Android在完成语句之前不等待数据库响应

Question

I have an interesting problem that I've never run into in programming before. I have an onClickListener that does a lot of username and password checks (makes sure the username is proper length, not taken, etc). I'm using MobDB, and I was using a conditional statement that would return a row if the username already existed. The problem is that the Listener skips the DB and goes to the final check that, if everything works, posts a new username and password to my DB. How can I make it wait for a response from the DB before skipping to the last check?

Here is the relevant code:

usernamecheck3 = true;
                    MobDB.getInstance().execute(APP_KEY, null, rd, null, false, new MobDBResponseListener() {

                        @Override public void mobDBSuccessResponse() {
                            usernamecheck3 = false;
                            Log.e("mobdbSuccess:", "success");
                        }           

                        @Override public void mobDBResponse(Vector<HashMap<String, Object[]>> row) {
                        }        

                        @Override public void mobDBResponse(String jsonObj) {
                            /*Log.e("mobdbSuccess:", "jsonObj");
                            Log.e("mobdbSuccess:", jsonObj);
                            JSONObject mainObject;
                            try {
                                mainObject = new JSONObject(jsonObj);
                                // need to parse the json object.
                            } catch (JSONException e1) {

                                e1.printStackTrace();
                            } */
                        } 

                        @Override public void mobDBFileResponse(String fileName, byte[] fileData) {
                        //get file name with extension and file byte array
                        }           

                        @Override public void mobDBErrorResponse(Integer errValue, String errMsg) {
                            usernamecheck3 = false;
                            Log.e("doesnt", "work");
                        }
                    }); 
                    if(usernamecheck3 == false){
                        Toast.makeText(getApplicationContext(), "Username is taken, please choose another", Toast.LENGTH_SHORT).show();
                    }

Basically the check always returns true, and then logcat will say mobdbSuccess: success, which should have set the Bool to false.

Thanks.

Answer 1

MobDBResponseListener is executing on a different thread. What happens here is that the processing is split, while a thread is doing the query, the main thread on which you added the listener, skips right ahead to the validation. Your best bet is to place the validation inside the MobDBResponseListener, on the mobDBResponse method. Try to debug your code and calls, the Listener may be using an async task. If so, you may do anything you please from the response method, as it will be executing in the main thread again. Otherwise, you should look at solutions that handle threaded execution like Handlers