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android-notes/blogs/Android/IntentService.md

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---
IntentService
---
#### 目录
1. 思维导图
2. 概述
3. 具体使用
4. 源码分析
5. 参考
#### 思维导图
#### 概述
IntentService 是继承于 Service 并处理异步请求的一个类,内部实现是 HandlerThread,处理完子线程的事后自动 stopService。
#### 具体使用
首先创建:
```java
public class MyIntentService extends IntentService {
private static final String TAG = "MyIntentService";
public MyIntentService() {
//IntentService 工作线程的名字
super("MyIntentService");
}
@Override
public void onCreate() {
super.onCreate();
Log.i(TAG, "onCreate: ");
}
@Override
public int onStartCommand(@Nullable Intent intent, int flags, int startId) {
Log.i(TAG, "onStartCommand: ");
return super.onStartCommand(intent, flags, startId);
}
@Override
public void onDestroy() {
super.onDestroy();
Log.i(TAG, "onDestroy: ");
}
@Override
protected void onHandleIntent(@Nullable Intent intent) {
if (intent != null) {
String taskName = intent.getStringExtra("taskName");
Log.i(TAG, "onHandleIntent: " + taskName);
switch (taskName) {
case "task1":
//任务一
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
break;
case "task2":
//任务二
break;
default:
break;
}
}
}
}
```
Activity 中:
```java
public void onClick(View v) {
Intent intent = new Intent(this, MyIntentService.class);
switch (v.getId()) {
case R.id.btn1:
intent.putExtra("taskName", "task1");
startService(intent);
break;
case R.id.btn2:
intent.putExtra("taskName", "task2");
startService(intent);
break;
default:
break;
}
}
```
这里如果点击按钮一后立马点击按钮二,日志打印如下:
```
onCreate、onStartCommand、onHandleIntent: task1、
onStartCommand、onHandleIntent: task2、onDestroy
```
如果是等三秒后再点击按钮二,就是:
```
onCreate、onStartCommand、onHandleIntent: task1、onDestroy、
onCreate、onStartCommand、onHandleIntent: task2、onDestroy
```
这下就清楚了吧。
#### 源码分析
```java
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) {
//重写的方法,子线程需要做的事情
onHandleIntent((Intent)msg.obj);
//做完事,自动停止
stopSelf(msg.arg1);
}
}
public IntentService(String name) {
super();
//IntentService 的线程名
mName = name;
}
public void setIntentRedelivery(boolean enabled) {
mRedelivery = enabled;
}
@Override
public void onCreate() {
super.onCreate();
HandlerThread thread = new HandlerThread("IntentService[" + mName + "]");
thread.start();
//构造子线程 Handler
mServiceLooper = thread.getLooper();
mServiceHandler = new ServiceHandler(mServiceLooper);
}
@Override
public void onStart(@Nullable Intent intent, int startId) {
Message msg = mServiceHandler.obtainMessage();
msg.arg1 = startId;
msg.obj = intent;
//在 Service 启动的时候发送消息,子线程开始工作
mServiceHandler.sendMessage(msg);
}
@Override
public int onStartCommand(@Nullable Intent intent, int flags, int startId) {
//调用上面的那个方法,促使子线程开始工作
onStart(intent, startId);
return mRedelivery ? START_REDELIVER_INTENT : START_NOT_STICKY;
}
@Override
public void onDestroy() {
mServiceLooper.quit();
}
@Override
@Nullable
public IBinder onBind(Intent intent) {
return null;
}
@WorkerThread
protected abstract void onHandleIntent(@Nullable Intent intent);
}
```
总结如下:
1. Service onCreate 的时候通过 HandlerThread 构建子线程的 Handler
2. Service onStartCommand 中通过子线程 Handler 发送消息
3. 子线程 handlerMessage 中调用我们重写的 onHandlerIntent 执行异步任务,执行完之后 Service 销毁
#### 参考