编写:XizhiXu - 原文:http://developer.android.com/training/animation/cardflip.html
这节课展示如何使用自定义Fragment动画实现Card翻转动画。Card翻转动画通过模拟Card翻转的效果实现view内容的切换。
下面是card翻转动画的样子：
如果你想直接查看整个例子，下载并运行App样例然后选择Card翻转例子。查看下列文件中的代码实现：
src/CardFlipActivity.javaanimator/card_flip_right_in.xmlanimator/card_flip_right_out.xmlanimator/card_flip_left_in.xmlanimator/card_flip_left_out.xmllayout/fragment_card_back.xmllayout/fragment_card_front.xml创建Card翻转动画，我们需要两个Animator。一个让正面的card的右侧向左翻转渐出，一个让背面的Card向右翻转渐入。我们还需要两个 Animator让背面的card的右侧向左翻转渐入，一个让向右翻转渐入。
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" />
<!-- Half-way through the rotation (see startOffset), set the alpha to 1. -->
<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" />
<!-- Half-way through the rotation (see startOffset), set the alpha to 0. -->
<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" />
<!-- Half-way through the rotation (see startOffset), set the alpha to 1. -->
<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" />
<!-- Half-way through the rotation (see startOffset), set the alpha to 0. -->
<objectAnimator
android:valueFrom="1.0"
android:valueTo="0.0"
android:propertyName="alpha"
android:startOffset="@integer/card_flip_time_half"
android:duration="1" />
</set>Card的每一面是一个独立的布局，比如两屏文字，两张图片，或者任何View的组合。然后我们将在应用动画的Fragment里面用到这两个布局。下面的布局创建了展示文本Card的一面：
<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>Card另一面显示一个 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" />为Card正反面创建Fragment，这些类从 onCreateView() 方法中分别为每个Framgent返回你之前创建的布局。在想要显示Card的父Activity中，我们可以创建对应的Fragment 实例。下面的例子展示父Activity内嵌套的Fragment：
public class CardFlipActivity extends Activity {
...
/**
* 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);
}
}
}现在，我们需要在父Activity中展示Fragment。为此，首先创建Activity的布局。下面例子创建了一个可以在运行时添加Fragment的 FrameLayout。
<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，把先前创建的布局设置成其ContentVew。当Activity创建时展示一个默认的Fragment是个不错的注意。所以下面的Activity样例表明了如何默认显示卡片正面：
public class CardFlipActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_activity_card_flip);
if (savedInstanceState == null) {
getFragmentManager()
.beginTransaction()
.add(R.id.container, new CardFrontFragment())
.commit();
}
}
...
}既然现在显示了卡片的正面，我们可以在合适时机用翻转动画显示卡片背面了。创建一个方法来显示背面，它需要做下面这些事情：
将Fragment转换设置我们刚做的自定义动画
用新Fragment替换当前显示的Fragment，并且应用之前创建的动画到该事件中。
添加之前显示的Fragment到Fragment的回退栈（back stack）中，所以当用户按下 Back 键时，Card会翻转回来。
private void flipCard() {
if (mShowingBack) {
getFragmentManager().popBackStack();
return;
}
// Flip to the back.
mShowingBack = 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.
getFragmentManager()
.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 (e.g. 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 currently 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, allowing users to press Back
// to get to the front of the card.
.addToBackStack(null)
// Commit the transaction.
.commit();
}