AsyncTask异步加载图片示例

import java.io.IOException;

import org.apache.http.HttpEntity;
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.os.AsyncTask;
import android.os.Bundle;
import android.app.Activity;
import android.app.ProgressDialog;
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 {
        public Button button;
        public ImageView imageView;
        public ProgressDialog progressDialog;
        public String image_path = "http://www.eoeandroid.com/static/image/common/eoe_logo.png";

        @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);
                progressDialog = new ProgressDialog(MainActivity.this);
                progressDialog.setTitle("提示信息");
                progressDialog.setMessage("正在下载图片，请稍后");
                button.setOnClickListener(new View.OnClickListener() {

                        @Override
                        public void onClick(View v) {
                                // 执行异步任务下载图片
                                new Mytask().execute(image_path);
                        }
                });
        }

        @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;
        }

        // 需要先继承AsyncTask接口，第一个参数是执行路径，第二个是进度，第三个是返回值
        public class Mytask extends AsyncTask<String, Void, Bitmap> {

                // 可以在这里执行耗时操作
                protected Bitmap doInBackground(String... params) {
                        // 实例化网络客户端对象
                        HttpClient httpClient = new DefaultHttpClient();
                        // 实例化请求对象，并且取出参数列表中的参数
                        HttpGet httpGet = new HttpGet(params[0]);
                        Bitmap bitmap = null;
                        try {
                                // 发送请求
                                HttpResponse httpResponse = httpClient.execute(httpGet);
                                // 判断返回状态，并接收图片
                                if (httpResponse.getStatusLine().getStatusCode() == 200) {
                                        HttpEntity httpEntity = httpResponse.getEntity();
                                        byte[] data = EntityUtils.toByteArray(httpEntity);
                                        bitmap = BitmapFactory
                                                        .decodeByteArray(data, 0, data.length);

                                }
                        } catch (ClientProtocolException e) {
                                // TODO 自动生成的 catch 块
                                e.printStackTrace();
                        } catch (IOException e) {
                                // TODO 自动生成的 catch 块
                                e.printStackTrace();
                        }
                        return bitmap;
                }

                // 表示任务执行之前的操作
                protected void onPreExecute() {
                        // TODO 自动生成的方法存根
                        super.onPreExecute();
                        // 下载之前显示弹出框然后下载图片，下载完会结束弹出框
                        progressDialog.show();
                }

                @Override
                // 在这个方法里进行更新UI操作
                protected void onPostExecute(Bitmap result) {
                        // TODO 自动生成的方法存根
                        super.onPostExecute(result);
                        // 给图片控件设置下载的图片
                        imageView.setImageBitmap(result);
                        // 隐藏弹出框
                        progressDialog.dismiss();
                }

        }
}