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一个实例,新建的任务只能执行一次,否则会出现异常
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) {
//取消一个正在执行的任务,onCancelled方法将会被调用
mTask.cancel(true);
}
});
progressBar = (ProgressBar) findViewById(R.id.progress_bar);
textView = (TextView) findViewById(R.id.text_view);
}
private class MyTask extends AsyncTask<String, Integer, String> {
//onPreExecute方法用于在执行后台任务前做一些UI操作
@Override
protected void onPreExecute() {
Log.i(TAG, "onPreExecute() called");
textView.setText("loading...");
}
//doInBackground方法内部执行后台任务,不可在此方法内修改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;
//调用publishProgress公布进度,最后onProgressUpdate方法将被执行
publishProgress((int) ((count / (float) total) * 100));
//为了演示进度,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方法用于更新进度信息
@Override
protected void onProgressUpdate(Integer... progresses) {
Log.i(TAG, "onProgressUpdate(Progress... progresses) called");
progressBar.setProgress(progresses[0]);
textView.setText("loading..." + progresses[0] + "%");
}
//onPostExecute方法用于在执行完后台任务后更新UI,显示结果
@Override
protected void onPostExecute(String result) {
Log.i(TAG, "onPostExecute(Result result) called");
textView.setText(result);
execute.setEnabled(true);
cancel.setEnabled(false);
}
//onCancelled方法用于在取消执行中的任务时更改UI
@Override
protected void onCancelled() {
Log.i(TAG, "onCancelled() called");
textView.setText("cancelled");
progressBar.setProgress(0);
execute.setEnabled(true);
cancel.setEnabled(false);
}
}
}
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