TapGestureRecognizer not restricting multiple rapid clicks?!

betcss

Currently with the NumberOfTapsRequired = 1 and tapping rapidly I get at least 3 pages opened in succession.

The question is how should I prevent multiple rapid clicks e.g. on an entry View - (Focused View gives the same obviously)?

Should I refer to the Lock mechanism ?

Thanks in advance.

JohnHardman

@betcss

There are various ways of doing this. The simplest is just to check whether the page is already open, and not to open it again if so. That's a solution that has appeared many times in the forum previously. See https://forums.xamarin.com/discussion/comment/210530/#Comment_210530

JohnHardman

@betcss

There are various ways of doing this. The simplest is just to check whether the page is already open, and not to open it again if so. That's a solution that has appeared many times in the forum previously. See https://forums.xamarin.com/discussion/comment/210530/#Comment_210530

Jarvan

Try to use lock statement to detect if the view has been tapped.

bool IsClicked = false;
object _lock= new object();
private void TapGestureRecognizer_Tapped(object sender, EventArgs e)
{
    lock (_lock)
    {

        if (IsClicked)
            return;
        else
            IsClicked = true;

    }
    //do the work

    IsClicked = false;
}

betcss

@Jarvan

Tried it already, it doesn't work for the rapid multi-click on an entry, at least; still opens > 1 page.

betcss

I've done something like this:

Page page = new GivenPage();

private void OnEntryChange(object sender, EventArgs e)
{
    var stack= page.Navigation.NavigationStack;

        if(stack.Count > 0)
        {
            if(stack[stack.Count - 1].GetType() != typeof(GivenPage))
            {
                   Navigation.PushAsync(new GivenPage());
            }
            return;
         }
         else
              Navigation.PushAsync(page);
}

I don't think it's correct though. I'm confused about the parent page part...

JohnHardman

@betcss

You don't need that page variable at all. Your OnEntryChange is presumably within the context of a ContentPage, so you can just use Navigation (or this.Navigation) rather than page.Navigation.

I've never needed the if(stack.Count > 0) test either, as there'd already be at least one page on the NavigationStack when called from an event handler in an existing page.

betcss

@John You're right. Can you tell me why the solution with lock statement can't work and how can I improve this even further e.g. make it faster?

Best regards.

JohnHardman

@betcss said:
@John You're right. Can you tell me why the solution with lock statement can't work and how can I improve this even further e.g. make it faster?

The "solution" with lock statements doesn't work because the "//do the work" bit would be asynchronous. Call PushAsync there and the PushAsync returns before the new page is actually displayed. The current page remains responsive for a brief period before the new one appears. Because the current page is still responsive for that brief period, the user can (accidentally or intentionally) tap the View again. That results in TapGestureRecognizer_Tapped being called again. Once the awaited PushAsync has returned, IsClicked is set to false. If timing of things happening is such that IsClicked is false when TapGestureRecognizer_Tapped is called again, another page will be pushed.

Using the test for the type of page at the top of the NavigationStack avoids this problem.

betcss

Last question: How could you make this even faster ?

JohnHardman

@betcss said:
Last question: How could you make this even faster ?

You cannot , or put another way, if you find a way, let me know :-)