Android攻城狮AsyncTask

 1 public class ImageTest extends Activity {
 2     private ImageView imageView;
 3     private ProgressBar progressBar;
 4     String URL = "http://p4.so.qhimgs1.com/sdr/1228_768_/t01f7ed810efbfe800a.jpg";
 5 
 6     @Override
 7     protected void onCreate(Bundle savedInstanceState) {
 8         // TODO Auto-generated method stub
 9         super.onCreate(savedInstanceState);
10         setContentView(R.layout.image);
11         imageView = (ImageView) findViewById(R.id.image);
12         progressBar = (ProgressBar) findViewById(R.id.bar);
13 
14         MyAsynctask1 task = new MyAsynctask1();
15         task.execute(URL);
16 
17     }
18 
19     // params：启动任务时输入参数的类型。
20     // progress：后台任务执行中，返回进度值的类型。
21     // Result：后台执行任务完成后，返回结果的类型。
22     class MyAsynctask1 extends AsyncTask<String, Void, Bitmap> {
23         @Override
24         // 异步初始化
25         protected void onPreExecute() {
26             // TODO Auto-generated method stub
27             super.onPreExecute();
28             // 显示进度条
29             progressBar.setVisibility(View.VISIBLE);
30         }
31 
32         @Override
33         protected void onPostExecute(Bitmap result) {
34             // TODO Auto-generated method stub
35             super.onPostExecute(result);
36             progressBar.setVisibility(View.GONE);
37             imageView.setImageBitmap(result);
38 
39         }
40 
41         @Override
42         protected Bitmap doInBackground(String... params) {
43             // TODO Auto-generated method stub
44 
45             // 从params中取出参数值，传给url
46             String url = params[0];
47             // 初始化参数
48             Bitmap bitmap = null;
49             URLConnection connection;
50             InputStream inputStream;
51 
52             try {
53                 connection = new URL(url).openConnection();
54                 inputStream = connection.getInputStream();// 获取输入流
55                 BufferedInputStream bis = new BufferedInputStream(inputStream);
56                 Thread.sleep(3000);// 睡3秒
57                 // 通过decodeStream（）解析输入流
58                 bitmap = BitmapFactory.decodeStream(bis);
59                 inputStream.close();
60                 bis.close();
61 
62             } catch (IOException e) {
63                 // TODO Auto-generated catch block
64                 e.printStackTrace();
65             } catch (InterruptedException e) {
66                 // TODO Auto-generated catch block
67                 e.printStackTrace();
68             }
69             return bitmap;
70         }
71 
72     }
73 
74 }

 1 public class ProgressBarTest extends Activity {
 2 
 3     ProgressBar progressBar;
 4     MyAsycnTask2 task;
 5     @Override
 6     protected void onCreate(Bundle savedInstanceState) {
 7         // TODO Auto-generated method stub
 8         super.onCreate(savedInstanceState);
 9         setContentView(R.layout.progressbar);
10         progressBar = (ProgressBar) findViewById(R.id.progressBar1);
11 
12          task = new MyAsycnTask2();
13         task.execute();
14     }
15 
16     @Override
17     protected void onPause() {
18         // TODO Auto-generated method stub
19         super.onPause();
20         if (task!=null&&task.getStatus()==AsyncTask.Status.RUNNING) {
21             task.cancel(true);//cancel()只是将对应的task标记为cancel状态，并不是真正取消线程执行
22         }
23     }
24 
25     class MyAsycnTask2 extends AsyncTask<Void, Integer, Void> {
26 
27         @Override
28         protected void onProgressUpdate(Integer... values) {
29             // TODO Auto-generated method stub
30             // 获取进度更新值
31             super.onProgressUpdate(values);
32             if (isCancelled()) {
33                 return;
34             }
35             progressBar.setProgress(values[0]);
36         }
37 
38         @Override
39         protected Void doInBackground(Void... params) {
40             // TODO Auto-generated method stub
41             
42             // 模拟进度更新
43             for (int i = 0; i < 100; i++) {
44                 if (isCancelled()) {
45                 break;
46             }
47                 publishProgress(i);
48                 try {
49                     Thread.sleep(300);
50                 } catch (InterruptedException e) {
51                     // TODO Auto-generated catch block
52                     e.printStackTrace();
53                 }
54             }
55             return null;
56         }
57     }
58 }