Commands

Commands are supported in Catel. The base class for commands is Command.

Code snippets

Explanation

To implement commands, and still be able to unit test the view models, a separate command is introduced. This command allows a developer to implement a command that can be invoked both via code (unit testing) and UI.

There are several classes to represent a command:

The TCanExecuteParameter is the parameter that is passed to the CanExecute of the command, ands saves the developer from casting the object (as in the interface ICommand to a typed object). The same goes for TExecuteParameter which makes the Execute of the command typed.

Examples

Xaml (assuming that the view model is set as datacontext):

<Button Content="Click me" Command="{Binding MyCommand}" />

Async

Code:

private readonly IMessageService _messageService;
 
public void MyViewModel(IMessageService messageService)
{
    Argument.IsNotNull(() => messageService);
 
    _messageService = messageService;

    // Add commands
    MyAction = new TaskCommand(MyAction_ExecuteAsyc);
}

/// <summary>
/// Gets the MyAction command.
/// </summary>
public TaskCommand MyAction { get; private set; }

/// <summary>
/// Method to invoke when the MyAction command is executed.
/// </summary>
/// <param name="parameter">The parameter of the command.</param>
private async Task MyAction_ExecuteAsync(object parameter)
{
    // Show message box
    await _messageService.ShowInfoAsync("My action in MVVM");
}

Sync

Code:

private readonly IMessageService _messageService;
 
public void MyViewModel(IMessageService messageService)
{
    Argument.IsNotNull(() => messageService);
 
    _messageService = messageService;

    // Add commands
    MyAction = new Command(MyAction_Execute);
}

/// <summary>
/// Gets the MyAction command.
/// </summary>
public Command MyAction { get; private set; }

/// <summary>
/// Method to invoke when the MyAction command is executed.
/// </summary>
/// <param name="parameter">The parameter of the command.</param>
private void MyAction_Execute(object parameter)
{
    // Show message box
    _messageService.ShowInfo("My action in MVVM");
}

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