Question

我试图使用JsonArrayRequest检索json数据。这是我执行此操作的代码

public class QuestionDetailFragment extends Fragment {
   private static final String url = "http://10.0.2.2:80/forumtest/readquestion.php?format=json";
   private String data;
   RequestQueue requestQueue;

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.question_details_layout, container, false);
   readQuestionDetails();
    Log.d("user","data:"+data);
    return view;
}

private void readQuestionDetails() {
    requestQueue = Volley.newRequestQueue(getActivity().getApplicationContext());
    JsonArrayRequest jsonArrayRequest = new JsonArrayRequest(Request.Method.POST, url, new Response.Listener<JSONArray>() {
        @Override
        public void onResponse(JSONArray response) {

                try {
                    for (int i=0;i<response.length();i++) {
                        JSONObject jsonObject = response.getJSONObject(i);

                        data=jsonObject.getString("user");



                    }

                } catch (JSONException e) {
                    e.printStackTrace();
                    Log.e("user",e.getMessage());
            }
        }
    }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
            Log.e("user", error.getMessage());

        }
    });

    requestQueue.add(jsonArrayRequest);
}
}

问题在于，当我在循环中使用数据变量时，它返回所需的值，但每当我尝试在循环外使用数据变量时（让我们说当我使用onCreateView中的数据时），它返回null值。

Answer 1

这是因为JsonArrayRequest被添加到异步执行任务的排队队列中。因此，即使您在Log.d("tag","data:"+data);之后调用readQuestionDetails()请求尚未执行，也意味着data为空。

这样的事情会起作用：

public class QuestionDetailFragment extends Fragment {
    private static final String url = "http://10.0.2.2:80/forumtest/readquestion.php?format=json";
    private String data;
    RequestQueue requestQueue;

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.question_details_layout, container, false);
        readQuestionDetails();
        return view;
    }

    private void readQuestionDetails() {
        requestQueue = Volley.newRequestQueue(getActivity().getApplicationContext());
        JsonArrayRequest jsonArrayRequest = new JsonArrayRequest(Request.Method.POST, url, new Response.Listener<JSONArray>() {
            @Override
            public void onResponse(JSONArray response) {

                try {
                    for (int i=0;i<response.length();i++) {
                        JSONObject jsonObject = response.getJSONObject(i);

                        data=jsonObject.getString("user");
                        printData(data);
                    }

                } catch (JSONException e) {
                    e.printStackTrace();
                    Log.e("user",e.getMessage());
                }
            }
        }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                Log.e("user", error.getMessage());
            }
        });

        requestQueue.add(jsonArrayRequest);
    }

    private void printData(String data){
        Log.d("user","data:"+data);
    }
}

使用jsonArrayRequest从json获取数据

1 个答案: