Android面试题经典之Glide取消加载以及线程池优化

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Glide通过生命周期取消加载

生命周期回调过程
onStop
—>RequestManager.onStop
–>RequestTracker.pauseRequest
–> SingleRequest.pause
–> SingleRequest.cancel
—> Engine.cancel
—> EngineJob.removeCallback
—> 如果所有的回调监听都移除了
–> DecodeJob.cancel

//EngineJob.class
synchronized void removeCallback(ResourceCallback cb) {
   
   
   stateVerifier.throwIfRecycled();
   cbs.remove(cb);
   if (cbs.isEmpty()) {
   
   
     cancel();
     boolean isFinishedRunning = hasResource || hasLoadFailed;
     if (isFinishedRunning && pendingCallbacks.get() == 0) {
   
   
       release();
     }
   }
}

• 如果任务没有执行，就从队列里移除，取消任务
• 如果任务已经执行，就利用isCancelled标记在停止流程

//DecodeJob.class
public void cancel() {
   
   
  	isCancelled = true;
  	DataFetcherGenerator local = currentGenerator;
  	if (local != null) {
   
   
  		local.cancel();
  	}
}

上面最终会调用到具体的获取图片的任务，比如从网络获取图片的HttpUrlFetcher

 //HttpUrlFetcher.class
private volatile boolean isCancelled;
@Override
public void cancel() {
   
   
    // TODO: we should consider disconnecting the url connection here, but we can't do so
    // directly because cancel is often called on the main thread.
    isCancelled = true;
}

//内部是通过HttpURLConnection来从网络获取数据
private InputStream loadDataWithRedirects(
      URL url, int redirects,