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。一切说明都在代码中......................................................
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<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]);
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>
