使用應用程式時,螢幕上會顯示新資訊,舊資訊也會移除。變更螢幕上顯示的內容可能會很突兀,且使用者可能會錯過突然出現的新內容。動畫會減慢變更速度,並利用動態效果吸引使用者的目光,使更新更顯而易見。
您可以使用三種常見的動畫來顯示或隱藏檢視畫面:顯示動畫、交叉漸變動畫和卡片翻轉動畫。
建立交叉漸變動畫
交叉淡出動畫 (也稱為「溶接」) 會逐漸淡出一個 View
或 ViewGroup
,同時淡入另一個 View
或 ViewGroup
。這個動畫很適合用於在應用程式中切換內容或檢視畫面的情況。這裡顯示的交叉漸變動畫使用 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漸變範例:
建立檢視畫面
建立要交叉漸變的兩個檢視畫面。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>
設定交叉漸變動畫
如要設定交叉漸變動畫,請按照下列步驟操作:
- 為要交叉淡出的檢視畫面建立成員變數。之後修改動畫期間的檢視畫面時,需要用到這些參照。
- 將要淡入
GONE
的檢視畫面顯示設定。這樣可以防止檢視畫面使用版面配置空間,並在版面配置計算時省略,加快處理速度 - 在成員變數中快取
config_shortAnimTime
系統屬性。這個屬性定義動畫的標準「短」時間長度。對於經常出現的細微動畫或動畫來說,這個時間長度就很適合。您也可以使用config_longAnimTime
和config_mediumAnimTime
。
以下範例使用先前程式碼片段的版面配置,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); } ... }
交叉淡出檢視畫面
正確設定檢視畫面後,如要交叉淡出,請按照下列步驟操作:
- 針對淡入效果的檢視畫面,將 Alpha 值設為 0,並將顯示設定從
GONE
的初始設定設為VISIBLE
。這樣一來,檢視區塊就會顯示,但會保持透明。 - 針對淡入效果的檢視區塊,為其 Alpha 值 0 到 1 加上動畫效果。針對淡出的檢視畫面,為 Alpha 值 1 到 0 加上動畫效果。
- 請在
Animator.AnimatorListener
中使用onAnimationEnd()
,設定淡出至GONE
的檢視畫面的顯示設定。雖然 Alpha 值為 0,但將檢視畫面的顯示設定設為GONE
會防止檢視畫面使用版面配置空間,並在版面配置計算作業中省略該空間,加快處理速度。
以下方法舉例說明相關做法:
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); } }); } }
建立資訊卡翻轉動畫
資訊卡會顯示模擬資訊卡翻轉的動畫,切換內容檢視畫面。這裡顯示的資訊卡翻轉動畫使用 FragmentTransaction
。
卡片外觀如下:
建立動畫物件
如要建立資訊卡翻轉動畫,請備妥 4 個動畫。兩個動畫器適用於卡片正面動畫向左側和左邊的動畫,以及動畫從左側和左側移動時的動畫效果。另外兩個動畫器適用於卡片背面動畫的右側和右側動畫,以及動畫向右方和右側移動時的動畫效果。
<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>
<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>
<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>
<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,可包含任何您需要的內容,例如兩個文字檢視區塊、兩張圖片,或是可切換的任意檢視畫面組合。稍後在製作動畫的片段中使用兩個版面配置。下列版面配置會建立資訊卡的一側,並顯示文字:
<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資訊卡的另一端,並顯示 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
為資訊卡正面和背面建立片段類別。在片段類別中,傳回您透過 onCreateView()
方法建立的版面配置。接著,您可以在要顯示資訊卡的父項活動中建立這個片段的例項。
以下範例顯示在使用這些片段的父項活動中的巢狀片段類別:
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); } } }
為卡片翻轉動畫
顯示父項活動中的片段。為此,請建立活動的版面配置。以下範例會建立 FrameLayout
,您可以在執行階段新增片段:
<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資訊卡正面:
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(); } } ... }
顯示資訊卡正面後,即可在適當時機顯示資訊卡背面及翻轉動畫。建立顯示卡片另一端可執行下列操作的方法:
- 設定您建立的自訂動畫,用於片段轉換功能。
- 將顯示的片段取代為新片段,並以您建立的自訂動畫將此事件加入動畫效果。
- 將先前顯示的片段新增至片段返回堆疊,因此當使用者輕觸返回按鈕時,資訊卡就會返回。
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(); } }
建立循環顯示動畫
顯示動畫可以在您顯示或隱藏一組 UI 元素時,為使用者提供視覺連貫性。ViewAnimationUtils.createCircularReveal()
方法可讓您為裁剪圓形建立動畫,藉此顯示或隱藏檢視畫面。此動畫提供 ViewAnimationUtils
類別,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畫面:
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()
動畫採用五個參數。第一個參數是您想要在畫面中隱藏或顯示的檢視畫面。接下來兩個參數是剪裁圓形中心的 X 和 Y 座標。一般而言,這會是檢視區塊的中心,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動畫。第四個參數是剪裁圓的起始半徑。
在上例中,初始半徑設為零,因此圓形隱藏顯示的檢視畫面。最後一個參數是圓形的最終半徑顯示檢視畫面時,最終半徑應大於檢視畫面,這樣檢視畫面就能在動畫結束前完整顯示。
如要隱藏之前可見的檢視畫面,請執行下列步驟:
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); }
在這種情況下,剪裁圓形的初始半徑會設為與檢視畫面大相大,這樣檢視畫面就會在動畫開始前顯示。最後一個半徑設為 0,因此系統在動畫結束時隱藏檢視畫面。在動畫中新增事件監聽器,以便在動畫完成時,將檢視畫面的顯示設定設為 INVISIBLE
。