【Android Service】IntentService
IntentService
简单使用
/**
* Create by SunnyDay /03/13 17:40:59
*/
class DownLoadService : IntentService("FileDownLoadThread") {
private val tag = "DownLoadService"
override fun onHandleIntent(intent: Intent?) {
Log.d(tag, "onHandleIntent Thread info: thread id -> ${Thread.currentThread().id} thread name -> ${Thread.currentThread().name}")
Log.d(tag, "开始下载->")
Log.d(tag, "下载ing...")
SystemClock.sleep(3000)
Log.d(tag, "下载完成")
}
override fun onCreate() {
super.onCreate()
Log.d(tag, "onCreate")
}
override fun onStart(intent: Intent?, startId: Int) {
super.onStart(intent, startId)
Log.d(tag, "onStart")
}
override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int {
Log.d(tag, "onStartCommand:startId->$startId")
return super.onStartCommand(intent, flags, startId)
}
override fun onBind(intent: Intent?): IBinder? {
Log.d(tag, "onBind")
return super.onBind(intent)
}
override fun onUnbind(intent: Intent?): Boolean {
Log.d(tag, "onUnbind")
return super.onUnbind(intent)
}
override fun onDestroy() {
super.onDestroy()
Log.d(tag, "onDestroy")
}
}
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
findViewById<Button>(R.id.downLoad).setOnClickListener {
startService(Intent(this,DownLoadService::class.java))
}
}
}
//第一次开启
D/DownLoadService: onCreate
D/DownLoadService: onStartCommand:startId->1
D/DownLoadService: onStart
D/DownLoadService: onHandleIntent Thread info: thread id -> 62 thread name -> IntentService[FileDownLoadThread]
D/DownLoadService: 开始下载->
D/DownLoadService: 下载ing...
//第二次开启
D/DownLoadService: onStartCommand:startId->2
D/DownLoadService: onStart
D/DownLoadService: 下载完成
D/DownLoadService: onHandleIntent Thread info: thread id -> 62 thread name -> IntentService[FileDownLoadThread]
D/DownLoadService: 开始下载->
D/DownLoadService: 下载ing...
D/DownLoadService: 下载完成
D/DownLoadService: onDestroy
连续点击两次按钮,可以观察到log:
(1) IntentService的生命周期是这样的
onCreate -> onStartCommand -> onStart -> onHandleIntent -> onDestroy
(2) 系统默认帮我们开启一个子线程,我们可以在onHandleIntent中做一些耗时任务
(3) Service只会被创建一次,多次绑定onStartCommand回调多次
(4) 所有任务完成时onDestroy自动回调
IntentService介绍
- IntentService是Service的一个子类,内部维护了一个工作线程,他会把所有的任务都放到工作线程中处理。
- 多次开启IntentService时,每一次的开启的任务都会放到工作线程中处理,当所有的任务完成时他会自动调用stopSelf方法来结束Service
- onBind方法不会回调
- onStart方法内部进行了默认实现是IntentService的核心
源码分析
在分析IntentService的源码之前我们需要了解一点东西~
1、handler消息机制
之前总结过,可以看这里:参考
2、HandlerThread
啥是handlerThread呢?其实就是官方封装的一个api方便我们进行"主线程发送消息,子线程处理消息",了解了handler的消息机制后我们可以尝试写下这个demo
(1)主线程发送消息,子线程处理消息demo
class HandlerThreadActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_handler_thread)
// open a subThread
thread {
Looper.prepare()
val handler = Handler{
when (it.what) {
0x11 ->{
Log.d("HandlerThreadActivity","${Thread.currentThread()}收到:${it.obj}")
}
}
return@Handler true
}
runOnUiThread {
Log.d("HandlerThreadActivity","${Thread.currentThread()}UI线程发送一条消息")
// ui 线程发送消息
handler.sendMessage(Message().apply {
what = 0x11
obj = "UI线程发送一条消息"
})
}
Looper.loop()
}
}
}
D/HandlerThreadActivity: Thread[main,5,main]UI线程发送一条消息
D/HandlerThreadActivity: Thread[Thread-4,5,main]收到:UI线程发送一条消息
观察log发现我们实验成功了,其实不难理解主要是handler与Looper与Thread存在一定的绑定关系。接下来可以看下HandlerThread如何使用的。
(2)HandlerThread使用
/**
* test:HandlerThread usage
* */
private fun test2() {
// 1、创建对象,并开启线程
val handlerThread = HandlerThread("HandlerThread")
handlerThread.start()
// 2、核心,使用两个参数的构造(这里的handleMessage 回调再子线程中的)
val handler = Handler(handlerThread.looper) {
// 处理消息
return@Handler true
}
// 3、发送消息
handler.sendEmptyMessage(0x11)
}
借助系统的api就快速了不少,我们可以很方便实现"主线程发送消息,子线程处理消息",接下来看看源码实现。
(3)HandlerThread源码
// 1、首先HandlerThread是一个普通的线程,只是这个线程绑定可Looper(持有Looper成员变成)
public class HandlerThread extends Thread {
int mPriority;
int mTid = -1;
Looper mLooper;
// 构造传递的是线程名字
public HandlerThread(String name) {
super(name);
mPriority = Process.THREAD_PRIORITY_DEFAULT;
}
public HandlerThread(String name, int priority) {
super(name);
mPriority = priority;
}
protected void onLooperPrepared() {
}
// 2、run方法内部进行了实现,核心有两步:
// (1) 创建Looper对象
// (2) 开启Loop轮训
@Override
public void run() {
mTid = Process.myTid();
Looper.prepare();
synchronized (this) {
mLooper = Looper.myLooper();
notifyAll();
}
Process.setThreadPriority(mPriority);
onLooperPrepared();
Looper.loop();
mTid = -1;
}
// 3、提供了getLooper、getThreadHandler来获取对应的对象
public Looper getLooper() {
if (!isAlive()) {
return null;
}
boolean wasInterrupted = false;
// If the thread has been started, wait until the looper has been created.
synchronized (this) {
while (isAlive() && mLooper == null) {
try {
wait();
} catch (InterruptedException e) {
wasInterrupted = true;
}
}
}
if (wasInterrupted) {
Thread.currentThread().interrupt();
}
return mLooper;
}
@NonNull
public Handler getThreadHandler() {
if (mHandler == null) {
mHandler = new Handler(getLooper());
}
return mHandler;
}
}
可以看到实现十分简单,只要明白handler的消息机制这个还是很好明白的。
3、IntentService源码
public abstract class IntentService extends Service {
// 1、定义个Looper类型的成员变量(注意这个Looper绑定的线程为HandlerThread工作线程,这就意味着消息的处理是在工作线程)
private volatile Looper mServiceLooper;
private volatile ServiceHandler mServiceHandler;
private String mName;
private boolean mRedelivery;
//2、定义个Handler,这个handler的handleMessage回调在工作线程(Looper绑定的为工作线程)
private final class ServiceHandler extends Handler {
public ServiceHandler(Looper looper) {
super(looper);
}
@Override
public void handleMessage(Message msg) {
onHandleIntent((Intent)msg.obj);
stopSelf(msg.arg1);
}
}
public IntentService(String name) {
super();
mName = name;
}
public void setIntentRedelivery(boolean enabled) {
mRedelivery = enabled;
}
@Override
public void onCreate() {
super.onCreate();
//3、创建HandlerThread并绑定Looper
HandlerThread thread = new HandlerThread("IntentService[" + mName + "]");
thread.start();
mServiceLooper = thread.getLooper();
mServiceHandler = new ServiceHandler(mServiceLooper);
}
@Override
public void onStart(@Nullable Intent intent, int startId) {
Message msg = mServiceHandler.obtainMessage();
msg.arg1 = startId;
msg.obj = intent;
mServiceHandler.sendMessage(msg);
}
@Override
public int onStartCommand(@Nullable Intent intent, int flags, int startId) {
onStart(intent, startId);
return mRedelivery ? START_REDELIVER_INTENT : START_NOT_STICKY;
}
@Override
public void onDestroy() {
mServiceLooper.quit();
}
// 这里需要注意 方法默认返回为空。从源码也可看出无bindService
@Override
@Nullable
public IBinder onBind(Intent intent) {
return null;
}
protected abstract void onHandleIntent(@Nullable Intent intent);
}
IntentService替代方案
参考
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