I am using the MVVM Light library. From this library I use RelayCommand<T>
to define commands with an argument of type T
.
Now I have defined a RelayCommand
that requires an argument of type Nullable<bool>
:
private RelayCommand<bool?> _cmdSomeCommand;
public RelayCommand<bool?> CmdSomeCommand
{
get
{
if (_cmdSomeCommand == null)
{ _cmdSomeCommand = new RelayCommand<bool?>(new Action<bool?>((val) => { /* do work */ })); }
return _cmdSomeCommand;
}
}
How can I assign the CommandParameter from my XAML code?
I've tried to pass a boolean value, but that causes the following exception:
System.InvalidCastException: Invalid cast from 'System.Boolean' to 'System.Nullable`1[[System.Boolean, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]'.
I've also tried to define static properties containing the bool? values and reference them from XAML:
public static class BooleanHelper
{
public static bool True { get { return true; } }
public static bool False { get { return false; } }
public static bool? NullableTrue { get { return true; } }
public static bool? NullableFalse { get { return false; } }
}
XAML:
<Button Command="{Binding CmdSomeCommand}" CommandParameter="{x:Static my:BooleanHelper.NullableTrue}" />
But this causes the same exception to be thrown. I've also tried to return new Nullable<bool>(true)
, but as expected, this has the same result.
Looks like MVVM Light is at fault for handling the parameter differently between
Execute
andCanExecute
and not handling nullable in a proper way.See the code at https://github.com/paulcbetts/mvvmlight/blob/master/GalaSoft.MvvmLight/GalaSoft.MvvmLight%20(NET35)/Command/RelayCommandGeneric.cs#L198 Lines 198-205
What happens there leads to your exception and can be easily reproduced with the following code:
I suspect you can only file a bug report, because you can perfectly pass the nullable as parameter, it is handled with errors.