自定义fragment出入栈时候的动画
在fragment出入栈时候添加动画，主要用到FragmentTransaction类中的方法:
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Set specific animation resources to run for the fragments that are entering and exiting in this transaction. These animations will not be played when popping the back stack.
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Set specific animation resources to run for the fragments that are entering and exiting in this transaction. The?popEnter?and?popExit?animations will be played for enter/exit operations specifically when popping the back stack.
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相关的方法还有（可直接设置标准的动画）：
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Select a standard transition animation for this transaction. May be one of?TRANSIT_NONE,?TRANSIT_FRAGMENT_OPEN, or?TRANSIT_FRAGMENT_CLOSE
Set a custom style resource that will be used for resolving transit animations.
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下面看一个示例：
1.主activity布局文件：
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<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:padding="4dip" android:gravity="center_horizontal" android:layout_width="match_parent" android:layout_height="match_parent"> <FrameLayout android:id="@+id/simple_fragment" android:layout_width="match_parent" android:layout_height="0px" android:layout_weight="1"> </FrameLayout> <Button android:id="@+id/new_fragment" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_weight="0" android:text="@string/new_fragment"> <requestFocus /> </Button></LinearLayout>?
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2.主activity，包括一个fragment类：CountingFragment
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public class FragmentCustomAnimations extends Activity { int mStackLevel = 1; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.fragment_stack); // Watch for button clicks. Button button = (Button)findViewById(R.id.new_fragment); button.setOnClickListener(new OnClickListener() { public void onClick(View v) { addFragmentToStack(); } }); if (savedInstanceState == null) { // Do first time initialization -- add initial fragment. Fragment newFragment = CountingFragment.newInstance(mStackLevel); FragmentTransaction ft = getFragmentManager().beginTransaction(); ft.add(R.id.simple_fragment, newFragment).commit(); } else { mStackLevel = savedInstanceState.getInt("level"); } } @Override public void onSaveInstanceState(Bundle outState) { super.onSaveInstanceState(outState); outState.putInt("level", mStackLevel); } void addFragmentToStack() { mStackLevel++; // Instantiate a new fragment. Fragment newFragment = CountingFragment.newInstance(mStackLevel); // Add the fragment to the activity, pushing this transaction // on to the back stack. FragmentTransaction ft = getFragmentManager().beginTransaction(); ft.setCustomAnimations(R.animator.fragment_slide_left_enter, R.animator.fragment_slide_left_exit, R.animator.fragment_slide_right_enter, R.animator.fragment_slide_right_exit); ft.replace(R.id.simple_fragment, newFragment); ft.addToBackStack(null); ft.commit(); } public static class CountingFragment extends Fragment { int mNum; /** * Create a new instance of CountingFragment, providing "num" * as an argument. */ static CountingFragment newInstance(int num) { CountingFragment f = new CountingFragment(); // Supply num input as an argument. Bundle args = new Bundle(); args.putInt("num", num); f.setArguments(args); return f; } /** * When creating, retrieve this instance's number from its arguments. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); mNum = getArguments() != null ? getArguments().getInt("num") : 1; } /** * The Fragment's UI is just a simple text view showing its * instance number. */ @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { View v = inflater.inflate(R.layout.hello_world, container, false); View tv = v.findViewById(R.id.text); ((TextView)tv).setText("Fragment #" + mNum); return v; } }}??
2.用户fragment出入站时候的动画文件（在res/animator目录下的四个文件）：
? ?fragment_slide_left_enter.xml
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<?xml version="1.0" encoding="utf-8"?><set xmlns:android="http://schemas.android.com/apk/res/android"> <objectAnimator android:interpolator="@android:interpolator/decelerate_quint" android:valueFrom="100dp" android:valueTo="0dp" android:valueType="floatType" android:propertyName="translationX" android:duration="@android:integer/config_mediumAnimTime" /> <objectAnimator android:interpolator="@android:interpolator/decelerate_quint" android:valueFrom="0.0" android:valueTo="1.0" android:valueType="floatType" android:propertyName="alpha" android:duration="@android:integer/config_mediumAnimTime" /></set>
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?fragment_slide_left_exit.xml
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<set xmlns:android="http://schemas.android.com/apk/res/android"> <objectAnimator android:interpolator="@android:interpolator/decelerate_quint" android:valueFrom="0dp" android:valueTo="-100dp" android:valueType="floatType" android:propertyName="translationX" android:duration="@android:integer/config_mediumAnimTime" /> <objectAnimator android:interpolator="@android:interpolator/decelerate_quint" android:valueFrom="1.0" android:valueTo="0.0" android:valueType="floatType" android:propertyName="alpha" android:duration="@android:integer/config_mediumAnimTime" /></set>
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?fragment_slide_right_enter.xml：
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<set xmlns:android="http://schemas.android.com/apk/res/android"> <objectAnimator android:interpolator="@android:interpolator/decelerate_quint" android:valueFrom="-100dp" android:valueTo="0dp" android:valueType="floatType" android:propertyName="translationX" android:duration="@android:integer/config_mediumAnimTime" /> <objectAnimator android:interpolator="@android:interpolator/decelerate_quint" android:valueFrom="0.0" android:valueTo="1.0" android:valueType="floatType" android:propertyName="alpha" android:duration="@android:integer/config_mediumAnimTime" /></set>
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?fragment_slide_right_exit.xml
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<set xmlns:android="http://schemas.android.com/apk/res/android"> <objectAnimator android:interpolator="@android:interpolator/decelerate_quint" android:valueFrom="0dp" android:valueTo="100dp" android:valueType="floatType" android:propertyName="translationX" android:duration="@android:integer/config_mediumAnimTime" /> <objectAnimator android:interpolator="@android:interpolator/decelerate_quint" android:valueFrom="1.0" android:valueTo="0.0" android:valueType="floatType" android:propertyName="alpha" android:duration="@android:integer/config_mediumAnimTime" /></set>?
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3.fragment中的createView()方法用到的布局文件hello_world.xml：
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<TextView xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/text" android:layout_width="match_parent" android:layout_height="match_parent" android:gravity="center_vertical|center_horizontal" android:textAppearance="?android:attr/textAppearanceMedium" android:text="@string/hello_world"/>?
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问题：objectAnimator是什么？怎么使用？