Transition
概念
在Transition中，有一些新的概念，例如Scene, Transition, TransitionSet, TransitionManager. 除了Scene, 其他的概念其实和简单的View动画差不多。
Scene
Scene的构造
Scene是一个新的概念，它被翻译成了“场景”，这个描述很准确，但是比较难以理解。下面通过源码分析
/ * Constructs a Scene which, when entered, will remove any * children from the sceneRoot container and add the layout * object as a new child of that container. * * @param sceneRoot The root of the hierarchy in which scene changes * and transitions will take place. * @param layout The view hierarchy of this scene, added as a child * of sceneRoot when this scene is entered. */ public Scene(ViewGroup sceneRoot, View layout) { mSceneRoot = sceneRoot; mLayout = layout; }下面是Scene的另一个构造器
/ * Constructs a Scene which, when entered, will remove any * children from the sceneRoot container and will inflate and add * the hierarchy specified by the layoutId resource file. * * This method is hidden because layoutId-based scenes should be * created by the caching factory method {@link Scene#getCurrentScene(View)}.
* * @param sceneRoot The root of the hierarchy in which scene changes * and transitions will take place. * @param layoutId The id of a resource file that defines the view * hierarchy of this scene. * @param context The context used in the process of inflating * the layout resource. */ private Scene(ViewGroup sceneRoot, int layoutId, Context context) { mContext = context; mSceneRoot = sceneRoot; mLayoutId = layoutId; }注释：构造一个场景，当进入这个场景时，将从场景的sceneRoot中移除其他所有的children, 并inflate和添加由layoutId指定的资源文件的view层。 这是一个私有的构造器，因为基于layoutId构造的场景，使用了缓存，即可以进行多次复用。
下面是会调用上面的私有构造器的一个静态方法
/ * Returns a Scene described by the resource file associated with the given * layoutId parameter. If such a Scene has already been created for * the given sceneRoot, that same Scene will be returned. * This caching of layoutId-based scenes enables sharing of common scenes * between those created in code and those referenced by {@link TransitionManager} * XML resource files. * * @param sceneRoot The root of the hierarchy in which scene changes * and transitions will take place. * @param layoutId The id of a standard layout resource file. * @param context The context used in the process of inflating * the layout resource. * @return The scene for the given root and layout id */ public static Scene getSceneForLayout(ViewGroup sceneRoot, int layoutId, Context context) { SparseArray
scenes = (SparseArray
) sceneRoot.getTag( com.android.internal.R.id.scene_layoutid_cache);
if (scenes ==
null) { scenes =
new SparseArray
(); sceneRoot.setTagInternal(com.android.internal.R.id.scene_layoutid_cache, scenes); } Scene scene = scenes.get(layoutId);
if (scene !=
null) {
return scene; }
else { scene =
new Scene(sceneRoot, layoutId, context); scenes.put(layoutId, scene);
return scene; } }
Scene的分析
下面是Scene.enter()方法
/ * Enters this scene, which entails changing all values that * are specified by this scene. These may be values associated * with a layout view group or layout resource file which will * now be added to the scene root, or it may be values changed by * an {@link #setEnterAction(Runnable)} enter action}, or a * combination of the these. No transition will be run when the * scene is entered. To get transition behavior in scene changes, * use one of the methods in {@link TransitionManager} instead. */ public void enter() { // Apply layout change, if any if (mLayoutId > 0 || mLayout != null) { // empty out parent container before adding to it getSceneRoot().removeAllViews(); if (mLayoutId > 0) { LayoutInflater.from(mContext).inflate(mLayoutId, mSceneRoot); } else { mSceneRoot.addView(mLayout); } } // Notify next scene that it is entering. Subclasses may override to configure scene. if (mEnterAction != null) { mEnterAction.run(); } setCurrentScene(mSceneRoot, this); }下面是Scene.exit()方法
/ * Exits this scene, if it is the current scene * on the scene's {@link #getSceneRoot() scene root}. The current scene is * set when {@link #enter() entering} a scene. * Exiting a scene runs the {@link #setExitAction(Runnable) exit action} * if there is one. */ public void exit() { if (getCurrentScene(mSceneRoot) == this) { if (mExitAction != null) { mExitAction.run(); } } }Transition
简单分析：Transition是一个抽象类，保留了两个抽象方法由子类实现captureStartValues(TransitionValues transitionValues)和captureEndValues(TransitionValues transitionValues). 而Transition有一个常见的子类Visibility, Android中已经有的很多Transition的子类都是继承自这个Visibility.
直接继承自Transition的类：ChangeBounds, ChangeClipBounds, ChangeImageTransform, ChangeScroll, ChangeTransform, TransitionSet
继承自Visibility的类：Explode, Fade, Slide
下面是Visibility的注释
/ * This transition tracks changes to the visibility of target views in the * start and end scenes. Visibility is determined not just by the * {@link View#setVisibility(int)} state of views, but also whether * views exist in the current view hierarchy. The class is intended to be a * utility for subclasses such as {@link Fade}, which use this visibility * information to determine the specific animations to run when visibility * changes occur. Subclasses should implement one or both of the methods * {@link #onAppear(ViewGroup, TransitionValues, int, TransitionValues, int)}, * {@link #onDisappear(ViewGroup, TransitionValues, int, TransitionValues, int)} or * {@link #onAppear(ViewGroup, View, TransitionValues, TransitionValues)}, * {@link #onDisappear(ViewGroup, View, TransitionValues, TransitionValues)}. */ public abstract class Visibility extends Transition {
// 省略... }注释：这个transition跟踪目标view在场景开始和场景结束时visibility的变化。Visibility不仅仅是决定view的visibility状态， 也决定了view是否存在在当前sceneRoot的view层次中。使用这个类想为其子类作为一个工具，例如Fade这种，使用view的visibility信息来决定当visibility发生变化时特定动画的运行。子类应该实现其中一个或成组的两个方法{@link #onAppear(ViewGroup, TransitionValues, int, TransitionValues, int)}, {@link #onDisappear(ViewGroup, TransitionValues, int, TransitionValues, int)} 或{@link #onAppear(ViewGroup, View, TransitionValues, TransitionValues)},{@link #onDisappear(ViewGroup, View, TransitionValues, TransitionValues)}.
下面是Transition的注释
/ * A Transition holds information about animations that will be run on its * targets during a scene change. Subclasses of this abstract class may * choreograph several child transitions ({@link TransitionSet} or they may * perform custom animations themselves. Any Transition has two main jobs: * (1) capture property values, and (2) play animations based on changes to * captured property values. A custom transition knows what property values * on View objects are of interest to it, and also knows how to animate * changes to those values. For example, the {@link Fade} transition tracks * changes to visibility-related properties and is able to construct and run * animations that fade items in or out based on changes to those properties. * * Note: Transitions may not work correctly with either {@link SurfaceView} * or {@link TextureView}, due to the way that these views are displayed * on the screen. For SurfaceView, the problem is that the view is updated from * a non-UI thread, so changes to the view due to transitions (such as moving * and resizing the view) may be out of sync with the display inside those bounds. * TextureView is more compatible with transitions in general, but some * specific transitions (such as {@link Fade}) may not be compatible * with TextureView because they rely on {@link ViewOverlay} functionality, * which does not currently work with TextureView.
* * Transitions can be declared in XML resource files inside the res/transition * directory. Transition resources consist of a tag name for one of the Transition * subclasses along with attributes to define some of the attributes of that transition. * For example, here is a minimal resource file that declares a {@link ChangeBounds} transition: * * {@sample development/samples/ApiDemos/res/transition/changebounds.xml ChangeBounds} * *
This TransitionSet contains {@link android.transition.Explode} for visibility, * {@link android.transition.ChangeBounds}, {@link android.transition.ChangeTransform}, * and {@link android.transition.ChangeClipBounds} and * {@link android.transition.ChangeImageTransform}:
* * {@sample development/samples/ApiDemos/res/transition/explode_move_together.xml MultipleTransform} * * Custom transition classes may be instantiated with a transition tag:
*
*
Custom transition classes loaded from XML should have a public constructor taking * a {@link android.content.Context} and {@link android.util.AttributeSet}.
* *
Note that attributes for the transition are not required, just as they are * optional when declared in code; Transitions created from XML resources will use * the same defaults as their code-created equivalents. Here is a slightly more * elaborate example which declares a {@link TransitionSet} transition with * {@link ChangeBounds} and {@link Fade} child transitions:
* * {@sample * development/samples/ApiDemos/res/transition/changebounds_fadeout_sequential.xml TransitionSet} * *
In this example, the transitionOrdering attribute is used on the TransitionSet * object to change from the default {@link TransitionSet#ORDERING_TOGETHER} behavior * to be {@link TransitionSet#ORDERING_SEQUENTIAL} instead. Also, the {@link Fade} * transition uses a fadingMode of {@link Fade#OUT} instead of the default * out-in behavior. Finally, note the use of the targets sub-tag, which * takes a set of {@link android.R.styleable#TransitionTarget target} tags, each * of which lists a specific targetId, targetClass, * targetName, excludeId, excludeClass, or * excludeName, which this transition acts upon. * Use of targets is optional, but can be used to either limit the time spent checking * attributes on unchanging views, or limiting the types of animations run on specific views. * In this case, we know that only the grayscaleContainer will be * disappearing, so we choose to limit the {@link Fade} transition to only that view.
* * Further information on XML resource descriptions for transitions can be found for * {@link android.R.styleable#Transition}, {@link android.R.styleable#TransitionSet}, * {@link android.R.styleable#TransitionTarget}, {@link android.R.styleable#Fade}, * {@link android.R.styleable#Slide}, and {@link android.R.styleable#ChangeTransform}. * */
public abstract class Transition implements Cloneable {
// 省略... }
TransitionManager
目前还不清楚TransitionManager的具体管理Transition的方式是什么。就使用而言，除了可以在代码中直接构造，还可以通过在xml中定义的方式来获取。
// transition-v21/manager <transitionManager xmlns:android="http://schemas.android.com/apk/res/android"> <transition android:fromScene="@layout/card_one" android:toScene="@layout/card_two" android:transition="@transition/decrease"/> <transition android:fromScene="@layout/card_two" android:toScene="@layout/card_one" android:transition="@android:transition/move"/>
transitionManager> // transition-v21/descrease <transitionSet xmlns:android="http://schemas.android.com/apk/res/android"> <fade android:fadingMode="fade_out"> <targets android:targetId="@id/red"/>
fade> <fade android:fadingMode="fade_out"> <targets android:targetId="@id/blue"/>
fade> <changeBounds> <targets android:targetId="@id/green"/>
changeBounds> <changeBounds> <targets android:targetId="@id/yellow"/>
changeBounds>
transitionSet> // layout/card_one <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="wrap_content" android:layout_height="wrap_content"> <TextView android:id="@+id/red" android:layout_width="120dp" android:layout_height="120dp" android:background="@android:color/holo_red_light"/> <TextView android:id="@+id/blue" android:layout_width="120dp" android:layout_height="120dp" android:layout_toEndOf="@id/red" android:background="@android:color/holo_blue_bright"/> <TextView android:id="@+id/green" android:layout_width="120dp" android:layout_height="120dp" android:layout_below="@id/red" android:background="@android:color/holo_green_light"/> <TextView android:id="@+id/yellow" android:layout_width="120dp" android:layout_height="120dp" android:layout_alignTop="@id/green" android:layout_toEndOf="@id/green" android:background="@android:color/holo_orange_light"/>
RelativeLayout> // layout/card_two <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="wrap_content" android:layout_height="wrap_content"> <TextView android:id="@+id/green" android:layout_width="120dp" android:layout_height="120dp" android:background="@android:color/holo_green_light"/> <TextView android:id="@+id/yellow" android:layout_width="120dp" android:layout_height="120dp" android:layout_alignTop="@id/green" android:layout_toEndOf="@id/green" android:background="@android:color/holo_orange_light"/>
RelativeLayout>
如上，在xml中定义一个TransitionManager, 在transitionManager中可以定义多个transition .
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) { TransitionManager transitionManager = TransitionInflater.from(this).inflateTransitionManager(R.transition.manger, mContainer); if (isFirst) { isFirst = false; transitionManager.transitionTo(Scene.getSceneForLayout(mContainer, R.layout.card_one, this)); } else { isFirst = true; transitionManager.transitionTo(Scene.getSceneForLayout(mContainer, R.layout.card_two, this)); } }
如上，在代码中inflate出在xml中定义的TransitionManager, 然后进行动画。
这里可以看一下TransitionInflater.inflateTransitionManager方法进行inflate的过程
private TransitionManager createTransitionManagerFromXml(XmlPullParser parser, AttributeSet attrs, ViewGroup sceneRoot) throws XmlPullParserException, IOException { // Make sure we are on a start tag. int type; int depth = parser.getDepth(); TransitionManager transitionManager = null; while (((type=parser.next()) != XmlPullParser.END_TAG || parser.getDepth() > depth) && type != XmlPullParser.END_DOCUMENT) { if (type != XmlPullParser.START_TAG) { continue; } String name = parser.getName(); if (name.equals("transitionManager")) { transitionManager = new TransitionManager(); } else if (name.equals("transition") && (transitionManager != null)) { loadTransition(attrs, sceneRoot, transitionManager); } else { throw new RuntimeException("Unknown scene name: " + parser.getName()); } } return transitionManager; } private void loadTransition(AttributeSet attrs, ViewGroup sceneRoot, TransitionManager transitionManager) throws Resources.NotFoundException { TypedArray a = mContext.obtainStyledAttributes(attrs, R.styleable.TransitionManager); int transitionId = a.getResourceId(R.styleable.TransitionManager_transition, -1); int fromId = a.getResourceId(R.styleable.TransitionManager_fromScene, -1); Scene fromScene = (fromId < 0) ? null: Scene.getSceneForLayout(sceneRoot, fromId, mContext); int toId = a.getResourceId(R.styleable.TransitionManager_toScene, -1); Scene toScene = (toId < 0) ? null : Scene.getSceneForLayout(sceneRoot, toId, mContext); if (transitionId >= 0) { Transition transition = inflateTransition(transitionId); if (transition != null) { if (toScene == null) { throw new RuntimeException("No toScene for transition ID " + transitionId); } if (fromScene == null) { transitionManager.setTransition(toScene, transition); } else { transitionManager.setTransition(fromScene, toScene, transition); } } } a.recycle(); }
分析：在inflate TransitionManager的过程中，实际上是直接构造TransitionManger的。对其中的transition标签进行处理，也是调用TransitionManager.setTransition(Scene, Scene, Transiton)方法。这个方法有一个重载方法。在上面可以看到，toScene是必须存在的，如果fromScene存在，则调用TransitionManager.setTransition(Scene, Scene, Transiton), 否则调用TransitionManager.setTransition(Scene, Transiton).
我们可以从中看到什么呢？这个需要从TransitionManager.transitionTo(Scene)中看出来
/ * Change to the given scene, using the * appropriate transition for this particular scene change * (as specified to the TransitionManager, or the default * if no such transition exists). * * @param scene The Scene to change to */ public void transitionTo(Scene scene) { // Auto transition if there is no transition declared for the Scene, but there is // a root or parent view changeScene(scene, getTransition(scene)); }
使用
TransitionManager.beginDelayedTransition(ViewGroup sceneRoot, Transition transition)
很大一部分动画其实都可以使用这个方法来进行动画。这个方法有一个重载方法TransitionManager.beginDelayedTransition(ViewGroup sceneRoot), 在这个重载方法中，使用一个默认的AutoTransition.
public void transition(View view) { if (android.os.Build.VERSION.SDK_INT < Build.VERSION_CODES.KITKAT) { return; } final ViewGroup parent = (ViewGroup) findViewById(R.id.parent); final ViewGroup container = (ViewGroup) findViewById(R.id.container); TransitionManager.beginDelayedTransition(parent, new ChangeBounds()); container.removeViewAt(0); container.removeViewAt(0); }
如上，有一个id为parent的ViewGroup, 其中有一个id为container的ViewGroup, 在container中，还有多个children, 我们以id为parent的ViewGroup作为sceneRoot, 在改变其hirerarchy前调用TransitionManager.beginDelayedTransition(ViewGroup sceneRoot, Transition transition), 然后对其hirerarchy进行操作, 这样就完成了动画的操作。
这里需要说明一下，我们以id为parent的ViewGroup作为sceneRoot, 而操作的并不是它的直接children, 也产生了效果，说明操作的是以sceneRoot为根的整个hirerarchy.
对于原理，这里暂时放在后面进行分析。
TransitionManager.go(Scene, Transition)
@TargetApi(Build.VERSION_CODES.LOLLIPOP) public void remove(View view) { final ViewGroup group = (ViewGroup) findViewById(R.id.container); final Scene scene = new Scene(group, group.getChildAt(0)); TransitionManager.go(scene); }
如上所示，我们将一个id为container的ViewGroup作为sceneRoot, 然后将其第一个child作为场景切换后添加到sceneRoot中的view, 然后调用TransitionManager.go(Scene)方法。当然，这样达到的效果和使用TransitionManager.beginDelayedTransition(ViewGroup sceneRoot, Transition transition)的效果是一样的。我们也可以像上面一样使用，保留id为container的第一个child, 移除其他所有的children, 在这些操作之前调用TransitionManager.beginDelayedTransition(ViewGroup sceneRoot, Transition transition)“`方法即可。
TransitionManager.transitionTo(Scene)
在上面我们已经演示了这个方法的使用。这里就不再赘述。
总结
参考
使用 Transition API为安卓应用创建动画
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