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Basic animation

  • Artikkeli

The .NET Multi-platform App UI (.NET MAUI) animation classes target different properties of visual elements, with a typical basic animation progressively changing a property from one value to another over a period of time.

Basic animations can be created with extension methods provided by the ViewExtensions class, which operate on VisualElement objects:

By default, each animation will take 250 milliseconds. However, a duration for each animation can be specified when creating the animation.

Note

The ViewExtensions class also provides a LayoutTo extension method. However, this method is intended to be used by layouts to animate transitions between layout states that contain size and position changes.

The animation extension methods in the ViewExtensions class are all asynchronous and return a Task<bool> object. The return value is false if the animation completes, and true if the animation is cancelled. Therefore, when animation operations are combined with the await operator it becomes possible to create sequential animations with subsequent animation methods executing after the previous method has completed. For more information, see Compound animations.

If there's a requirement to let an animation complete in the background, then the await operator can be omitted. In this scenario, the animation extension methods will quickly return after initiating the animation, with the animation occurring in the background. This operation can be taken advantage of when creating composite animations. For more information, see Composite animations.

On Android, animations respect the system animation settings:

  • If the system's animations are disabled (either by accessibility features or developer features), new animations will jump immediately to their finished state.
  • If the device's power saving mode is activated while animations are in progress, the animations will immediately jump to their finished state.
  • If the device's animation durations is set to zero (disabled) while animations are in progress and the API version is 33 or greater, the animations will immediately jump to their finished state.

Single animations

Each extension method in the ViewExtensions class implements a single animation operation that progressively changes a property from one value to another value over a period of time.

Rotation

Rotation is performed with the RotateTo method, which progressively changes the Rotation property of an element:

await image.RotateTo(360, 2000);
image.Rotation = 0;

In this example, an Image instance is rotated up to 360 degrees over 2 seconds (2000 milliseconds). The RotateTo method obtains the current Rotation property value of the element for the start of the animation, and then rotates from that value to its first argument (360). Once the animation is complete, the image's Rotation property is reset to 0. This ensures that the Rotation property doesn't remain at 360 after the animation concludes, which would prevent additional rotations.

Note

In addition to the RotateTo method, there are also RotateXTo and RotateYTo methods that animate the RotationX and RotationY properties, respectively.

Relative rotation

Relative rotation is performed with the RelRotateTo method, which progressively changes the Rotation property of an element:

await image.RelRotateTo(360, 2000);

In this example, an Image instance is rotated 360 degrees from its starting position over 2 seconds (2000 milliseconds). The RelRotateTo method obtains the current Rotation property value of the element for the start of the animation, and then rotates from that value to the value plus its first argument (360). This ensures that each animation will always be a 360 degrees rotation from the starting position. Therefore, if a new animation is invoked while an animation is already in progress, it will start from the current position and may end at a position that is not an increment of 360 degrees.

Scaling

Scaling is performed with the ScaleTo method, which progressively changes the Scale property of an element:

await image.ScaleTo(2, 2000);

In this example, an Image instance is scaled up to twice its size over 2 seconds (2000 milliseconds). The ScaleTo method obtains the current Scale property value of the element for the start of the animation, and then scales from that value to its first argument. This has the effect of expanding the size of the image to twice its size.

Note

In addition to the ScaleTo method, there are also ScaleXTo and ScaleYTo methods that animate the ScaleX and ScaleY properties, respectively.

Relative scaling

Relative scaling is performed with the RelScaleTo method, which progressively changes the Scale property of an element:

await image.RelScaleTo(2, 2000);

In this example, an Image instance is scaled up to twice its size over 2 seconds (2000 milliseconds). The RelScaleTo method obtains the current Scale property value of the element for the start of the animation, and then scales from that value to the value plus its first argument. This ensures that each animation will always be a scaling of 2 from the starting position.

Scaling and rotation with anchors

The AnchorX and AnchorY properties of a visual element set the center of scaling or rotation for the Rotation and Scale properties. Therefore, their values also affect the RotateTo and ScaleTo methods.

Given an Image that has been placed at the center of a layout, the following code example demonstrates rotating the image around the center of the layout by setting its AnchorY property:

double radius = Math.Min(absoluteLayout.Width, absoluteLayout.Height) / 2;
image.AnchorY = radius / image.Height;
await image.RotateTo(360, 2000);

To rotate the Image instance around the center of the layout, the AnchorX and AnchorY properties must be set to values that are relative to the width and height of the Image. In this example, the center of the Image is defined to be at the center of the layout, and so the default AnchorX value of 0.5 does not require changing. However, the AnchorY property is redefined to be a value from the top of the Image to the center point of the layout. This ensures that the Image makes a full rotation of 360 degrees around the center point of the layout.

Translation

Translation is performed with the TranslateTo method, which progressively changes the TranslationX and TranslationY properties of an element:

await image.TranslateTo(-100, -100, 1000);

In this example, the Image instance is translated horizontally and vertically over 1 second (1000 milliseconds). The TranslateTo method simultaneously translates the image 100 device-independent units to the left, and 100 device-independent units upwards. This is because the first and second arguments are both negative numbers. Providing positive numbers would translate the image to the right, and down.

Important

If an element is initially laid out off screen and then translated onto the screen, after translation the element's input layout remains off screen and the user can't interact with it. Therefore, it's recommended that a view should be laid out in its final position, and then any required translations performed.

Fading

Fading is performed with the FadeTo method, which progressively changes the Opacity property of an element:

image.Opacity = 0;
await image.FadeTo(1, 4000);

In this example, the Image instance fades in over 4 seconds (4000 milliseconds). The FadeTo method obtains the current Opacity property value of the element for the start of the animation, and then fades in from that value to its first argument.

Compound animations

A compound animation is a sequential combination of animations, and can be created with the await operator:

await image.TranslateTo(-100, 0, 1000);    // Move image left
await image.TranslateTo(-100, -100, 1000); // Move image diagonally up and left
await image.TranslateTo(100, 100, 2000);   // Move image diagonally down and right
await image.TranslateTo(0, 100, 1000);     // Move image left
await image.TranslateTo(0, 0, 1000);       // Move image up

In this example, the Image instance is translated over 6 seconds (6000 milliseconds). The translation of the Image uses five animations, with the await operator indicating that each animation executes sequentially. Therefore, subsequent animation methods execute after the previous method has completed.

Composite animations

A composite animation is a combination of animations where two or more animations run simultaneously. Composite animations can be created by combining awaited and non-awaited animations:

image.RotateTo(360, 4000);
await image.ScaleTo(2, 2000);
await image.ScaleTo(1, 2000);

In this example, the Image instance is scaled and simultaneously rotated over 4 seconds (4000 milliseconds). The scaling of the Image uses two sequential animations that occur at the same time as the rotation. The RotateTo method executes without an await operator and returns immediately, with the first ScaleTo animation then beginning. The await operator on the first ScaleTo method delays the second ScaleTo method until the first ScaleTo method has completed. At this point the RotateTo animation is half completed and the Image will be rotated 180 degrees. During the final 2 seconds (2000 milliseconds), the second ScaleTo animation and the RotateTo animation both complete.

Run multiple animations concurrently

The Task.WhenAny and Task.WhenAll methods can be used to run multiple asynchronous methods concurrently, and therefore can create composite animations. Both methods return a Task object and accept a collection of methods that each return a Task object. The Task.WhenAny method completes when any method in its collection completes execution, as demonstrated in the following code example:

await Task.WhenAny<bool>
(
  image.RotateTo(360, 4000),
  image.ScaleTo(2, 2000)
);
await image.ScaleTo(1, 2000);

In this example, the Task.WhenAny method contains two tasks. The first task rotates an Image instance over 4 seconds (4000 milliseconds), and the second task scales the image over 2 seconds (2000 milliseconds). When the second task completes, the Task.WhenAny method call completes. However, even though the RotateTo method is still running, the second ScaleTo method can begin.

The Task.WhenAll method completes when all the methods in its collection have completed, as demonstrated in the following code example:

// 10 minute animation
uint duration = 10 * 60 * 1000;
await Task.WhenAll
(
  image.RotateTo(307 * 360, duration),
  image.RotateXTo(251 * 360, duration),
  image.RotateYTo(199 * 360, duration)
);

In this example, the Task.WhenAll method contains three tasks, each of which executes over 10 minutes. Each Task makes a different number of 360 degree rotations – 307 rotations for RotateTo, 251 rotations for RotateXTo, and 199 rotations for RotateYTo. These values are prime numbers, therefore ensuring that the rotations aren't synchronized and hence won't result in repetitive patterns.

Canceling animations

An app can cancel one or more animations with a call to the CancelAnimations extension method:

image.CancelAnimations();

In this example, all animations that are running on the Image instance are immediately canceled.