Android Studio中Fragment调用REST API后ListView无内容展示问题求助

核心问题1：异步请求完成后未通知列表刷新 #

Volley的网络请求是异步执行的，你在onViewCreated中调用getEvents()之后立刻初始化并绑定了适配器，此时matches列表是空的。等网络请求回调onResponse中往matches里新增数据后，适配器感知不到数据变化，不会重新渲染列表。
修复方法：把适配器提升为Fragment的全局变量，在onResponse中添加完数据后调用adapter.notifyDataSetChanged()刷新列表。 #

核心问题2：ArrayAdapter构造函数传参错误 #

你自定义的MatchesAdapter继承自ArrayAdapter，但构造函数调用super(context, matches_layout)时没有传入数据源，ArrayAdapter内部默认的item数量为0，就算你本地持有了matchList也不会生效。
修复方法：修改构造函数的super调用，传入数据源：

public MatchesAdapter(Context context, int matches_layout, ArrayList<Matches> matches) {
    super(context, matches_layout, matches); // 新增第三个参数传入数据源
    this.matchList = matches;
}

潜在问题：int类型的比分直接setText会崩溃 #

你的setResultHome/setResultAway传入的是int类型数值，调用setText()的时候如果直接传入int，系统会把这个数值当成字符串资源ID去查找，找不到就会抛异常崩溃。
修复方法：把int转成字符串再设置：

home_result.setText(String.valueOf(matchList.get(position).getResultHome()));
away_result.setText(String.valueOf(matchList.get(position).getResultAway()));

完整修改后的代码示例 #

1. Calendar Fragment修改： #

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<>();
    MatchesAdapter adapter; // 提升为全局变量

    @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);
        ListView lv = (ListView)view.findViewById(R.id.matches);
        adapter = new MatchesAdapter(this.getContext(), R.layout.matches_layout, matches);
        lv.setAdapter(adapter);
        this.getEvents(); // 先设适配器再发请求不影响逻辑
    }

    private void getEvents() {
        RequestQueue queue = Volley.newRequestQueue(getActivity().getApplicationContext());
        String url =getString(R.string.baseUrl) + getString(R.string.eventsEndpoit);
        StringRequest stringRequest = new StringRequest(Request.Method.GET, url,
                new Response.Listener<String>() {
                    @Override
                    public void onResponse(String response) {
                        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);
                        adapter.notifyDataSetChanged(); // 通知适配器刷新列表
                        System.out.println(matches.size());
                    }
                }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                // 建议新增错误提示逻辑，方便后续排查问题
            }
        }){
            @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;
            }
        };
        queue.add(stringRequest);
    }
}

2. MatchesAdapter修改： #

public class MatchesAdapter extends ArrayAdapter<Matches> {
    private ArrayList<Matches> matchList;

    public MatchesAdapter(Context context, int matches_layout, ArrayList<Matches> matches) {
        super(context, matches_layout, matches); // 修复构造函数传参
        this.matchList = matches;
    }

    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        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(String.valueOf(matchList.get(position).getResultHome())); // 数值转字符串避免崩溃
        away_result.setText(String.valueOf(matchList.get(position).getResultAway())); // 数值转字符串避免崩溃
        // 注意如果group字段没有赋值，这里设置会显示空值，无对应字段可以注释此行或者设置默认值
        // group.setText(matchList.get(position).getGroup());
        date.setText(matchList.get(position).getDate());

        return convertView;
    }
}

内容的提问来源于stack exchange，提问作者user3484121