Android 教你怎么使用IntentService , 源码给你们讲清楚了一切
IntentService是继承并处理异步请求的一个类,在IntentService内有一个工作线程来处理耗时操作,启动IntentService的方式和启动传统的Service一样,同时,当任务执行完后,IntentService会自动停止,而不需要我们手动去控制或stopSelf()。另外,可以启动IntentService多次,而每一个耗时操作会以工作队列的方式在IntentService的onHandleIntent回调方法中执行,并且,每次只会执行一个工作线程,执行完第一个再执行第二个,以此类推。
使用了IntentService最起码有两个好处:
1. 一方面不需要自己去new Thread了;
2. 另一方面不需要考虑在什么时候关闭该Service了。
接下来让大家看一下实现的效果图:
这里写了一个耗时操作,每隔三秒请求一下数据
当请求数据的时候,会发送消息让后台service去处理,Service处理之后会返回给Activity , 然后Activity会更新UI
UploadImgService
继承自IntentService的实现类,会自动生成一个onHandlerIntent的方法
import android.app.IntentService; import android.content.Context; import android.content.Intent; import android.util.Log; public class UploadImgService extends IntentService { private static final String ACTION_UPLOAD_IMG = "yangyang"; public static final String EXTRA_IMG_PATH = "haha"; public static void startUploadImg(Context context, String path) { Intent intent = new Intent(context, UploadImgService.class); //要设置相同action才能启动 intent.setAction(ACTION_UPLOAD_IMG); intent.putExtra(EXTRA_IMG_PATH, path); //启动服务 context.startService(intent); } public UploadImgService() { super("UploadImgService"); } @Override protected void onHandleIntent(Intent intent) { if (intent != null) { final String action = intent.getAction(); //判断消息是否一致 if (ACTION_UPLOAD_IMG.equals(action)) { //通过EXTRA_IMG_PATH标志,获取数据 final String path = intent.getStringExtra(EXTRA_IMG_PATH); handleUploadImg(path); } } } private void handleUploadImg(String path) { try { //模拟上传耗时操作,在intentservice里面不需要自己创建线程 Thread.sleep(3000); Intent intent = new Intent(MainActivity.UPLOAD_RESULT); intent.putExtra(EXTRA_IMG_PATH, path); //发送广播 sendBroadcast(intent); } catch (InterruptedException e) { e.printStackTrace(); } } @Override public void onCreate() { super.onCreate(); Log.e("TAG", "onCreate"); } @Override public void onDestroy() { super.onDestroy(); Log.e("TAG", "onDestroy"); } }
MainActivity
import android.content.BroadcastReceiver; import android.content.Context; import android.content.Intent; import android.content.IntentFilter; import android.os.Bundle; import android.support.v7.app.AppCompatActivity; import android.view.View; import android.widget.LinearLayout; import android.widget.TextView; public class MainActivity extends AppCompatActivity { public static final String UPLOAD_RESULT = "com.example.intent_service_MainActivity"; private LinearLayout mLine; private BroadcastReceiver uploadImgReceiver = new BroadcastReceiver() { @Override public void onReceive(Context context, Intent intent) { if (intent.getAction() == UPLOAD_RESULT) { String path = intent.getStringExtra(UploadImgService.EXTRA_IMG_PATH); handleResult(path); } } }; private void handleResult(String path) { TextView tv = (TextView) mLine.findViewWithTag(path); tv.setText(path + " 请求成功"); } @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); mLine = (LinearLayout) findViewById(R.id.mLine); registerReceiver(); } private void registerReceiver() { IntentFilter filter = new IntentFilter(); filter.addAction(UPLOAD_RESULT); registerReceiver(uploadImgReceiver, filter); } int i = 0; public void addTask(View view) { //模拟发送消息 String path = "这是我发送第" + (++i) + "条消息"; //调用IntentService方法,传入路径 UploadImgService.startUploadImg(this, path); TextView tv = new TextView(this); //把TextView添加到LineLayout当中 mLine.addView(tv); tv.setText(path + " 请求消息中"); tv.setTag(path); } @Override protected void onDestroy() { super.onDestroy(); //我用的广播来发送消息,所以退出的时候要解除广播 unregisterReceiver(uploadImgReceiver); } }
xml布局:
<LinearLayout android:id="@+id/mLine" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical"> <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:onClick="addTask" android:text="发送请求" /> </LinearLayout>
最后要在配置清单注册,不注册的话是不会执行其中的方法。
带大家了解一下源码:
可以看到IntentService是基于Service来实现的,就是每次调用onStartCommand的时候,通过mServiceHandler发送一个消息,消息中包含我们的intent。然后在该mServiceHandler的handleMessage中去回调onHandleIntent(intent);就可以了。
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); } } public IntentService(String name) { super(); mName = name; } public void setIntentRedelivery(boolean enabled) { mRedelivery = enabled; } @Override public void onCreate() { // TODO: It would be nice to have an option to hold a partial wakelock // during processing, and to have a static startService(Context, Intent) // method that would launch the service & hand off a wakelock. super.onCreate(); HandlerThread thread = new HandlerThread("IntentService[" + mName + "]"); thread.start(); 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; mServiceHandler.sendMessage(msg); } @Override public int onStartCommand(@Nullable Intent intent, int flags, int startId) { 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); }
具体点来说就是在onStartCommand中回调了onStart,onStart中通过mServiceHandler发送消息到该handler的handleMessage中去。最后handleMessage中回调onHandleIntent(intent)。回调完成后回调用 stopSelf(msg.arg1),注意这个msg.arg1是个int值,相当于一个请求的唯一标识。每发送一个请求,会生成一个唯一的标识,然后将请求放入队列,当全部执行完成(最后一个请求也就相当于getLastStartId == startId)。
在源码里面可以看到在onstart()方法和onStartCommand()方法中,都声明了一个int startId; 的参数,或者当前发送的标识是最近发出的那一个(getLastStartId == startId),则会销毁我们的Service.如果传入的是-1则直接销毁。那么,当任务完成销毁Service回调onDestory,可以看到在onDestroy中释放了我们的Looper:mServiceLooper.quit()。(这也把不用关闭service说清楚了,喜欢的朋友给大家分享一下吧)
public interface Callback { /** * @param msg A {@link android.os.Message Message} object * @return True if no further handling is desired */ public boolean handleMessage(Message msg); }
在IntentService里面不需要开启线程是因为在底层封装了一个Handler,在handler里面写一个Callback接口,而且子类必须实现这个接收消息。