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">

    <application
        android: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">
        <service
            android:name=".LongWaitingService"
            android:exported="false"></service>

        <activity
            android:name=".MainActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>

            <meta-data
                android: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");
    }

    @Override
    public void onStart(Intent intent, int startId) {
        Log.i(TAG, ">>>>>>onStart");
    }
        @Override
    protected 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();
        }
    }
    @Override
    public 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
    @Override
    public void onDestroy() {
        super.onDestroy();
        Log.i(TAG, ">>>>>>onDestroyed方法被调用!");
    }
    @Override

    public 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();
    @Override
    protected 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
        @Override
        public void onServiceDisconnected(ComponentName name) {
            Log.i(TAG, ">>>>>>Service DisConnected");
        }

        //Activity与Service连接成功时回调该方法
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            Log.i(TAG, ">>>>>>Service Connected");
            stdBinder = (LongWaitingService.StudentBinder) service;
            LongWaitingService stdService = stdBinder.getService();
            stdService.setCallback(new LongWaitingService.Callback() {
                @Override
                public void onDataChange(String data) {
                    Message msg = new Message();
                    msg.obj = data;
                    stdHandler.sendMessage(msg);
                }
            });
        }
    };

    class OnClickListener implements View.OnClickListener {
        @Override
        public 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 {
        @Override
        public 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);
        }
    }
}