摘要：注意每次需一個實例新建的任務只能執行一次否則會出現異常取消一個正在執行的任務方法將會被調用方法用于在執行后臺任務前做一些操作方法內部執行后臺任務不可在此方法內修改調用公布進度最后方法將被執行為了演示進度休眠毫秒方法用于更新進度信息方法用

private MyTask mTask;  
  
    @Override  
    public void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        setContentView(R.layout.main);  
  
        execute = (Button) findViewById(R.id.execute);  
        execute.setOnClickListener(new View.OnClickListener() {  
            @Override  
            public void onClick(View v) {  
                //注意每次需new一個實例,新建的任務只能執行一次,否則會出現異常  
                mTask = new MyTask();  
                mTask.execute("http://www.baidu.com");  
  
                execute.setEnabled(false);  
                cancel.setEnabled(true);  
            }  
        });  
        cancel = (Button) findViewById(R.id.cancel);  
        cancel.setOnClickListener(new View.OnClickListener() {  
            @Override  
            public void onClick(View v) {  
                //取消一個正在執行的任務,onCancelled方法將會被調用  
                mTask.cancel(true);  
            }  
        });  
        progressBar = (ProgressBar) findViewById(R.id.progress_bar);  
        textView = (TextView) findViewById(R.id.text_view);  
  
    }  
  
    private class MyTask extends AsyncTask {  
        //onPreExecute方法用于在執行后臺任務前做一些UI操作  
        @Override  
        protected void onPreExecute() {  
            Log.i(TAG, "onPreExecute() called");  
            textView.setText("loading...");  
        }  
  
        //doInBackground方法內部執行后臺任務,不可在此方法內修改UI  
        @Override  
        protected String doInBackground(String... params) {  
            Log.i(TAG, "doInBackground(Params... params) called");  
            try {  
                HttpClient client = new DefaultHttpClient();  
                HttpGet get = new HttpGet(params[0]);  
                HttpResponse response = client.execute(get);  
                if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {  
                    HttpEntity entity = response.getEntity();  
                    InputStream is = entity.getContent();  
                    long total = entity.getContentLength();  
                    ByteArrayOutputStream baos = new ByteArrayOutputStream();  
                    byte[] buf = new byte[1024];  
                    int count = 0;  
                    int length = -1;  
                    while ((length = is.read(buf)) != -1) {  
                        baos.write(buf, 0, length);  
                        count += length;  
                        //調用publishProgress公布進度,最后onProgressUpdate方法將被執行  
                        publishProgress((int) ((count / (float) total) * 100));  
                        //為了演示進度,休眠500毫秒  
                        Thread.sleep(500);  
                    }  
                    return new String(baos.toByteArray(), "gb2312");  
                }  
            } catch (Exception e) {  
                Log.e(TAG, e.getMessage());  
            }  
            return null;  
        }  
  
        //onProgressUpdate方法用于更新進度信息  
        @Override  
        protected void onProgressUpdate(Integer... progresses) {  
            Log.i(TAG, "onProgressUpdate(Progress... progresses) called");  
            progressBar.setProgress(progresses[0]);  
            textView.setText("loading..." + progresses[0] + "%");  
        }  
  
        //onPostExecute方法用于在執行完后臺任務后更新UI,顯示結果  
        @Override  
        protected void onPostExecute(String result) {  
            Log.i(TAG, "onPostExecute(Result result) called");  
            textView.setText(result);  
  
            execute.setEnabled(true);  
            cancel.setEnabled(false);  
        }  
  
        //onCancelled方法用于在取消執行中的任務時更改UI  
        @Override  
        protected void onCancelled() {  
            Log.i(TAG, "onCancelled() called");  
            textView.setText("cancelled");  
            progressBar.setProgress(0);  
  
            execute.setEnabled(true);  
            cancel.setEnabled(false);  
        }  
    }  
}