android中异步aynctask执行

class ExcutePing extends AsyncTask<Void, String, String> {
String result = "诊断结束";
String p_tv = "";
String str_api;
String str_ping;
      
@Override
protected String doInBackground(Void... arg0) {
// TODO Auto-generated method stub

String s_ping = FileReadHelper.readSDString(sfile_ping).toString();
String[] s = s_ping.split(";");
for (int i = 0; i < s.length && !stopflag; i++) {
str_api = "";
str_ping = "ping -c 1 ";
str_api = s[i].trim();
String result = CommandHelper.excuteCommand(str_ping, str_api);
publishProgress(result);
}// 线程中多次循环
return result;
}

public void setBreak(){
stopflag = true;
}
@Override
protected void onProgressUpdate(String... values) {
// TODO Auto-generated method stub
super.onProgressUpdate(values);
tv_pTextView.setText(tv_pTextView.getText() + "=================\n" + values[0]);