android handler

根据我的理解大概是这样

handler其实相当于一个监听器,这个监听器可以向线程的消息队列发送消息,looper相当于消息队列的监听器,它一直在监听消息队列,当有消息到达时,调用handler的handlemessage方法来处理.

关于handlerthread,为啥要用这个?

免得你在主线程里启动n个线程,另外使用handlerthread的looper可以降低mainlooper的压力,猜的呵呵.

mainactivity.java:

package com.ydd.handler;import android.app.Activity;import android.os.Bundle;import android.os.Handler;import android.os.HandlerThread;import android.os.Looper;import android.os.Message;import android.view.Menu;import android.view.MenuItem;import android.view.View;import android.widget.Button;import android.widget.ProgressBar;import android.widget.TextView;public class MainActivity extends Activity {private Button start = null;private ProgressBar progressBar = null;private Handler UIhandler= null;private Handler childhandler= null;private HandlerThread handlerThread = null;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        start = (Button) findViewById(R.id.start);        progressBar = (ProgressBar) findViewById(R.id.progressBar);        handlerThread = new HandlerThread("testThread");        handlerThread.start();        childhandler = new Handler(handlerThread.getLooper(), new Handler.Callback() {                @Overridepublic boolean handleMessage(Message arg0) {Message message = UIhandler.obtainMessage();System.out.println("handleMessage in "+Thread.currentThread().getName());message.arg1 = arg0.what;UIhandler.sendMessage(message);return false;}});        UIhandler = new Handler(){        @Override        public void handleMessage(Message msg) {        // TODO Auto-generated method stub        super.handleMessage(msg);        System.out.println("handleMessage in "+Thread.currentThread().getName());        progressBar.setProgress(msg.arg1);        }        };                start.setOnClickListener(new View.OnClickListener(){@Overridepublic void onClick(View arg0) {progressBar.setVisibility(ProgressBar.VISIBLE);for(int i=1;i<=10;i++){childhandler.sendEmptyMessageDelayed(10*i, 1000*i);}}                });            }    @Override    public boolean onCreateOptionsMenu(Menu menu) {        // Inflate the menu; this adds items to the action bar if it is present.        getMenuInflater().inflate(R.menu.main, menu);        return true;    }    @Override    public boolean onOptionsItemSelected(MenuItem item) {        // Handle action bar item clicks here. The action bar will        // automatically handle clicks on the Home/Up button, so long        // as you specify a parent activity in AndroidManifest.xml.        int id = item.getItemId();        if (id == R.id.action_settings) {            return true;        }        return super.onOptionsItemSelected(item);    }         }

xml:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="vertical"    tools:context="com.ydd.handlerprogressbar.MainActivity" >    <ProgressBar         android:id="@+id/progressBar"        android:layout_width="match_parent"        android:layout_height="wrap_content"        style="?android:attr/progressBarStyleHorizontal"        android:visibility="gone"        />    <Button         android:id="@+id/start"        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:gravity="center"        android:text="Start"        /></LinearLayout>