This lesson demonstrates how to do a touch-to-zoom animation, which is useful for apps such as photo galleries to animate a view from a thumbnail to a full-size image that fills the screen.
Here's what a touch-to-zoom animation looks like that expands an image thumbnail to fill the screen:
Zoom animation
If you want to jump ahead and see a full working example, see the
UIAnimation class from the android-WearSpeakerSample
project on GitHub.
Create the views
Create a layout file that contains the small and large version of the content that you want
to zoom. The following example creates an ImageButton for clickable image thumbnail
and an ImageView that displays the enlarged view of the image:
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent">
<LinearLayout android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="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="@drawable/thumb1"
android:scaleType="centerCrop"
android:contentDescription="@string/description_image_1" />
</LinearLayout>
<!-- This initially-hidden ImageView will hold the expanded/zoomed version of
the images above. Without transformations applied, it takes up the entire
screen. To achieve the "zoom" animation, this view's bounds are animated
from the bounds of the thumbnail button above, to its final laid-out
bounds.
-->
<ImageView
android:id="@+id/expanded_image"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:visibility="invisible"
android:contentDescription="@string/description_zoom_touch_close" />
</FrameLayout>
Set up the zoom animation
Once you apply your layout, set up the event handlers that trigger the zoom animation.
The following example adds a View.OnClickListener to the ImageButton to execute the zoom animation when the user
clicks the image button:
Kotlin
class ZoomActivity : FragmentActivity() {
// Hold a reference to the current animator,
// so that it can be canceled mid-way.
private var currentAnimator: Animator? = null
// The system "short" animation time duration, in milliseconds. This
// duration is ideal for subtle animations or animations that occur
// very frequently.
private var shortAnimationDuration: Int = 0
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_zoom)
// Hook up clicks on the thumbnail views.
val thumb1View: View = findViewById(R.id.thumb_button_1)
thumb1View.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
// very frequently.
private int shortAnimationDuration;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_zoom);
// Hook up clicks on the thumbnail views.
final View thumb1View = findViewById(R.id.thumb_button_1);
thumb1View.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);
}
...
}
Zoom the view
You'll now need to animate from the normal sized view to the zoomed view when appropriate. In general, you need to animate from the bounds of the normal-sized view to the bounds of the larger-sized view. The following method shows you how to implement a zoom animation that zooms from an image thumbnail to an enlarged view by doing the following things:
- Assign the high-res image to the hidden "zoomed-in" (enlarged)
ImageView. The following example loads a large image resource on the UI thread for simplicity. You will want to do this loading in a separate thread to prevent blocking on the UI thread and then set the bitmap on the UI thread. Ideally, the bitmap should not be larger than the screen size. - Calculate the starting and ending bounds for the
ImageView. - Animate each of the four positioning and sizing properties
XYSCALE_X, andSCALE_YAnimatorSetso that they can be started at the same time. - Zoom back out by running a similar animation but in reverse when the user touches the
screen when the image is zoomed in. You can do this by adding a
View.OnClickListenerto theImageView. When clicked, theImageViewminimizes back down to the size of the image thumbnail and sets its visibility toGONEto hide it.
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.
val expandedImageView: ImageView = findViewById(R.id.expanded_image)
expandedImageView.setImageResource(imageResId)
// Calculate the starting and ending bounds for the zoomed-in image.
// This step involves lots of math. Yay, math.
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. Also 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)
findViewById<View>(R.id.container)
.getGlobalVisibleRect(finalBoundsInt, globalOffset)
startBoundsInt.offset(-globalOffset.x, -globalOffset.y)
finalBoundsInt.offset(-globalOffset.x, -globalOffset.y)
val startBounds = RectF(startBoundsInt)
val finalBounds = RectF(finalBoundsInt)
// Adjust the start bounds to be the same aspect ratio as the final
// bounds using the "center crop" technique. This prevents undesirable
// stretching during the animation. Also 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 will position the zoomed-in view in the place of the
// thumbnail.
thumbView.alpha = 0f
expandedImageView.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).
expandedImageView.pivotX = 0f
expandedImageView.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(
expandedImageView,
View.X,
startBounds.left,
finalBounds.left)
).apply {
with(ObjectAnimator.ofFloat(expandedImageView, View.Y, startBounds.top, finalBounds.top))
with(ObjectAnimator.ofFloat(expandedImageView, View.SCALE_X, startScale, 1f))
with(ObjectAnimator.ofFloat(expandedImageView, 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()
}
// Upon clicking the zoomed-in image, it should zoom back down
// to the original bounds and show the thumbnail instead of
// the expanded image.
expandedImageView.setOnClickListener {
currentAnimator?.cancel()
// Animate the four positioning/sizing properties in parallel,
// back to their original values.
currentAnimator = AnimatorSet().apply {
play(ObjectAnimator.ofFloat(expandedImageView, View.X, startBounds.left)).apply {
with(ObjectAnimator.ofFloat(expandedImageView, View.Y, startBounds.top))
with(ObjectAnimator.ofFloat(expandedImageView, View.SCALE_X, startScale))
with(ObjectAnimator.ofFloat(expandedImageView, View.SCALE_Y, startScale))
}
duration = shortAnimationDuration.toLong()
interpolator = DecelerateInterpolator()
addListener(object : AnimatorListenerAdapter() {
override fun onAnimationEnd(animation: Animator) {
thumbView.alpha = 1f
expandedImageView.visibility = View.GONE
currentAnimator = null
}
override fun onAnimationCancel(animation: Animator) {
thumbView.alpha = 1f
expandedImageView.visibility = View.GONE
currentAnimator = null
}
})
start()
}
}
}
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.
final ImageView expandedImageView = (ImageView) findViewById(
R.id.expanded_image);
expandedImageView.setImageResource(imageResId);
// Calculate the starting and ending bounds for the zoomed-in image.
// This step involves lots of math. Yay, math.
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. Also 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);
// Adjust the start bounds to be the same aspect ratio as the final
// bounds using the "center crop" technique. This prevents undesirable
// stretching during the animation. Also calculate the start scaling
// factor (the end scaling factor is always 1.0).
float startScale;
if ((float) finalBounds.width() / finalBounds.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 will position the zoomed-in view in the place of the
// thumbnail.
thumbView.setAlpha(0f);
expandedImageView.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).
expandedImageView.setPivotX(0f);
expandedImageView.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(expandedImageView, View.X,
startBounds.left, finalBounds.left))
.with(ObjectAnimator.ofFloat(expandedImageView, View.Y,
startBounds.top, finalBounds.top))
.with(ObjectAnimator.ofFloat(expandedImageView, View.SCALE_X,
startScale, 1f))
.with(ObjectAnimator.ofFloat(expandedImageView,
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;
// Upon clicking the zoomed-in image, it should zoom back down
// to the original bounds and show the thumbnail instead of
// the expanded image.
final float startScaleFinal = startScale;
expandedImageView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if (currentAnimator != null) {
currentAnimator.cancel();
}
// Animate the four positioning/sizing properties in parallel,
// back to their original values.
AnimatorSet set = new AnimatorSet();
set.play(ObjectAnimator
.ofFloat(expandedImageView, View.X, startBounds.left))
.with(ObjectAnimator
.ofFloat(expandedImageView,
View.Y,startBounds.top))
.with(ObjectAnimator
.ofFloat(expandedImageView,
View.SCALE_X, startScaleFinal))
.with(ObjectAnimator
.ofFloat(expandedImageView,
View.SCALE_Y, startScaleFinal));
set.setDuration(shortAnimationDuration);
set.setInterpolator(new DecelerateInterpolator());
set.addListener(new AnimatorListenerAdapter() {
@Override
public void onAnimationEnd(Animator animation) {
thumbView.setAlpha(1f);
expandedImageView.setVisibility(View.GONE);
currentAnimator = null;
}
@Override
public void onAnimationCancel(Animator animation) {
thumbView.setAlpha(1f);
expandedImageView.setVisibility(View.GONE);
currentAnimator = null;
}
});
set.start();
currentAnimator = set;
}
});
}