添加从ArrayList对象解码的数据后，JSon仍然是空的。

Question

我在Android中有这个java代码，当我创建新的专业并打印m.getName()时。它们被打印出来，数据被正确地从Json对象中解码出来，但是在将数据添加到ArrayList majorsArrayList之后，它仍然是空的，并且没有添加数据。

在这里，我检查了ArrayList (在onCreate()中)，结果是: ARRAYLIST[]

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        RecyclerView recyclerView=(RecyclerView) findViewById(R.id.recyclerViewMajors);
        getmajors("Al-Kafaat University","Faculty of Pedagogy","faculty","en");
        System.out.println("ARRAYLIST"+majorsArrayList);
        recycler_majorAdapter recyclerMajorAdapter=new recycler_majorAdapter(this,majorsArrayList);
        recyclerView.setAdapter(recyclerMajorAdapter);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        System.out.println("ARRAYLIST"+majorsArrayList);}

下面是getmajors()函数

private void getmajors(String uni, String faculty, String dest, String lang)
{
    StringRequest stringRequest=new StringRequest(Request.Method.GET, "https://...", new Response.Listener<String>() {
        @Override
        public void onResponse(String response) {
            try {
                JSONArray opp =new JSONArray(response);
                for (int i = 0; i< opp.length(); i++)
                {
                    JSONObject pollObject= opp.getJSONObject(i);
                    String major=pollObject.getString("maj");
                    String university=pollObject.getString("univ");
                    int id=pollObject.getInt("id");
                    Majors m=new Majors(major,university, id);
                    System.out.println(m.getName());
                    System.out.println(m.getUniversity());
                    System.out.println(m.getId());
                    majorsArrayList.add(m);
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }
        }
    }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
            Toast.makeText(MainActivity.this,error.getMessage(),Toast.LENGTH_LONG).show();
        }
    });
    Volley.newRequestQueue(this).add(stringRequest);
}

Answer 1

修正了，只是在onCreate()中添加了两行：

recycler_majorAdapter recyclerMajorAdapter=new recycler_majorAdapter(this,majorsArrayList);
recyclerView.setAdapter(recyclerMajorAdapter);

函数到for循环之后的getmajors()函数。