当我尝试在我的应用程序中注册新用户时，抛出mySQL db应用程序不起作用并发送此错误消息：
E / AndroidRuntime：致命异常：主要 过程：com.example.io.biolite6，PID：17633 java.lang.NullPointerException：尝试在空对象上调用虚方法'int java.lang.String.length（）' 参考 在org.json.JSONTokener.nextCleanInternal（JSONTokener.java:116） at org.json.JSONTokener.nextValue（JSONTokener.java:94） 在org.json.JSONObject。（JSONObject.java:156） 在org.json.JSONObject。（JSONObject.java:173） 在com.example.io.biolite6.BackgroundsTask.onPostExecute（BackgroundsTask.java:114） 在com.example.io.biolite6.BackgroundsTask.onPostExecute（BackgroundsTask.java:30） 在android.os.AsyncTask.finish（AsyncTask.java:636） 在android.os.AsyncTask.access $ 500（AsyncTask.java:177） 在android.os.AsyncTask $ InternalHandler.handleMessage（AsyncTask.java:653） 在android.os.Handler.dispatchMessage（Handler.java:111） 在android.os.Looper.loop（Looper.java:194） 在android.app.ActivityThread.main（ActivityThread.java:5637） at java.lang.reflect.Method.invoke（Native Method） 在java.lang.reflect.Method.invoke（Method.java:372） 在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:959） 在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:754） I /处理：发送信号。 PID：17633 SIG：9
public class BackgroundsTask extends AsyncTask<String,Void,String> {
String register_url = "http://192.168.1.104/loginapp/register.php";
Context ctx;
ProgressDialog progressDialog;
Activity activity;
AlertDialog.Builder builder;
public BackgroundsTask(Context ctx)
{
this.ctx = ctx;
activity = (Activity) ctx;
}
@Override
protected void onPreExecute()
{
builder = new AlertDialog.Builder(activity);
progressDialog = new ProgressDialog(ctx);
progressDialog.setTitle("Please wait");
progressDialog.setMessage("Connecting to server...");
progressDialog.setIndeterminate(true);
progressDialog.setCancelable(false);
progressDialog.show();
}
@Override
protected String doInBackground(String... params) {
String method = params[0];
if (method.equals("register"))
{
try {
URL url = new URL(register_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 name = params[1];
String email = params[2];
String password = params[3];
String data = URLEncoder.encode("name","UTF-8")+"="+URLEncoder.encode(name,"UTF-8")+"&"+
URLEncoder.encode("email","UTF-8")+"="+URLEncoder.encode(email,"UTF-8")+"&"+
URLEncoder.encode("password","UTF-8")+"="+URLEncoder.encode(password,"UTF-8");
bufferedWriter.write(data);
bufferedWriter.flush();
bufferedWriter.close();
outputStream.close();
InputStream inputStream = httpURLConnection.getInputStream();
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
StringBuilder stringBuilder = new StringBuilder();
String line = "";
while ((line = bufferedReader.readLine())!=null)
{
stringBuilder.append(line+"\n");
}
httpURLConnection.disconnect();
Thread.sleep(5000);
return stringBuilder.toString().trim();
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
return null;
}
@Override
protected void onProgressUpdate(Void... values) {
super.onProgressUpdate(values);
}
@Override
protected void onPostExecute(String json) {
try {
progressDialog.dismiss();
JSONObject jsonObject = new JSONObject(json);
JSONArray jsonArray = jsonObject.getJSONArray("server_response");
JSONObject JO = jsonArray.getJSONObject(0);
String code = JO.getString("code");
String message = JO.getString("message");
if (code.equals("reg_true"))
{
showDialog("Registration Success", message,code);
}
else if (code.equals("reg_false"))
{
showDialog("Registration Failed",message,code);
}
} catch (JSONException e) {
e.printStackTrace();
}
}
public void showDialog(String title, String message, String code)
{
builder.setTitle(title);
if (code.equals("reg_true")||code.equals("reg_false"))
{
builder.setMessage(message);
builder.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
activity.finish();
}
});
AlertDialog alertDialog = builder.create();
alertDialog.show();
}
}
}