How to handle Checkbox Checked/Unchecked event with Command in ViewModel in Silverlight?

Question

I have a view (X.Xaml) which has some controls, including a CheckBox.

When I check the CheckBox it should make a session True and when I uncheck it, it has to make the session False.

If I do it in the X.Xaml.cs code-behind, it would be easy but I want my code to be clean.

Is there anyway to use Command and handle it in ViewModel side?

Answer 1

To answer your question: yes, there is.

You have to create Command class implementing ICommand:

public class MyCommand : ICommand
{
    Action<bool> _action;
    public MyCommand(Action<bool> action)
    {
        _action = action;
    }

    public bool CanExecute(object parameter)
    {
        return true;
    }

    public event System.EventHandler CanExecuteChanged;

    public void Execute(object parameter)
    {
        _action((bool)parameter);
    }
}

then in your ViewModel create the command itself:

private MyCommand simpleCommand;
public MyCommand SimpleCommand
{
    get { return simpleCommand; }
    set { simpleCommand = value; }
}

public MainViewModel()
{
    SimpleCommand = new MyCommand(new Action<bool>(DoSomething));
}

public void DoSomething(bool isChecked)
{
    //something
}

And bind your Checkbox command to it, and the CommandParameter to Checkbox.IsChecked

<CheckBox Name="checkBox1" Command="{Binding Path=SimpleCommand}" CommandParameter="{Binding ElementName=checkBox1, Path=IsChecked}" />

But that's a bit exaggerated. You're probably better off creating respective bool property in the ViewModel, bind to it and invoke required code within the accessor.

Answer 2

Why can't you simply create a TwoWay-Binding on the IsChecked-Property to a ViewModel-Property and react on that property change?

in the viewModel:

private bool _IsSessionEnabled;
public bool IsSessionEnabled
{
    get { return _IsSessionEnabled; }
    set {
        if (_IsSessionEnabled != value) {
            _IsSessionEnabled = value;
            this.OnPropertyChanged();
            this.switchSession(value); /* this is your session code */
        }
    }
}

and in the view:

<CheckBox IsChecked={Binding IsSessionEnabled, Mode=TwoWay}
          Content="Session active" />

It would be even cleaner to respond on the Property Change in your own OnPropertyChanged implementation before (or after, as you like) raising the event.