Question

我开发了一个Andriod应用程序。我从数据库中读取了一些字符串，并将其输出到ListView中。我的问题是，如果我采用逐步模式，则DB的返回字符串效果很好。如果我处于运行模式，或者即使我将断点放在接收结果的行之后。则字符串变量将为空。

 BackgroundWorker backgroundWorker = new BackgroundWorker( this);
 backgroundWorker.execute("Names");
 res = backgroundWorker.FinalRes;
 res = res.replace("[","");
 res = res.replace("]","");
 res = res.replace("\"","");
 ParsedStringsResult = PasrString(res);
 ArrayList<ListNames> NameSs= new ArrayList<ListNames>();
 int size = ParsedStringsResult.length;
 for ( int i=0; i<size;i++ )
 NameSs.add(new ListNames(ParsedStringsResult[i]));

如果我将断点放在res=backgroundWorker.FinalRes;
它运作良好并显示出价值如果我将其放在此行之后甚至是默认运行模式下，则res将为空！

为什么会发生这种情况，我该如何解决？

我的背景课

public class BackgroundWorker extends AsyncTask<String , Void, String> {

Context context;

public String FinalRes="";
AlertDialog alertDialog;
BackgroundWorker(Context ctx)
{
    context = ctx;
}
@Override
protected String doInBackground(String... params) {
    String type = params[0];

    if (type == "Names") {
        String url_login = "http://192.168.1.2/MyApp/getNames.php";

        try {
            URL url = new URL(url_login);
            HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
            httpURLConnection.setRequestMethod("POST");
            httpURLConnection.setDoOutput(true);
            httpURLConnection.setDoInput(true);


          /*  OutputStream outputStream = httpURLConnection.getOutputStream();
            BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(outputStream, "UTF-8"));
            String post_data = URLEncoder.encode("name", "UTF-8") + "=" + URLEncoder.encode(name, "UTF-8");// +"&"+ w nkml tany
            bufferedWriter.write(post_data);
            bufferedWriter.flush();
            bufferedWriter.close();
            outputStream.close();*/


            InputStream inputStream = httpURLConnection.getInputStream();
            BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream, "iso-8859-1"));
            String result = "";
            String line;
            while ((line = bufferedReader.readLine()) != null) {
                result += line;
            }
            bufferedReader.close();
            inputStream.close();
            httpURLConnection.disconnect();
            FinalRes = result;
            return result;

        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }
    else
        return null;
}

@Override
protected void onPreExecute(){
   // alertDialog = new AlertDialog.Builder(context).create();
 //   alertDialog.setTitle("Login Status");
}

@Override
protected void onPostExecute(String result){
    //alertDialog.setMessage(result);
    //alertDialog.show();
    //FinalRes = result;
}

}

Answer 1

您在启动后台工作程序和设置其最终结果之间存在竞争条件。

通过设置断点，您只需等待足够长的时间即可完成该过程。

通过某种方式，您只需要等待FinalRes的设置即可。没有看到您的BackgroundWorker类的代码，就不可能说出如何做到最好。

Answer 2

那样尝试：

BackgroundWorker backgroundWorker = new BackgroundWorker( this);
backgroundWorker.execute("Names");
while(backgroundWorker.getStatus() != AsyncTask.Status.FINISHED) // While the status is different from "FINISHED" you wait for the task to finished
    Thread.sleep(100)
res = backgroundWorker.FinalRes;

也显示在这里： Android, AsyncTask, check status?

Java代码在逐步调试模式下（而不是默认运行模式下）能很好地工作

2 个答案: