Can someone help me translating DelegateCommand to ReactiveCommand

[Martin H. Andersen]

I have this

 public ICommand ClosingCommand

 {

     get { return _closingCommand ?? (_closingCommand = new DelegateCommand(ExecuteClosing, CanExecuteClosing)); }

 }

  private void ExecuteClosing()

        {

            Exit();

        }

        private bool CanExecuteClosing()

        {

            var result = MessageBoxResult.None;

            if (IsDirty)

            {

                const string confirmText = "There are unsaved changes. Do you want to save your changes before exit?";

                const string header = "Save changes?";

                const MessageBoxButton button = MessageBoxButton.YesNoCancel;

                const MessageBoxImage icon = MessageBoxImage.Warning;

                result = MessageBox.Show(confirmText, header, button, icon);

                if (result == MessageBoxResult.Yes)

                    Commands.SaveCommand.Execute(null);

            }

            return result != MessageBoxResult.Cancel;

And have tried this:

CloseCommand = new ReactiveCommand(this.WhenAny(x => x.CanExecuteClosing, x => x.Value));

CloseCommand.Subscribe(x => ExecuteClosing());

but CanExecuteClosing is never executed

[Paul Betts]

Hi Martin,

I'm not exactly sure what you're trying to do here in the ReactiveCommand
constructor. What is the type of CanExecuteClosing?

It might make more sense to do:

CloseCommand = new ReactiveCommand();

CloseCommand
.Where(_ => AskUserIfWeShouldClose() == true)
.Subscribe(_ => Exit());

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Paul Betts <pa...@paulbetts.org>

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[IanYates]

Hi,

The WhenAny() method is used to monitor properties / observables for
changes - your CanExecuteClosing call is a method. I'm a little
surprised it's actually compiling without the brackets after
CanExecuteClosing in the WhenAny() call.

The guard condition that you can give to the ReactiveCommand
constructor shouldn't include blocking calls, especially those that
prompt the user. The condition could be evaluated *many* times and
you don't want that prompt being thrown up to the user over and over.

Paul's suggestion makes sense to me. It will also have the (probably
desired) effect of leaving your command available for execution, then
the Where() clause will ensure your method is called and block until
there's an answer from the user. If the user answers in the
affirmative then Where clause will let the subscription run.


On May 8, 11:05 pm, "Martin H. Andersen"

[Martin H. Andersen]

Thanks to both of you

I am using the code from this article http://www.codeproject.com/Articles/73251/Handling-a-Window-s-Closed-and-Closing-events-in-t

to handle closing of my application.

But it's not working with the code that Paul recommended. This is the code that is executed on window.closing

private static void Window_Closing(object sender, CancelEventArgs e)

        {

            ICommand closing = GetClosing(sender as Window);

            if (closing == null) return;

            if (closing.CanExecute(null))

                closing.Execute(null);

            else

            {

                ICommand cancelClosing = GetCancelClosing(sender as Window);

                if (cancelClosing != null)

                    cancelClosing.Execute(null);

                e.Cancel = true;

            }

        }

 

closing.CanExecute is always true

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Med venlig hilsen / Best regards

Martin H.  Andersen

System developer