Android 处理多线程时，不能在线程范围内调用UI，通过这个方式能够很好的在线程中，对UI进行控制。
/*多线程处理-程序加载线程*/
private class LoginFromTask extends UserTask<String, Integer, String>
{
/**
* 线程启动初始化操作
*/
@Override
public void onPreExecute()
{
//在这儿进行线程运行前的初始化，比如显示一个提示框或进度条
}
/**
* 需要长时间阻塞处理的任务
*/
@Override
public String doInBackground(String...stgs)
{线程中的处理，这儿不能操作UI
return null;
//publishProgress();//调用这个函数好后会激活onProgressUpdate()事件
}
/**
* 线程内更新处理
*/
@Override
public void onProgressUpdate(Integer... progress){
//这边用于处理线程未完成的提示处理，例如进度条更新
}
/**
* 阻塞任务执行完后的清理工作
*/
@Override
public void onPostExecute(String result)
{
//线程处理结束，操作UI，关闭提示框或者关闭进度条
}
}
完整代码如下：
/*
* Copyright (C) 2008 Google Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.android.photostream;
import android.os.*;
import android.os.Process;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.Callable;
import java.util.concurrent.FutureTask;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.CancellationException;
import java.util.concurrent.atomic.AtomicInteger;
/**
* <p>UserTask enables proper and easy use of the UI thread. This class allows to
* perform background operations and publish results on the UI thread without
* having to manipulate threads and/or handlers.</p>
*
* <p>A user task is defined by a computation that runs on a background thread and
* whose result is published on the UI thread. A user task is defined by 3 generic
* types, called <code>Params</code>, <code>Progress</code> and <code>Result</code>,
* and 4 steps, called <code>begin</code>, <code>doInBackground</code>,
* <code>processProgress<code> and <code>end</code>.</p>
*
* <h2>Usage</h2>
* <p>UserTask must be subclassed to be used. The subclass will override at least
* one method ({@link #doInBackground(Object[])}), and most often will override a
* second one ({@link #onPostExecute(Object)}.)</p>
*
* <p>Here is an example of subclassing:</p>
* <pre>
* private class DownloadFilesTask extends UserTask<URL, Integer, Long> {
*public File doInBackground(URL... urls) {
*int count = urls.length;
*long totalSize = 0;
*for (int i = 0; i < count; i++) {
*totalSize += Downloader.downloadFile(urls[i]);
*publishProgress((int) ((i / (float) count) * 100));
*}
*}
*
*public void onProgressUpdate(Integer... progress) {
*setProgressPercent(progress[0]);
*}
*
*public void onPostExecute(Long result) {
*showDialog("Downloaded " + result + " bytes");
*}
* }
* </pre>
*
* <p>Once created, a task is executed very simply:</p>
* <pre>
* new DownloadFilesTask().execute(new URL[] { ... });
* </pre>
*
* <h2>User task's generic types</h2>
* <p>The three types used by a user task are the following:</p>
* <ol>
*<li><code>Params</code>, the type of the parameters sent to the task upon
*execution.</li>
*<li><code>Progress</code>, the type of the progress units published during
*the background computation.</li>
*<li><code>Result</code>, the type of the result of the background
*computation.</li>
* </ol>
* <p>Not all types are always used by a user task. To mark a type as unused,
* simply use the type {@link Void}:</p>
* <pre>
* private class MyTask extends UserTask<Void, Void, Void) { ... }
* </pre>
*
* <h2>The 4 steps</h2>
* <p>When a user task is executed, the task goes through 4 steps:</p>
* <ol>
*<li>{@link #onPreExecute()}, invoked on the UI thread immediately after the task
*is executed. This step is normally used to setup the task, for instance by
*showing a progress bar in the user interface.</li>
*<li>{@link #doInBackground(Object[])}, invoked on the background thread
*immediately after {@link # onPreExecute ()} finishes executing. This step is used
*to perform background computation that can take a long time. The parameters
*of the user task are passed to this step. The result of the computation must
*be returned by this step and will be passed back to the last step. This step
*can also use {@link #publishProgress(Object[])} to publish one or more units
*of progress. These values are published on the UI thread, in the
*{@link #onProgressUpdate(Object[])} step.</li>
*<li>{@link # onProgressUpdate (Object[])}, invoked on the UI thread after a
*call to {@link #publishProgress(Object[])}. The timing of the execution is
*undefined. This method is used to display any form of progress in the user
*interface while the background computation is still executing. For instance,
*it can be used to animate a progress bar or show logs in a text field.</li>
*<li>{@link # onPostExecute (Object)}, invoked on the UI thread after the background
*computation finishes. The result of the background computation is passed to
*this step as a parameter.</li>
* </ol>
*
* <h2>Threading rules</h2>
* <p>There are a few threading rules that must be followed for this class to
* work properly:</p>
* <ul>
*<li>The task instance must be created on the UI thread.</li>
*<li>{@link #execute(Object[])} must be invoked on the UI thread.</li>
*<li>Do not call {@link # onPreExecute ()}, {@link # onPostExecute (Object)},
*{@link #doInBackground(Object[])}, {@link # onProgressUpdate (Object[])}
*manually.</li>
*<li>The task can be executed only once (an exception will be thrown if
*a second execution is attempted.)</li>
* </ul>
*/
public abstract class UserTask<Params, Progress, Result> {
private static final String LOG_TAG = "UserTask";
private static final int CORE_POOL_SIZE = 1;
private static final int MAXIMUM_POOL_SIZE = 10;
private static final int KEEP_ALIVE = 10;
private static final BlockingQueue<Runnable> sWorkQueue =
new LinkedBlockingQueue<Runnable>(MAXIMUM_POOL_SIZE);
private static final ThreadFactory sThreadFactory = new ThreadFactory() {
private final AtomicInteger mCount = new AtomicInteger(1);
public Thread newThread(Runnable r) {
return new Thread(r, "UserTask #" + mCount.getAndIncrement());
}
};
private static final ThreadPoolExecutor sExecutor = new ThreadPoolExecutor(CORE_POOL_SIZE,
MAXIMUM_POOL_SIZE, KEEP_ALIVE, TimeUnit.SECONDS, sWorkQueue, sThreadFactory);
private static final int MESSAGE_POST_RESULT = 0x1;
private static final int MESSAGE_POST_PROGRESS = 0x2;
private static final int MESSAGE_POST_CANCEL = 0x3;
private static final InternalHandler sHandler = new InternalHandler();
private final WorkerRunnable<Params, Result> mWorker;
private final FutureTask<Result> mFuture;
private volatile Status mStatus = Status.PENDING;
/**
* Indicates the current status of the task. Each status will be set only once
* during the lifetime of a task.
*/
public enum Status {
/**
* Indicates that the task has not been executed yet.
*/
PENDING,
/**
* Indicates that the task is running.
*/
RUNNING,
/**
* Indicates that {@link UserTask#onPostExecute(Object)} has finished.
*/
FINISHED,
}
/**
* Creates a new user task. This constructor must be invoked on the UI thread.
*/
public UserTask() {
mWorker = new WorkerRunnable<Params, Result>() {
public Result call() throws Exception {
Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
return doInBackground(mParams);
}
};
mFuture = new FutureTask<Result>(mWorker) {
@Override
protected void done() {
Message message;
Result result = null;
try {
result = get();
} catch (InterruptedException e) {
android.util.Log.w(LOG_TAG, e);
} catch (ExecutionException e) {
throw new RuntimeException("An error occured while executing doInBackground()",
e.getCause());
} catch (CancellationException e) {
message = sHandler.obtainMessage(MESSAGE_POST_CANCEL,
new UserTaskResult<Result>(UserTask.this, (Result[]) null));
message.sendToTarget();
return;
} catch (Throwable t) {
throw new RuntimeException("An error occured while executing "
+ "doInBackground()", t);
}
message = sHandler.obtainMessage(MESSAGE_POST_RESULT,
new UserTaskResult<Result>(UserTask.this, result));
message.sendToTarget();
}
};
}
/**
* Returns the current status of this task.
*
* @return The current status.
*/
public final Status getStatus() {
return mStatus;
}
/**
* Override this method to perform a computation on a background thread. The
* specified parameters are the parameters passed to {@link #execute(Object[])}
* by the caller of this task.
*
* This method can call {@link #publishProgress(Object[])} to publish updates
* on the UI thread.
*
* @param params The parameters of the task.
*
* @return A result, defined by the subclass of this task.
*
* @see #onPreExecute()
* @see #onPostExecute(Object)
* @see #publishProgress(Object[])
*/
public abstract Result doInBackground(Params... params);
/**
* Runs on the UI thread before {@link #doInBackground(Object[])}.
*
* @see #onPostExecute(Object)
* @see #doInBackground(Object[])
*/
public void onPreExecute() {
}
/**
* Runs on the UI thread after {@link #doInBackground(Object[])}. The
* specified result is the value returned by {@link #doInBackground(Object[])}
* or null if the task was cancelled or an exception occured.
*
* @param result The result of the operation computed by {@link #doInBackground(Object[])}.
*
* @see #onPreExecute()
* @see #doInBackground(Object[])
*/
@SuppressWarnings({"UnusedDeclaration"})
public void onPostExecute(Result result) {
}
/**
* Runs on the UI thread after {@link #publishProgress(Object[])} is invoked.
* The specified values are the values passed to {@link #publishProgress(Object[])}.
*
* @param values The values indicating progress.
*
* @see #publishProgress(Object[])
* @see #doInBackground(Object[])
*/
@SuppressWarnings({"UnusedDeclaration"})
public void onProgressUpdate(Progress... values) {
}
/**
* Runs on the UI thread after {@link #cancel(boolean)} is invoked.
*
* @see #cancel(boolean)
* @see #isCancelled()
*/
public void onCancelled() {
}
/**
* Returns <tt>true</tt> if this task was cancelled before it completed
* normally.
*
* @return <tt>true</tt> if task was cancelled before it completed
*
* @see #cancel(boolean)
*/
public final boolean isCancelled() {
return mFuture.isCancelled();
}
/**
* Attempts to cancel execution of this task.This attempt will
* fail if the task has already completed, already been cancelled,
* or could not be cancelled for some other reason. If successful,
* and this task has not started when <tt>cancel</tt> is called,
* this task should never run.If the task has already started,
* then the <tt>mayInterruptIfRunning</tt> parameter determines
* whether the thread executing this task should be interrupted in
* an attempt to stop the task.
*
* @param mayInterruptIfRunning <tt>true</tt> if the thread executing this
*task should be interrupted; otherwise, in-progress tasks are allowed
*to complete.
*
* @return <tt>false</tt> if the task could not be cancelled,
*typically because it has already completed normally;
*<tt>true</tt> otherwise
*
* @see #isCancelled()
* @see #onCancelled()
*/
public final boolean cancel(boolean mayInterruptIfRunning) {
return mFuture.cancel(mayInterruptIfRunning);
}
/**
* Waits if necessary for the computation to complete, and then
* retrieves its result.
*
* @return The computed result.
*
* @throws CancellationException If the computation was cancelled.
* @throws ExecutionException If the computation threw an exception.
* @throws InterruptedException If the current thread was interrupted
*while waiting.
*/
public final Result get() throws InterruptedException, ExecutionException {
return mFuture.get();
}
/**
* Waits if necessary for at most the given time for the computation
* to complete, and then retrieves its result.
*
* @param timeout Time to wait before cancelling the operation.
* @param unit The time unit for the timeout.
*
* @return The computed result.
*
* @throws CancellationException If the computation was cancelled.
* @throws ExecutionException If the computation threw an exception.
* @throws InterruptedException If the current thread was interrupted
*while waiting.
* @throws TimeoutException If the wait timed out.
*/
public final Result get(long timeout, TimeUnit unit) throws InterruptedException,
ExecutionException, TimeoutException {
return mFuture.get(timeout, unit);
}
/**
* Executes the task with the specified parameters. The task returns
* itself (this) so that the caller can keep a reference to it.
*
* This method must be invoked on the UI thread.
*
* @param params The parameters of the task.
*
* @return This instance of UserTask.
*
* @throws IllegalStateException If {@link #getStatus()} returns either
*{@link UserTask.Status#RUNNING} or {@link UserTask.Status#FINISHED}.
*/
public final UserTask<Params, Progress, Result> execute(Params... params) {
if (mStatus != Status.PENDING) {
switch (mStatus) {
case RUNNING:
throw new IllegalStateException("Cannot execute task:"
+ " the task is already running.");
case FINISHED:
throw new IllegalStateException("Cannot execute task:"
+ " the task has already been executed "
+ "(a task can be executed only once)");
}
}
mStatus = Status.RUNNING;
onPreExecute();
mWorker.mParams = params;
sExecutor.execute(mFuture);
return this;
}
/**
* This method can be invoked from {@link #doInBackground(Object[])} to
* publish updates on the UI thread while the background computation is
* still running. Each call to this method will trigger the execution of
* {@link #onProgressUpdate(Object[])} on the UI thread.
*
* @param values The progress values to update the UI with.
*
* @see # onProgressUpdate (Object[])
* @see #doInBackground(Object[])
*/
protected final void publishProgress(Progress... values) {
sHandler.obtainMessage(MESSAGE_POST_PROGRESS,
new UserTaskResult<Progress>(this, values)).sendToTarget();
}
private void finish(Result result) {
onPostExecute(result);
mStatus = Status.FINISHED;
}
private static class InternalHandler extends Handler {
@SuppressWarnings({"unchecked", "RawUseOfParameterizedType"})
@Override
public void handleMessage(Message msg) {
UserTaskResult result = (UserTaskResult) msg.obj;
switch (msg.what) {
case MESSAGE_POST_RESULT:
// There is only one result
result.mTask.finish(result.mData[0]);
break;
case MESSAGE_POST_PROGRESS:
result.mTask.onProgressUpdate(result.mData);
break;
case MESSAGE_POST_CANCEL:
result.mTask.onCancelled();
break;
}
}
}
private static abstract class WorkerRunnable<Params, Result> implements Callable<Result> {
Params[] mParams;
}
@SuppressWarnings({"RawUseOfParameterizedType"})
private static class UserTaskResult<Data> {
final UserTask mTask;
final Data[] mData;
UserTaskResult(UserTask task, Data... data) {
mTask = task;
mData = data;
}
}
}
