IntentService介绍及使用
IntentService是一个通过
Context.startService(Intent)启动可以处理异步请求的Service,使用时你只需要继承IntentService和重写其中的
onHandleIntent(Intent)方法接收一个Intent对象,在适当的时候会停止自己(一般在工作完成的时候). 所有的请求的处理都在一个工作线程中完成,它们会交替执行(但不会阻塞主线程的执行),一次只能执行一个请求.
下面是要分析的源码:
public
abstract
class IntentService
extends Service {
private volatile Looper mServiceLooper;
private volatile ServiceHandler mServiceHandler;
private String mName;
private boolean mRedelivery;
private final class ServiceHandler extends Handler {
public ServiceHandler(Looper looper) {
super(looper);
}
@Override
public void handleMessage(Message msg) {
onHandleIntent((Intent)msg.obj);
stopSelf(msg.arg1);
}
}
private volatile Looper mServiceLooper;
private volatile ServiceHandler mServiceHandler;
private String mName;
private boolean mRedelivery;
private final class ServiceHandler extends Handler {
public ServiceHandler(Looper looper) {
super(looper);
}
@Override
public void handleMessage(Message msg) {
onHandleIntent((Intent)msg.obj);
stopSelf(msg.arg1);
}
}
IntentService 实际上是Looper,Handler,Service 的集合体,他不仅有服务的功能,还有处理和循环消息的功能.
下面是onCreate()的源码:
@Override
public void onCreate() {
super.onCreate();
HandlerThread thread = new HandlerThread( "IntentService[" + mName + "]");
thread.start();
mServiceLooper = thread.getLooper();
mServiceHandler = new ServiceHandler(mServiceLooper);
}
public void onCreate() {
super.onCreate();
HandlerThread thread = new HandlerThread( "IntentService[" + mName + "]");
thread.start();
mServiceLooper = thread.getLooper();
mServiceHandler = new ServiceHandler(mServiceLooper);
}
下面是onStart()的源码:
@Override
public void onStart(Intent intent, int startId) {
Message msg = mServiceHandler.obtainMessage();
msg.arg1 = startId;
msg.obj = intent;
mServiceHandler.sendMessage(msg);
}
public void onStart(Intent intent, int startId) {
Message msg = mServiceHandler.obtainMessage();
msg.arg1 = startId;
msg.obj = intent;
mServiceHandler.sendMessage(msg);
}
@Override
public void handleMessage(Message msg) {
onHandleIntent((Intent)msg.obj);
stopSelf(msg.arg1);
}
public void handleMessage(Message msg) {
onHandleIntent((Intent)msg.obj);
stopSelf(msg.arg1);
}
当所有的工作执行完后:就会执行onDestroy方法,源码如下:
@Override
public void onDestroy() {
mServiceLooper.quit();
}
public void onDestroy() {
mServiceLooper.quit();
}
通过对源码的分析得出:
这是一个基于消息的服务,每次启动该服务并不是马上处理你的工作,而是首先会创建对应的Looper,Handler并且在MessageQueue中添加的附带客户Intent的Message对象,当Looper发现有Message的时候接着得到Intent对象通过在onHandleIntent((Intent)msg.obj)中调用你的处理程序.处理完后即会停止自己的服务.意思是Intent的生命周期跟你的处理的任务是一致的.所以这个类用下载任务中非常好,下载任务结束后服务自身就会结束退出.
下面通过一个小例子说明。
1、创建一个Activity，添加两个按钮
package com.example.hornsey.myapplication.IntentServiceDemo;
import android.app.IntentService;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import com.example.hornsey.myapplication.R;
public class ISDemoActivity extends AppCompatActivity {
private static final String ACTION_FOO = "com.example.hornsey.myapplication.IntentServiceDemo.action.FOO";
private static final String ACTION_BAZ = "com.example.hornsey.myapplication.IntentServiceDemo.action.BAZ";
private static final String EXTRA_PARAM1 = "Name";
private static final String EXTRA_PARAM2 = "Question";
private static final String EXTRA_PARAM3 = "Answer";
private static Context context;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_isdemo);
context = ISDemoActivity.this;
findViewById(R.id.btn_action1).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
startActionFoo(context,"Jack","How are you?");
}
});
findViewById(R.id.btn_action2).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
startActionBaz(context,"Tom","Fine!");
}
});
}
/**
* Starts this service to perform action Foo with the given parameters. If
* the service is already performing a task this action will be queued.
*
* @see IntentService
*/
public static void startActionFoo(Context context, String param1, String param2) {
Intent intent = new Intent(context, MyIntentService.class);
intent.setAction(ACTION_FOO);
intent.putExtra(EXTRA_PARAM1, param1);
intent.putExtra(EXTRA_PARAM2, param2);
context.startService(intent);
}
/**
* Starts this service to perform action Baz with the given parameters. If
* the service is already performing a task this action will be queued.
*
* @see IntentService
*/
public static void startActionBaz(Context context, String param1, String param2) {
Intent intent = new Intent(context, MyIntentService.class);
intent.setAction(ACTION_BAZ);
intent.putExtra(EXTRA_PARAM1, param1);
intent.putExtra(EXTRA_PARAM3, param2);
context.startService(intent);
}
}
2、定义一个继承自IntentService的Service
package com.example.hornsey.myapplication.IntentServiceDemo;
import android.app.IntentService;
import android.content.Intent;
import android.os.IBinder;
import android.util.Log;
import java.util.concurrent.TimeUnit;
/**
* An {@link IntentService} subclass for handling asynchronous task requests in
* a service on a separate handler thread.
* <p>
* helper methods.
*/
public class MyIntentService extends IntentService {
private static final String TAG = "MyIntentService";
private static final String ACTION_FOO = "com.example.hornsey.myapplication.IntentServiceDemo.action.FOO";
private static final String ACTION_BAZ = "com.example.hornsey.myapplication.IntentServiceDemo.action.BAZ";
private static final String EXTRA_PARAM1 = "Name";
private static final String EXTRA_PARAM2 = "Question";
private static final String EXTRA_PARAM3 = "Answer";
public MyIntentService() {
super("MyIntentService");
}
@Override
protected void onHandleIntent(Intent intent) {
if (intent != null) {
final String action = intent.getAction();
if (ACTION_FOO.equals(action)) {
final String param1 = intent.getStringExtra(EXTRA_PARAM1);
final String param2 = intent.getStringExtra(EXTRA_PARAM2);
handleActionFoo(param1, param2);
} else if (ACTION_BAZ.equals(action)) {
final String param1 = intent.getStringExtra(EXTRA_PARAM1);
final String param2 = intent.getStringExtra(EXTRA_PARAM3);
handleActionBaz(param1, param2);
}
}
}
/**
* Handle action Foo in the provided background thread with the provided
* parameters.
*/
private void handleActionFoo(String param1, String param2) {
Log.d(TAG, "handleActionFoo." + param1 + " : " + param2);
try {
TimeUnit.SECONDS.sleep(5);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
/**
* Handle action Baz in the provided background thread with the provided
* parameters.
*/
private void handleActionBaz(String param1, String param2) {
Log.d(TAG, "handleActionBaz." + param1 + " : " + param2);
}
public MyIntentService(String name) {
super(name);
Log.d(TAG, "MyIntentService: ");
}
@Override
public IBinder onBind(Intent intent) {
Log.d(TAG, "onBind: ");
return super.onBind(intent);
}
@Override
public void onCreate() {
super.onCreate();
Log.d(TAG, "onCreate: ");
}
@Override
public void onDestroy() {
Log.d(TAG, "onDestroy: ");
super.onDestroy();
}
@Override
public void onStart(Intent intent, int startId) {
super.onStart(intent, startId);
Log.d(TAG, "onStart: ");
}
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
Log.d(TAG, "onStartCommand: ");
return super.onStartCommand(intent, flags, startId);
}
}
3、在Manifest.xml中声明
<activity
android:name=".IntentServiceDemo.ISDemoActivity"
android:label="@string/title_activity_isdemo"
android:theme="@style/AppTheme">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<service
android:name=".IntentServiceDemo.MyIntentService"
android:exported="false">
<intent-filter>
<action android:name="com.example.hornsey.myapplication.IntentServiceDemo.action.FOO" />
<action android:name="com.example.hornsey.myapplication.IntentServiceDemo.action.BAZ" />
</intent-filter>
</service>
4、运行结果如下：
02-26 11:10:07.635 6624-6624/com.example.hornsey.myapplication D/MyIntentService: onCreate: 02-26 11:10:07.635 6624-6624/com.example.hornsey.myapplication D/MyIntentService: onStartCommand: 02-26 11:10:07.635 6624-6624/com.example.hornsey.myapplication D/MyIntentService: onStart: 02-26 11:10:07.645 6624-7217/com.example.hornsey.myapplication D/MyIntentService: handleActionFoo.Jack : How are you? 02-26 11:10:09.185 6624-6624/com.example.hornsey.myapplication D/MyIntentService: onStartCommand: 02-26 11:10:09.185 6624-6624/com.example.hornsey.myapplication D/MyIntentService: onStart: 02-26 11:10:12.645 6624-7217/com.example.hornsey.myapplication D/MyIntentService: handleActionBaz.Tom : Fine! 02-26 11:10:12.645 6624-6624/com.example.hornsey.myapplication D/MyIntentService: onDestroy: 02-26 11:10:33.855 6624-6624/com.example.hornsey.myapplication D/MyIntentService: onCreate: 02-26 11:10:33.855 6624-6624/com.example.hornsey.myapplication D/MyIntentService: onStartCommand: 02-26 11:10:33.855 6624-6624/com.example.hornsey.myapplication D/MyIntentService: onStart: 02-26 11:10:33.855 6624-7668/com.example.hornsey.myapplication D/MyIntentService: handleActionFoo.Jack : How are you? 02-26 11:10:38.865 6624-6624/com.example.hornsey.myapplication D/MyIntentService: onDestroy: 02-26 11:10:41.915 6624-6624/com.example.hornsey.myapplication D/MyIntentService: onCreate: 02-26 11:10:41.915 6624-6624/com.example.hornsey.myapplication D/MyIntentService: onStartCommand: 02-26 11:10:41.915 6624-6624/com.example.hornsey.myapplication D/MyIntentService: onStart: 02-26 11:10:41.925 6624-7790/com.example.hornsey.myapplication D/MyIntentService: handleActionBaz.Tom : Fine! 02-26 11:10:41.925 6624-6624/com.example.hornsey.myapplication D/MyIntentService: onDestroy:
因为在第一个任务处理过程中，我让服务sleep了5秒，所以第一次两个按钮点击相差2秒时，service只start了一次，当第二个按钮点击启动service时，service已经启动，只是把任务加入处理队列。第二次点击两个按钮相差8秒，所以第一个任务处理完毕后，service已经destroy，当点击第二个按钮时，service又重新启动，处理完任务后再次关闭。
参考：
http://www.2cto.com/kf/201409/331983.html
http://android.blog.51cto.com/268543/528166