在使用应用的过程中，屏幕上会显示新信息以及旧信息 信息。你可以立即更改屏幕上显示的内容 令人不悦，并且用户可能会错过突然出现的新内容。动画播放速度缓慢 向下移动并用运动吸引用户的注意力 更加明显
有三种常见的动画可用于显示或隐藏视图：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 View 或
ViewGroup（同时启用）
慢慢地淡入另一个此动画适合在以下情形下
切换内容或视图。此处显示的淡入淡出动画使用了
ViewPropertyAnimator、
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：
<ph type="x-smartling-placeholder">图 1.淡入淡出动画。
创建视图
创建两个您想要淡入淡出的视图。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：
- 为想要淡入淡出的视图创建成员变量。您需要 这些引用。
- 将淡入视图的可见性设置为
GONE。这会阻止视图 并将其从布局计算中省略， 正在处理 - 缓存
config_shortAnimTime系统属性。该属性定义了一个标准的“简短” 动画时长该时长非常适合用于精细动画或 频繁出现的动画效果config_longAnimTime和config_mediumAnimTime。
以下示例使用上一个代码段中的布局作为 活动内容视图：
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
正确设置视图后，可通过执行以下操作实现淡入淡出：
- 对于淡入的视图，请将 alpha 值设置为 0，并将可见性设置为
从初始值更改为
VISIBLE设置为GONE。这会使视图可见但处于透明状态。 - 对于淡入的视图，以动画形式呈现其 0 到 1 的 Alpha 值。对于 视图，以动画方式将 alpha 值从 1 到 0。
- 使用
onAnimationEnd()以Animator.AnimatorListener, 将淡出视图的可见性设置为GONE。虽然 alpha 值为 0，将视图的可见性设置为GONE会阻止视图 并将其从布局计算中省略， 处理。
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
卡片翻转操作通过显示模拟动画，在内容视图之间切换
翻转卡片此处显示的卡片翻转动画使用了
FragmentTransaction。
卡片翻转的效果如下：
<ph type="x-smartling-placeholder">图 2.卡片翻转动画。
创建 animator 对象
如需创建卡片翻转动画，您需要四个 Animator。两个 Animator 当卡片正面以动画形式呈现出来时，向左侧以动画形式呈现，以及当卡片以动画形式呈现时 左边和左边。另外两个 Animator 适用于在卡背面 分别以动画方式移入和移出右侧元素，以及向右侧以动画形式呈现。
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
卡片的每一面都是一个单独的布局，可以包含您在 例如要翻转的两个文本视图、两张图片或任意视图组合 。使用您稍后要添加动画效果的 fragment 中的两个布局。通过 以下布局会创建卡片的一侧（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，
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 中
类，则返回从
onCreateView()
方法。然后，您可以在父 activity 中创建此 fragment 的实例
卡片的显示位置
以下示例展示了父 activity 中的嵌套 fragment 类 使用它们：
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，请创建布局
以下示例创建了一个
您可以添加的FrameLayout
fragment 在运行时：
<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。通过 以下示例 activity 展示了如何按照 默认值：
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();
}
}
...
}
在显示卡片正面时，您可以同时显示卡片背面和 在适当的时间播放翻转动画。创建方法以显示 可执行以下操作的卡片：
- 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，并为此事件添加动画效果 自定义动画效果
- 将之前显示的 fragment 添加到 fragment 返回堆栈中，这样当 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
当您显示或隐藏组时，揭露动画可为用户提供视觉连续性
界面元素组成元素通过
ViewAnimationUtils.createCircularReveal()
方法，您可以通过动画方式呈现裁剪圆形来显示或隐藏视图。这个
中提供了
ViewAnimationUtils 类，
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() 动画采用五个参数。
第一个参数是要在屏幕上隐藏或显示的视图。通过
接下来的两个参数是裁剪中心的 X 和 Y 坐标。
圆圈。这通常是视图的中心，但您也可以使用
用户点按的点，以便动画从用户选择的位置开始。通过
第四个参数是裁剪圆形的起始半径。
在前面的示例中，初始半径设置为零，使视图 正在显示的圆圈被圆圈隐藏了。最后一个参数是 圆圈。显示视图时，使最终半径大于 视图，以便在动画播放完毕之前完全显示视图。
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设置为
视图，使视图在动画开始播放前可见。最后一个
radius 设置为 0，以便在动画播放完毕时隐藏视图。
为动画添加监听器，以便将视图的可见性设置为
INVISIBLE
。