使用动画显示或隐藏视图

试用 Compose 方式
Jetpack Compose 是推荐用于 Android 的界面工具包。了解如何在 Compose 中使用动画。

在使用应用时,屏幕上会显示新信息并移除旧信息。立即更改屏幕上显示的内容可能会令人不快,并且用户可能会错过突然出现的新内容。动画会减慢更改速度,并通过动作吸引用户的注意力,使更新更明显。

您可以使用以下三种常见的动画来显示或隐藏视图:显示动画、淡入淡出动画和卡片翻转动画。

创建淡入淡出动画

淡入淡出动画(也称为“渐隐”)会逐渐淡出一个 ViewViewGroup,同时淡入另一个。如果您想在应用中切换内容或视图,此动画会非常有用。此处显示的淡入淡出动画使用 ViewPropertyAnimator,它适用于 Android 3.1(API 级别 12)及更高版本。

以下是从进度指示器切换到文本内容的淡入淡出示例:

图 1.淡入淡出动画。

创建视图

创建两个要淡入淡出的视图。以下示例创建了一个进度指示器和可滚动的文本视图:

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/content"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <TextView style="?android:textAppearanceMedium"
            android:lineSpacingMultiplier="1.2"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="@string/lorem_ipsum"
            android:padding="16dp" />

    </ScrollView>

    <ProgressBar android:id="@+id/loading_spinner"
        style="?android:progressBarStyleLarge"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center" />

</FrameLayout>

设置淡入淡出动画

如需设置淡入淡出动画,请执行以下操作:

  1. 为想要淡入淡出的视图创建成员变量。之后在动画播放期间修改视图时,需要使用这些引用。
  2. 将淡入的视图的可见性设置为 GONE。这可以防止视图使用布局空间,并在布局计算中省略它,从而加快处理速度
  3. config_shortAnimTime 系统属性缓存在成员变量中。此属性用于定义动画的标准“短”时长。此时长非常适合频繁出现的细微动画或动画。您也可以使用 config_longAnimTimeconfig_mediumAnimTime

以下示例使用上一个代码段中的布局作为 activity 内容视图:

Kotlin

class CrossfadeActivity : Activity() {

    private lateinit var contentView: View
    private lateinit var loadingView: View
    private var shortAnimationDuration: Int = 0
    ...
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_crossfade)

        contentView = findViewById(R.id.content)
        loadingView = findViewById(R.id.loading_spinner)

        // Initially hide the content view.
        contentView.visibility = View.GONE

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

Java

public class CrossfadeActivity extends Activity {

    private View contentView;
    private View loadingView;
    private int shortAnimationDuration;
    ...
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_crossfade);

        contentView = findViewById(R.id.content);
        loadingView = findViewById(R.id.loading_spinner);

        // Initially hide the content view.
        contentView.setVisibility(View.GONE);

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

淡入淡出视图

正确设置视图之后,可通过执行以下操作来实现淡入淡出:

  1. 对于淡入的视图,从初始设置 GONE 将 Alpha 值设置为 0,将可见性设置为 VISIBLE。这会使视图可见但透明。
  2. 对于淡入的视图,为其 Alpha 值从 0 变为 1 以动画形式呈现。对于淡出的视图,为 Alpha 值添加从 1 到 0 的动画效果。
  3. Animator.AnimatorListener 中使用 onAnimationEnd(),将淡出视图的可见性设置为 GONE。即使 Alpha 值为 0,将视图的可见性设置为 GONE 也会阻止视图使用布局空间,并在布局计算中将其省去,从而加快处理速度。

以下方法通过示例说明了如何执行此操作:

Kotlin

class CrossfadeActivity : Activity() {

    private lateinit var contentView: View
    private lateinit var loadingView: View
    private var shortAnimationDuration: Int = 0
    ...
    private fun crossfade() {
        contentView.apply {
            // Set the content view to 0% opacity but visible, so that it is
            // visible but fully transparent during the animation.
            alpha = 0f
            visibility = View.VISIBLE

            // Animate the content view to 100% opacity and clear any animation
            // listener set on the view.
            animate()
                    .alpha(1f)
                    .setDuration(shortAnimationDuration.toLong())
                    .setListener(null)
        }
        // Animate the loading view to 0% opacity. After the animation ends,
        // set its visibility to GONE as an optimization step so it doesn't
        // participate in layout passes.
        loadingView.animate()
                .alpha(0f)
                .setDuration(shortAnimationDuration.toLong())
                .setListener(object : AnimatorListenerAdapter() {
                    override fun onAnimationEnd(animation: Animator) {
                        loadingView.visibility = View.GONE
                    }
                })
    }
}

Java

public class CrossfadeActivity extends Activity {

    private View contentView;
    private View loadingView;
    private int shortAnimationDuration;
    ...
    private void crossfade() {

        // Set the content view to 0% opacity but visible, so that it is
        // visible but fully transparent during the animation.
        contentView.setAlpha(0f);
        contentView.setVisibility(View.VISIBLE);

        // Animate the content view to 100% opacity and clear any animation
        // listener set on the view.
        contentView.animate()
                .alpha(1f)
                .setDuration(shortAnimationDuration)
                .setListener(null);

        // Animate the loading view to 0% opacity. After the animation ends,
        // set its visibility to GONE as an optimization step so it doesn't
        // participate in layout passes.
        loadingView.animate()
                .alpha(0f)
                .setDuration(shortAnimationDuration)
                .setListener(new AnimatorListenerAdapter() {
                    @Override
                    public void onAnimationEnd(Animator animation) {
                        loadingView.setVisibility(View.GONE);
                    }
                });
    }
}

创建卡片翻转动画

卡片翻转通过显示模拟卡片翻转的动画来在内容视图之间切换。此处显示的卡片翻转动画使用 FragmentTransaction

卡片翻转的效果如下:

图 2.卡片翻转动画。

创建 Animator 对象

若要制作卡片翻转动画,您需要四个 Animator。两个 Animator 分别对应于卡片正面从左侧和左侧淡出动画的情况,以及从左侧动画呈现的情况。其他两个 Animator 分别适用于卡片背面何时从右侧移入和从右侧呈现动画效果,以及何时从右侧移入动画效果。

card_flip_left_in.xml

<set xmlns:android="http://schemas.android.com/apk/res/android">
    <!-- Before rotating, immediately set the alpha to 0. -->
    <objectAnimator
        android:valueFrom="1.0"
        android:valueTo="0.0"
        android:propertyName="alpha"
        android:duration="0" />

    <!-- Rotate. -->
    <objectAnimator
        android:valueFrom="-180"
        android:valueTo="0"
        android:propertyName="rotationY"
        android:interpolator="@android:interpolator/accelerate_decelerate"
        android:duration="@integer/card_flip_time_full" />

    <!-- Halfway through the rotation, set the alpha to 1. See startOffset. -->
    <objectAnimator
        android:valueFrom="0.0"
        android:valueTo="1.0"
        android:propertyName="alpha"
        android:startOffset="@integer/card_flip_time_half"
        android:duration="1" />
</set>

card_flip_left_out.xml

<set xmlns:android="http://schemas.android.com/apk/res/android">
    <!-- Rotate. -->
    <objectAnimator
        android:valueFrom="0"
        android:valueTo="180"
        android:propertyName="rotationY"
        android:interpolator="@android:interpolator/accelerate_decelerate"
        android:duration="@integer/card_flip_time_full" />

    <!-- Halfway through the rotation, set the alpha to 0. See startOffset. -->
    <objectAnimator
        android:valueFrom="1.0"
        android:valueTo="0.0"
        android:propertyName="alpha"
        android:startOffset="@integer/card_flip_time_half"
        android:duration="1" />
</set>

card_flip_right_in.xml

<set xmlns:android="http://schemas.android.com/apk/res/android">
    <!-- Before rotating, immediately set the alpha to 0. -->
    <objectAnimator
        android:valueFrom="1.0"
        android:valueTo="0.0"
        android:propertyName="alpha"
        android:duration="0" />

    <!-- Rotate. -->
    <objectAnimator
        android:valueFrom="180"
        android:valueTo="0"
        android:propertyName="rotationY"
        android:interpolator="@android:interpolator/accelerate_decelerate"
        android:duration="@integer/card_flip_time_full" />

    <!-- Halfway through the rotation, set the alpha to 1. See startOffset. -->
    <objectAnimator
        android:valueFrom="0.0"
        android:valueTo="1.0"
        android:propertyName="alpha"
        android:startOffset="@integer/card_flip_time_half"
        android:duration="1" />
</set>

card_flip_right_out.xml

<set xmlns:android="http://schemas.android.com/apk/res/android">
    <!-- Rotate. -->
    <objectAnimator
        android:valueFrom="0"
        android:valueTo="-180"
        android:propertyName="rotationY"
        android:interpolator="@android:interpolator/accelerate_decelerate"
        android:duration="@integer/card_flip_time_full" />

    <!-- Halfway through the rotation, set the alpha to 0. See startOffset. -->
    <objectAnimator
        android:valueFrom="1.0"
        android:valueTo="0.0"
        android:propertyName="alpha"
        android:startOffset="@integer/card_flip_time_half"
        android:duration="1" />
</set>

创建视图

卡片的每一侧都是独立的布局,可以包含您需要的任何内容,例如两个文本视图、两张图片或要在其间翻转的任意视图组合。在稍后您添加动画的 fragment 中使用两种布局。以下布局会创建卡片的一侧,其中显示文本:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:background="#a6c"
    android:padding="16dp"
    android:gravity="bottom">

    <TextView android:id="@android:id/text1"
        style="?android:textAppearanceLarge"
        android:textStyle="bold"
        android:textColor="#fff"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/card_back_title" />

    <TextView style="?android:textAppearanceSmall"
        android:textAllCaps="true"
        android:textColor="#80ffffff"
        android:textStyle="bold"
        android:lineSpacingMultiplier="1.2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/card_back_description" />

</LinearLayout>

下一个布局会创建卡片的另一面,后者会显示一个 ImageView

<ImageView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:src="@drawable/image1"
    android:scaleType="centerCrop"
    android:contentDescription="@string/description_image_1" />

创建 Fragment

为卡片的正面和背面创建 Fragment 类。在 fragment 类中,返回您通过 onCreateView() 方法创建的布局。然后,您可以在要显示卡片的父 activity 中创建此 fragment 的实例。

以下示例显示了父 activity 中使用嵌套 fragment 类:

Kotlin

class CardFlipActivity : FragmentActivity() {
    ...
    /**

                    *   A fragment representing the front of the card.
     */
    class CardFrontFragment : Fragment() {

    override fun onCreateView(
                inflater: LayoutInflater,
                container: ViewGroup?,
                savedInstanceState: Bundle?
    ): View = inflater.inflate(R.layout.fragment_card_front, container, false)
    }

    /**
    *   A fragment representing the back of the card.
    */
    class CardBackFragment : Fragment() {

    override fun onCreateView(
                inflater: LayoutInflater,
                container: ViewGroup?,
                savedInstanceState: Bundle?
    ): View = inflater.inflate(R.layout.fragment_card_back, container, false)
    }
}

Java

public class CardFlipActivity extends FragmentActivity {
    ...
    /**
    *   A fragment representing the front of the card.
    */
    public class CardFrontFragment extends Fragment {
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            return inflater.inflate(R.layout.fragment_card_front, container, false);
    }
    }

    /**
    *   A fragment representing the back of the card.
    */
    public class CardBackFragment extends Fragment {
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            return inflater.inflate(R.layout.fragment_card_back, container, false);
    }
    }
}

为卡片翻转添加动画

显示父 activity 内的 fragment。为此,请为您的 activity 创建布局。以下示例创建了一个 FrameLayout,您可以在运行时向其中添加 fragment:

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

在 activity 代码中,将内容视图设置为您创建的布局。最好在创建 activity 时显示默认 fragment。以下示例 activity 展示了如何默认显示卡片的正面:

Kotlin

class CardFlipActivity : FragmentActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_activity_card_flip)
        if (savedInstanceState == null) {
            supportFragmentManager.beginTransaction()
                    .add(R.id.container, CardFrontFragment())
                    .commit()
        }
    }
    ...
}

Java

public class CardFlipActivity extends FragmentActivity {

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

        if (savedInstanceState == null) {
            getSupportFragmentManager()
                    .beginTransaction()
                    .add(R.id.container, new CardFrontFragment())
                    .commit();
        }
    }
    ...
}

显示卡片正面后,您可以在适当的时间显示卡片背面和翻转动画。创建一种方法来显示卡片的另一面,该方法需要执行以下操作:

  • 设置您为 Fragment 转换创建的自定义动画。
  • 将显示的 fragment 替换为新的 fragment,并使用您创建的自定义动画为此事件添加动画效果。
  • 将之前显示的 fragment 添加到 fragment 返回堆栈,以便当用户点按返回按钮时,卡片会翻转回来。

Kotlin

class CardFlipActivity : FragmentActivity() {
    ...
    private fun flipCard() {
        if (showingBack) {
            supportFragmentManager.popBackStack()
            return
        }

        // Flip to the back.

        showingBack = true

        // Create and commit a new fragment transaction that adds the fragment
        // for the back of the card, uses custom animations, and is part of the
        // fragment manager's back stack.

        supportFragmentManager.beginTransaction()

                // Replace the default fragment animations with animator
                // resources representing rotations when switching to the back
                // of the card, as well as animator resources representing
                // rotations when flipping back to the front, such as when the
                // system Back button is tapped.
                .setCustomAnimations(
                        R.animator.card_flip_right_in,
                        R.animator.card_flip_right_out,
                        R.animator.card_flip_left_in,
                        R.animator.card_flip_left_out
                )

                // Replace any fragments in the container view with a fragment
                // representing the next page, indicated by the just-incremented
                // currentPage variable.
                .replace(R.id.container, CardBackFragment())

                // Add this transaction to the back stack, letting users press
                // the Back button to get to the front of the card.
                .addToBackStack(null)

                // Commit the transaction.
                .commit()
    }
}

Java

public class CardFlipActivity extends FragmentActivity {
    ...
    private void flipCard() {
        if (showingBack) {
            getSupportFragmentManager().popBackStack();
            return;
        }

        // Flip to the back.

        showingBack = true;

        // Create and commit a new fragment transaction that adds the fragment
        // for the back of the card, uses custom animations, and is part of the
        // fragment manager's back stack.

        getSupportFragmentManager()
                .beginTransaction()

                // Replace the default fragment animations with animator
                // resources representing rotations when switching to the back
                // of the card, as well as animator resources representing
                // rotations when flipping back to the front, such as when the
                // system Back button is pressed.
                .setCustomAnimations(
                        R.animator.card_flip_right_in,
                        R.animator.card_flip_right_out,
                        R.animator.card_flip_left_in,
                        R.animator.card_flip_left_out)

                // Replace any fragments in the container view with a fragment
                // representing the next page, indicated by the just-incremented
                // currentPage variable.
                .replace(R.id.container, new CardBackFragment())

                // Add this transaction to the back stack, letting users press
                // Back to get to the front of the card.
                .addToBackStack(null)

                // Commit the transaction.
                .commit();
    }
}

创建圆形揭露动画

当您显示或隐藏一组界面元素时,揭露动画可为用户提供视觉连续性。借助 ViewAnimationUtils.createCircularReveal() 方法,您可以为裁剪圆形添加动画以显示或隐藏视图。此动画在 ViewAnimationUtils 类中提供,适用于 Android 5.0(API 级别 21)及更高版本。

以下示例展示了如何揭露之前不可见的视图:

Kotlin

// A previously invisible view.
val myView: View = findViewById(R.id.my_view)

// Check whether the runtime version is at least Android 5.0.
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
    // Get the center for the clipping circle.
    val cx = myView.width / 2
    val cy = myView.height / 2

    // Get the final radius for the clipping circle.
    val finalRadius = Math.hypot(cx.toDouble(), cy.toDouble()).toFloat()

    // Create the animator for this view. The start radius is 0.
    val anim = ViewAnimationUtils.createCircularReveal(myView, cx, cy, 0f, finalRadius)
    // Make the view visible and start the animation.
    myView.visibility = View.VISIBLE
    anim.start()
} else {
    // Set the view to invisible without a circular reveal animation below
    // Android 5.0.
    myView.visibility = View.INVISIBLE
}

Java

// A previously invisible view.
View myView = findViewById(R.id.my_view);

// Check whether the runtime version is at least Android 5.0.
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
    // Get the center for the clipping circle.
    int cx = myView.getWidth() / 2;
    int cy = myView.getHeight() / 2;

    // Get the final radius for the clipping circle.
    float finalRadius = (float) Math.hypot(cx, cy);

    // Create the animator for this view. The start radius is 0.
    Animator anim = ViewAnimationUtils.createCircularReveal(myView, cx, cy, 0f, finalRadius);

    // Make the view visible and start the animation.
    myView.setVisibility(View.VISIBLE);
    anim.start();
} else {
    // Set the view to invisible without a circular reveal animation below
    // Android 5.0.
    myView.setVisibility(View.INVISIBLE);
}

ViewAnimationUtils.createCircularReveal() 动画接受五个参数。第一个参数是要在屏幕上隐藏或显示的视图。接下来的两个参数是裁剪圆形中心的 X 和 Y 坐标。通常,这是视图的中心,但您也可以使用用户点按的点,让动画从用户选择的位置开始。第四个参数是裁剪圆形的起始半径。

在前面的示例中,初始半径设置为 0,因此圆形会隐藏所显示的视图。最后一个参数是圆的最终半径。显示视图时,请使最终半径大于视图,以便视图在动画结束之前完全显示。

如需隐藏之前可见的视图,请执行以下操作:

Kotlin

// A previously visible view.
val myView: View = findViewById(R.id.my_view)

// Check whether the runtime version is at least Android 5.0.
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
    // Get the center for the clipping circle.
    val cx = myView.width / 2
    val cy = myView.height / 2

    // Get the initial radius for the clipping circle.
    val initialRadius = Math.hypot(cx.toDouble(), cy.toDouble()).toFloat()

    // Create the animation. The final radius is 0.
    val anim = ViewAnimationUtils.createCircularReveal(myView, cx, cy, initialRadius, 0f)

    // Make the view invisible when the animation is done.
    anim.addListener(object : AnimatorListenerAdapter() {

        override fun onAnimationEnd(animation: Animator) {
            super.onAnimationEnd(animation)
            myView.visibility = View.INVISIBLE
        }
    })

    // Start the animation.
    anim.start()
} else {
    // Set the view to visible without a circular reveal animation below
    // Android 5.0.
    myView.visibility = View.VISIBLE
}

Java

// A previously visible view.
final View myView = findViewById(R.id.my_view);

// Check whether the runtime version is at least Android 5.0.
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
    // Get the center for the clipping circle.
    int cx = myView.getWidth() / 2;
    int cy = myView.getHeight() / 2;

    // Get the initial radius for the clipping circle.
    float initialRadius = (float) Math.hypot(cx, cy);

    // Create the animation. The final radius is 0.
    Animator anim = ViewAnimationUtils.createCircularReveal(myView, cx, cy, initialRadius, 0f);

    // Make the view invisible when the animation is done.
    anim.addListener(new AnimatorListenerAdapter() {
        @Override
        public void onAnimationEnd(Animator animation) {
            super.onAnimationEnd(animation);
            myView.setVisibility(View.INVISIBLE);
        }
    });

    // Start the animation.
    anim.start();
} else {
    // Set the view to visible without a circular reveal animation below Android
    // 5.0.
    myView.setVisibility(View.VISIBLE);
}

在本例中,裁剪圆形的初始半径被设置为与视图一样大,以便视图在动画开始播放之前可见。最终半径应设置为零,以便在动画播放完毕时隐藏视图。为动画添加监听器,以便在动画播放完毕后将视图的可见性设置为 INVISIBLE

其他资源