Android线程及进程笔记

来源：互联网发布：炒股神经病知乎编辑：程序博客网时间：2024/06/05 16:45

1. UI线程需要在主线程中进行操作，否则会影响线程安全

2.若在Adapter中的getView方法进行耗时操作，会影响listView滑动效果

3.Handler:线程中实现切换机制的线程类

Looper：每个线程均有的消息循环

Looper.getMainLooper(); 主线程中的循环 Looper.myLooper();当前线程的循环若两个一致，则当前线程为主线程不是后台线程。

activity.this.runOnUiThread(new Runnable(){}); 强制切换到主线程中

在内部类里面的handler对象需要采用final形式

public void onClick(View v){final Handler handler = new Handler();final Runnable handlerTask = new Runnable(){public void run(){}};Runnable task = new Runnable(){public void run(){handler.post(handlerTask);}};final Thread t= new Thread(task);t.start();}

在handleMessage中，通过msg.what判断message 的类。 sendMessage和handleMessage的用法。

public void onButtonClick(View v){final Handler handler = new Handler(){public void handleMessage(Message msg){String  tost="None";switch(msg.what){case 0:tost="--"+msg.obj;break;}MainActivity.this.makeToast(toast);}};Thread t = new Thread(new Runnable()){public void run(){Message msg0= Message.obtain(handler,0,"参数0");handler.sendMessage(msg0);}});t.start();}

handler线程切换：public final boolean post(Runnable r)

a,在UI线程中创建handler b,手动创建looper

handlerThread 是thread子类，自动创建Looper

取消消息： public final void removeCallbacks(Runnable r )

Looper的退出： handlerThread.quit();

消息队列中全部的等待消息均退出，包括原先在消息队列但是未被处理的消息

handlerThread.quitSafely();若当前消息结束，后续等待着的消息可以立刻执行，并不会移除到消息队列外

public void onButtonClick(View v){final handlerThread outerThread = new handlerThread("HandlerThread");outerThread.start();final Handler handler = new Handler(outerThread.getLopper());Thread t = new Thread (new Runnable(){public void run(){handler.postDelayed(new Runnable(){public void run(){SecondActivity.this.makeToast("postDelayed  消息")}}，1000)；handler.post(new Runnable(){public void run(){outerThread.quit();String msg="HandlerThread Loop 退出"SecondActivity.this.makeToast}});}});t.start();}

主线程默认存在Looper，后台线程Looper可能未被创建。MessageQueue属于主线程的Looper

public class FirstActivity extends AppCompatActivity{//当handler不为静态的或者是弱引用会造成内存泄漏private  Handler mHandler = new Handler(){public void handleMessage(Message msg){//普通内部类对外部类进行引用获取到activityToast.makeText(FirstActivity.this,"消息来啦",Toast.LENGTH_SHORT).show();}};protected void onCreat(Bundle saveInstanceState){super.onCreate(savedInstanceState);setContentView(R.layout.activity_first);Message msg= Message.obtain(mHandler,1);mHandler.sendMessageAtTime(msg,SystemClock.uptimeMillis()+60000);}}

MessageQueue-> msg -> mHandler ->FirstActivity 这个activity无法被GC

自定义Handler

public class FirstActivity extends AppCompatActivity{//静态内部类不存在对外部类的引用private int mMessageWhat;private Handler mHandler = new MyHandler(this);private static class MyHandler extends Handler{private weakReference<FirstActivity> mActivityRef;public MyHandler(FirstActivity activity){mActivityRef=new WeakReference<FirstActivity>(activity);}public void handleMessage(Message msg){if(mActivityRef.get()!=null){Toast.makeText(mActivityRef.get(),"消息来啦",Toast.LENGTH_SHORT).show();}}}protected void onCreat(Bundle saveInstanceState){super.onCreate(savedInstanceState);setContentView(R.layout.activity_first);mMessageWhat=1;Message msg= Message.obtain(mHandler,mMessageWhat);mHandler.sendMessageAtTime(msg,SystemClock.uptimeMillis()+60000);}protected void onDestory(){super.onDestory();mHandler.removeMessages(mMessageWhat);}}

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