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”。
Android开发者官网说过：
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。
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。
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。
<?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>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;
}
}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);
}
}
}来看看运行效果吧
看，再也没有ANR了，结果成功通过CALL BACK回传Activity。
因此我们一般都会这么使用IntentService来实现一些资源异步加载、第三方API回调。
