Tap Into Clickable Images with GestureRecognizer

Tappable images and icons are common in mobile applications for actions and navigation. Like many Xamarin.Forms views, the Image doesn’t have a click or tap event and must be wired up using the GestureRecognizer class. A gesture recognizer is a class that can be added to many views to respond to user interaction. It currently supports just the tap gesture. The terms click and tap are used interchangeably in mobile UI development.

First we need to start with an image on our ContentPage. The Image view holds an image for display on your page from a local or online file:

    Image image = new Image
    {
        Source = “monkey.png”,
        Aspect = Aspect.AspectFit,
        HorizontalOptions = LayoutOptions.End,
        VerticalOptions = LayoutOptions.Fill
    };

This is part of a larger example which shows the monkey image at the bottom right.

Android_Code_Completeblog

Now for the gesture recognizer.

Declare the gesture recognizer and a handler to create and manage the Tapped event, then the gesture recognizer is added to the target view, an image in this case. Change the image’s Opacity to .5 in the handler, which will fade the image slightly when tapped.

    var tapGestureRecognizer = new TapGestureRecognizer();
    tapGestureRecognizer.Tapped += (s, e) => {
        image.Opacity = .5;
    };
    image.GestureRecognizers.Add(tapGestureRecognizer);

Give that a try  so you can see that the gesture recognizer works.

An alternative implementation of GestureRecognizer uses the Command property.

    image.GestureRecognizers.Add (new TapGestureRecognizer {
       Command = new Command (()=> { /*handle tap*/ }),
    });

User feedback is a crucial concept in mobile UI development. Any time a user does something in the UI there should be some subtle acknowledgment by the app. A tap, for instance, should respond to the user with visible feedback. Usually an image will gray out or have a white background for a sec when touched. Let’s do that professionally using the image’s Opacity property but adding async/await to create a slight delay in our fade without affecting the app’s performance.

Replace the Tapped handler with this one that will cause the image to fade slightly for a fraction of a second. Remember to add using System.Threading.Tasks; to the top of your file for async/await.

  tapGestureRecognizer.Tapped +=  async (sender, e) =>
        {
            image.Opacity = .5;
            await Task.Delay(200);
            image.Opacity = 1;
        };

Tapping on the image will now fade the image slightly, then back to normal, providing a responsive user experience.

In your own projects you’ll use gesture recognizers (and async/await) to actually do something when an image is tapped. If you want to see async/await in action in this example, bump up the Delay to 2000, then try and do something else in your app (like tap another button, for example) and and you’ll see that the app is still responsive. You could do many things in this Tapped handler without interrupting the flow of the app. Often when a button or image is pressed, the result should be backgrounded using async/await for an optimal user experience.

Check out this free GitHub example here. Check out my book that all this is based on here.

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