Using commands in wpf is not working properly for a button

Question

There is a button in the following xaml code:

<Button Grid.Row="1" x:Name="First" Content="First" HorizontalAlignment="Left" VerticalAlignment="Center" Margin="40,91,0,67" />

In the constructor of the window I have assigned ApplicationCommands.Copy to the button.

public MainWindow()
{ 
    InitializeComponent();

    this.doc.Unit = DevExpress.Office.DocumentUnit.Point;

    this.First.Command = ApplicationCommands.Copy;
    First.CommandTarget = this.doc;
}

this.doc in the above code is a typical richTextBox. The problem is that the button is always disabled. Why?
The entire xaml code is as follows:

<Window
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:WpfApplication1"
    xmlns:system="clr-namespace:System;assembly=mscorlib"
    xmlns:com="clr-namespace:DevExpress.XtraRichEdit.Commands;assembly=DevExpress.RichEdit.v16.1.Core"
    xmlns:dxre="http://schemas.devexpress.com/winfx/2008/xaml/richedit" xmlns:dxe="http://schemas.devexpress.com/winfx/2008/xaml/editors" xmlns:ig="http://schemas.infragistics.com/xaml" xmlns:telerik="http://schemas.telerik.com/2008/xaml/presentation" xmlns:dx="http://schemas.devexpress.com/winfx/2008/xaml/core" x:Class="WpfApplication1.MainWindow"
    Title="MainWindow" Height="700" Width="1000" x:Name="wnd">


<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="163*"  />
        <RowDefinition Height="60*"  />
    </Grid.RowDefinitions>

    <dxre:RichEditControl x:Name="doc" Grid.Row="0" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Margin="0,0,0,23" Unit="Point" ActiveViewType="PrintLayout"/>

    <!--<telerik:RadToggleButton 
        Content="B" HorizontalAlignment="Left" Height="Auto" IsThreeState="False" IsChecked="False" Margin="10,32,0,0" Grid.Row="1" VerticalAlignment="Top" Width="26"/>-->

    <Button Grid.Row="1" x:Name="First" Content="First" HorizontalAlignment="Left" VerticalAlignment="Center" Margin="40,91,0,67" />


</Grid></Window>

Can you show all the relevant XAML? It might be that your button is in a container that is disabled for some reason. — rory.ap, Oct 02 '16 at 13:05
So when you say "disabled" do you mean "grayed out"? Or what? Even if you just have the button, it would be in at least a Window control. — rory.ap, Oct 02 '16 at 13:10
actually it is grayed and not working, it is visible. In winForms it was called disabled state. — Green Falcon, Oct 02 '16 at 13:11
Well, something you aren't showing is disabling it. We can't really help you if you aren't showing all relevant code. By default, the button would be enabled. — rory.ap, Oct 02 '16 at 13:14
Not sure. What happens if you add "Enabled=True" to the button? — rory.ap, Oct 02 '16 at 13:22
not working, I do not know the reason. it is not logical at all. the command does not work and there is no reason for that — Green Falcon, Oct 02 '16 at 13:23
http://stackoverflow.com/questions/7563666/copy-and-paste-commands-with-wpf-buttons — blins, Oct 02 '16 at 13:32
Also somewhat similar: http://stackoverflow.com/questions/7641656/how-to-bind-applicationcommands-to-a-viewmodel — blins, Oct 02 '16 at 13:34

score 2 · Accepted Answer · answered Oct 02 '16 at 13:25

The Button.Command property is a type if ICommand, which includes a CanExecute method. When this method returns false the Button will be disabled.

I believe that's what's happening here, the ApplicationCommands.Copy command is returning false for CanExecute. Perhaps someone else can offer an explanation as to why this is in this case?

Are you able to use a CommandBinding as described here to implement your own CanExecute event handler?

<Window x:Class="WCSamples.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="CloseCommand"
    Name="RootWindow"
    >
  <Window.CommandBindings>
    <CommandBinding Command="ApplicationCommands.Copy"
                    CanExecute="CanExecuteHandler"
                    />
  </Window.CommandBindings>
  <StackPanel Name="MainStackPanel">
    <Button Command="ApplicationCommands.Copy" 
            Content="Copy" />
  </StackPanel>
</Window>

private void CanExecuteHandler(object sender, CanExecuteRoutedEventArgs e)
{
    // CanExecute logic in here.
    e.CanExecute = true;
}

Using commands in wpf is not working properly for a button

1 Answers1