【安卓笔记】Handler+Thread使用浅析

package com.example.messagedemo2;
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
public class MainActivity extends Activity implements OnClickListener
{
    protected static final int TEST = 1;
    protected static final String TAG = "MainActivity";
    private Button but = null;
    private Handler myHandler = new Handler()
    {
        public void handleMessage(android.os.Message msg)
        {
            switch (msg.what)
            {
            case TEST:
                //可以执行UI操作
                Log.i(TAG,(String)msg.obj);
                break;
            }
        }
    };
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        but = (Button) findViewById(R.id.but);
        but.setOnClickListener(this);
    }
    @Override
    public void onClick(View v)
    {
        if(v.getId() == R.id.but)
        {
            new Thread(new Runnable()
            {
                @Override
                public void run()
                {
                    //TODO 执行耗时任务
                    Message msg = Message.obtain();
                    msg.what = TEST;
                    msg.obj = "Rowandjj";
//                    msg.setTarget(myHandler);//如果不设置target那么调用sendToTarget将抛空针
//                    msg.sendToTarget();//其实是调用target也就是handler的sendMessage方法
                    myHandler.sendMessage(msg);//让handlet处理message
                }
            }).start();
        }
    }
}

class LooperThread extends Thread {
      public Handler mHandler;

      public void run() {
          Looper.prepare();

          mHandler = new Handler() {
              public void handleMessage(Message msg) {
                  // process incoming messages here
              }
          };
          Looper.loop();
      }
  }

package com.example.messagedemo1;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.util.EntityUtils;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.BitmapFactory.Options;
import android.os.Bundle;
import android.os.Handler;
import android.view.Gravity;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup.LayoutParams;
import android.widget.Button;
import android.widget.FrameLayout;
import android.widget.ImageView;
import android.widget.ProgressBar;

/**
 * @author Rowand jj
 *
 *一个使用handler+thread的简单示例
 *下载网络图片
 */
public class MainActivity extends Activity implements OnClickListener
{
    protected static final String PATH = "http://c.hiphotos.baidu.com/image/w%3D2048/sign=4facebbeb0b7d0a27bc9039dffd77709/8d5494eef01f3a29cf6d52c29b25bc315c607c11.jpg";
    protected static final int SET_IMAGE = 1;
    private Button but_load = null;
    private ImageView iv_show = null;
    private ProgressBar pb = null;
    
    private Handler myhandler = new Handler()
    {
        public void handleMessage(android.os.Message msg) 
        {
            if(msg.what == SET_IMAGE)
            {
                iv_show.setImageBitmap((Bitmap) msg.obj);
                
                pb.setVisibility(View.GONE);
                iv_show.setVisibility(View.VISIBLE);
                but_load.setVisibility(View.VISIBLE);
            }
        }
    };
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    
        iv_show = (ImageView) findViewById(R.id.iv_show);
        but_load = (Button) findViewById(R.id.but_load);
        but_load.setOnClickListener(this);
        pb = createProgressBar();
    }
    @Override
    public void onClick(View v)
    {
        if(v.getId() == R.id.but_load)
        {
            pb.setVisibility(View.VISIBLE);
            iv_show.setVisibility(View.GONE);
            but_load.setVisibility(View.GONE);
            
            new Thread(new Runnable()
            {
                @Override
                public void run()
                {
                    HttpClient client = new DefaultHttpClient();
                    HttpGet get = new HttpGet(PATH);
                    try
                    {
                        HttpResponse resp = client.execute(get);
                        if(resp.getStatusLine().getStatusCode() == 200)
                        {
                            HttpEntity entity = resp.getEntity();
                            if(entity != null)
                            {
                                byte[] data = EntityUtils.toByteArray(entity);
                                Options opts = new Options();
                                opts.inSampleSize = 2;
                                final Bitmap bitmap = BitmapFactory.decodeByteArray(data, 0,data.length,opts);
                                
                                myhandler.post(new Runnable()
                                {
                                    @Override
                                    public void run()
                                    {
                                        iv_show.setImageBitmap(bitmap);
                                        
                                        pb.setVisibility(View.GONE);
                                        iv_show.setVisibility(View.VISIBLE);
                                        but_load.setVisibility(View.VISIBLE);
                                    }
                                });
                               
                            }
                        }
                    } catch (Exception e)
                    {
                        e.printStackTrace();
                    }
                    
                }
            }).start();
        }
    }
    public ProgressBar createProgressBar()
    {
        FrameLayout rootContainer = (FrameLayout) findViewById(android.R.id.content);
        FrameLayout.LayoutParams params = new FrameLayout.LayoutParams(LayoutParams.WRAP_CONTENT,LayoutParams.WRAP_CONTENT);
        params.gravity = Gravity.CENTER;
        ProgressBar pb = new ProgressBar(this);
        pb.setLayoutParams(params);

        pb.setVisibility(View.GONE);
        rootContainer.addView(pb);
        return pb;
    }
}

Message msg = Message.obtain(myhandler,SET_IMAGE,bitmap);
msg.sendToTarget();

Message msg = myhandler.obtainMessage(SET_IMAGE,bitmap);
msg.sendToTarget();

Message msg = Message.obtain(myhandler,SET_IMAGE,bitmap);
myhandler.sendMessage(msg);