Android--异步加载图片

    /*      * Android 异步任务AsyncTask      * AsyncTask定义了三种泛型类,Params,Progress,Result       */      package rw.ansync;      import android.app.Activity;      import android.os.Bundle;      import android.view.View;      import android.view.View.OnClickListener;      import android.widget.Button;      import android.widget.EditText;      import android.widget.ImageView;      import android.widget.ProgressBar;      public class AsynaTask_TestActivity extends Activity {          /** Called when the activity is first created. */          private EditText editText;          private Button button;          private ProgressBar progressBar;          private ImageView imageView;          private static final String URL_STRING="http://photocdn.sohu.com/20110927/Img320705637.jpg";          @Override          public void onCreate(Bundle savedInstanceState) {              super.onCreate(savedInstanceState);              setContentView(R.layout.main);              editText=(EditText) findViewById(R.id.editText1);              editText.setText(URL_STRING);              button=(Button) findViewById(R.id.button1);              progressBar=(ProgressBar) findViewById(R.id.progressBar1);              imageView=(ImageView) findViewById(R.id.imageView1);              button.setOnClickListener(new ButtonListener());          }          class ButtonListener implements OnClickListener{              @Override              public void onClick(View v) {                  // TODO Auto-generated method stub                       MyAsynaTask mTask=new MyAsynaTask(imageView, progressBar,button);                      mTask.execute(URL_STRING);              }          }      }  

    package rw.ansync;      import java.io.InputStream;      import java.net.HttpURLConnection;      import java.net.URL;      import android.R.integer;      import android.graphics.Bitmap;      import android.graphics.BitmapFactory;      import android.os.AsyncTask;      import android.widget.Button;      import android.widget.ImageView;      import android.widget.ProgressBar;      public class MyAsynaTask extends AsyncTask<String, Integer, Bitmap>{          private ImageView imageView;          private ProgressBar progressBar;          private Button button;          public MyAsynaTask( ImageView imageView,                  ProgressBar progressBar,Button button) {              super();              this.imageView = imageView;              this.progressBar = progressBar;              this.button=button;          }          @Override          protected void onPreExecute() {              // TODO Auto-generated method stub               /*              * 改方法在执行实际的后台操作时被UI线程调用，可以在该方法中做一些准备工作，比如              *  Toast.makeText(context, "准备下载", Toast.LENGTH_LONG).show();              */              super.onPreExecute();          }          @Override          protected Bitmap doInBackground(String... params) {//输入编变长的可变参数 和ＵＩ线程中的Asyna.execute()对应               // TODO Auto-generated method stub           /*          * 该方法在OnpreExecute执行以后马上执行，改方法执行在后台线程当中，负责耗时的计算，可以调用publishProcess方法来实时更新任务进度          */              Bitmap bitmap=null;              try {                   URL url=new URL(params[0]);                   HttpURLConnection connection=(HttpURLConnection) url.openConnection();                   connection.setDoInput(true);                   connection.connect();                   progressBar.setMax(connection.getContentLength());                   InputStream inputStream=connection.getInputStream();                   bitmap=BitmapFactory.decodeStream(inputStream);                  // inputStream.close();                    /*                   * 以下完全为了演示进度条，如果为了显示进度条可以把这个去掉                   */                   /*                  byte []buf=new byte[1024*4];                  inputStream=connection.getInputStream();                  int len=0;                  while ((inputStream.read(buf))!=-1) {                     len+=buf.length;                     publishProgress(len);                 }              */                  inputStream.close();              } catch (Exception e) {                  // TODO: handle exception               }              return bitmap;          }          @Override          protected void onProgressUpdate(Integer... values) {              // TODO Auto-generated method stub               /*              * 当publichProcess 呗调用以后，ＵＩ线程将调用这个有方法在界面上展示任务的情况，比如一个额进度条。这里是更新进度条              */              int value=values[0];              progressBar.setProgress(value);              super.onProgressUpdate(values);          }          @Override          protected void onPostExecute(Bitmap result) {              // TODO Auto-generated method stub               /*              * 在doInbackground执行完成以后，onPostExecute将被调用，后台的结果将返回给UI线程，将获得图片显示出来              */              imageView.setImageBitmap(result);              button.setText("下载完成");              super.onPostExecute(result);          }      }