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87 lines
2.1 KiB
87 lines
2.1 KiB
---
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IdleHandler 原理
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---
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1. 了解 IdleHandler 的作用以及调用方式
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2. 了解 IdleHandler 有哪些使用场景
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3. 熟悉 IdleHandler 的实现原理
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```java
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public static interface IdleHandler{
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boolean queueIdle();
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}
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```
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```java
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Looper.myQueue().addIdleHandler(new MessageQueue.IdleHandler()){
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@Override
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public boolean queueIdle(){
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return true;
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}
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}
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public void addIdleHandler(IdleHandler handler){
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synchronized(this){
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mIdleHandler.add(handler);
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}
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}
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Message next(){
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for(;;){
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nativePollOnce(ptr, nextPollTimeoutMillis);
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// 看消息列表是否有消息可以分发的，如果有，就返回该消息
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// 走到这说明没有消息可以分发，下一个 for 循环就要进入休眠了
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if(pendingIdleHandlerCount<0){
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pendingIdleHandlercount = mIdleHandlers.size();
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}
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if(pendingIdleHandlerCount<0){
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continue;
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}
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mPendingIdleHandlers = mIdleHandlers.toArray(mPendingIdleHandlers);
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for(int i=0;i<pendingIdleHandlerCount;i++){
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final IdleHandler idler = mPendingIdleHandlers[i];
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if(!(idler.queueIdle())){
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mIdleHandlers.remove(idler);
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}
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}
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}
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}
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```
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Framework 哪些地方用到了 IdleHandler 呢？
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```java
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// ActivityThread#scheduleGcIdler
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void scheduleGcIdler(){
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if(!mGcIdlerScheduled){
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mGcIdlerScheduled = true;
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Looper.myQueue().addIdleHandler(mGcIdler);
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}
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mH.removeMessages(H.GC_WHEN_IDLE);
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}
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final class GcIdler implements MessageQueue.IdleHandler{
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@Override
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public final boolean queueIdle(){
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// BinderInternal.forceGc("bg");
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doGcIfNeeded();
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return false;
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}
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}
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// ActivityThread#waitForIdle
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public void waitForIdle(Runnable recipient){
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mMessageQueue.addIdleHandler(new Idler(recipient));
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mThread.getHandler().post(new EmptyRunnable());
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}
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private static final class Idler implements MessageQueue.IdleHandler{
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public final boolean queueIdle(){
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if(mCallback!=null){
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mCallback.run();
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}
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return false;
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}
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}
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```
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#### 适用场景
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1. 延时处理
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2. 批量任务 |