Xamarin.Forms - Global tapped event on application level

Question

How can I intercept a tapped/clicked event on application level in an Xamarin.Forms app?

I tried on the MainPage to use something like

    <Grid.GestureRecognizers>
        <TapGestureRecognizer Command="{Binding TappedCommand}" Tapped="TapGestureRecognizer_OnTapped"></TapGestureRecognizer>
    </Grid.GestureRecognizers>

but it works only if I tap empty areas, touching a button doesn't fire the events.

Additionally I often navigate by changing the MainPage, so I would have to add such recognizer even if it worked.

I want to handle any touch/tap/click event in my app globally, is it possible in Xamarin.Forms?

Answer 1

This can be easily setup within the platform-specific apps and then use a Xamarin.Forms dependency service to subscribe/unsubscribe to the events.

What you capture within those events is up to your needs, in this example I am just capturing and eventing the x/y values.

A generic EventArgs Class and DP Interface:

public class TouchEventArgs<T> : EventArgs
{
    public T EventData { get; private set; }

    public TouchEventArgs(T EventData)
    {
        this.EventData = EventData;
    }
}

public interface IGlobalTouch
{
    void Subscribe(EventHandler handler);
    void Unsubscribe(EventHandler handler);
}

Add the following to the MainActivity of your Xamarin.Android application:

public EventHandler globalTouchHandler;
public override bool DispatchTouchEvent(MotionEvent ev)
{
    globalTouchHandler?.Invoke(null, new TouchEventArgs<Point>(new Point(ev.GetX(), ev.GetY())));
    return base.DispatchTouchEvent(ev);
}

Android Dependency Implementation:

public class GlobalTouch : IGlobalTouch
{
    public GlobalTouch() {}

    public void Subscribe(EventHandler handler)
    {
        (Forms.Context as MainActivity).globalTouchHandler += handler;
    }

    public void Unsubscribe(EventHandler handler)
    {
        (Forms.Context as MainActivity).globalTouchHandler -= handler;
    }
}

Usage in your Xamarin.Forms project:

DependencyService.Get<IGlobalTouch>().Subscribe((sender, e) =>
{
    var point = (e as TouchEventArgs<Point>).EventData;
    System.Diagnostics.Debug.WriteLine($"{point.X}:{point.Y}");
});

Note: You should be assigning a delegate so can unsubscribe...

Output:

307.628997802734:365.563842773438
309.280151367188:365.197265625
311.883605957031:365.390991210938
312.694641113281:380.148590087891
308.030578613281:387.823364257813
291.513244628906:396.339416503906
286.220489501953:396.339416503906
282.100006103516:396.339416503906

The same technique can be used for iOS, there are TouchesBegan, TouchesEnded, TouchesMoved and TouchesCancelled that you can attach to depending upon your needs....

Answer 2

Using SushiHangover resolution, for iOS, it would be something like this:

In AppDelegate.cs implement IUIGestureRecognizerDelegate

public partial class AppDelegate : global::Xamarin.Forms.Platform.iOS.FormsApplicationDelegate, IUIGestureRecognizerDelegate
{

Inside AppDelegate.cs class, in FinishedLaunching method, add this:

Xamarin.Forms.DependencyService.Register<GlobalTouch>();
bool ret = base.FinishedLaunching(app, options);
if (ret)
{
    UITapGestureRecognizer tap = new UITapGestureRecognizer(Self, new ObjCRuntime.Selector("gestureRecognizer:shouldReceiveTouch:"));
    tap.Delegate = (IUIGestureRecognizerDelegate)Self;
    app.KeyWindow.AddGestureRecognizer(tap);
}
return ret;

Add this method in AppDelegate.cs:

[Export("gestureRecognizer:shouldReceiveTouch:")]
public bool ShouldReceiveTouch(UIGestureRecognizer gestureRecognizer, UITouch touch)
{
    Xamarin.Forms.DependencyService.Get<IGlobalTouch>().TapScreen();
    return false;
}

Add this into GlobalTouch:

EventHandler globalTouchHandler;

public void TapScreen()
{
    globalTouchHandler?.Invoke(this, null);
}

Add this into IGlobalTouch:

void TapScreen();