Doubletap/click couses trouble on Android.

Problems with double click/tap on binded navigation commands.

Ex.

        public Command AddContact {
            get {
                return new Command (async () => {
                    await CoreMethods.PushPageModel<ContactPageModel> ();
                });
            }
        }

Can be reproduced in the FreshMvvmSampleApp.Droid project on Nexus 5 (lollipop) emulator (mac os x).

“Basic Navigation” -> 2x click on Quotes. Opens the Quotes page 2 times. Two pages is put on the stack, before the application navigates to the one of them. (I have the same problem on my testapp on a physical Nexus 5X)

Clicking on the ADD button (ex. on Master detail page) like a maniac, crashes the app with NullReferenceException.

[danielkatz]

I think that it’s better to generalize the problem for disabling the command during any async process by implementing AsyncCommand. There are several implementations of this pattern, we used this as a base for our solution.

[oddbear]

@danielkatz Nice. This seems like a great solution, and actually quite similar to the PR.

It has a interesting approach to solve the “sharelock” issue also (through the ExecuteSubmitAsync, CanExecuteSubmit), that is, if you press one button, then immediately another button. Therefor a shared state between the commands is needed to not allow this.

I guess the biggest difference would be that the AsyncCommand is more Xamarin.Forms focused, and probably easier and more familiar to work with. While the approach in the PR is probably easier if you need that extra level of control, or also use it outside of XF.