REST API 对 Fragment 的响应 - Android Studio

Question

我是在 android 中开发 APP 的新手。我想开发一个分片的APP，每个分片都填充了调用REST API获得的数据。

我遵循了不同的教程，但我遇到了这个问题：片段没有显示任何内容。

我从 android studio 中的“Tabbed Activity”开始我的项目：

这是我的片段（我称之为 api）：

public class Calendar extends Fragment {

private static final String baseUrl = "https://xxx";
private static final String events = "/wp-json/sportspress/v2/events";
EventsJsonObjectToMatchesConverter converter;

ArrayList<Matches> matches = new ArrayList<>();

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

    View rootView = inflater.inflate(R.layout.calendar_layout,container, false);
    return rootView;
}

@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);

    this.getEvents();

    ListView lv = (ListView)view.findViewById(R.id.matches);

    MatchesAdapter adapter = new MatchesAdapter(this.getContext(),
            R.layout.matches_layout,
            matches);

    lv.setAdapter(adapter);
}

private void getEvents() {

    // Instantiate the RequestQueue.
    RequestQueue queue = Volley.newRequestQueue(getActivity().getApplicationContext());
    String url =getString(R.string.baseUrl) + getString(R.string.eventsEndpoit);

    // Request a string response from the provided URL.
    StringRequest stringRequest = new StringRequest(Request.Method.GET, url,
            new Response.Listener<String>() {
                @Override
                public void onResponse(String response) {
                    // Display the first 500 characters of the response string.
                    Matches match = new Matches();
                    match.setHomeTeam("simone");
                    match.setAwayTeam("gaspa");
                    match.setResultHome(2);
                    match.setResultAway(1);
                    match.setDate("05/10/2021 - 10:00");
                    matches.add(match);

                    System.out.println(matches.size());
                }
            }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {

        }
    }){
        //This is for Headers If You Needed
        @Override
        public Map<String, String> getHeaders() throws AuthFailureError {
            Map<String, String> params = new HashMap<String, String>();
            params.put("Content-Type", "application/json; charset=UTF-8");
            params.put(
                    "Authorization",
                    String.format("Basic %s", Base64.encodeToString(
                            String.format("%s:%s", getString(R.string.user), getString(R.string.password)).getBytes(), Base64.DEFAULT)));
            return params;
        }


    };

    // Add the request to the RequestQueue.
    queue.add(stringRequest);


}


}

这里是我的适配器：

public class MatchesAdapter extends ArrayAdapter<Matches> {

private ArrayList<Matches> matchList;

public MatchesAdapter(Context context, int matches_layout, ArrayList<Matches> matches) {
    super(context, matches_layout);
    this.matchList = matches;
}

@NonNull
@Override
public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
    int phraseIndex  = position;

    if(convertView == null){
        convertView = LayoutInflater.from(getContext()).inflate(R.layout.matches_layout,parent, false);
    }

    TextView home = convertView.findViewById(R.id.squadra_casa);
    TextView away = convertView.findViewById(R.id.squadra_trasferta);
    TextView home_result = convertView.findViewById(R.id.risultato_casa);
    TextView away_result = convertView.findViewById(R.id.risultato_trasferta);
    TextView group = convertView.findViewById(R.id.girone);
    TextView date = convertView.findViewById(R.id.data_ora);

    home.setText(matchList.get(position).getHomeTeam());
    away.setText(matchList.get(position).getAwayTeam());
    home_result.setText(matchList.get(position).getResultHome());
    away_result.setText(matchList.get(position).getResultAway());
    group.setText(matchList.get(position).getGroup());
    date.setText(matchList.get(position).getDate());

    return convertView;
}
}

我运行了应用程序，但我什么也没看到：

注意：我在 onResponse() 方法中模拟了对象 Match 来测试代码。我已经看到正确调用了 Rest API 并返回了所需的数据

感谢您的帮助！

Answer 1

从简短的代码来看，它似乎写得很好。您缺少的要点是 API 调用是异步的，并且在 API 返回任何结果之前填充了适配器。尝试在您的 StringRequest 调用的 OnResponse 回调中填充适配器，如下所示（抱歉，我没有尝试运行它，但我认为给您一个提示可能会有所帮助）：

StringRequest stringRequest = new StringRequest(Request.Method.GET, url,
        new Response.Listener<String>() {
            @Override
            public void onResponse(String response) {
                matches = ParseTextResultToMatchesObjects(response);
                adapter = new MatchesAdapter(this.getContext(),
                    R.layout.matches_layout,
                    matches);
            }
        }, new Response.ErrorListener() {
    @Override
    public void onErrorResponse(VolleyError error) {

    }
    ...

编辑： 对于将来担心这一点的任何人：整个操作都放在 onViewCreated 中，而不是 onCreateView 中，这导致了更多的复杂性（不知道为什么），但是我写的关于操作的异步性和错误地填充适配器的内容时间到了……