:
<Window x:Class="DragNDropCommands.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Window1" Height="485" SizeToContent="Width" Loaded="Window_Loaded">
<Window.CommandBindings>
<CommandBinding Command="ApplicationCommands.New" CanExecute="NewCanExecute" Executed="NewExecuted" />
<CommandBinding Command="ApplicationCommands.Save" CanExecute="SaveCanExecute" Executed="SaveExecuted" />
<CommandBinding Command="ApplicationCommands.Undo" CanExecute="UndoCanExecute" Executed="UndoExecuted" />
<CommandBinding Command="ApplicationCommands.Redo" CanExecute="RedoCanExecute" Executed="RedoExecuted" />
</Window.CommandBindings>
<Grid Margin="8">
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
<RowDefinition Height="*" />
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto" />
<ColumnDefinition Width="Auto" />
<ColumnDefinition Width="Auto" />
<ColumnDefinition Width="Auto" />
</Grid.ColumnDefinitions>
<Button Command="ApplicationCommands.New" Grid.Row="0" Grid.Column="0" FontWeight="Bold" Content="New" Width="80" Margin="8"></Button>
<Button Command="ApplicationCommands.Save" Grid.Row="0" Grid.Column="1" FontWeight="Bold" Content="Save" Width="80" Margin="8"></Button>
<Button Command="ApplicationCommands.Undo" Grid.Row="0" Grid.Column="2" FontWeight="Bold" Content="Undo" Width="80" Margin="8"></Button>
<Button Command="ApplicationCommands.Redo" Grid.Row="0" Grid.Column="3" FontWeight="Bold" Content="Redo" Width="80" Margin="8"></Button>
<CheckBox Grid.Row="1" Grid.Column="0" Margin="8" IsChecked="{Binding Path=AllowNew, Mode=TwoWay}">Allow New</CheckBox>
<CheckBox Grid.Row="1" Grid.Column="1" Margin="8" IsChecked="{Binding Path=AllowSave}">Allow Save</CheckBox>
<CheckBox Grid.Row="1" Grid.Column="2" Margin="8" IsChecked="{Binding Path=AllowUndo}">Allow Undo</CheckBox>
<CheckBox Grid.Row="1" Grid.Column="3" Margin="8" IsChecked="{Binding Path=AllowRedo}">Allow Redo</CheckBox>
<Label x:Name="labelDrag" Grid.Row="2" Grid.Column="1" Grid.ColumnSpan="2" BorderBrush="Black" BorderThickness="1" MouseDown="Label_MouseDown"
Background="LightBlue" HorizontalContentAlignment="Center" Margin="8">Drag this label...</Label>
<Label x:Name="labelDropNew" Grid.Row="3" Grid.Column="0" Grid.ColumnSpan="2" BorderBrush="Black" BorderThickness="1" Drop="labelDropNew_Drop"
Background="LightGray" HorizontalContentAlignment="Center" Margin="8" AllowDrop="True">...here to toggle AllowNew</Label>
<Label x:Name="labelDropSave" Grid.Row="3" Grid.Column="2" Grid.ColumnSpan="2" BorderBrush="Black" BorderThickness="1" Drop="labelDropSave_Drop"
Background="LightGray" HorizontalContentAlignment="Center" Margin="8" AllowDrop="True">...here to toggle AllowSave</Label>
<ListBox x:Name="listViewLog" Grid.Row="4" Grid.ColumnSpan="4" Margin="8" Width="500">
</ListBox>
<Button Grid.Row="5" Grid.Column="1" Grid.ColumnSpan="2" Margin="8" Click="Button_Click">Clear list</Button>
</Grid>
</Window>
C#:
using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;
namespace DragNDropCommands
{
/// <summary>
/// Interaction logic for Window1.xaml
/// </summary>
public partial class Window1 : Window
{
private CommandControl commandControl = new CommandControl();
private int canExecuteCount = 1;
public Window1()
{
InitializeComponent();
}
private void Window_Loaded(object sender, RoutedEventArgs e)
{
this.DataContext = commandControl;
}
private void NewCanExecute(object sender, CanExecuteRoutedEventArgs e)
{
if (this.commandControl == null || listViewLog == null)
return;
e.CanExecute = this.commandControl.AllowNew;
listViewLog.Items.Add
(
String.Format
(
"{0} - NewCanExecute: {1} - commandControl.AllowNew: {2}",
canExecuteCount++, e.CanExecute, commandControl.AllowNew
)
);
}
private void NewExecuted(object sender, ExecutedRoutedEventArgs e)
{
MessageBox.Show("New executed");
}
private void SaveCanExecute(object sender, CanExecuteRoutedEventArgs e)
{
if (this.commandControl == null || listViewLog == null)
return;
e.CanExecute = this.commandControl.AllowSave;
listViewLog.Items.Add
(
String.Format
(
"{0} - SaveCanExecute: {1} - commandControl.AllowSave: {2}",
canExecuteCount++, e.CanExecute, commandControl.AllowSave
)
);
}
private void SaveExecuted(object sender, ExecutedRoutedEventArgs e)
{
MessageBox.Show("Save executed");
}
private void UndoCanExecute(object sender, CanExecuteRoutedEventArgs e)
{
if (this.commandControl == null || listViewLog == null)
return;
e.CanExecute = this.commandControl.AllowUndo;
listViewLog.Items.Add
(
String.Format
(
"{0} - UndoCanExecute: {1} - commandControl.AllowUndo: {2}",
canExecuteCount++, e.CanExecute, commandControl.AllowUndo
)
);
}
private void UndoExecuted(object sender, ExecutedRoutedEventArgs e)
{
MessageBox.Show("Undo executed");
}
private void RedoCanExecute(object sender, CanExecuteRoutedEventArgs e)
{
if (this.commandControl == null || listViewLog == null)
return;
e.CanExecute = this.commandControl.AllowRedo;
listViewLog.Items.Add
(
String.Format
(
"{0} - RedoCanExecute: {1} - commandControl.AllowRedo: {2}",
canExecuteCount++, e.CanExecute, commandControl.AllowRedo
)
);
}
private void RedoExecuted(object sender, ExecutedRoutedEventArgs e)
{
MessageBox.Show("Redo executed");
}
private void Button_Click(object sender, RoutedEventArgs e)
{
listViewLog.Items.Clear();
}
private void Label_MouseDown(object sender, MouseButtonEventArgs e)
{
Label label = (Label)sender;
if(e.LeftButton == MouseButtonState.Pressed)
DragDrop.DoDragDrop(label, label, DragDropEffects.Move);
}
private void labelDropNew_Drop(object sender, DragEventArgs e)
{
this.commandControl.AllowNew = !this.commandControl.AllowNew;
}
private void labelDropSave_Drop(object sender, DragEventArgs e)
{
this.commandControl.AllowSave = !this.commandControl.AllowSave;
}
}
public class CommandControl : DependencyObject
{
public bool AllowNew
{
get { return (bool)GetValue(AllowNewProperty); }
set { SetValue(AllowNewProperty, value); }
}
// Using a DependencyProperty as the backing store for AllowNew. This enables animation, styling, binding, etc...
public static readonly DependencyProperty AllowNewProperty =
DependencyProperty.Register("AllowNew", typeof(bool), typeof(CommandControl), new UIPropertyMetadata(false));
public bool AllowSave
{
get { return (bool)GetValue(AllowSaveProperty); }
set { SetValue(AllowSaveProperty, value); }
}
// Using a DependencyProperty as the backing store for AllowSave. This enables animation, styling, binding, etc...
public static readonly DependencyProperty AllowSaveProperty =
DependencyProperty.Register("AllowSave", typeof(bool), typeof(CommandControl), new UIPropertyMetadata(false));
public bool AllowUndo
{
get { return (bool)GetValue(AllowUndoProperty); }
set { SetValue(AllowUndoProperty, value); }
}
// Using a DependencyProperty as the backing store for AllowUndo. This enables animation, styling, binding, etc...
public static readonly DependencyProperty AllowUndoProperty =
DependencyProperty.Register("AllowUndo", typeof(bool), typeof(CommandControl), new UIPropertyMetadata(false));
public bool AllowRedo
{
get { return (bool)GetValue(AllowRedoProperty); }
set { SetValue(AllowRedoProperty, value); }
}
// Using a DependencyProperty as the backing store for AllowRedo. This enables animation, styling, binding, etc...
public static readonly DependencyProperty AllowRedoProperty =
DependencyProperty.Register("AllowRedo", typeof(bool), typeof(CommandControl), new UIPropertyMetadata(false));
}
}
You should be able to just copy paste and do a few name changes (files, namespaces) to get it running. I'd really love your help since this has been driving me nuts, and now that I finally discover the reason for the bug, I don't know what to do about it.
Any suggestion is really apreciatted.
Thanks in advance.

Answer 1

Just a quick suggestion:
You could use CommandManager.InvalidateRequerySuggested() in the drag and drop event handler to force the reexecution of CanExecute(). (Link)