Android中的异步处理技术之IntentService

目录

定义

IntentService为Service的子类，它能够进行耗时任务。

原理

IntentService具有和Service一样的生命周期，同时提供了在后台线程中处理异步任务的机制，与HandlerThread类似，IntentService也是在一个后台线程中顺序执行所有任务，我们通过给Context.startService传递一个Intent类型的参数可以启动IntentService的异步执行，如果此时IntentService正在运行中，那么这个新的Intent将会进入队列进行排队，直到后台线程处理完队列前面的任务；如果此时IntentService没有在运行，那么将会启动一个新的IntentService，当后台线程队列中所有的任务处理完之后，IntentService将会结束它的生命周期，因此IntentService不需要开发者手动结束。

实现

IntentService是一个抽象类因此我们需要继承IntentService并实现它的onHandleIntent方法，并在这个方法中实现后台处理的业务逻辑，同时在子类的构造方法中需要调用super(String name)，传入一个名称。

public class MyIntentService extends IntentService { /** * Creates an IntentService. Invoked by your subclass's constructor. * * @param name Used to name the worker thread, important only for debugging. */ public MyIntentService() { super("MyIntentService"); mLocalBroadcastManager=LocalBroadcastManager.getInstance(this); setIntentRedelivery(true); } @Override protected void onHandleIntent(@Nullable Intent intent) { //执行后台任务 } } 

上面代码中的setIntentRedelivery方法如果设置为true，那么IntentService的onStartCommand方法将会返回START_REDELIVER_INTENT。这时如果onHandleIntent方法返回之前进程死了，那么进程将会重新启动，intent将会重新投递。同时类似Service还需要在AndroidManifest.xml文件中注册

<service android:name=".MyIntentService"/> 

案例

在IntentService中进行进度条数据的更新，然后通过本地广播在来刷新UI界面。

• MyIntentService代码

public class MyIntentService extends IntentService { /** * Creates an IntentService. Invoked by your subclass's constructor. * * @param name Used to name the worker thread, important only for debugging. */ private int count=0; private boolean isRunning=true; private LocalBroadcastManager mLocalBroadcastManager; public MyIntentService() { super("MyIntentService"); mLocalBroadcastManager=LocalBroadcastManager.getInstance(this); setIntentRedelivery(true); } @Override protected void onHandleIntent(@Nullable Intent intent) { count=0; isRunning=true; while (isRunning){ try { count++; if(count>=100){ isRunning=false; } Thread.sleep(100); sendThreadStatus(count); } catch (InterruptedException e) { e.printStackTrace(); } } } private void sendThreadStatus(int progress) { Intent intent = new Intent(MainActivity.ACTION); intent.putExtra("progress", progress); mLocalBroadcastManager.sendBroadcast(intent); } } 

• MainActivity代码

public class MainActivity extends AppCompatActivity { public static final String ACTION="com.itfitness.intentservicedemo.myintentserviceaction"; private LocalBroadcastManager mLocalBroadcastManager; private MyBroadcastReceiver mMyBroadcastReceiver; private TextView tv; private ProgressBar pb; private Button mButton; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); initView(); initBroadcastReceiver(); } private void initView() { mButton = findViewById(R.id.bt); tv = (TextView) findViewById(R.id.tv); pb = (ProgressBar) findViewById(R.id.prb); mButton.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { //启动IntentService Intent intent=new Intent(MainActivity.this,MyIntentService.class); startService(intent); } }); } private void initBroadcastReceiver() { if (mLocalBroadcastManager==null) { mLocalBroadcastManager=LocalBroadcastManager.getInstance(this); } if(mMyBroadcastReceiver==null){ mMyBroadcastReceiver = new MyBroadcastReceiver(); } IntentFilter intentFilter=new IntentFilter(); intentFilter.addAction(ACTION); mLocalBroadcastManager.registerReceiver(mMyBroadcastReceiver,intentFilter); } @Override protected void onDestroy() { super.onDestroy(); if(mLocalBroadcastManager!=null&&mMyBroadcastReceiver!=null){ mLocalBroadcastManager.unregisterReceiver(mMyBroadcastReceiver); } } public class MyBroadcastReceiver extends BroadcastReceiver{ @Override public void onReceive(Context context, Intent intent) { //根据IntentService中的发送的广播来进行UI更新 if(intent.getAction().equals(ACTION)){ int progress = intent.getIntExtra("progress", 0); if(progress>0&&progress<100){ tv.setText("线程进行中。。。。"); }else if(progress>=100){ tv.setText("线程结束"); } pb.setProgress(progress); } } } } 

• MainActivity布局代码

<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" tools:context=".MainActivity"> <Button android:layout_width="wrap_content" android:text="开始线程" android:id="@+id/bt" android:layout_gravity="center" android:layout_height="wrap_content" /> <TextView android:layout_width="wrap_content" android:layout_marginTop="20dp" android:layout_gravity="center" android:id="@+id/tv" android:text="线程未开启" android:textSize="15sp" android:layout_height="wrap_content" /> <ProgressBar android:layout_width="match_parent" android:layout_marginTop="10dp" android:max="100" android:id="@+id/prb" style="@style/Widget.AppCompat.ProgressBar.Horizontal" android:layout_height="wrap_content" /> </LinearLayout> 

项目源码：https://github.com/myml666/IntentServiceDemo

个人技术博客：https://myml666.github.io