Question

I am having a problem with xaml … a button I have created is not enable. here is the xaml part:

<Button Margin="0,2,2,2" Width="70" Content="Line" 
        Command="{x:Static local:DrawingCanvas.DrawShape}"
        CommandTarget="{Binding RelativeSource={RelativeSource Mode=FindAncestor, 
            AncestorType={x:Type Window}}, Path=DrawingTarget}"
        CommandParameter="Line">           
</Button>

Before Constructor it goes:

    public static RoutedCommand DrawShape = new RoutedCommand();

in ctor I have:

this.CommandBindings.Add(new CommandBinding(DrawingCanvas.DrawShape, DrawShape_Executed, DrawShapeCanExecute));

Then I have:

private void DrawShapeCanExecute(object sender, CanExecuteRoutedEventArgs e)
{
    e.CanExecute = true;  **//Isn't this enough to make it enable?**
    en.Handled = true;

}

private void DrawShape_Executed(object sender, ExecutedRoutedEventArgs e)
{
    switch (e.Parameter.ToString())
    {
        case "Line":
            //some code here (incomplete yet)
            break;
    }

When I remove the first line (Command="{x:Static ...}") in the block it gets enable again!

Answer 1

Be sure the CanExecute property of that command is returning true. If it returns false, it automatically disables the control that utilizes that command.

Can execute should return a bool, I’m a little surprised that doesn’t give a compile error. Anyway try to change it to this.

private bool DrawShapeCanExecute(object sender, CanExecuteRoutedEventArgs e) 
{
    return true; 
}

EDIT:

Ok since you just revealed all you want is a simple button that executes a command here’s a very simple implementation copied from one of my recent projects. First define this class somewhere.

public class GenericCommand : ICommand
{
    public event EventHandler CanExecuteChanged { add{} remove{} } 

    public Predicate<object> CanExecuteFunc{ get; set; }

    public Action<object> ExecuteFunc{ get; set; }

    public bool CanExecute(object parameter)
    {
        return CanExecuteFunc(parameter);
    }

    public void Execute(object parameter)
    {
        ExecuteFunc(parameter);
    }
}

Next define a command in your view model and define both the properties I created in the generic command (it’s just the basic stuff that comes along with implementing the ICommand interface).

 public GenericCommand MyCommand { get; set; }

 MyCommand = new GenericCommand();
 MyCommand.CanExecuteFunc = obj => true;
 MyCommand.ExecuteFunc = obj => MyMethod;

 private void MyMethod(object parameter)
 {
      //define your command here
 }

Then just wire up the button to your command.

<Button Command="{Binding MyCommand}" />

If this is all too much for you (MVVM does require a little extra initial setup). You can always just do this…

<Button Click="MyMethod"/>

private void MyMethod(object sender, RoutedEventArgs e)
{
    //define your method
}