我还是 Android 初学者,也是 Stackowerflow 的新手,希望你能理解我的问题。我使用 Volley 库和 Singleton 类。我有 JsonParser 类,解析后应返回包含对象的填充列表。
public class JsonParse {
Context context;
public ArrayList<ParseItem> parseItemList = new ArrayList<>();
String json_url = "myurl";
public JsonParse(Context context) {
this.context = context;
}
public ArrayList<ParseItem> getList() {
JsonArrayRequest jsonArrayRequest = new JsonArrayRequest(Request.Method.POST, json_url, null,
new Response.Listener<JSONArray>() {
@Override
public void onResponse(JSONArray response) {
for (int i = 0; i < response.length(); i++) {
try {
JSONObject jsonObject = response.getJSONObject(i);
ParseItem parseItem = new ParseItem();
String naslov = jsonObject.getString("naslov");
String url = jsonObject.getString("url");
parseItem.setTitle(naslov);
parseItem.setUrl(url);
JSONArray niz = jsonObject.getJSONArray("niz");
ArrayList<String> podnaslovTMP = new ArrayList<>();
ArrayList<String> podurlTMP = new ArrayList<>();
for (int j = 0; j < niz.length(); j++) {
JSONObject nizOBJ = niz.getJSONObject(j);
String podnaslov = nizOBJ.getString("podnaslov");
String podurl = nizOBJ.getString("podurl");
podnaslovTMP.add(podnaslov);
podurlTMP.add(podurl);
}
parseItemList.add(parseItem);
} catch (JSONException e) {
e.printStackTrace();
}
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
error.printStackTrace();
}
});
MySingleton.getInstance(context).addToRequestQueue(jsonArrayRequest);
return parseItemList;
}}
然后我尝试调用 getList 并在 HomeFragment 中获取我的列表。
public class HomeFragment extends Fragment implements View.OnClickListener {
private Context context;
private static final int REQUEST_CALL = 1;
private View view;
private ParseItem parseItem = new ParseItem();
public ArrayList<ParseItem>arrayList = new ArrayList<>();
public HomeFragment() {
}
@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable final ViewGroup container, @Nullable Bundle savedInstanceState) {
view = inflater.inflate(R.layout.fragment_home, container, false);
init();
JsonParse jsonParse = new JsonParse(getActivity());
arrayList = jsonParse.getList();
return view;
}
我的arrayList始终为空。我希望有人能帮助我。
最佳答案
创建监听器
public interface GetArrayListListner{
void getArrayData(ArrayList<ParseItem>);
}
和
public class JsonParse {
private GetArrayListListner arrayListListner;// add this line
Context context;
public ArrayList<ParseItem> parseItemList = new ArrayList<>();
String json_url = "myurl";
public JsonParse(Context context,GetArrayListListner arrayListListner) {
this.context = context;
this.arrayListListner = arrayListListner; //Add this line
}
public void getList() {
new JsonArrayRequest(Request.Method.POST, json_url, null,
new Response.Listener<JSONArray>() {
@Override
public void onResponse(JSONArray response) {
for (int i = 0; i < response.length(); i++) {
try {
JSONObject jsonObject = response.getJSONObject(i);
ParseItem parseItem = new ParseItem();
String naslov = jsonObject.getString("naslov");
String url = jsonObject.getString("url");
parseItem.setTitle(naslov);
parseItem.setUrl(url);
JSONArray niz = jsonObject.getJSONArray("niz");
ArrayList<String> podnaslovTMP = new ArrayList<>();
ArrayList<String> podurlTMP = new ArrayList<>();
for (int j = 0; j < niz.length(); j++) {
JSONObject nizOBJ = niz.getJSONObject(j);
String podnaslov = nizOBJ.getString("podnaslov");
String podurl = nizOBJ.getString("podurl");
podnaslovTMP.add(podnaslov);
podurlTMP.add(podurl);
}
parseItemList.add(parseItem);
} catch (JSONException e) {
e.printStackTrace();
}
}
arrayListListner.getArrayData(parseItemList);//add this line
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
error.printStackTrace();
}
});
MySingleton.getInstance(context).addToRequestQueue(jsonArrayRequest);
return parseItemList;
}
}
并命名它
JsonParse jsonParse = new JsonParse(getActivity(),new GetArrayListListner(){
@Overrid void getArrayData(ArrayList<ParseItem>){
arrayList = jsonParse.getList();
}
});
关于java - 无法从另一个类获取 ArrayList。它总是空的,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/59986031/