现在在我的应用程序中下载代码正在工作，但当我下载多个文件时，它随机下载而不在队列中，我需要它在队列中下载，并且当前下载不显示在通知栏中，只显示在活动中。我想知道如何在通知栏中显示多次下载，并在当前活动中显示进度栏。感谢
环路
通过使用looper，您可以逐个下载队列中的多个文件。
步骤1：让我们创建DownloadThreadListener.java接口，该接口将用于获取线程更新。
package com.example.looper;
public interface DownloadThreadListener {
void handleDownloadThreadUpdate();
}
步骤2：现在创建一个名为DownloadTask.java的类，它将模拟下载。我们将使用随机睡眠时间来模拟下载时间。
package com.example.looper;
import java.util.Random;
import android.util.Log;
/**
* This is not a real download task. It just sleeps for some random time when
* it's launched. The idea is not to require a connection and not to eat it.
*
*/
public class DownloadTask implements Runnable {
private static final String TAG = DownloadTask.class.getSimpleName();
private static final Random random = new Random();
private int lengthSec;
public DownloadTask() {
lengthSec = random.nextInt(3) + 1;
}
@Override
public void run() {
try {
Thread.sleep(lengthSec * 1000);
// it's a good idea to always catch Throwable
// in isolated "codelets" like Runnable or Thread
// otherwise the exception might be sunk by some
// agent that actually runs your Runnable - you
// never know what it might be.
} catch (Throwable t) {
Log.e(TAG, "Error in DownloadTask", t);
}
}
}
步骤3：现在让我们创建将充当管道的线程子类。首先，我们将调用Looper.prepare（），使该线程充当管道。下一个新的Handler（）将被调用来处理该线程上的消息队列。最后将调用Looper.loop（）来开始运行消息循环。新任务将使用enqueueDownload（最终的DownloadTask任务）添加。
package com.example.looper;
import android.os.Handler;
import android.os.Looper;
import android.util.Log;
public final class DownloadThread extends Thread {
private static final String TAG = DownloadThread.class.getSimpleName();
private Handler handler;
private int totalQueued;
private int totalCompleted;
private DownloadThreadListener listener;
public DownloadThread(DownloadThreadListener listener) {
this.listener = listener;
}
@Override
public void run() {
try {
// preparing a looper on current thread
// the current thread is being detected implicitly
Looper.prepare();
Log.i(TAG, "DownloadThread entering the loop");
// now, the handler will automatically bind to the
// Looper that is attached to the current thread
// You don't need to specify the Looper explicitly
handler = new Handler();
// After the following line the thread will start
// running the message loop and will not normally
// exit the loop unless a problem happens or you
// quit() the looper (see below)
Looper.loop();
Log.i(TAG, "DownloadThread exiting gracefully");
} catch (Throwable t) {
Log.e(TAG, "DownloadThread halted due to an error", t);
}
}
// This method is allowed to be called from any thread
public synchronized void requestStop() {
// using the handler, post a Runnable that will quit()
// the Looper attached to our DownloadThread
// obviously, all previously queued tasks will be executed
// before the loop gets the quit Runnable
handler.post(new Runnable() {
@Override
public void run() {
// This is guaranteed to run on the DownloadThread
// so we can use myLooper() to get its looper
Log.i(TAG, "DownloadThread loop quitting by request");
Looper.myLooper().quit();
}
});
}
public synchronized void enqueueDownload(final DownloadTask task) {
// Wrap DownloadTask into another Runnable to track the statistics
handler.post(new Runnable() {
@Override
public void run() {
try {
task.run();
} finally {
// register task completion
synchronized (DownloadThread.this) {
totalCompleted++;
}
// tell the listener something has happened
signalUpdate();
}
}
});
totalQueued++;
// tell the listeners the queue is now longer
signalUpdate();
}
public synchronized int getTotalQueued() {
return totalQueued;
}
public synchronized int getTotalCompleted() {
return totalCompleted;
}
// Please note! This method will normally be called from the download
// thread.
// Thus, it is up for the listener to deal with that (in case it is a UI
// component,
// it has to execute the signal handling code in the UI thread using Handler
// - see
// DownloadQueueActivity for example).
private void signalUpdate() {
if (listener != null) {
listener.handleDownloadThreadUpdate();
}
}
}
步骤4：现在将全部功能添加到MainActivity.java。在这里，我们还将创建处理程序，以便在主线程上发布事件。
package com.example.looper;
import java.util.Random;
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Vibrator;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.TextView;
public class MainActivity extends Activity implements DownloadThreadListener,
OnClickListener {
private DownloadThread downloadThread;
private Handler handler;
private ProgressBar progressBar;
private TextView statusText;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Create and launch the download thread
downloadThread = new DownloadThread(this);
downloadThread.start();
// Create the Handler. It will implicitly bind to the Looper
// that is internally created for this thread (since it is the UI
// thread)
handler = new Handler();
progressBar = (ProgressBar) findViewById(R.id.progress_bar);
statusText = (TextView) findViewById(R.id.status_text);
Button scheduleButton = (Button) findViewById(R.id.schedule_button);
scheduleButton.setOnClickListener(this);
}
@Override
protected void onDestroy() {
super.onDestroy();
// request the thread to stop
downloadThread.requestStop();
}
// note! this might be called from another thread
@Override
public void handleDownloadThreadUpdate() {
// we want to modify the progress bar so we need to do it from the UI
// thread
// how can we make sure the code runs in the UI thread? use the handler!
handler.post(new Runnable() {
@Override
public void run() {
int total = downloadThread.getTotalQueued();
int completed = downloadThread.getTotalCompleted();
progressBar.setMax(total);
progressBar.setProgress(0); // need to do it due to a
// ProgressBar bug
progressBar.setProgress(completed);
statusText.setText(String.format("Downloaded %d/%d", completed,
total));
// vibrate for fun
if (completed == total) {
((Vibrator) getSystemService(VIBRATOR_SERVICE))
.vibrate(100);
}
}
});
}
@Override
public void onClick(View source) {
if (source.getId() == R.id.schedule_button) {
int totalTasks = new Random().nextInt(3) + 1;
for (int i = 0; i < totalTasks; ++i) {
downloadThread.enqueueDownload(new DownloadTask());
}
}
}
}
步骤5：添加振动权限
<uses-permission android:name="android.permission.VIBRATE" />
这里是原始的Post Complete教程。