WPF ListView Control

We build framework, you build application.

This should be the motto for Microsoft, and any framework provider. But thing is different in WPF world, try google how many people are working so hard to make ListView header click sortable.

I don’t like code behind, the classic event hook up isn’t a clean solution at all. There are a few smart guys using attached property to implement this sort feature, xaml can be much simpler, and we can slowly build our own WPF framewrok extension. (?)

The idea can be found from this post, but the attached source code are missing, this post uses same technology with full version of source code. In fact, I think Thomas’ solution is better, he is using a technique called Adorner, which is cleaner than the other one using switching template. The only part I don’t like is the extra GridViewSort.PropertyName in his xmal to set the sorting property name. Why not just use the native binding name? like this:

propertyName = ((System.Windows.Data.Binding)headerClicked.Column.DisplayMemberBinding).Path.Path;

That’s for click-header-sorting.

How about double-click to trigger event/command in view model? Check this post.

Is there an open source project somewhere called WPF contrib? Yes, check out the WPF tool kit on codeplex, at least the click-header-sorting is supported, including some other fancy feature, such as the alternate row color.

Popup messagebox in ViewModel

Very interesting topic, Jeremy’s IMessageBoxService idea is very easy to handle, unit-test. The pain is have to inject this IMessageBox to every class needed.

Glenn Block’s suggestion is using event handler, code can be a little bit cleanner. Test is a little bit harder.

[Test]
 public void should_validate_new_mail_role_and_raise_show_message_event()
 {
    var subscriber = MockRepository.GenerateMock<IEventSubscriber>();
     _emailRoleMaintViewModel.ShowMessageEvent
     += new System.EventHandler<EventArgs<string>>(subscriber.Handler);

     subscriber.Expect(x=>x.Handler( _emailRoleMaintViewModel, new EventArgs<string>("") ))
     .IgnoreArguments();

     _emailRoleMaintViewModel.AddEmailRole("");

     subscriber.VerifyAllExpectations();

 }

More difficult problem is to get the confirmation from view, Glenn’s solution is ‘to raise a separate event to indicate selection which the VM subscribes to‘. Too much overkill for a simple messagebox.

Dong Scott’ s post about CancellableCommand is another option, ViewModel only focus on success logic, but give options to view to ‘cancel’ the action. The comfirmation rending and analyzing code won’t be testable then, but who cares? It’s just a messagebox.

public class CancellableCommand : RelayCommand
{

   public void Execute(object parameter)
   {
   var eventHandler = Executing;
   CancelEventArgs cancelEventArgs = new CancelEventArgs(true);
   if (eventHandler != null)
   {
     eventHandler(parameter, cancelEventArgs);
   }

   if (cancelEventArgs.Cancel) return;

    _execute(parameter);
   }

    public event CancelEventHandler Executing;

}

[Test]
 public void should_stop_if_view_cancel()
 {
 var subscriber = MockRepository.GenerateMock<IEventSubscriber<CancelEventArgs>>();
 _emailRoleMaintViewModel.DeleteCommandObject.Executing +=
 new CancelEventHandler(subscriber.Handler);

 subscriber.Expect(x => x.Handler(_emailRoleMaintViewModel, new CancelEventArgs(true)))
 .IgnoreArguments();

 _emailRoleMaintViewModel.DeleteCommandObject.Execute("");

 subscriber.VerifyAllExpectations();
 _mockLookupProxy.AssertWasNotCalled(x => x.DeleteEmailRole(null), opt => opt.IgnoreArguments());

 }

 [Test]
 public void should_delete_if_view_did_not_cancel()
 {
 var subscriber = MockRepository.GenerateMock<IEventSubscriber<CancelEventArgs>>();
 _emailRoleMaintViewModel.DeleteCommandObject.Executing +=
 new CancelEventHandler(subscriber.Handler);

 subscriber.Expect(x => x.Handler(_emailRoleMaintViewModel, new CancelEventArgs(true)))
 .IgnoreArguments()
 .Do(new EventHandler<CancelEventArgs>(
 (o, e) => { e.Cancel = false; }
 ));

 _emailRoleMaintViewModel.DeleteCommandObject.Execute("");

 subscriber.VerifyAllExpectations();
 _mockLookupProxy.AssertWasCalled(x => x.DeleteEmailRole(null), opt => opt.IgnoreArguments());
 }

    public interface IEventSubscriber<TEventArgs> where TEventArgs : EventArgs
    {
        void Handler(object sender, TEventArgs e);
    }

Twoway databinding selectedItem in WPF listbox

Found this neat feature from Jonas’ ppt. What a great feature from WPF data-binding! See page 18.