如何中断AsyncTaskLoader后台线程？
Posted
tags:
篇首语：本文由小常识网(cha138.com)小编为大家整理，主要介绍了如何中断AsyncTaskLoader后台线程？相关的知识，希望对你有一定的参考价值。
当我打电话给AsyncTaskLoader时，有没有办法打断loadInBackground()的cancelLoad()线程？我相信AsyncTask.cancel()这样做，但任务变量是私有的，无法访问。
答案
使用stopLoading()或abandon()或reset()
文章：https://plus.google.com/117981280628062796190/posts/8b9RmQvxudb
另一答案
添加该功能相对简单，这是它的Gist：
public abstract class InterruptibleAsyncTaskLoader<D> extends AsyncTaskLoader<D> {
private volatile Thread thread;
public InterruptibleAsyncTaskLoader(Context context) {
super(context);
}
public boolean isLoadInBackgroundRunning() {
return thread != null;
}
@Override
public void cancelLoadInBackground() {
Thread t = thread;
if (t != null) t.interrupt();
}
@Override
public final D loadInBackground() {
try {
thread = Thread.currentThread();
return doLoadInBackground();
} catch (InterruptedException e) {
OperationCanceledException oce = new OperationCanceledException(e.toString());
oce.initCause(e);
throw oce;
} finally {
Thread.interrupted();
thread = null;
}
}
public abstract D doLoadInBackground() throws InterruptedException;
}
另一答案
我检查了可用的方法，似乎没有真正中断在后台运行的线程。
看一下代码，似乎AsyncTask正在被引用。我已经尝试找到一个可以用来中断asyncTask的“漏洞”，但我找不到（除非你对反射很好）。我认为你可以制作自己的装载机，它具有这种功能。
我认为您可以根据需要修改代码。也许添加“forceCancel”，它将检查asyncTask的值，如果它不为null，则在其上调用“cancel（true）”。这是我看过的代码：
A sync task loader.Java
package android.support.v4.content;
import android.content.Context;
import android.os.Handler;
import android.os.SystemClock;
import android.support.v4.util.TimeUtils;
import android.util.Log;
import java.io.FileDescriptor;
import java.io.PrintWriter;
import java.util.concurrent.CountDownLatch;
/**
* Static library support version of the framework's {@link android.content.AsyncTaskLoader}.
* Used to write apps that run on platforms prior to Android 3.0. When running
* on Android 3.0 or above, this implementation is still used; it does not try
* to switch to the framework's implementation. See the framework SDK
* documentation for a class overview.
*/
public abstract class AsyncTaskLoader<D> extends Loader<D> {
static final String TAG = "AsyncTaskLoader";
static final boolean DEBUG = false;
final class LoadTask extends ModernAsyncTask<Void, Void, D> implements Runnable {
D result;
boolean waiting;
private CountDownLatch done = new CountDownLatch(1);
/* Runs on a worker thread */
@Override
protected D doInBackground(Void... params) {
if (DEBUG) Log.v(TAG, this + " >>> doInBackground");
result = AsyncTaskLoader.this.onLoadInBackground();
if (DEBUG) Log.v(TAG, this + " <<< doInBackground");
return result;
}
/* Runs on the UI thread */
@Override
protected void onPostExecute(D data) {
if (DEBUG) Log.v(TAG, this + " onPostExecute");
try {
AsyncTaskLoader.this.dispatchOnLoadComplete(this, data);
} finally {
done.countDown();
}
}
@Override
protected void onCancelled() {
if (DEBUG) Log.v(TAG, this + " onCancelled");
try {
AsyncTaskLoader.this.dispatchOnCancelled(this, result);
} finally {
done.countDown();
}
}
@Override
public void run() {
waiting = false;
AsyncTaskLoader.this.executePendingTask();
}
}
volatile LoadTask mTask;
volatile LoadTask mCancellingTask;
long mUpdateThrottle;
long mLastLoadCompleteTime = -10000;
Handler mHandler;
public AsyncTaskLoader(Context context) {
super(context);
}
/**
* Set amount to throttle updates by. This is the minimum time from
* when the last {@link #onLoadInBackground()} call has completed until
* a new load is scheduled.
*
* @param delayMS Amount of delay, in milliseconds.
*/
public void setUpdateThrottle(long delayMS) {
mUpdateThrottle = delayMS;
if (delayMS != 0) {
mHandler = new Handler();
}
}
@Override
protected void onForceLoad() {
super.onForceLoad();
cancelLoad();
mTask = new LoadTask();
if (DEBUG) Log.v(TAG, "Preparing load: mTask=" + mTask);
executePendingTask();
}
/**
* Attempt to cancel the current load task. See {@link android.os.AsyncTask#cancel(boolean)}
* for more info. Must be called on the main thread of the process.
*
* <p>Cancelling is not an immediate operation, since the load is performed
* in a background thread. If there is currently a load in progress, this
* method requests that the load be cancelled, and notes this is the case;
* once the background thread has completed its work its remaining state
* will be cleared. If another load request comes in during this time,
* it will be held until the cancelled load is complete.
*
* @return Returns <tt>false</tt> if the task could not be cancelled,
* typically because it has already completed normally, or
* because {@link #startLoading()} hasn't been called; returns
* <tt>true</tt> otherwise.
*/
public boolean cancelLoad() {
if (DEBUG) Log.v(TAG, "cancelLoad: mTask=" + mTask);
if (mTask != null) {
if (mCancellingTask != null) {
// There was a pending task already waiting for a previous
// one being canceled; just drop it.
if (DEBUG) Log.v(TAG,
"cancelLoad: still waiting for cancelled task; dropping next");
if (mTask.waiting) {
mTask.waiting = false;
mHandler.removeCallbacks(mTask);
}
mTask = null;
return false;
} else if (mTask.waiting) {
// There is a task, but it is waiting for the time it should
// execute. We can just toss it.
if (DEBUG) Log.v(TAG, "cancelLoad: task is waiting, dropping it");
mTask.waiting = false;
mHandler.removeCallbacks(mTask);
mTask = null;
return false;
} else {
boolean cancelled = mTask.cancel(false);
if (DEBUG) Log.v(TAG, "cancelLoad: cancelled=" + cancelled);
if (cancelled) {
mCancellingTask = mTask;
}
mTask = null;
return cancelled;
}
}
return false;
}
/**
* Called if the task was canceled before it was completed. Gives the class a chance
* to properly dispose of the result.
*/
public void onCanceled(D data) {
}
void executePendingTask() {
if (mCancellingTask == null && mTask != null) {
if (mTask.waiting) {
mTask.waiting = false;
mHandler.removeCallbacks(mTask);
}
if (mUpdateThrottle > 0) {
long now = SystemClock.uptimeMillis();
if (now < (mLastLoadCompleteTime+mUpdateThrottle)) {
// Not yet time to do another load.
if (DEBUG) Log.v(TAG, "Waiting until "
+ (mLastLoadCompleteTime+mUpdateThrottle)
+ " to execute: " + mTask);
以上是关于如何中断AsyncTaskLoader后台线程？的主要内容，如果未能解决你的问题，请参考以下文章
Android ListView 由 AsyncTaskLoader 更新