Adding a swipe gesture recognizer

Download Sample Download the sample

A swipe gesture occurs when a finger is moved across the screen in a horizontal or vertical direction, and is often used to initiate navigation through content. The code examples in this article are taken from the Swipe Gesture sample.

To make a View recognize a swipe gesture, create a SwipeGestureRecognizer instance, set the Direction property to a SwipeDirection enumeration value (Left, Right, Up, or Down), optionally set the Threshold property, handle the Swiped event, and add the new gesture recognizer to the GestureRecognizers collection on the view. The following code example shows a SwipeGestureRecognizer attached to a BoxView:

<BoxView Color="Teal" ...>
    <BoxView.GestureRecognizers>
        <SwipeGestureRecognizer Direction="Left" Swiped="OnSwiped"/>
    </BoxView.GestureRecognizers>
</BoxView>

Here is the equivalent C# code:

var boxView = new BoxView { Color = Color.Teal, ... };
var leftSwipeGesture = new SwipeGestureRecognizer { Direction = SwipeDirection.Left };
leftSwipeGesture.Swiped += OnSwiped;

boxView.GestureRecognizers.Add(leftSwipeGesture);

The SwipeGestureRecognizer class also includes a Threshold property, that can be optionally set to a uint value that represents the minimum swipe distance that must be achieved for a swipe to be recognized, in device-independent units. The default value of this property is 100, meaning that any swipes that are less than 100 device-independent units will be ignored.

Recognizing the swipe direction

In the examples above, the Direction property is set to single a value from the SwipeDirection enumeration. However, it's also possible to set this property to multiple values from the SwipeDirection enumeration, so that the Swiped event is fired in response to a swipe in more than one direction. However, the constraint is that a single SwipeGestureRecognizer can only recognize swipes that occur on the same axis. Therefore, swipes that occur on the horizontal axis can be recognized by setting the Direction property to Left and Right:

<SwipeGestureRecognizer Direction="Left,Right" Swiped="OnSwiped"/>

Similarly, swipes that occur on the vertical axis can be recognized by setting the Direction property to Up and Down:

var swipeGesture = new SwipeGestureRecognizer { Direction = SwipeDirection.Up | SwipeDirection.Down };

Alternatively, a SwipeGestureRecognizer for each swipe direction can be created to recognize swipes in every direction:

<BoxView Color="Teal" ...>
    <BoxView.GestureRecognizers>
        <SwipeGestureRecognizer Direction="Left" Swiped="OnSwiped"/>
        <SwipeGestureRecognizer Direction="Right" Swiped="OnSwiped"/>
        <SwipeGestureRecognizer Direction="Up" Swiped="OnSwiped"/>
        <SwipeGestureRecognizer Direction="Down" Swiped="OnSwiped"/>
    </BoxView.GestureRecognizers>
</BoxView>

Here is the equivalent C# code:

var boxView = new BoxView { Color = Color.Teal, ... };
var leftSwipeGesture = new SwipeGestureRecognizer { Direction = SwipeDirection.Left };
leftSwipeGesture.Swiped += OnSwiped;
var rightSwipeGesture = new SwipeGestureRecognizer { Direction = SwipeDirection.Right };
rightSwipeGesture.Swiped += OnSwiped;
var upSwipeGesture = new SwipeGestureRecognizer { Direction = SwipeDirection.Up };
upSwipeGesture.Swiped += OnSwiped;
var downSwipeGesture = new SwipeGestureRecognizer { Direction = SwipeDirection.Down };
downSwipeGesture.Swiped += OnSwiped;

boxView.GestureRecognizers.Add(leftSwipeGesture);
boxView.GestureRecognizers.Add(rightSwipeGesture);
boxView.GestureRecognizers.Add(upSwipeGesture);
boxView.GestureRecognizers.Add(downSwipeGesture);

Note

In the above examples, the same event handler responds to the Swiped event firing. However, each SwipeGestureRecognizer instance can use a different event handler if required.

Responding to the swipe

An event handler for the Swiped event is shown in the following example:

void OnSwiped(object sender, SwipedEventArgs e)
{
    switch (e.Direction)
    {
        case SwipeDirection.Left:
            // Handle the swipe
            break;
        case SwipeDirection.Right:
            // Handle the swipe
            break;
        case SwipeDirection.Up:
            // Handle the swipe
            break;
        case SwipeDirection.Down:
            // Handle the swipe
            break;
    }
}

The SwipedEventArgs can be examined to determine the direction of the swipe, with custom logic responding to the swipe as required. The direction of the swipe can be obtained from the Direction property of the event arguments, which will be set to one of the values of the SwipeDirection enumeration. In addition, the event arguments also have a Parameter property that will be set to the value of the CommandParameter property, if defined.

Using commands

The SwipeGestureRecognizer class also includes Command and CommandParameter properties. These properties are typically used in applications that use the Model-View-ViewModel (MVVM) pattern. The Command property defines the ICommand to be invoked when a swipe gesture is recognized, with the CommandParameter property defining an object to be passed to the ICommand. The following code example shows how to bind the Command property to an ICommand defined in the view model whose instance is set as the page BindingContext:

var boxView = new BoxView { Color = Color.Teal, ... };
var leftSwipeGesture = new SwipeGestureRecognizer { Direction = SwipeDirection.Left, CommandParameter = "Left" };
leftSwipeGesture.SetBinding(SwipeGestureRecognizer.CommandProperty, "SwipeCommand");
boxView.GestureRecognizers.Add(leftSwipeGesture);

The equivalent XAML code is:

<BoxView Color="Teal" ...>
    <BoxView.GestureRecognizers>
        <SwipeGestureRecognizer Direction="Left" Command="{Binding SwipeCommand}" CommandParameter="Left" />
    </BoxView.GestureRecognizers>
</BoxView>

SwipeCommand is a property of type ICommand defined in the view model instance that is set as the page BindingContext. When a swipe gesture is recognized, the Execute method of the SwipeCommand object will be executed. The argument to the Execute method is the value of the CommandParameter property. For more information about commands, see The Command Interface.

Creating a swipe container

The SwipeContainer class, which is shown in the following code example, is a generalized swipe recognition class that be wrapped around a View to perform swipe gesture recognition:

public class SwipeContainer : ContentView
{
    public event EventHandler<SwipedEventArgs> Swipe;

    public SwipeContainer()
    {
        GestureRecognizers.Add(GetSwipeGestureRecognizer(SwipeDirection.Left));
        GestureRecognizers.Add(GetSwipeGestureRecognizer(SwipeDirection.Right));
        GestureRecognizers.Add(GetSwipeGestureRecognizer(SwipeDirection.Up));
        GestureRecognizers.Add(GetSwipeGestureRecognizer(SwipeDirection.Down));
    }

    SwipeGestureRecognizer GetSwipeGestureRecognizer(SwipeDirection direction)
    {
        var swipe = new SwipeGestureRecognizer { Direction = direction };
        swipe.Swiped += (sender, e) => Swipe?.Invoke(this, e);
        return swipe;
    }
}

The SwipeContainer class creates SwipeGestureRecognizer objects for all four swipe directions, and attaches Swipe event handlers. These event handlers invoke the Swipe event defined by the SwipeContainer.

The following XAML code example shows the SwipeContainer class wrapping a BoxView:

<ContentPage ...>
    <StackLayout>
        <local:SwipeContainer Swipe="OnSwiped" ...>
            <BoxView Color="Teal" ... />
        </local:SwipeContainer>
    </StackLayout>
</ContentPage>

The following code example shows how the SwipeContainer wraps a BoxView in a C# page:

public class SwipeContainerPageCS : ContentPage
{
    public SwipeContainerPageCS()
    {
        var boxView = new BoxView { Color = Color.Teal, ... };
        var swipeContainer = new SwipeContainer { Content = boxView, ... };
        swipeContainer.Swipe += (sender, e) =>
        {
          // Handle the swipe
        };

        Content = new StackLayout
        {
            Children = { swipeContainer }
        };
    }
}

When the BoxView receives a swipe gesture, the Swiped event in the SwipeGestureRecognizer is fired. This is handled by the SwipeContainer class, which fires its own Swipe event. This Swipe event is handled on the page. The SwipedEventArgs can then be examined to determine the direction of the swipe, with custom logic responding to the swipe as required.