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?

You can set InputTransparent on an element if you want it to pass input events down instead of capturing them. I don't know of a way to have a global handler - but you could create a base page class with a gesture recognizer that all of your pages inherit from. — Jason, Dec 19 '16 at 04:45

SushiHangover · Accepted Answer · 2016-12-19T06:14:22.393

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....

Implemented slight differently according to my requirements, but based on your snippets, worked like a charm, thanks! :) — alek kowalczyk, Dec 19 '16 at 18:47
This works but be aware that these locations are device dependent (have DPI) on newer devices so divide results by `Context.Resources.DisplayMetrics.Density` to get DIPs (device independent pixels) — tkefauver, Jul 31 '21 at 01:27
I meant density not device, Xam points won't match up with the touches see here for converting: https://stackoverflow.com/a/51422564/105028 — tkefauver, Jul 31 '21 at 06:48
Dont forget to register in mainActivity and AppDelegate: Xamarin.Forms.DependencyService.Register(); — innom, Feb 16 '22 at 16:04

score 3 · Answer 2 · answered Nov 10 '18 at 16:46

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();

Do you also have a working version that returns the positon and pressed state like the android one? — Gabriel Weidmann, Jul 14 '21 at 13:33

score 0 · Answer 3 · answered Oct 09 '22 at 20:14

iOS part for SushiHangover solution:

TouchCoordinatesRecognizer.cs:

public class TouchCoordinatesRecognizer : UIGestureRecognizer
{
    public override void TouchesBegan(NSSet touches, UIEvent evt)
    {
        base.TouchesBegan(touches, evt);
        SendCoords(touches);
    }

    public override void TouchesMoved(NSSet touches, UIEvent evt)
    {
        base.TouchesMoved(touches, evt);
        SendCoords(touches);
    }

    public override void TouchesEnded(NSSet touches, UIEvent evt)
    {
        base.TouchesEnded(touches, evt);
        SendCoords(touches);
    }

    public override void TouchesCancelled(NSSet touches, UIEvent evt)
    {
        base.TouchesCancelled(touches, evt);
        SendCoords(touches);
    }

    void SendCoords(NSSet touches)
    {
        foreach (UITouch touch in touches.Cast<UITouch>())
        {
            var window = UIApplication.SharedApplication.KeyWindow;
            var vc = window.RootViewController;

            AppDelegate.Current.globalTouchHandler?.Invoke(null,
                new TouchEventArgs<Point>(
                    new Point(
                        touch.LocationInView(vc.View).X,
                        touch.LocationInView(vc.View).Y)));
            return;
        }
    }
}

AppDelegate.cs:

public static AppDelegate Current { get; private set; }

public EventHandler globalTouchHandler;

public override bool FinishedLaunching(UIApplication app, NSDictionary options)
{
    Current = this;

    global::Xamarin.Forms.Forms.Init();
    LoadApplication(new App());
    var res = base.FinishedLaunching(app, options);
    app.KeyWindow.AddGestureRecognizer(new TouchCoordinatesRecognizer()); // <--
    return res;
}

GlobalTouch.cs:

public class GlobalTouch : IGlobalTouch
{
    public void Subscribe(EventHandler handler) => AppDelegate.Current.globalTouchHandler += handler;

    public void Unsubscribe(EventHandler handler) => AppDelegate.Current.globalTouchHandler -= handler;
}

Don't forget to divide x and y coordinates by DeviceDisplay.MainDisplayInfo.Density in necessary places of android and iOS parts.

Xamarin.Forms - Global tapped event on application level

3 Answers3

A generic EventArgs Class and DP Interface:

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

Android Dependency Implementation:

Usage in your Xamarin.Forms project:

Output:

Linked

Xamarin.Forms - Global tapped event on application level

3 Answers3

A generic EventArgs Class and DP Interface:

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

Android Dependency Implementation:

Usage in your Xamarin.Forms project:

Output:

Linked

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