【移动开发】Android中异步加载数据（一）Handler + Thread

import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
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.ImageView;
import android.widget.Toast;
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
/**
* Handler + Thread 实现异步加载图片
* @author ZHF
*
*/
public class MainActivity extends Activity {
private static final int MSG_SUCCESS = 0;//成功获取图片
private static final int MSG_FAILURE = 1;//获取图片失败
public static final String IMG_URL = "http://images.51cto.com/images/index/Images/Logo.gi";

Button btn_handler;
ImageView imageView;

private DownloadImgThread downloadImgThread;

private Handler mHandler = new Handler(){
public void handleMessage(Message msg) { //该方法是在UI主线程中执行
switch(msg.what) {
case MSG_SUCCESS:
imageView.setImageBitmap((Bitmap)msg.obj);  //显示图片
break;
case MSG_FAILURE:
Toast.makeText(MainActivity.this, "获取图片失败", Toast.LENGTH_LONG);
break;
}
};
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

imageView = (ImageView) this.findViewById(R.id.imageView);

btn_handler = (Button) this.findViewById(R.id.btn_handler);
btn_handler.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
//开启一个非UI线程，用于下载图片
downloadImgThread = new DownloadImgThread();
downloadImgThread.start();
}
});
}

/**图片下载线程**/
private class DownloadImgThread extends Thread{
HttpURLConnection conn;
InputStream inputStream;
Bitmap imgBitmap;

@Override
public void run() {
try {
URL url = new URL(IMG_URL);
if(url != null) {
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setConnectTimeout(2000);
connection.setDoInput(true);
connection.setRequestMethod("GET");
int code = connection.getResponseCode();
if(200 == code) {
inputStream = connection.getInputStream();
imgBitmap = BitmapFactory.decodeStream(inputStream);
//获取图片成功，向ui线程发送MSG_SUCCESS标识和bitmap对象
mHandler.obtainMessage(MSG_SUCCESS,imgBitmap).sendToTarget();
}else {
//获取图片失败，向ui线程发送MSG_FAILURE
mHandler.obtainMessage(MSG_FAILURE).sendToTarget();
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
}

}

<uses-permission android:name="android.permission.INTERNET"/>

//另外一种更简洁的发送消息给ui线程的方法。
mImageView.post(new Runnable() {
@Override
public void run() {//run()方法会在ui线程执行
mImageView.setImageBitmap(bm);
}
});