Android线程及进程笔记

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activity
			Toast.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);
	}
}

Android线程及进程笔记

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