上次我们讲到如何实现一个可更新的进度通知,实现的方式是启动一个线程模拟一个下载任务,然后根据任务进度向UI线程消息队列发送进度消息,UI线程根据进度消息更新通知的UI界面。可是在实际应用中,我们一般会将上传、下载等比较耗时的后台任务以服务的形式运行,更新进度通知也是交由后台服务来完成的。 不过有的时候,除了在通知里面显示进度信息,我们也要在Activity中显示当前进度,很多下载系统都有这样的功能,例如Android自带浏览器的下载系统、QQ浏览器的下载系统等等。那么如何实现这一功能呢?实现方式有很多,我们今天先来介绍其中的一种:在Activity中主动监听服务的进度。
具体的思路是:让Activity与后台服务绑定,通过中间对象Binder的实例操作后台服务,获取进度信息和服务的状态以及在必要的时候停止服务。
关于服务的生命周期,如果有些朋友们不太熟悉的话,可以去查阅相关资料;如果以后有时间,我可能也会总结一些与服务相关的知识。
为了让大家对这个过程更清晰一些,在上代码之前,我们先来看看几个截图:
整个过程如上图所示:在我们点击开始按钮后,下载任务开始运行,同事更新通知上的进度,当前Activity也从后台服务获取进度信息,显示到按钮下方;当我们点击通知后,跳转到下载管理界面,在这里我们也从后台服务获取进度,还可以做取消任务等操作。
了解了整个过程的情况后,我们就来分析一下具体的代码实现。
首先是/res/main.xml布局文件:
- <?xml version="1.0" encoding="utf-8"?>
- <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
- android:orientation="vertical"
- android:layout_width="fill_parent"
- android:layout_height="fill_parent">
- <Button
- android:layout_width="fill_parent"
- android:layout_height="wrap_content"
- android:text="start"
- android:onClick="start"/>
- <TextView
- android:id="@+id/text"
- android:layout_width="fill_parent"
- android:layout_height="wrap_content"
- android:gravity="center"/>
- </LinearLayout>
其中Button是用来启动服务的,TextView是用来显示进度信息的。
然后再在看一下MainActivity.java的代码:
- package com.scott.notification;
-
- import android.app.Activity;
- import android.content.ComponentName;
- import android.content.Context;
- import android.content.Intent;
- import android.content.ServiceConnection;
- import android.os.Bundle;
- import android.os.Handler;
- import android.os.IBinder;
- import android.os.Message;
- import android.view.View;
- import android.widget.TextView;
-
- public class MainActivity extends Activity {
-
- private DownloadService.DownloadBinder binder;
- private TextView text;
-
- private boolean binded;
-
- private Handler handler = new Handler() {
- public void handleMessage(android.os.Message msg) {
- int progress = msg.arg1;
- text.setText("downloading..." + progress + "%");
- };
- };
-
- private ServiceConnection conn = new ServiceConnection() {
-
- @Override
- public void onServiceConnected(ComponentName name, IBinder service) {
- binder = (DownloadService.DownloadBinder) service;
- binded = true;
-
- binder.start();
-
- listenProgress();
- }
-
- @Override
- public void onServiceDisconnected(ComponentName name) {
- }
- };
-
- @Override
- public void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.main);
- text = (TextView) findViewById(R.id.text);
- }
-
- @Override
- protected void onDestroy() {
- super.onDestroy();
- if (binded) {
- unbindService(conn);
- }
- }
-
- public void start(View view) {
- if (binded) {
- binder.start();
- listenProgress();
- return;
- }
- Intent intent = new Intent(this, DownloadService.class);
- startService(intent);
- bindService(intent, conn, Context.BIND_AUTO_CREATE);
- }
-
-
-
-
- private void listenProgress() {
- new Thread() {
- public void run() {
- while (!binder.isCancelled() && binder.getProgress() <= 100) {
- int progress = binder.getProgress();
- Message msg = handler.obtainMessage();
- msg.arg1 = progress;
- handler.sendMessage(msg);
- if (progress == 100) {
- break;
- }
- try {
- Thread.sleep(200);
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- }
- };
- }.start();
- }
- }
我们可以看到,当点击开始按钮后,以bindService的方式绑定服务,用获取到的DownloadService.DownloadBinder实例启动服务,并在Activity中启动一个线程监听服务的进度信息,及时的显示到按钮下方。
服务类DownloadService.java代码如下:
- package com.scott.notification;
-
- import android.app.Notification;
- import android.app.NotificationManager;
- import android.app.PendingIntent;
- import android.app.Service;
- import android.content.Context;
- import android.content.Intent;
- import android.os.Binder;
- import android.os.Handler;
- import android.os.IBinder;
- import android.os.Message;
- import android.widget.RemoteViews;
-
- public class DownloadService extends Service {
-
- private static final int NOTIFY_ID = 0;
- private boolean cancelled;
- private int progress;
-
- private Context mContext = this;
-
- private NotificationManager mNotificationManager;
- private Notification mNotification;
-
- private DownloadBinder binder = new DownloadBinder();
-
- private Handler handler = new Handler() {
- public void handleMessage(android.os.Message msg) {
- switch (msg.what) {
- case 1:
- int rate = msg.arg1;
- if (rate < 100) {
-
- RemoteViews contentView = mNotification.contentView;
- contentView.setTextViewText(R.id.rate, rate + "%");
- contentView.setProgressBar(R.id.progress, 100, rate, false);
- } else {
-
- mNotification.flags = Notification.FLAG_AUTO_CANCEL;
- mNotification.contentView = null;
- Intent intent = new Intent(mContext, FileMgrActivity.class);
-
- intent.putExtra("completed", "yes");
-
- PendingIntent contentIntent = PendingIntent.getActivity(mContext, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT);
- mNotification.setLatestEventInfo(mContext, "下载完成", "文件已下载完毕", contentIntent);
- stopSelf();
- }
-
-
- mNotificationManager.notify(NOTIFY_ID, mNotification);
- break;
- case 0:
-
- mNotificationManager.cancel(NOTIFY_ID);
- break;
- }
- };
- };
-
- @Override
- public void onCreate() {
- super.onCreate();
- mNotificationManager = (NotificationManager) getSystemService(android.content.Context.NOTIFICATION_SERVICE);
- }
-
- @Override
- public IBinder onBind(Intent intent) {
-
- return binder;
- }
-
- @Override
- public void onDestroy() {
- super.onDestroy();
- cancelled = true;
- }
-
-
-
-
- private void setUpNotification() {
- int icon = R.drawable.down;
- CharSequence tickerText = "开始下载";
- long when = System.currentTimeMillis();
- mNotification = new Notification(icon, tickerText, when);
-
-
- mNotification.flags = Notification.FLAG_ONGOING_EVENT;
-
- RemoteViews contentView = new RemoteViews(mContext.getPackageName(), R.layout.download_notification_layout);
- contentView.setTextViewText(R.id.fileName, "AngryBird.apk");
-
- mNotification.contentView = contentView;
-
- Intent intent = new Intent(this, FileMgrActivity.class);
- PendingIntent contentIntent = PendingIntent.getActivity(mContext, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT);
-
- mNotification.contentIntent = contentIntent;
- mNotificationManager.notify(NOTIFY_ID, mNotification);
- }
-
-
-
-
- private void startDownload() {
- cancelled = false;
- int rate = 0;
- while (!cancelled && rate < 100) {
- try {
-
- Thread.sleep(500);
- rate = rate + 5;
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- Message msg = handler.obtainMessage();
- msg.what = 1;
- msg.arg1 = rate;
- handler.sendMessage(msg);
-
- this.progress = rate;
- }
- if (cancelled) {
- Message msg = handler.obtainMessage();
- msg.what = 0;
- handler.sendMessage(msg);
- }
- }
-
-
-
-
-
-
-
- public class DownloadBinder extends Binder {
-
-
-
-
- public void start() {
-
- progress = 0;
-
- setUpNotification();
- new Thread() {
- public void run() {
-
- startDownload();
- };
- }.start();
- }
-
-
-
-
-
-
- public int getProgress() {
- return progress;
- }
-
-
-
-
- public void cancel() {
- cancelled = true;
- }
-
-
-
-
-
-
- public boolean isCancelled() {
- return cancelled;
- }
- }
- }
我们看到,在服务中有个DownloadBinder类,它继承自Binder,定义了一系列方法,获取服务状态以及操作当前服务,刚才我们在MainActivity中获取的就是这个类的实例。最后,不要忘了在AndroidManifest.xml中配置该服务。关于进度通知的布局文件/res/layout/download_notification_layout.xml,在这里就不需贴出了,朋友们可以参考一下Notification使用详解之二中进度通知布局的具体代码。
下面我们来介绍一下FileMgrActivity,它就是点击通知之后跳转到的界面,布局文件/res/filemgr.xml如下:
- <?xml version="1.0" encoding="utf-8"?>
- <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
- android:orientation="vertical"
- android:layout_width="fill_parent"
- android:layout_height="fill_parent">
- <ProgressBar
- android:id="@+id/progress"
- style="?android:attr/progressBarStyleHorizontal"
- android:layout_width="fill_parent"
- android:layout_height="wrap_content"
- android:max="100"
- android:progress="0"/>
- <Button
- android:id="@+id/cancel"
- android:layout_width="fill_parent"
- android:layout_height="wrap_content"
- android:text="cancel"
- android:onClick="cancel"/>
- </LinearLayout>
我们来看一下FileMgrActivity.java具体的代码:
- package com.scott.notification;
-
- import android.app.Activity;
- import android.content.ComponentName;
- import android.content.Context;
- import android.content.Intent;
- import android.content.ServiceConnection;
- import android.os.Bundle;
- import android.os.Handler;
- import android.os.IBinder;
- import android.os.Message;
- import android.view.View;
- import android.widget.Button;
- import android.widget.ProgressBar;
-
- public class FileMgrActivity extends Activity {
- private DownloadService.DownloadBinder binder;
- private ProgressBar progressBar;
- private Button cancel;
- private boolean binded;
-
- private Handler handler = new Handler() {
- public void handleMessage(android.os.Message msg) {
- int progress = msg.arg1;
- progressBar.setProgress(progress);
- if (progress == 100) {
- cancel.setEnabled(false);
- }
- };
- };
-
- private ServiceConnection conn = new ServiceConnection() {
-
- @Override
- public void onServiceConnected(ComponentName name, IBinder service) {
- binder = (DownloadService.DownloadBinder) service;
-
- listenProgress();
- }
-
- @Override
- public void onServiceDisconnected(ComponentName name) {
- }
- };
-
- @Override
- public void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.filemgr);
- progressBar = (ProgressBar) findViewById(R.id.progress);
- cancel = (Button) findViewById(R.id.cancel);
-
- if ("yes".equals(getIntent().getStringExtra("completed"))) {
-
- progressBar.setProgress(100);
-
- cancel.setEnabled(false);
- } else {
-
- Intent intent = new Intent(this, DownloadService.class);
- bindService(intent, conn, Context.BIND_AUTO_CREATE);
- binded = true;
- }
- }
-
- @Override
- protected void onDestroy() {
- super.onDestroy();
-
- if (binded) {
- unbindService(conn);
- }
- }
-
- public void cancel(View view) {
-
- binder.cancel();
- }
-
-
-
-
- private void listenProgress() {
- new Thread() {
- public void run() {
- while (!binder.isCancelled() && binder.getProgress() <= 100) {
- int progress = binder.getProgress();
- Message msg = handler.obtainMessage();
- msg.arg1 = progress;
- handler.sendMessage(msg);
- try {
- Thread.sleep(200);
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- }
- };
- }.start();
- }
- }
我们发现,它和MainActivity实现方式很相似,恩,他们都是通过和服务绑定后获取到的Binder对象来跟服务通信的,都是主动和服务打招呼来获取信息和控制服务的。
这两个Activity和一个Service似乎像是复杂的男女关系,两个男人同时喜欢一个女人,都通过自己的手段试图从那个女人获取爱情,两个男人都很主动,那个女人显得很被动。
以上就是今天的全部内容,也许朋友们会有疑问,能不能让Service主动告知Activity当前的进度信息呢?答案是可以。下一次,我就会和大家分享一下,如何变Service为主动方,让一个女人脚踏两只船的方式。