开篇

在前一篇中我们讲了bindService的使用。并且我们留下了一个念想，即在bindService取值时故意阻塞30秒，引起了一次ANR并引出了今天的章节-IntentService。

IntentService的生命周期中有一个非常好的方法-onHandleIntent方法，它是一个abstract方法，开发者在实现IntentService时可以覆盖它来处理“长事务”。

IntentService

Android开发者官网说过：

Service不是一个单独的进程,它和它的应用程序在同一个进程中
Service不是一个线程,这样就意味着我们应该避免在Service中进行耗时操作

于是乎，Android给我们提供了解决上述问题的替代品，就是下面要讲的IntentService； IntentService是继承与Service并处理异步请求的一个类,在IntentService中有一个工作线程来处理耗时操作,请求的Intent记录会加入队列。

这么神奇？

我们来看演示，如何来验证这个IntentService里的onHandleIntent处理这种长事务。

课程目标

设Service里有一个字符型数组：

   private String[] stdNames = new String[]{"小王", "小明", "小张"};

在Activity里输入数组下标后、等待30秒、然后把相对应的数组下标所对应的StudentName显示在Toast里，看看是不是会发生ANR。

该点击动作可以反复点击，因为每次点击后都会执行unbindService。

代码核心设计

IntentService没什么特殊的，它只是extends 自 IntentService，同时它拥有一个可以被覆盖的：onHandleIntent方法。

我们这次使用CallBack模式来实现Service里长事务结束后回调activity里的handler实现数值传递；
我们使用intent.putExtra来实现activity里的数值传递到service中去；

service注册

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"><applicationandroid:allowBackup="true"android:dataExtractionRules="@xml/data_extraction_rules"android:fullBackupContent="@xml/backup_rules"android:icon="@mipmap/ic_launcher"android:label="@string/app_name"android:roundIcon="@mipmap/ic_launcher_round"android:supportsRtl="true"android:theme="@style/Theme.DemoRealIntentService"tools:targetApi="31"><serviceandroid:name=".LongWaitingService"android:exported="false"></service><activityandroid:name=".MainActivity"android:exported="true"><intent-filter><action android:name="android.intent.action.MAIN" /><category android:name="android.intent.category.LAUNCHER" /></intent-filter><meta-dataandroid:name="android.app.lib_name"android:value="" /></activity></application></manifest>

Service类-LongWaitingService

package org.mk.android.demorealintentservice;import android.app.IntentService;
import android.content.Intent;
import android.content.Context;
import android.os.IBinder;
import android.util.Log;public class LongWaitingService extends IntentService {private final String TAG = "LongWaitingService";private String[] stdNames = new String[]{"小王", "小明", "小张"};private Callback callback;private int stdNo;public class StudentBinder extends android.os.Binder {public LongWaitingService getService() {return LongWaitingService.this;}}public void setCallback(Callback callback) {this.callback = callback;}public static interface Callback {void onDataChange(String data);}public LongWaitingService() {super("LongWaitingService");}@Overridepublic void onStart(Intent intent, int startId) {Log.i(TAG, ">>>>>>onStart");}@Overrideprotected void onHandleIntent(Intent intent) {if (intent != null) {Log.i(TAG, ">>>>>>onHandleIntent");Log.i(TAG, ">>>>>>into a long waiting");new Thread() {public void run() {try {Thread.sleep(30000);if (callback != null) {String stdName = stdNames[stdNo];callback.onDataChange(stdName);}} catch (Exception e) {}}}.start();}}@Overridepublic IBinder onBind(Intent intent) {// TODO: Return the communication channel to the service.Log.i(TAG, ">>>>>>onBind方法被调用");this.stdNo = intent.getIntExtra("stdNo", -1);onHandleIntent(intent);return new StudentBinder();}//Service被关闭前回调@Overridepublic void onDestroy() {super.onDestroy();Log.i(TAG, ">>>>>>onDestroyed方法被调用!");}@Overridepublic boolean onUnbind(Intent intent) {Log.i(TAG,">>>>>>onUnbind");return false;}
}

主类-MainActivity.java

package org.mk.android.demorealintentservice;import androidx.appcompat.app.AppCompatActivity;import android.app.Service;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.content.ServiceConnection;
import android.os.Bundle;
import android.os.Handler;
import android.os.IBinder;
import android.os.Message;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;public class MainActivity extends AppCompatActivity {private final String TAG = "LongWaitingService";private Button buttonGetValueFromBinder;private Button buttonClose;private Context ctx;private Intent intent;private LongWaitingService.StudentBinder stdBinder;private EditText etStdNo;Handler stdHandler = new StudentHandler();@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);buttonGetValueFromBinder = (Button) findViewById(R.id.buttonGetValueFromBinder);etStdNo = (EditText) findViewById(R.id.etStdNo);ctx = MainActivity.this;intent = new Intent(ctx, LongWaitingService.class);buttonGetValueFromBinder.setOnClickListener(new OnClickListener());}private ServiceConnection conn = new ServiceConnection() {//Activity与Service断开连接时回调该方法@Overridepublic void onServiceDisconnected(ComponentName name) {Log.i(TAG, ">>>>>>Service DisConnected");}//Activity与Service连接成功时回调该方法@Overridepublic void onServiceConnected(ComponentName name, IBinder service) {Log.i(TAG, ">>>>>>Service Connected");stdBinder = (LongWaitingService.StudentBinder) service;LongWaitingService stdService = stdBinder.getService();stdService.setCallback(new LongWaitingService.Callback() {@Overridepublic void onDataChange(String data) {Message msg = new Message();msg.obj = data;stdHandler.sendMessage(msg);}});}};class OnClickListener implements View.OnClickListener {@Overridepublic void onClick(View view) {Intent eIntent;switch (view.getId()) {case R.id.buttonGetValueFromBinder:int stdNo = Integer.valueOf(etStdNo.getText().toString());intent.putExtra("stdNo", stdNo);bindService(intent, conn, Service.BIND_AUTO_CREATE);break;}}}class StudentHandler extends Handler {@Overridepublic void handleMessage(Message msg) {Log.i(TAG,">>>>>>Service的count" + "的值为:" + msg.obj.toString());Toast.makeText(getApplicationContext(), "Service的count" + "的值为:" + msg.obj.toString(), Toast.LENGTH_LONG).show();unbindService(conn);}}
}