Android JSON解析凌空库？

Question

I have been struggling to understand the logic of the Android JSON Parsing with volley libraries.I am trying to get JSON Array and parse with Volley Libraries.I understand how JSON data is extracted from PHP file but I have big problems. makeJsonArrayRequest() function runs correctly and parse JSON Array from get_data.php file and add users ArrayList from User class in each iteration.I called this function in onCreate and userLogin function individually.Size of users ArrayList equals to 0 when I call makeJsonArrayRequest() function in onCreate method .However,Size of users ArrayList equals to nonzero number when I call makeJsonArrayRequest() function in userLogin method(This method called when clicked on Login Button).This is my problem.Why makeJsonArrayRequest() doesn't run on Create() method ?

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    ET_NAME = (EditText) findViewById(R.id.user_name);
    ET_PASS = (EditText) findViewById(R.id.user_pass);
    pDialog = new ProgressDialog(this);
    pDialog.setMessage("Please wait...");
    pDialog.setCancelable(false);
    makeJsonArrayRequest();
    Toast.makeText(getApplicationContext(),"Size:" + users.size(),Toast.LENGTH_LONG).show();

}


public  void userLogin(View view) {
    login_name = ET_NAME.getText().toString();
    login_pass = ET_PASS.getText().toString();
    String method = "login";
    String status = "1";
    BackgroundTask backgroundTask = new BackgroundTask(this);
    backgroundTask.execute(method, login_name, login_pass, status);
    Intent i = new Intent(this,MapsActivity.class);
    i.putExtra("username",login_name);
    i.putExtra("userpass", login_pass);
    makeJsonArrayRequest();
    startActivity(i);
    Toast.makeText(getApplicationContext(),"Size:" + users.size(),Toast.LENGTH_LONG).show();
}

private void makeJsonArrayRequest() {


    showpDialog();

    JsonArrayRequest req = new JsonArrayRequest(JSON_URL,
            new Response.Listener<JSONArray>() {
                @Override
                public void onResponse(JSONArray response) {
                    Log.d(TAG, response.toString());

                    try {
                        // Parsing json array response
                        // loop through each json object


                        jsonResponse ="";
                        for (int i = 0; i < response.length(); i++) {


                            JSONObject person = (JSONObject) response.get(i);

                            String name = person.getString("name");
                            String username = person.getString("username");
                            String password = person.getString("password");
                            double latitude = Double.parseDouble(person.getString("latitude"));
                            double longitude = Double.parseDouble(person.getString("longitude"));
                            String status = person.getString("status");

                            User  user = new User(name,username,password,latitude,longitude,status);

                            users.add(user);

                        }



                    } catch (JSONException e) {
                        e.printStackTrace();
                        Toast.makeText(getApplicationContext(),
                                "Error: " + e.getMessage(),
                                Toast.LENGTH_LONG).show();
                    }
                    hidepDialog();


                }
            }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
            VolleyLog.d(TAG, "Error: " + error.getMessage());
            Toast.makeText(getApplicationContext(),
                    error.getMessage(), Toast.LENGTH_SHORT).show();
            hidepDialog();

        }
    });

    // Adding request to request queue
    AppController.getInstance().addToRequestQueue(req);
}

Answer 1

If what you're saying is :

I run the request in onCreate() and check - it's empty.

and then:

I run it again LATER, and Check - it's full.

then have you considered the request latency? it takes time (albeit - not much time) for the request to return, you might be checking before it does

EDIT: Run what you want inside the onResponse(), that's only called when the request returns.

Hope this helps.