Question

我的应用程序在虚拟设备中运行良好但是当我在实际设备上运行时，我得到“我的应用程序停止工作”错误..并且日志中出现此错误

06-07 12:20:09.022 28371-28371/my.amirul.psm E/AndroidRuntime: FATAL EXCEPTION: main
java.lang.NullPointerException at     my.amirul.psm.BackgroundTask.onPostExecute(BackgroundTask.java:113)
at my.amirul.psm.BackgroundTask.onPostExecute(BackgroundTask.java:22)
at android.os.AsyncTask.finish(AsyncTask.java:631)
at android.os.AsyncTask.access$600(AsyncTask.java:177)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:194)
at android.app.ActivityThread.main(ActivityThread.java:5391)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
at dalvik.system.NativeStart.main(Native Method)

这是我的后台任务代码......

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

AlertDialog alertDialog;
Context ctx;
BackgroundTask(Context ctx)
{
this.ctx = ctx;
}
@Override
protected void onPreExecute() {
    alertDialog = new AlertDialog.Builder(ctx).create();
    alertDialog.setTitle("Login Information......");
}

@Override
protected String doInBackground(String... params) {
    String reg_url = "http://10.0.2.2/webapp/register.php";
    String login_url = "http://10.0.2.2/webapp/login.php";
    String method = params[0];
    if(method.equals("register"))
    {
    String name = params[1];
    String user_name = params[2];
    String user_pass = params [3];

        try {
            URL url = new URL(reg_url);
            HttpURLConnection httpURLConnection =(HttpURLConnection) url.openConnection();
            httpURLConnection.setRequestMethod("POST");
            httpURLConnection.setDoOutput(true);
            OutputStream OS = httpURLConnection.getOutputStream();
            BufferedWriter bufferedWriter= new BufferedWriter(new OutputStreamWriter(OS,"UTF-8"));
            String data = URLEncoder.encode("user","UTF-8") + "=" + URLEncoder.encode(name,"UTF-8")+"&"+
                    URLEncoder.encode("user_name","UTF-8") + "=" + URLEncoder.encode(user_name,"UTF-8")+"&"+
                    URLEncoder.encode("user_pass","UTF-8") + "=" + URLEncoder.encode(user_pass,"UTF-8");

            bufferedWriter.write(data);
            bufferedWriter.flush();
            bufferedWriter.close();
            OS.close();
            InputStream IS = httpURLConnection.getInputStream();
            IS.close();
            return "Registration Success...";
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    else if (method.equals("login"))
    {
       String login_name = params[1];
        String login_pass = params[2];
        try {
            URL url = new URL(login_url);
            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 data = URLEncoder.encode("login_name","UTF-8")+"="+URLEncoder.encode(login_name,"UTF-8")+"&"+
              URLEncoder.encode("login_pass","UTF-8")+"="+URLEncoder.encode(login_pass,"UTF-8");
            bufferedWriter.write(data);
            bufferedWriter.flush();
            bufferedWriter.close();
            outputStream.close();

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

        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    return null;
}
@Override
protected void onPostExecute(String result) {
    if (result.equals("Registration Success...")) {
        Toast.makeText(ctx, result, Toast.LENGTH_LONG).show();
    } else if(result.contains("Hello")) {
        Intent i = new Intent(ctx, FormActivity.class);
        ctx.startActivity(i);
    } else {
        alertDialog.setMessage(result);
        alertDialog.show();
    }
}
}

请帮助我...

Answer 1

实际上，网络不可用，并且在与网络连接时系统收到null。在模拟器上，您正在使用系统的网络。我希望它会对你有所帮助。

Answer 2

将您的设备连接到网络，即WiFi /数据连接。然后

假设您在同一个无线网络上......

找到您当地的IP地址（应该是 192.168.1.x ） - 转到命令提示符并输入＆＃39; ipconfig＆＃39;得到这个。其中x是服务器计算机的已分配本地IP。使用本地IP地址为您的Android设备连接到您的本地主机。

它对我有用。

注意：要在模拟器上访问localhost：10.0.2.2。但是，如果您拥有除Web服务器之外的其他内容（例如XMPP服务器），则可能并不总是有效。

这可能对你有所帮助。

Answer 3

我是唯一一个看到

的人

return null;

在doInBackground结束时的每个if / else语句中？

如果成功，那没关系，因为第一个if语句中有return "Registration Success...";，但如果失败，则为null，因此空指针异常。

MyApp停止在实际设备上工作

3 个答案: