Adding a Tap Gesture Gesture Recognizer

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last updated: 2016-01

The tap gesture is used for tap detection and is implemented with the TapGestureRecognizer class.

Overview

To make a user interface element clickable with the tap gesture, create a TapGestureRecognizer instance, handle the Tapped event and add the new gesture recognizer to the GestureRecognizers collection on the user interface element. The following code example shows a TapGestureRecognizer attached to an Image element:

var tapGestureRecognizer = new TapGestureRecognizer();
tapGestureRecognizer.Tapped += (s, e) => {
    // handle the tap
};
image.GestureRecognizers.Add(tapGestureRecognizer);

By default the image will respond to single taps. Set the NumberOfTapsRequired property to wait for a double-tap (or more taps if required).

tapGestureRecognizer.NumberOfTapsRequired = 2; // double-tap

When NumberOfTapsRequired is set above one, the event handler will only be executed if the taps occur within a set period of time (this period is not configurable). If the second (or subsequent) taps do not occur within that period they are effectively ignored and the 'tap count' restarts.

Using Xaml

A gesture recognizer can be added to a control in Xaml using attached properties. The syntax to add a TapGestureRecognizer to an image is shown below (in this case defining a double tap event):

<Image Source="tapped.jpg">
    <Image.GestureRecognizers>
        <TapGestureRecognizer
                Tapped="OnTapGestureRecognizerTapped"
                NumberOfTapsRequired="2" />
  </Image.GestureRecognizers>
</Image>

The code for the event handler (in the sample) increments a counter and changes the image from color to black & white.

void OnTapGestureRecognizerTapped(object sender, EventArgs args) {}
    tapCount++;
    var imageSender = (Image)sender;
    // watch the monkey go from color to black&white!
    if (tapCount % 2 == 0) {
        imageSender.Source = "tapped.jpg";
    } else {
        imageSender.Source = "tapped_bw.jpg";
    }
}

Using ICommand

Applications that use the Mvvm pattern typically use ICommand rather than wiring up event handlers directly. The TapGestureRecognizer can easily support ICommand either by setting the binding in code:

var tapGestureRecognizer = new TapGestureRecognizer();
tapGestureRecognizer.SetBinding (TapGestureRecognizer.CommandProperty, "TapCommand");
image.GestureRecognizers.Add(tapGestureRecognizer);

or using Xaml:

<Image Source="tapped.jpg">
    <Image.GestureRecognizers>
        <TapGestureRecognizer
            Command="{Binding TapCommand}"
            CommandParameter="Image1" />
    </Image.GestureRecognizers>
</Image>

The complete code for this view model can be found in the sample. The relevant Command implementation details are shown below:

public class TapViewModel : INotifyPropertyChanged {
    int taps = 0;
    ICommand tapCommand;
    public TapViewModel () {
        // configure the TapCommand with a method
        tapCommand = new Command (OnTapped);
    }
    public ICommand TapCommand {
        get { return tapCommand; }
    }
    void OnTapped (object s)  {
        taps++;
        Debug.WriteLine ("parameter: " + s);
    }
    //region INotifyPropertyChanged code omitted
}

Summary

The tap gesture is used for tap detection and is implemented with the TapGestureRecognizer class. The number of taps can be specified to recognize double-tap (or triple-tap, or more taps) behavior.

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