MVVCross: Pass an enum value as a CommandParameter for Android

Question

I want to pass an enum value as a CommandParameter. My enum is defined as:

public enum MyEnum
{
   One,
   Two
}

And in my axml I have:

local:MvxBind="Click MyCommand, CommandParameter=MyEnum.One"
...
local:MvxBind="Click MyCommand, CommandParameter=MyEnum.Two"

and MyCommand is defined in my ViewModel as

public IMvxCommand MyCommand
{
  get { return new MvxCommand<MyEnum>(myfunction); }
}

private void myfunction(MyEnum p_enumParam)
{
  switch (p_enumParam)
  {
      case MyEnum.One:
          doSomething1();
          break;
      case MyEnum.Two:
          doSomething2();
          break;
  }
}

When I run it, I get the error "System.InvalidCastException: Cannot cast from source type to destination type."

Obviously, because it cannot cast MyEnum.One and MyEnum.Two to the MyEnum type. So how can I convince it that MyEnum.One and MyEnum.Two are of MyEnum type?

Thanks, Pap

Answer 1

MvvmCross can't guess the type of enum from the binding statement - so it can't perform this binding.

The easiest route on this is probably to workaround this using strings instead - and you will then need to use Enum.Parse from the string to the enum in your ViewModel.

---

An alternative is that you could also implement an enum parsing ValueConverter which just parsed the string - e.g. you could base on https://github.com/MvvmCross/MvvmCross/blob/v3.1/Cirrious/Cirrious.MvvmCross.Binding/ValueConverters/MvxCommandParameterValueConverter.cs - you could add Enum.Parse to this to create:

public class MyEnumCommandValueConverter
    : MvxValueConverter<ICommand, ICommand>
{
    protected override ICommand Convert(ICommand value, System.Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return new MvxWrappingCommand(value, Enum.Parse(typeof(MyEnum), parameter.ToString()));
    }
}

You could then bind using nesting - using something like:

local:MvxBind="Click MyEnumCommand(MyCommand, 'Two')"