不要在片段中显示列表视图项

Question

我把一个listView放在一个fragment中，把一个fragment放在activiti_main.xml中，从volley库中得到一个json文件，然后解析那个json文件并用listView显示它，下面的代码工作正常。

MainActivity.java

public class MainActivity extends AppCompatActivity {

public ListView listView;
private RequestQueue queue;
private ArrayList<Category> categories;
public CategoryAdapter adapter;

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

    queue = Volley.newRequestQueue(MainActivity.this);
    String url = "***";

    StringRequest request = new StringRequest(Request.Method.GET, url, new Response.Listener<String>() {
        @Override
        public void onResponse(String response) {
            CategoriesJsonParser jsonParser = new CategoriesJsonParser();
            try {
                categories = jsonParser.parseJson(response);
                adapter = new CategoryAdapter(getApplicationContext(), categories, R.layout.category_item);
                listView.setAdapter(adapter);
            } catch (JSONException e) {
                e.printStackTrace();
            }

        }
    }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {

        }
    });
    queue.add(request);
}

} 但是当我在片段中编写相同的代码时 程序关闭后我该怎么办？

BlankFragment.java

public class BlankFragment extends Fragment {

// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";

// TODO: Rename and change types of parameters
private String mParam1;
private String mParam2;

public ListView listView;
private RequestQueue queue;
private ArrayList<Category> categories;
public CategoryAdapter adapter;

public BlankFragment() {
    // Required empty public constructor
}

/**
 * Use this factory method to create a new instance of
 * this fragment using the provided parameters.
 *
 * @param param1 Parameter 1.
 * @param param2 Parameter 2.
 * @return A new instance of fragment BlankFragment.
 */
// TODO: Rename and change types and number of parameters
public static BlankFragment newInstance(String param1, String param2) {
    BlankFragment fragment = new BlankFragment();
    Bundle args = new Bundle();
    args.putString(ARG_PARAM1, param1);
    args.putString(ARG_PARAM2, param2);
    fragment.setArguments(args);
    return fragment;
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (getArguments() != null) {
        mParam1 = getArguments().getString(ARG_PARAM1);
        mParam2 = getArguments().getString(ARG_PARAM2);
    }
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

    listView = getActivity().findViewById(R.id.listview);
    queue = Volley.newRequestQueue(getActivity());
    String url = "https://dikushop.ir/android/category/getCategories.php";

    StringRequest request = new StringRequest(Request.Method.GET, url, new Response.Listener<String>() {
        @Override
        public void onResponse(String response) {
            CategoriesJsonParser jsonParser = new CategoriesJsonParser();
            try {
                categories = jsonParser.parseJson(response);
                adapter = new CategoryAdapter(getContext(), categories, R.layout.category_item);
                //   listView.setAdapter(adapter);
            } catch (JSONException e) {
                e.printStackTrace();
            }

        }
    }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {

        }
    });
    queue.add(request);        
    listView.setAdapter(adapter);
    // Inflate the layout for this fragment
    return inflater.inflate(R.layout.fragment_blank, container, false);
}

Answer 1

首先，从片段代码中删除下面不必要的部分

`

// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";

// TODO: Rename and change types of parameters
private String mParam1;
private String mParam2;

/**
 * Use this factory method to create a new instance of
 * this fragment using the provided parameters.
 *
 * @param param1 Parameter 1.
 * @param param2 Parameter 2.
 * @return A new instance of fragment BlankFragment.
 */
// TODO: Rename and change types and number of parameters
public static BlankFragment newInstance(String param1, String param2) {
    BlankFragment fragment = new BlankFragment();
    Bundle args = new Bundle();
    args.putString(ARG_PARAM1, param1);
    args.putString(ARG_PARAM2, param2);
    fragment.setArguments(args);
    return fragment;
}

    
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (getArguments() != null) {
        mParam1 = getArguments().getString(ARG_PARAM1);
        mParam2 = getArguments().getString(ARG_PARAM2);
    }
}

`

并将其添加到 onCreateView

View view = inflater.inflate(your xml which contain list view eg. R.layout.list, container, false);

最后

//return view which you inflated
     return view;