note 14 Handler and Looper

1. instance a new HandlerThread , and start it .

2. instance a new Handler , set a looper from HandlerThread .

3. Two thread can communicate by Message  (for exp , press a button to stop the download thread);

package com.android;

import android.app.Activity;
import android.os.*;

public class HandlerTest03 extends Activity
{
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        System.out.println("start thread:"+Thread.currentThread().getId());
        
        HandlerThread handlerThread=new HandlerThread("handler_thread");
        handlerThread.start();
        
        MyHandler myHandler=new MyHandler(handlerThread.getLooper());
        
        Message msg=myHandler.obtainMessage();
        
        msg.setData(new Bundle());
        msg.sendToTarget();
        
    }
    
    private class MyHandler extends Handler{

        private MyHandler(Looper looper) {
//            throw new UnsupportedOperationException("Not yet implemented");
            super(looper);
        }
        
        @Override
        public void handleMessage(Message msg){
            Bundle b=msg.getData();
            System.out.println("handle thread:"+Thread.currentThread().getId());
        }
        
    };
}

if use handler.post(Runable runable)  and  handler.removeCallbacks(Runable runable) . It is run in the same main thread :

package com.android;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ProgressBar;
import java.util.logging.Level;
import java.util.logging.Logger;

public class HandlerTest02 extends Activity
{
    
    private Button startButt;
    private ProgressBar bar;
    
    
    private int barCount=0;
    
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        startButt=(Button)this.findViewById(R.id.startButton);
        startButt.setOnClickListener(startListener);
        
        bar=(ProgressBar)this.findViewById(R.id.bar);
    }
    
    private OnClickListener startListener=new OnClickListener(){

        public void onClick(View v) {
//            throw new UnsupportedOperationException("Not supported yet.");
            bar.setProgress(barCount);
            bar.setVisibility(View.VISIBLE);
            handler.post(barThread);
        }
        
    };
    
    private Handler handler=new Handler(){
        
        @Override
        public void handleMessage(Message msg){
            bar.setProgress(msg.arg1);
            handler.post(barThread);
        }
        
    };
    
    private Runnable barThread=new Runnable(){

        public void run() {
//            throw new UnsupportedOperationException("Not supported yet.");
            
            
            
            if(barCount<100){
                
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException ex) {
                    System.out.println(ex.getMessage());
                }
                
                barCount+=10;
                Message msg=handler.obtainMessage();
                msg.arg1=barCount;
                handler.sendMessage(msg);
            }
            else{
                handler.removeCallbacks(barThread);
                bar.setVisibility(View.GONE);
                barCount=0;
            }
        }
        
    };
}

 

 Message is a  weird value container . it has 2 arg(int) for quick store . and also can container a bundle.

Handler can obtain a new Message , so the message can .sendToTarget to send back to the handler.

Message msg=myHandler.obtainMessage();
        
        msg.setData(new Bundle());
        msg.sendToTarget();