Casting in MVVM Light CommandParameterValue

Question

here is my Problem, I want to pass the integer 1 when this canvas is pressed. Every time I click the canvas, I get a An unhandled exception of type 'System.InvalidCastException' occurred in GalaSoft.MvvmLight.dll. Now I could make my life easier and just do the RelayCommand to accept a String instead of int but for the sake of learning. How would i go about doing it this way,

    <i:Interaction.Triggers>
   <i:EventTrigger EventName="MouseLeftButtonDown">
         <cmd:EventToCommand Command="{Binding ButtonPress}"
                 CommandParameterValue="1"
              </i:EventTrigger>
    </i:Interaction.Triggers>

Answer 1

Hi,

You just found a limitation of the generic casting. I am sorry about this. I will try to find a better way to handle simple values in a further version (maybe with some reflection to check if the Parse method is present on the type) and opened a bug in my backlog. In the mean time, please use RelayCommand and do the parsing yourself.

Cheers, Laurent

Answer 2

You can pass datatypes other than string to the command using the following syntax:

<i:EventTrigger EventName="MouseLeftButtonDown">
    <cmd:EventToCommand Command="{Binding ButtonPress}">
        <cmd:EventToCommand.CommandParameterValue>
            <s:Int32>1</s:Int32>
        </cmd:EventToCommand.CommandParameterValue>
    </cmd:EventToCommand>
</i:EventTrigger>

Add the flowing namespace declaration for s:

xmlns:s="clr-namespace:System;assembly=mscorlib"