Delegate System.Action does not take 1 arguments

Question

The action :

readonly Action _execute;

public RelayCommand(Action execute)
             : this(execute, null)
{
}

public RelayCommand(Action execute, Func<Boolean> canExecute)
{
    if (execute == null)
        throw new ArgumentNullException("execute");
    _execute = execute;
    _canExecute = canExecute;
}

Other class's code:

public void CreateCommand()
{
    RelayCommand command = new RelayCommand((param)=> RemoveReferenceExcecute(param));}
}

private void RemoveReferenceExcecute(object param)
{
    ReferenceViewModel referenceViewModel = (ReferenceViewModel) param;
    ReferenceCollection.Remove(referenceViewModel);
}

Why do I get the following exception, how can I fix it?

Delegate 'System.Action' does not take 1 arguments

Answer 1

System.Action is a delegate for parameterless function. Use System.Action<T>.

To fix this, replace your RelayAction class with something like the following

class RelayAction<T> {
    readonly Action<T> _execute;
    public RelayCommand(Action<T> execute, Func<Boolean> canExecute){
        //your code here
    }
    // the rest of the class definition
}

Note RelayAction class should become generic. Another way is to directly specify the type of parameter _execute will receive, but this way you'll be restricted in usage of your RelayAction class. So, there are some tradeoff between flexibility and robustness.

Some MSDN links:

1. System.Action
2. System.Action<T>

Answer 2

You can define your command 'RemoveReferenceExcecute' without any parameters

RelayCommand command = new RelayCommand(RemoveReferenceExcecute);}

or you can pass some parameters / objects into it:

RelayCommand<object> command = new RelayCommand<object>((param)=> RemoveReferenceExcecute(param));}

In the second case do not forget to pass CommandParameter from your view;