使用動畫顯示或隱藏視圖

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淡入淡出 →

使用應用程式時，畫面上會顯示新資訊，並移除舊資訊。如果畫面上的內容突然變更，可能會讓使用者感到不適，也可能錯過突然出現的新內容。動畫會減緩變更速度，並透過動作吸引使用者目光，讓更新更明顯。

您可以使用三種常見動畫顯示或隱藏檢視區塊：顯示動畫、淡入淡出動畫和翻轉動畫。

建立淡入淡出動畫

淡入淡出動畫 (又稱「溶解」) 會逐漸淡出View或ViewGroup，同時淡入另一個View或ViewGroup。如果您想在應用程式中切換內容或檢視區塊，這個動畫就非常實用。這裡顯示的淡入淡出動畫使用 ViewPropertyAnimator，適用於 Android 3.1 (API 級別 12) 以上版本。

以下是從進度指標到文字內容的交叉淡化效果範例：

圖 1. 交叉漸變動畫。

建立檢視畫面

建立要淡入淡出的兩個檢視區塊。以下範例會建立進度指標和可捲動的文字檢視區塊：

<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>

設定淡入淡出動畫

如要設定淡入淡出動畫，請按照下列步驟操作：

  1. 為要淡入淡出的檢視區塊建立成員變數。您稍後在動畫期間修改檢視區塊時，需要這些參照。
  2. 將要淡入的檢視畫面瀏覽權限設為 GONE。這樣可防止檢視區塊使用版面配置空間，並從版面配置計算中省略檢視區塊，進而加快處理速度
  3. 將 config_shortAnimTime 系統屬性快取到成員變數中。這項屬性會定義動畫的標準「短」時間長度。這個時間長度適合用於細微的動畫或經常發生的動畫。config_longAnimTime 和 config_mediumAnimTime 也適用。

以下範例使用先前程式碼片段中的版面配置做為活動內容檢視畫面：

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);
    }
    ...
}

交叉漸變檢視畫面

正確設定檢視區塊後，請執行下列操作，讓檢視區塊淡入淡出：

  1. 針對淡入的檢視區塊，將 Alpha 值設為 0，並將顯示設定從初始的 GONE 設為 VISIBLE。這會讓檢視畫面顯示出來，但呈現透明狀態。
  2. 針對淡入的檢視區塊，將 Alpha 值從 0 設為 1。針對淡出的檢視區塊，將 Alpha 值從 1 設為 0。
  3. 在 Animator.AnimatorListener 中使用 onAnimationEnd()，將淡出檢視區塊的顯示設定設為 GONE。即使 alpha 值為 0，將檢視區塊的可見度設為 GONE 仍可避免檢視區塊使用版面配置空間，並將其從版面配置計算中省略，進而加快處理速度。

以下方法提供相關範例：

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);
                    }
                });
    }
}

建立卡片翻轉動畫

資訊卡翻轉會顯示模擬資訊卡翻轉的動畫，藉此在內容檢視畫面之間切換。這裡顯示的卡片翻轉動畫使用 FragmentTransaction。

卡片翻轉效果如下：

圖 2. 卡片翻轉動畫。

建立動畫師物件

如要建立卡片翻轉動畫，需要四個動畫師。兩個動畫師分別負責卡片正面動畫向左移出，以及從左側移入。另外兩個動畫師則用於卡片背面從右側動畫進入畫面，以及動畫移出畫面並移至右側時。

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>

建立檢視畫面

資訊卡的每一面都是獨立的版面配置，可包含任何您想要的內容，例如兩個文字檢視畫面、兩張圖片，或任何要翻轉切換的檢視畫面組合。在稍後要製作動畫的片段中使用這兩個版面配置。下列版面配置會建立資訊卡的一面，顯示文字：

<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>

下一個版面配置會建立卡片的另一面，顯示 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" />

建立片段

為卡片正面和背面建立片段類別。在片段類別中，從 onCreateView() 方法傳回您建立的版面配置。然後，您可以在要顯示資訊卡的父項活動中，建立這個片段的執行個體。

以下範例顯示父項活動中使用的巢狀片段類別：

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);
    }
    }
}

為卡片翻轉加入動畫效果

在父項活動中顯示片段。如要這麼做，請為活動建立版面配置。以下範例會建立 FrameLayout，您可以在執行階段將片段新增至該物件：

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

在活動程式碼中，將內容檢視畫面設為您建立的版面配置。 建議您在建立活動時顯示預設片段。以下範例活動說明如何預設顯示卡片正面：

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();
        }
    }
    ...
}

顯示卡片正面後，您可以在適當時間使用翻轉動畫顯示卡片背面。建立方法來顯示卡片的另一面，並執行下列操作：

  • 設定您為片段轉場效果建立的自訂動畫。
  • 以新片段取代顯示的片段，並使用您建立的自訂動畫，為這個事件加上動畫效果。
  • 將先前顯示的片段新增至片段返回堆疊，因此使用者輕觸「返回」按鈕時，系統會將資訊卡翻回正面。

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();
    }
}

建立圓形揭露動畫

顯示或隱藏一組 UI 元素時，顯示動畫可為使用者提供視覺連續性。ViewAnimationUtils.createCircularReveal() 方法可讓您將裁剪圓形動畫化，以顯示或隱藏檢視區塊。這項動畫是在 ViewAnimationUtils 類別中提供，適用於 Android 5.0 (API 級別 21) 以上版本。

以下範例說明如何顯示先前隱藏的檢視區塊：

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() 動畫會使用五個參數。 第一個參數是要在畫面上隱藏或顯示的檢視區塊。接下來的兩個參數是裁剪圓形的中心點 X 和 Y 座標。這通常是檢視區塊的中心，但您也可以使用使用者輕觸的點，讓動畫從他們選取的位置開始。第四個參數是裁剪圓形的起始半徑。

在上一個範例中，初始半徑設為零，因此顯示的檢視區塊會隱藏在圓圈中。最後一個參數是圓形的最終半徑。顯示檢視區塊時，請將最終半徑設為大於檢視區塊，這樣檢視區塊就能在動畫結束前完全顯示。

如要隱藏先前顯示的檢視畫面，請按照下列步驟操作：

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，裁剪圓形的初始半徑會設為與檢視區塊一樣大，因此檢視區塊會在動畫開始前顯示。最終半徑設為零，因此動畫完成時檢視畫面會隱藏。在動畫中新增監聽器，以便在動畫完成時，將檢視區塊的顯示設定設為 INVISIBLE。

其他資源

  • 使用 Jetpack Compose 製作動畫。
  • 使用 Jetpack Compose 實作手勢。