文章目录
- 一、Handler 常用用法
- 二、HandlerThread 简介
- 三、HandlerThread 源码
一、Handler 常用用法
主线程 Handler 主要作用 : Looper 和 Message 都在 主线程 , Handler 也在 主线程 初始化 , 在子线程中调用该 Handler , 通知主线程进行一些操作 , 一般是更新 UI ;
子线程 Handler 主要作用 : Looper 和 Message 都在 子线程 , Handler 也在 子线程 初始化 , 在主线程中调用该 Handler , 通知子线程进行一些操作 , 一般是网络操作 , 计算 , 或其它耗时任务 ;
二、HandlerThread 简介
HandlerThread 就是使用了 Handler 机制的线程 , 其本质是一个 线程 Thread ; 属于上述介绍的 子线程 Handler 机制 ;
在运行 HandlerThread 线程的 run 方法时 ,
在 run 方法开始处 , 会调用 Looper.prepare() 方法 , 初始化该线程的 Looper ,
在 run 方法结束处 , 会调用 Looper.loop() 方法 , 开启无限循环 , 从 Looper 中的 MessageQueue 中循环获取消息 , 并转发给 取出的 Message 消息对应的 Handler 进行相关任务处理 ;
HandlerThread 线程的 run() 方法如下 :
代码语言：javascript复制public class HandlerThread extends Thread {
@Override
public void run() {
mTid = Process.myTid();
Looper.prepare();
synchronized (this) {
mLooper = Looper.myLooper();
notifyAll();
}
Process.setThreadPriority(mPriority);
onLooperPrepared();
Looper.loop();
mTid = -1;
}
}三、HandlerThread 源码
/**
* 含有 Looper 的线程.
* Looper 用于创建 Handler.
* <p>
* 该类是一个线程类, 必须调用 start 方法开启线程.
*/
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;
}
/**
* 创建 HandlerThread.
* @param name
* @param priority 线程运行优先级
*/
public HandlerThread(String name, int priority) {
super(name);
mPriority = priority;
}
/**
* Looper 无限循环之前执行的操作
*/
protected void onLooperPrepared() {
}
@Override
public void run() {
mTid = Process.myTid();
// Looper 初始化
Looper.prepare();
synchronized (this) {
mLooper = Looper.myLooper();
notifyAll();
}
Process.setThreadPriority(mPriority);
onLooperPrepared();
// 无限循环获取消息并执行
Looper.loop();
mTid = -1;
}
/**
* 返回与该线程关联的 Looper .
* 如果线程没有启动 , 或者线程不处于活动状态 , 返回空.
* 如果线程已经启动 , 该方法会阻塞 , 直到 Looper 被初始化完毕后 , 返回 Looper.
* @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 返回一个与该线程关联的共享 Handler
* @hide
*/
@NonNull
public Handler getThreadHandler() {
if (mHandler == null) {
mHandler = new Handler(getLooper());
}
return mHandler;
}
/**
* 退出 Looper 循环.
* <p>
* Causes the handler thread's looper to terminate without processing any
* more messages in the message queue.
* </p><p>
* Any attempt to post messages to the queue after the looper is asked to quit will fail.
* For example, the {@link Handler#sendMessage(Message)} method will return false.
* </p><p class="note">
* Using this method may be unsafe because some messages may not be delivered
* before the looper terminates. Consider using {@link #quitSafely} instead to ensure
* that all pending work is completed in an orderly manner.
* </p>
*
* @return True if the looper looper has been asked to quit or false if the
* thread had not yet started running.
*
* @see #quitSafely
*/
public boolean quit() {
Looper looper = getLooper();
if (looper != null) {
looper.quit();
return true;
}
return false;
}
/**
* 安全退出线程 loop.
* <p>
* Causes the handler thread's looper to terminate as soon as all remaining messages
* in the message queue that are already due to be delivered have been handled.
* Pending delayed messages with due times in the future will not be delivered.
* </p><p>
* Any attempt to post messages to the queue after the looper is asked to quit will fail.
* For example, the {@link Handler#sendMessage(Message)} method will return false.
* </p><p>
* If the thread has not been started or has finished (that is if
* {@link #getLooper} returns null), then false is returned.
* Otherwise the looper is asked to quit and true is returned.
* </p>
*
* @return True if the looper looper has been asked to quit or false if the
* thread had not yet started running.
*/
public boolean quitSafely() {
Looper looper = getLooper();
if (looper != null) {
looper.quitSafely();
return true;
}
return false;
}
/**
* 返回线程 ID
*/
public int getThreadId() {
return mTid;
}
}
