Cómo ampliar una vista usando animaciones con zoom

En esta lección, se explica cómo hacer una animación de tocar para acercar. Este tipo de animación es útil para apps como las galerías de fotos, ya que permite animar una vista de una miniatura a una imagen de tamaño completo que ocupa la pantalla.

A continuación, se muestra una animación de tocar para acercar que expande la miniatura de una imagen para ocupar la pantalla:

Animación de zoom
 

Si quieres adelantar y ver un ejemplo en funcionamiento, consulta la clase UIAnimation del proyecto android-WearSpeakerSample en GitHub.

Cómo crear las vistas

Crea un archivo de diseño que contenga la versión pequeña y grande del contenido que quieres acercar. En el siguiente ejemplo, se crea un ImageButton para una miniatura de imagen en la que se puede hacer clic y una ImageView que muestra una vista agrandada de la imagen:

    <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>
    

Cómo configurar la animación de zoom

Una vez que apliques tu diseño, configura los controladores de eventos que activan la animación de zoom. En el siguiente ejemplo, se agrega un View.OnClickListener al ImageButton a fin de ejecutar la animación de zoom cuando el usuario hace clic en el botón de la imagen:

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);
        }
        ...
    }
    

Cómo acercar la vista

Ahora, deberás animar de la vista de tamaño normal a la vista con zoom cuando corresponda. En general, debes animar de los límites de la vista de tamaño normal a los límites de la vista de tamaño más grande. En el siguiente método, se muestra cómo implementar una animación de zoom que pase de la miniatura de una imagen a una vista agrandada. Para ello, sigue estos pasos:

  1. Asigna la imagen de alta resolución a la ImageView (agrandada) "con zoom" oculta. En el siguiente ejemplo, para simplificar, se carga un recurso de imagen grande en el subproceso de IU. Realiza esta carga en un subproceso por separado para evitar bloquear el subproceso de IU y, luego, define el mapa de bits en el subproceso de IU. Idealmente, el mapa de bits no debería superar el tamaño de la pantalla.
  2. Calcula los límites de inicio y finalización de ImageView.
  3. Anima cada una de las cuatro propiedades de posicionamiento y tamaño X, Y, (SCALE_X y SCALE_Y) al mismo tiempo, desde los límites de inicio hasta los límites de finalización. Estas cuatro animaciones se agregan a un AnimatorSet a fin de que se puedan iniciar al mismo tiempo.
  4. Para alejar la imagen, ejecuta una animación similar, pero al revés, cuando el usuario toca la pantalla con la imagen con zoom. Para ello, puedes agregar un View.OnClickListener a la ImageView. Cuando el usuario hace clic, se minimiza la ImageView y regresa al tamaño de la miniatura de imagen. Además, su visibilidad se define en GONE para ocultarla.

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;
            }
        });
    }