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