Android 异步加载图片-AsyncTask

AsyncTask定义了三种泛型类型 Params，Progress和Result。
    •Params 启动任务执行的输入参数，比如HTTP请求的URL。
    •Progress 后台任务执行的百分比。
    •Result 后台执行任务最终返回的结果，比如String。
Activity

/*   * 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);    }             }             }

MyAsynaTask.java

package rw.ansync;    import java.io.ByteArrayOutputStream;  import java.io.File;  import java.io.FileOutputStream;  import java.io.InputStream;  import java.io.OutputStream;  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.os.IInterface;  import android.util.Log;  import android.widget.Button;  import android.widget.ImageView;  import android.widget.ProgressBar;      public class MyAsynaTask extends AsyncTask{            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]);               Log.i("------------->", url+"");               HttpURLConnection connection=(HttpURLConnection) url.openConnection();                              connection.connect();               int MAX=connection.getContentLength();               progressBar.setMax(MAX);                             InputStream inputStream=connection.getInputStream();                           ByteArrayOutputStream outputStream=new ByteArrayOutputStream();               /*                * 为了显示进度条，每接受1024字节要求更新一次ＵＩ，为了看效果                */               byte []buf=new byte[1024];               int len = 0;               int processBarNum=0;               while( (len=inputStream.read(buf))!=-1){                   outputStream.write(buf, 0, len);                   processBarNum+=len;                                      publishProgress(processBarNum);//通知要更新processBar               }               bitmap=BitmapFactory.decodeByteArray(outputStream.toByteArray(),0, MAX);               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);          super.onPostExecute(result);      }      }

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



转自：http://blog.csdn.net/rwyz1314/article/details/6841639