使用缩放动画放大视图

试用 Compose 方式
Jetpack Compose 是推荐在 Android 设备上使用的界面工具包。了解如何在 Compose 中使用动画。
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本指南将演示如何实现轻触缩放动画。借助“点按缩放”功能，应用（例如图库）可以动画呈现缩略图，让视图填满整个屏幕。

下方演示了轻触缩放动画如何展开缩略图以填满整个屏幕：

如需查看完整的可运行示例，请参阅 GitHub 上的 WearSpeakerSample 项目中的 UIAnimation 类。

创建视图

创建一个布局文件，使其包含要缩放的内容的小版本和大版本。以下示例为可点按的图片缩略图创建了 ImageButton，并创建了用于显示图片的放大视图的 ImageView：

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/container"
    android:layout_width="match_parent"
    androi>d:layo<ut_height="match_parent"

    LinearLayout android:layout_width="match_parent"
        android:layout_height="wrap_content"
        a>ndroid:ori<entation="vertical"
        android:padding="16dp"

        ImageButton
            android:id="@+id/thumb_button_1"
            android:layout_width="100dp"
            android:layout_height="75dp"
            android:layout_marginRight="1dp"
            android:src="@drawa>ble/th<umb1"
  >      <    android:scaleType=&quot;centerCrop"
            android:contentDescription="@string/description_image_1" /

    /LinearLayout

    !-- This initially hidden ImageView holds the zoomed version of
         the preceding images. Without transformations applied, it fills the entire
         screen. To achieve the zoom an>imatio<n, this view's bounds are animated
         from the bounds of the preceding thumbnail button to its final laid-out
         bounds.
         --

    ImageView
        android:id="@+id/expanded_image"
        android:layout_width="matc>h_<parent">
        android:layout_height="match_parent"
        android:visibility="invisible"
        android:contentDescription="@string/description_zoom_touch_close" /

/FrameLayout

设置缩放动画

应用布局后，设置触发缩放动画的事件处理脚本。以下示例向 ImageButton 添加 View.OnClickListener，以在用户点按图片按钮时执行缩放动画：

Kotlin

class ZoomActivity : FragmentActivity() {

    // Hold a reference to the current animator so that it can be canceled
    // midway.
    private var currentAnimator: Animator? = null

    // The system "short" animation time duration in milliseconds. This duration
    // is ideal for subtle animations or animations that occur frequently.
    private var shortAnimationDuration: Int = 0

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_zoom)

        // Hook up taps on the thumbnail views.

        binding.thumbButton1.setOnClickListener {
            zoomImageFromThumb(thumb1View, R.drawable.image1)
        }

        // Retrieve and cache the system's default "short" animation time.
        shortAnimationDuration = resources.getInteger(android.R.integer.config_shortAnimTime)
    }
    ...
}

Java

public class ZoomActivity extends FragmentActivity {
    // Hold a reference to the current animator so that it can be canceled
    // mid-way.
    private Animator currentAnimator;

    // The system "short" animation time duration in milliseconds. This duration
    // is ideal for subtle animations or animations that occur frequently.
    private int shortAnimationDuration;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_zoom);

        // Hook up taps on the thumbnail views.

        binding.thumbButton1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                zoomImageFromThumb(thumb1View, R.drawable.image1);
            }
        });

        // Retrieve and cache the system's default "short" animation time.
        shortAnimationDuration = getResources().getInteger(
                android.R.integer.config_shortAnimTime);
    }
    ...
}

缩放视图

适时以动画形式呈现从正常大小的视图到放大的视图。通常，您需要在正常大小视图的边界与放大视图的边界之间添加动画。以下方法介绍了如何实现从缩略图缩放到放大视图的缩放动画。为此，请将高分辨率图片分配给隐藏的“放大”ImageView。

为简单起见，以下示例在界面线程中加载了一个大型图片资源。请在单独的线程中加载它，以防止界面线程上出现阻塞，然后在界面线程上设置位图。通常，位图不得大于屏幕尺寸。接下来，计算 ImageView 的起始边界和结束边界。

Kotlin

    private fun zoomImageFromThumb(thumbView: View, imageResId: Int) {
        // If there's an animation in progress, cancel it immediately and
        // proceed with this one.
        currentAnimator?.cancel()

        // Load the high-resolution "zoomed-in" image.
        binding.expandedImage.setImageResource(imageResId)

        // Calculate the starting and ending bounds for the zoomed-in image.
        val startBoundsInt = Rect()
        val finalBoundsInt = Rect()
        val globalOffset = Point()

        // The start bounds are the global visible rectangle of the thumbnail,
        // and the final bounds are the global visible rectangle of the
        // container view. Set the container view's offset as the origin for the
        // bounds, since that's the origin for the positioning animation
        // properties (X, Y).
        thumbView.getGlobalVisibleRect(startBoundsInt)
        binding.container.getGlobalVisibleRect(finalBoundsInt, globalOffset)
        startBoundsInt.offset(-globalOffset.x, -globalOffset.y)
        finalBoundsInt.offset(-globalOffset.x, -globalOffset.y)

        val startBounds = RectF(startBoundsInt)
        val finalBounds = RectF(finalBoundsInt)

        // Using the "center crop" technique, adjust the start bounds to be the
        // same aspect ratio as the final bounds. This prevents unwanted
        // stretching during the animation. Calculate the start scaling factor.
        // The end scaling factor is always 1.0.
        val startScale: Float
        if ((finalBounds>.width() / finalBounds.height()  startBounds.width() / startBounds.height())) {
            // Extend start bounds horizontally.
            startScale = startBounds.height() / finalBounds.height()
            val startWidth: Float = startScale * finalBounds.width()
            val deltaWidth: Float = (startWidth - startBounds.width()) / 2
            startBounds.left -= deltaWidth.toInt()
            startBounds.right += deltaWidth.toInt()
        } else {
            // Extend start bounds vertically.
            startScale = startBounds.width() / finalBounds.width()
            val startHeight: Float = startScale * finalBounds.height()
            val deltaHeight: Float = (startHeight - startBounds.height()) / 2f
            startBounds.top -= deltaHeight.toInt()
            startBounds.bottom += deltaHeight.toInt()
        }

        // Hide the thumbnail and show the zoomed-in view. When the animation
        // begins, it positions the zoomed-in view in the place of the
        // thumbnail.
        thumbView.alpha = 0f

        animateZoomToLargeImage(startBounds, finalBounds, startScale)

        setDismissLargeImageAnimation(thumbView, startBounds, startScale)
    }

Java

    private void zoomImageFromThumb(final View thumbView, int imageResId) {
        // If there's an animation in progress, cancel it immediately and
        // proceed with this one.
        if (currentAnimator != null) {
            currentAnimator.cancel();
        }

        // Load the high-resolution "zoomed-in" image.
        binding.expandedImage.setImageResource(imageResId);

        // Calculate the starting and ending bounds for the zoomed-in image.
        final Rect startBounds = new Rect();
        final Rect finalBounds = new Rect();
        final Point globalOffset = new Point();

        // The start bounds are the global visible rectangle of the thumbnail,
        // and the final bounds are the global visible rectangle of the
        // container view. Set the container view's offset as the origin for the
        // bounds, since that's the origin for the positioning animation
        // properties (X, Y).
        thumbView.getGlobalVisibleRect(startBounds);
        findViewById(R.id.container)
                .getGlobalVisibleRect(finalBounds, globalOffset);
        startBounds.offset(-globalOffset.x, -globalOffset.y);
        finalBounds.offset(-globalOffset.x, -globalOffset.y);

        // Using the "center crop" technique, adjust the start bounds to be the
        // same aspect ratio as the final bounds. This prevents unwanted
        // stretching during the animation. Calculate the start scaling factor.
        // The end scaling factor is always 1.0.
        float startScale;
        if ((float) finalBounds.width() / final>Bounds.height()
                 (float) startBounds.width() / startBounds.height()) {
            // Extend start bounds horizontally.
            startScale = (float) startBounds.height() / finalBounds.height();
            float startWidth = startScale * finalBounds.width();
            float deltaWidth = (startWidth - startBounds.width()) / 2;
            startBounds.left -= deltaWidth;
            startBounds.right += deltaWidth;
        } else {
            // Extend start bounds vertically.
            startScale = (float) startBounds.width() / finalBounds.width();
            float startHeight = startScale * finalBounds.height();
            float deltaHeight = (startHeight - startBounds.height()) / 2;
            startBounds.top -= deltaHeight;
            startBounds.bottom += deltaHeight;
        }

        // Hide the thumbnail and show the zoomed-in view. When the animation
        // begins, it positions the zoomed-in view in the place of the
        // thumbnail.
        thumbView.setAlpha(0f);

        animateZoomToLargeImage(startBounds, finalBounds, startScale);

        setDismissLargeImageAnimation(thumbView, startBounds, startScale);
    }

从起始边界到结束边界，同时为四个定位和大小调整属性（X、Y、SCALE_X 和 SCALE_Y）添加动画效果。将这四个动画添加到 AnimatorSet 中，以便它们同时启动。

Kotlin

    private fun animateZoomToLargeImage(startBounds: RectF, finalBounds: RectF, startScale: Float) {
        binding.expandedImage.visibility = View.VISIBLE

        // Set the pivot point for SCALE_X and SCALE_Y transformations to the
        // top-left corner of the zoomed-in view. The default is the center of
        // the view.
        binding.expandedImage.pivotX = 0f
        binding.expandedImage.pivotY = 0f

        // Construct and run the parallel animation of the four translation and
        // scale properties: X, Y, SCALE_X, and SCALE_Y.
        currentAnimator = AnimatorSet().apply {
            play(
                ObjectAnimator.ofFloat(
                    binding.expandedImage,
                    View.X,
                    startBounds.left,
                    finalBounds.left)
            ).apply {
                with(ObjectAnimator.ofFloat(binding.expandedImage, View.Y, startBounds.top, finalBounds.top))
                with(ObjectAnimator.ofFloat(binding.expandedImage, View.SCALE_X, startScale, 1f))
                with(ObjectAnimator.ofFloat(binding.expandedImage, View.SCALE_Y, startScale, 1f))
            }
            duration = shortAnimationDuration.toLong()
            interpolator = DecelerateInterpolator()
            addListener(object : AnimatorListenerAdapter() {

                override fun onAnimationEnd(animation: Animator) {
                    currentAnimator = null
                }

                override fun onAnimationCancel(animation: Animator) {
                    currentAnimator = null
                }
            })
            start()
        }
    }

Java

    private void animateZoomToLargeImage(Rect startBounds, Rect finalBounds, Float startScale) {

        binding.expandedImage.setVisibility(View.VISIBLE);

        // Set the pivot point for SCALE_X and SCALE_Y transformations to the
        // top-left corner of the zoomed-in view. The default is the center of
        // the view.
        binding.expandedImage.setPivotX(0f);
        binding.expandedImage.setPivotY(0f);

        // Construct and run the parallel animation of the four translation and
        // scale properties: X, Y, SCALE_X, and SCALE_Y.
        AnimatorSet set = new AnimatorSet();
        set
                .play(ObjectAnimator.ofFloat(binding.expandedImage, View.X,
                        startBounds.left, finalBounds.left))
                .with(ObjectAnimator.ofFloat(binding.expandedImage, View.Y,
                        startBounds.top, finalBounds.top))
                .with(ObjectAnimator.ofFloat(binding.expandedImage, View.SCALE_X,
                        startScale, 1f))
                .with(ObjectAnimator.ofFloat(binding.expandedImage,
                        View.SCALE_Y, startScale, 1f));
        set.setDuration(shortAnimationDuration);
        set.setInterpolator(new DecelerateInterpolator());
        set.addListener(new AnimatorListenerAdapter() {
            @Override
            public void onAnimationEnd(Animator animation) {
                currentAnimator = null;
            }

            @Override
            public void onAnimationCancel(Animator animation) {
                currentAnimator = null;
            }
        });
        set.start();
        currentAnimator = set;
    }

当用户在图片放大时点按屏幕时，通过反向运行类似的动画来缩小图片。将 View.OnClickListener 添加到 ImageView。点按后，ImageView 会最小化为图片缩略图的大小，并将其可见性设置为 GONE 以将其隐藏。

Kotlin

    private fun setDismissLargeImageAnimation(thumbView: View, startBounds: RectF, startScale: Float) {
        // When the zoomed-in image is tapped, it zooms down to the original
        // bounds and shows the thumbnail instead of the expanded image.
        binding.expandedImage.setOnClickListener {
            currentAnimator?.cancel()

            // Animate the four positioning and sizing properties in parallel,
            // back to their original values.
            currentAnimator = AnimatorSet().apply {
                play(ObjectAnimator.ofFloat(binding.expandedImage, View.X, startBounds.left)).apply {
                    with(ObjectAnimator.ofFloat(binding.expandedImage, View.Y, startBounds.top))
                    with(ObjectAnimator.ofFloat(binding.expandedImage, View.SCALE_X, startScale))
                    with(ObjectAnimator.ofFloat(binding.expandedImage, View.SCALE_Y, startScale))
                }
                duration = shortAnimationDuration.toLong()
                interpolator = DecelerateInterpolator()
                addListener(object : AnimatorListenerAdapter() {

                    override fun onAnimationEnd(animation: Animator) {
                        thumbView.alpha = 1f
                        binding.expandedImage.visibility = View.GONE
                        currentAnimator = null
                    }

                    override fun onAnimationCancel(animation: Animator) {
                        thumbView.alpha = 1f
                        binding.expandedImage.visibility = View.GONE
                        currentAnimator = null
                    }
                })
                start()
            }
        }
    }

Java

    private void setDismissLargeImageAnimation(View thumbView, Rect startBounds, Float startScale) {
        // When the zoomed-in image is tapped, it zooms down to the original
        // bounds and shows the thumbnail instead of the expanded image.
        final float startScaleFinal = startScale;
        binding.expandedImage.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (currentAnimator != null) {
                    currentAnimator.cancel();
                }

                // Animate the four positioning and sizing properties in
                // parallel, back to their original values.
                AnimatorSet set = new AnimatorSet();
                set.play(ObjectAnimator
                                .ofFloat(binding.expandedImage, View.X, startBounds.left))
                        .with(ObjectAnimator
                                .ofFloat(binding.expandedImage,
                                        View.Y,startBounds.top))
                        .with(ObjectAnimator
                                .ofFloat(binding.expandedImage,
                                        View.SCALE_X, startScaleFinal))
                        .with(ObjectAnimator
                                .ofFloat(binding.expandedImage,
                                        View.SCALE_Y, startScaleFinal));
                set.setDuration(shortAnimationDuration);
                set.setInterpolator(new DecelerateInterpolator());
                set.addListener(new AnimatorListenerAdapter() {
                    @Override
                    public void onAnimationEnd(Animator animation) {
                        thumbView.setAlpha(1f);
                        binding.expandedImage.setVisibility(View.GONE);
                        currentAnimator = null;
                    }

                    @Override
                    public void onAnimationCancel(Animator animation) {
                        thumbView.setAlpha(1f);
                        binding.expandedImage.setVisibility(View.GONE);
                        currentAnimator = null;
                    }
                });
                set.start();
                currentAnimator = set;
            }
        });
    }