Source: http://www.cnblogs.com/everhad/p/6271238.html
簡述:transitions framework
下面翻譯transition為“過渡”,強調動畫過程的含義,不過更多時候使用transition單詞本身。
Android 4.4.2 (API level 19) 引入了過渡框架
,它用來在兩個view hierarchies(就是ViewGroup實例)切換時執行改變動畫。它通過動態修改views對象的某些property值來實現動畫,實際上就是用的屬性動畫
。框架內建了一些transition效果,也可以自定義。并且可以監聽transition執行過程/生命周期(Lifecycle callbacks)各種回調。
框架概覽
在UI改變時——view hierarchy(視圖層級) 發生變化,過渡框架對包含的部分改變了的view對象執行屬性動畫
來表達這樣的視覺提示(visual cues)。
特性
過渡框架包括下面這些特性:
動畫組Group-level animations
視圖層級發生變化時,可以同時執行多個動畫,它們形成動畫組,類似AnimationSet
。Transition-based animation
Runs animations based on the changes between starting and ending view property values.Built-in animations
Includes predefined animations for common effects such as fade out or movement.Resource file support 支持資源文件方式的使用
Loads view hierarchies and built-in animations from layout resource files.Lifecycle callbacks
Defines callbacks that provide finer control over the animation and hierarchy change process.
框架結構
下圖是過渡框架涉及的相關概念和之間的關系:
Scene
一個Scene表示一個view hierarchy,存儲對應的views及其property值。
一個Scene必須關聯到一個scene-root
,它是一個ViewGroup,正是對應view hierarchy要添加到的容器。
Scene可以從layout文件創建(只能是整個布局文件對應的view hierarchy),或者代碼生成的View/ViewGroup。
如果僅指定目標Scene,那么框架使用當前scene-root對應的view hierarchy就作為開始的Scene。Transition
表示兩個Scene之間的過渡動畫,它保存了使用到的animations。
TransitionManager
用來執行專場效果。
TransitionListener
用來實現對過渡過程的監聽。
存在的限制
SurfaceView非UI線程不保證同步;
AdapterView管理childView行為沖突;
TextView改變尺寸時顯示問題;
TextureView非預期效果;
創建Scene
過渡涉及startScene和endScene,它們使用同一個sceneRoot,也就是變化的view hierarchy是在一個ViewGroup下的。
startScene可以不指定,那么就默認是當前view hierarchy。
如果連續執行多個Scene之前的切換,那么上一個endScene就是當前的startScene。
可以通過代碼或layout文件創建Scene。
- 代碼文件,生成需要的ViewGroup對象即可,適合“動態創建”界面這樣的需求。
Scene mScene;
// Obtain the scene root element
mSceneRoot = (ViewGroup) mSomeLayoutElement;
// Obtain the view hierarchy to add as a child of
// the scene root when this scene is entered
mViewHierarchy = (ViewGroup) someOtherLayoutElement;
// Create a scene
mScene = new Scene(mSceneRoot, mViewHierarchy);
- layout文件
/**
* Returns a Scene described by the resource file associated with the given
* <code>layoutId</code> parameter. If such a Scene has already been created for
* the given <code>sceneRoot</code>, 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);
NOTE:
The framework creates the scene from the entire view hierarchy in the file; you can not create a scene from part of a layout file.
Create Scene Actions
使用Scene.setExitAction() or Scene.setEnterAction() ,傳遞定義的Runnable實例。
可以執行一些操作,比如修改ListView等。
Note:
Do not use scene actions to pass data between views in the starting and ending scenes. For more information, see Defining Transition Lifecycle Callbacks.
應用Transition
創建好startScene、endScene后,在改變UI的邏輯的地方,就可以執行Transition來開啟專場動畫了。
創建Transition
- 資源文件
在res/transition/目錄下,創建表示Transition的文件,資源文件的方式更加復用而且簡單。
這種方式和定義動畫文件
的機制類似。
如res/transition/fade_transition.xml:
<fade xmlns:android="http://schemas.android.com/apk/res/android" />
然后加載它:
Transition mFadeTransition =
TransitionInflater.from(this).
inflateTransition(R.transition.fade_transition);
代碼方式
例如:Transition mFadeTransition = new Fade();
預提供的類型有ChangeBounds, ChangeClipBounds, ChangeImageTransform, ChangeTransform, TransitionSet, Visibility
詳見API文檔。
開啟過渡
使用下面的方法TransitionManager.go()
:
/**
* Convenience method to simply change to the given scene using
* the given transition.
*
* <p>Passing in <code>null</code> for the transition parameter will
* result in the scene changing without any transition running, and is
* equivalent to calling {@link Scene#exit()} on the scene root's
* current scene, followed by {@link Scene#enter()} on the scene
* specified by the <code>scene</code> parameter.</p>
*
* @param scene The Scene to change to
* @param transition The transition to use for this scene change. A
* value of null causes the scene change to happen with no transition.
*/
public static void go(Scene scene, Transition transition)
它有一個不含參數transition的重載,默認會使用AutoTransition
。
選擇指定的目標view
默認情況下Transition的執行是針對Scene關聯的view hierarchy中的所有views執行的。
可以通過Transition的方法removeTarget()、addTarget()來指定它影響的view。
比如若ListView不能通過框架正常完成過渡效果,那么移除它。
動畫組:同時執行多個過渡效果
<transitionSet xmlns:android="http://schemas.android.com/apk/res/android"
android:transitionOrdering="sequential">
<fade android:fadingMode="fade_out" />
<changeBounds />
<fade android:fadingMode="fade_in" />
</transitionSet>
對應一個TransitionSet ,它是Transition的子類。
單Scene的過渡
如果UI在變化前后差距很小,例如就是同一個ViewGroup的簡單的addView()/removeView()那么,此時可以不去執行像startScene、endScene那樣的變化,使用delayed transition
來在view hierarchy變化的時候開啟過渡:
// Start recording changes to the view hierarchy
TransitionManager.beginDelayedTransition(mRootView, mFade);
// Add the new TextView to the view hierarchy
mRootView.addView(mLabelText);
// When the system redraws the screen to show this update,
// the framework will animate the addition as a fade in
Transition Lifecycle Callbacks
調用public Transition addListener (Transition.TransitionListener listener)
。
回調方法見Transition.TransitionListener
。
自定義Transition
A custom transition, like one of the built-in transition types, applies animations to child views of both the starting and ending scenes. Unlike built-in transition types, however, you have to provide the code that captures property values and generates animations. You may also want to define a subset of target views for your animation.
定義Transition子類
public class CustomTransition extends Transition {
@Override
public void captureStartValues(TransitionValues values) {}
@Override
public void captureEndValues(TransitionValues values) {}
@Override
public Animator createAnimator(ViewGroup sceneRoot,
TransitionValues startValues,
TransitionValues endValues) {}
}
方法captureStartValues()和captureEndValues()用來獲取startScene、endScene關聯的view的property值。可以對關心的view的屬性值進行記錄。
類似下面這樣:
public class CustomTransition extends Transition {
// Define a key for storing a property value in
// TransitionValues.values with the syntax
// package_name:transition_class:property_name to avoid collisions
private static final String PROPNAME_BACKGROUND =
"com.example.android.customtransition:CustomTransition:background";
@Override
public void captureStartValues(TransitionValues transitionValues) {
// Call the convenience method captureValues
captureValues(transitionValues);
}
// For the view in transitionValues.view, get the values you
// want and put them in transitionValues.values
private void captureValues(TransitionValues transitionValues) {
// Get a reference to the view
View view = transitionValues.view;
// Store its background property in the values map
transitionValues.values.put(PROPNAME_BACKGROUND, view.getBackground());
}
...
}
TransitionValues是一個非常簡單的數據結構,它保存和view關聯的屬性值,startScene和endScene分別使用一個TransitionValues對象來記錄view hierarchy的各個view的狀態。
要記錄的“property_name”需要保存唯一,因為可能和其它Transition沖突,建議格式是:
package_name:transition_name:property_name
。
創建自定義Animator
過渡框架中的Transition使用屬性動畫作為動畫機制的實現。
子自定義Transition重寫createAnimator()方法來提供需要的動畫邏輯,工作就是根據startValues和endValues來創建Animator。
針對有些view的過渡只在endScene或者startScene中有,所以startValues和endValues可能為null。
框架會為每一個動畫的view創建一個Animator,也就是調用一次createAnimator()。
下面是一個案例ChangeColor.java:
public class ChangeColor extends Transition {
/** Key to store a color value in TransitionValues object */
private static final String PROPNAME_BACKGROUND = "customtransition:change_color:background";
// BEGIN_INCLUDE (capture_values)
/**
* Convenience method: Add the background Drawable property value
* to the TransitionsValues.value Map for a target.
*/
private void captureValues(TransitionValues values) {
// Capture the property values of views for later use
values.values.put(PROPNAME_BACKGROUND, values.view.getBackground());
}
@Override
public void captureStartValues(TransitionValues transitionValues) {
captureValues(transitionValues);
}
// Capture the value of the background drawable property for a target in the ending Scene.
@Override
public void captureEndValues(TransitionValues transitionValues) {
captureValues(transitionValues);
}
// END_INCLUDE (capture_values)
// BEGIN_INCLUDE (create_animator)
// Create an animation for each target that is in both the starting and ending Scene. For each
// pair of targets, if their background property value is a color (rather than a graphic),
// create a ValueAnimator based on an ArgbEvaluator that interpolates between the starting and
// ending color. Also create an update listener that sets the View background color for each
// animation frame
@Override
public Animator createAnimator(ViewGroup sceneRoot,
TransitionValues startValues, TransitionValues endValues) {
// This transition can only be applied to views that are on both starting and ending scenes.
if (null == startValues || null == endValues) {
return null;
}
// Store a convenient reference to the target. Both the starting and ending layout have the
// same target.
final View view = endValues.view;
// Store the object containing the background property for both the starting and ending
// layouts.
Drawable startBackground = (Drawable) startValues.values.get(PROPNAME_BACKGROUND);
Drawable endBackground = (Drawable) endValues.values.get(PROPNAME_BACKGROUND);
// This transition changes background colors for a target. It doesn't animate any other
// background changes. If the property isn't a ColorDrawable, ignore the target.
if (startBackground instanceof ColorDrawable && endBackground instanceof ColorDrawable) {
ColorDrawable startColor = (ColorDrawable) startBackground;
ColorDrawable endColor = (ColorDrawable) endBackground;
// If the background color for the target in the starting and ending layouts is
// different, create an animation.
if (startColor.getColor() != endColor.getColor()) {
// Create a new Animator object to apply to the targets as the transitions framework
// changes from the starting to the ending layout. Use the class ValueAnimator,
// which provides a timing pulse to change property values provided to it. The
// animation runs on the UI thread. The Evaluator controls what type of
// interpolation is done. In this case, an ArgbEvaluator interpolates between two
// #argb values, which are specified as the 2nd and 3rd input arguments.
ValueAnimator animator = ValueAnimator.ofObject(new ArgbEvaluator(),
startColor.getColor(), endColor.getColor());
// Add an update listener to the Animator object.
animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
@Override
public void onAnimationUpdate(ValueAnimator animation) {
Object value = animation.getAnimatedValue();
// Each time the ValueAnimator produces a new frame in the animation, change
// the background color of the target. Ensure that the value isn't null.
if (null != value) {
view.setBackgroundColor((Integer) value);
}
}
});
// Return the Animator object to the transitions framework. As the framework changes
// between the starting and ending layouts, it applies the animation you've created.
return animator;
}
}
// For non-ColorDrawable backgrounds, we just return null, and no animation will take place.
return null;
}
// END_INCLUDE (create_animator)
}
自定義Transition的使用和內建的Fade、ChangeBounds等是完全相同的。
(本文使用Atom編寫)
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