Question

This is not real code, I know. But it is what I would like to do.

MyBinding.CanExecute += (s, e) => 
{
    e.CanExecute = Something.Allow;
    if (!e.CanExecute)
        e.ToolTip = Something.Reason;
}

Is there a simple way to do it?

Thank you.

Answer 1

This is the best way I believe to accomplish this.

This is the Command definition:

class CustomCommand : RoutedUICommand, INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    private string m_Reason;
    public string Reason
    {
        get { return m_Reason; }
        set
        {
            if (m_Reason == value)
                return;
            m_Reason = value;
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs("Reason"));
        }
    }
}
public class MyCommands
{
    public static CustomCommand DoThis = new CustomCommand();
    public static CommandBinding DoThisBinding = new CommandBinding 
        { Command = DoThis };

    public static void SetupCommands()
    {
        DoThisBinding.CanExecute += (s, e) =>
        {
            var _Something = DoSomeTest(e.Parameter);
            e.CanExecute = _Something.Allow;     
            if (!e.CanExecute)         
                (e.Command as CustomCommand).Reason = _Something.Reason; 
        } 
    }
}

And this is the XAML implementation:

xmlns:commands="MyNamespace.WhereAreCommands"

<Button Command="{x:Static commands:MyCommands.DoThis}"
        ToolTip="{Binding Path=Reason, 
            Source={x:Static commands:MyCommands.DoThis}}">
    Click</Button>