Android开发之使用Handler封装下载图片工具类

          如果每下载一张图片，就得重写一次Http协议，多线程的启动和handler的信息传递就显得太麻烦了，我们直接来封装一个工具类，便于我们以后在开发时随时可以调用。

 （1）在清单文件添加权限

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

package com.example.g05_handler;

import java.io.IOException;

import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
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.annotation.SuppressLint;
import android.app.ProgressDialog;
import android.content.Context;
import android.os.Handler;
import android.os.Message;
import android.util.Log;

public class DownLoad {

	private ProgressDialog dialog;

	public DownLoad(Context context) {
		// TODO Auto-generated constructor stub
		dialog = new ProgressDialog(context);
		dialog.setTitle("提示");
		dialog.setMessage("玩命加载中");

	}

	@SuppressLint("HandlerLeak")
	public void Down(final String path, final DownLoadCallback callback) {
		final Handler handler = new Handler() {
			@Override
			public void handleMessage(Message msg) {
				// TODO Auto-generated method stub
				super.handleMessage(msg);
				byte[] result = (byte[]) msg.obj;

				callback.download(result);

				if (msg.what == 1) {
					dialog.dismiss();
				}
			}
		};
		class MyThread implements Runnable {
			@Override
			public void run() {
				// TODO Auto-generated method stub
				HttpClient client = new DefaultHttpClient();
				HttpGet httpGet = new HttpGet(path);
				try {
					HttpResponse httpResponse = client.execute(httpGet);
					Log.i("TAG", "------>"
							+ httpResponse.getStatusLine().getStatusCode());
					if (httpResponse.getStatusLine().getStatusCode() == 200) {
						byte[] result = EntityUtils.toByteArray(httpResponse
								.getEntity());
						Message message = Message.obtain();
						message.obj = result;
						message.what = 1;
						handler.sendMessage(message);
					}
				} catch (ClientProtocolException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				} catch (IOException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				} finally {
					if (client != null) {
						client.getConnectionManager().shutdown();
					}
				}
			};
		}
		new Thread(new MyThread()).start();
		dialog.show();
	}

	public interface DownLoadCallback {
		public void download(byte[] data);
	}
}

package com.example.g05_handler;

import com.example.g05_handler.DownLoad.DownLoadCallback;

import android.os.Bundle;
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;

public class MainActivity extends Activity {
    private Button button;
    private ImageView imageView;
    private final String path="http://avatar.csdn.net/D/7/5/1_u013900875.jpg";
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		button=(Button)this.findViewById(R.id.button1);
		imageView=(ImageView)this.findViewById(R.id.imageView1);
		button.setOnClickListener(new View.OnClickListener() {
			
			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				DownLoad downLoad=new DownLoad(MainActivity.this);
				downLoad.Down(path, new DownLoadCallback() {
					
					@Override
					public void download(byte[] data) {
						// TODO Auto-generated method stub
						Bitmap bitmap=BitmapFactory.decodeByteArray(data, 0, data.length);
						imageView.setImageBitmap(bitmap);
					}
				});
			}
		});
	}

	@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;
	}

}

原文：http://blog.csdn.net/gerogelin/article/details/24908457