搞客户端开发,时间也有点了,但是每次想起来,总感觉自己掌握的东西零零散散,没有一点集在的感觉,应用层的懂,framework的也懂,框架啥的了解一点,分层的思想也有一些,JVM的原理啊,内存分配和管理啊,运行机制啊啥的也知道一点,每次下班或者没事了,就在考虑,自己应该有一个主攻方向,往这个方向集中发展一下,首选的几个目标应该是非常清楚的,我们要掌握android,那么关于android的View机制、动画原理这些都是必须要掌握的,所以呢,自己想在这几个方面花些时间,好好研究一下,这样才能使自己更具竞争力。
好了,不管是要了解View机制,还是android动画,我们应该都需要有Choreographer的知识,明白系统刷新机制到底是怎么样的,这样才能对其他方面有更好的辅助。本章博客,我们就来学习一下Android中的Choreographer的运行机制。
我们都知道,应用层的一个Activity对应一个根View(也就是一个DecorView)、一个WindowState、一个ViewRootImpl,每个对象都非常重要,都是在Activity添加过程中重量级的对象,DecorView是当前Activity的根View,它里面管理着当前界面的View树;WindowState对象是当前Activity窗口在系统侧WindowManagerService中代理对象;ViewRootImpl则肩负着View的标准三步曲的处理和事件分发,而View绘制也是由Choreographer指导的,Choreographer的英文意思就是编舞者、舞蹈指挥,看着非常形象。那我们就从Choreographer对象的构建开始说起吧,它的构建是在ViewRootImpl的构造方法中的,代码如下:
public ViewRootImpl(Context context, Display display) {
mContext = context;
mWindowSession = WindowManagerGlobal.getWindowSession();
mDisplay = display;
mBasePackageName = context.getBasePackageName();
mDisplayAdjustments = display.getDisplayAdjustments();
mThread = Thread.currentThread();
mLocation = new WindowLeaked(null);
mLocation.fillInStackTrace();
mWidth = -1;
mHeight = -1;
mDirty = new Rect();
mTempRect = new Rect();
mVisRect = new Rect();
mWinFrame = new Rect();
mWindow = new W(this);
mTargetSdkVersion = context.getApplicationInfo().targetSdkVersion;
mViewVisibility = View.GONE;
mTransparentRegion = new Region();
mPreviousTransparentRegion = new Region();
// [+LEUI-9331]
mPreBlurParams = new BlurParams();
// [-LEUI-9331]
mFirst = true; // true for the first time the view is added
mAdded = false;
mAttachInfo = new View.AttachInfo(mWindowSession, mWindow, display, this, mHandler, this);
mAccessibilityManager = AccessibilityManager.getInstance(context);
mAccessibilityInteractionConnectionManager =
new AccessibilityInteractionConnectionManager();
mAccessibilityManager.addAccessibilityStateChangeListener(
mAccessibilityInteractionConnectionManager);
mHighContrastTextManager = new HighContrastTextManager();
mAccessibilityManager.addHighTextContrastStateChangeListener(
mHighContrastTextManager);
mViewConfiguration = ViewConfiguration.get(context);
mDensity = context.getResources().getDisplayMetrics().densityDpi;
mNoncompatDensity = context.getResources().getDisplayMetrics().noncompatDensityDpi;
mFallbackEventHandler = new PhoneFallbackEventHandler(context);
mChoreographer = Choreographer.getInstance();
mDisplayManager = (DisplayManager)context.getSystemService(Context.DISPLAY_SERVICE);
loadSystemProperties();
/**
* M: increase instance count and check log property to determine
* whether to enable/disable log system. @{
*/
mIdent = sIdent++;
checkViewRootImplLogProperty();
if (LOCAL_LOGV) {
enableLog(true, "a");
}
if (DEBUG_LIFECYCLE) {
Log.v(TAG, "ViewRootImpl construct: context = " + context + ", mThread = " + mThread
+ ", mChoreographer = " + mChoreographer + ", mTraversalRunnable = "
+ mTraversalRunnable + ", this = " + this);
}
}
从构造方法中可以看到Choreographer是单例模式的,也就是一个ViewRootImpl对象对应一个Choreographer,当界面需要重绘时,都会调用到ViewRootImp类的scheduleTraversals()方法,这里的实现也比较简单,代码如下:
void scheduleTraversals() {
if (!mTraversalScheduled) {
mTraversalScheduled = true;
mTraversalBarrier = mHandler.getLooper().postSyncBarrier();
mChoreographer.postCallback(
Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
scheduleConsumeBatchedInput();
}
}
mTraversalScheduled表示是否已经发起重绘,每次scheduleTraversals()方法调用之后,就会将它置为true,然后在下次调用doTraversal()又先将它置为false,然后调用mChoreographer.postCallback()添加一个Runnable,请注意,第一个参数是Choreographer.CALLBACK_TRAVERSAL,在Choreographer当前,添加的类型一共有三种,分别是:CALLBACK_INPUT、CALLBACK_ANIMATION、CALLBACK_TRAVERSAL,分别表示事件回调、动画回调、绘制回调。postCallback()方法是转而调用postCallbackDelayed()方法的,最后一个参数delayMillis传的是0,表示当前的重绘不需要延时,我们跟进去看一下添加的postCallbackDelayed()方法的代码:
/**
* Posts a callback to run on the next frame after the specified delay.
*
* The callback runs once then is automatically removed.
*
*
* @param callbackType The callback type.
* @param action The callback action to run during the next frame after the specified delay.
* @param token The callback token, or null if none.
* @param delayMillis The delay time in milliseconds.
*
* @see #removeCallback
* @hide
*/
public void postCallbackDelayed(int callbackType,
Runnable action, Object token, long delayMillis) {
if (action == null) {
throw new IllegalArgumentException("action must not be null");
}
if (callbackType < 0 || callbackType > CALLBACK_LAST) {
throw new IllegalArgumentException("callbackType is invalid");
}
postCallbackDelayedInternal(callbackType, action, token, delayMillis);
}
private void postCallbackDelayedInternal(int callbackType,
Object action, Object token, long delayMillis) {
if (DEBUG) {
Log.d(TAG, "PostCallback: type=" + callbackType
+ ", action=" + action + ", token=" + token
+ ", delayMillis=" + delayMillis);
}
synchronized (mLock) {
final long now = SystemClock.uptimeMillis();
final long dueTime = now + delayMillis;
mCallbackQueues[callbackType].addCallbackLocked(dueTime, action, token);
if (dueTime <= now) {
scheduleFrameLocked(now);
} else {
Message msg = mHandler.obtainMessage(MSG_DO_SCHEDULE_CALLBACK, action);
msg.arg1 = callbackType;
msg.setAsynchronous(true);
mHandler.sendMessageAtTime(msg, dueTime);
}
}
}