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之前Handler 分析的文章有分析过,子线程Thread中是不能直接使用Handler的,需要调用Looper.prepare()方法,因此Android就为我们提供了Handler和Thread结合的方法HandlerThread方法,我们先来看下HandlerThread的源码:
public class HandlerThread extends Thread {
int mPriority;
int mTid = -1;
Looper mLooper;
private @Nullable Handler mHandler;
public HandlerThread(String name) {
super(name);
mPriority = Process.THREAD_PRIORITY_DEFAULT;
}
/**
* Constructs a HandlerThread.
* @param name
* @param priority The priority to run the thread at. The value supplied must be from
* {@link android.os.Process} and not from java.lang.Thread.
*/
public HandlerThread(String name, int priority) {
super(name);
mPriority = priority;
}
/**
* Call back method that can be explicitly overridden if needed to execute some
* setup before Looper loops.
*/
protected void onLooperPrepared() {
}
@Override
public void run() {
mTid = Process.myTid();
Looper.prepare();
synchronized (this) {
mLooper = Looper.myLooper();
notifyAll();
}
Process.setThreadPriority(mPriority);
onLooperPrepared();
Looper.loop();
mTid = -1;
}
/**
* This method returns the Looper associated with this thread. If this thread not been started
* or for any reason isAlive() returns false, this method will return null. If this thread
* has been started, this method will block until the looper has been initialized.
* @return The looper.
*/
public Looper getLooper() {
if (!isAlive()) {
return null;
}
// If the thread has been started, wait until the looper has been created.
synchronized (this) {
while (isAlive() && mLooper == null) {
try {
wait();
} catch (InterruptedException e) {
}
}
}
return mLooper;
}
/**
* @return a shared {@link Handler} associated with this thread
* @hide
*/
@NonNull
public Handler getThreadHandler() {
if (mHandler == null) {
mHandler = new Handler(getLooper());
}
return mHandler;
}
public boolean quit() {
Looper looper = getLooper();
if (looper != null) {
looper.quit();
return true;
}
return false;
}
public boolean quitSafely() {
Looper looper = getLooper();
if (looper != null) {
looper.quitSafely();
return true;
}
return false;
}
/**
* Returns the identifier of this thread. See Process.myTid().
*/
public int getThreadId() {
return mTid;
}
}
很简单的源码HandlerThread继承Thread主要看:
@Override
public void run() {
mTid = Process.myTid();
Looper.prepare();//手动为子线程创建了looper
synchronized (this) {
mLooper = Looper.myLooper();
notifyAll();
}
Process.setThreadPriority(mPriority);
onLooperPrepared();
Looper.loop();//开始轮询
mTid = -1;
}
可以看到run方法中为子线程创建了looper,并把对象放到线程中,然后通过Looper.loop();开启循环消息。
其他方法:
getThreadHandler: 获取当前线程的handler
quit:清空所有消息
quitSafely:只情况延时消息
getLooper:获取线程中的looper对象
我们看下HandlerThread的使用:
private void startThread(){
HandlerThread handlerThread = new HandlerThread("thread_one");
handlerThread.start();
workHandler = new Handler(handlerThread.getLooper()){//子线程handler
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
try {
Thread.sleep(1000);//子线程中处理耗时操作
mainHandler.sendEmptyMessage(0);//处理完后发送消息给主线程更新UI
}catch (Exception e){
}
}
};
workHandler.sendEmptyMessage(0);
mainHandler = new Handler(){//主线程handler
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
mBtn.setText("start");//主线程中更新UI
}
};
}
例子中我们看到我们通过handlerThread.getLooper()获取子线程的looper然后与workHandler,我们知道handler的线程是依赖与与之关联的looper线程,所以workHandler是子线程的handler.
然后我们new 一个未传looper的handler,默认与主线程关联,所以mainHandler是主线程的handler.
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