Question

My EventToCommand definition contains some sophisticated CommandParameter which I want to be automatically updated (make binding value up-to-date) when event is fired. Is there any way to achieve this behaviour using EventToCommand?

Update. I have a CommandParameter binding which is bound to ElementName and has ValueConverter. ValueConverter retrieves mouse position:

Mouse.GetPosition(element)

So ValueConverter should be updated right before command is executed.

I know PassEventArgsToCommand could solve this problem, but I don’t like this solution.

Answer 1

I have downloaded MVVM Light source code and introduced UpdateCommandParameterBeforeExecuting which being set to true explicitly updates CommandParameterProperty before command executing.

Here is source code:

...
/// <summary>
/// Specifies whether CommandParameter property should be updated before Command execution
/// </summary>
public bool UpdateCommandParameterBeforeExecuting
{
    get; 
    set; 
}
...
protected override void Invoke(object parameter)
{
    ...
    var command = GetCommand();

    if (UpdateCommandParameterBeforeExecuting)
    {
        BindingOperations.GetBindingExpression(this, CommandParameterProperty).UpdateTarget();
    }

    var commandParameter = CommandParameterValue;
    ...
}
...