Question

I’m new to WPF so I’m not sure if what I’m doing makes any sense.. anyway: I’m trying to implement a command for a button that uses ApplicationCommands.Open.
In my XAML I have:

<Window x:Class="MainWindow"                
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"                
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"                
        xmlns:local="clr-namespace:ViewModel"                
        Title="MainWindow" Height="650" Width="1170">                
    <Window.DataContext>                
        <local:ResourceListViewModel/>                
    </Window.DataContext>

I want to have a command definition in a local:ResourceListViewModel class, so so far I got there:

void OpenCmdExecuted(object target, ExecutedRoutedEventArgs e)
        {

            MessageBox.Show("The command has been invoked");
        }

        void OpenCmdCanExecute(object sender, CanExecuteRoutedEventArgs e)
        {
            e.CanExecute = true;
        }

So what I think I must do is to bind these methods to a command, so I’m trying to do it this way:

 <Window.CommandBindings >
        <CommandBinding Command="ApplicationCommands.Open"
                  Executed="OpenCmdExecuted"
                  CanExecute="OpenCmdCanExecute"/>
    </Window.CommandBindings>

but the program is not compiling as it seems to be looking for these functions in MainWindow. How can I let the program know that my functions’ definitions are in a different class?

Answer 1

That’s not the way Commands work in MVVM. There is a difference between RoutedCommands (such as ApplicationCommands.Open, and DelegateCommands (a.k.a RelayCommands).

The first are View-related and bubble up the visual tree, etc, and have to be handled by the View in code-behind.

The second are ViewModel-related and are defined in the ViewModel (meaning the Command instance is a property member of the ViewModel itself)

public class ResourceListViewModel
{
    public RelayCommand OpenCommand {get;set;}

    public ResourceListViewModel()
    {
        OpenCommand = new RelayCommand(ExecuteOpenCommand, CanExecuteOpenCommand);
    }

    //etc etc
}