Spinner选中项无法刷新ListView，需基于选项值构建URL获取JSON更新列表

Let's break down how to fix your issue step by step, including a reusable method to fetch data from any URL:

1. Core Setup in Your Fragment #

First, ensure you have the necessary views and variables initialized in your Fragment's onCreateView:

public class YourFragment extends Fragment {
    private Spinner spinner;
    private ListView listView;
    private List<YourDataModel> dataList;
    private YourCustomAdapter listAdapter;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.your_fragment_layout, container, false);

        // Initialize views
        spinner = view.findViewById(R.id.your_spinner_id);
        listView = view.findViewById(R.id.your_listview_id);

        // Initialize data storage and adapter
        dataList = new ArrayList<>();
        listAdapter = new YourCustomAdapter(getContext(), dataList);
        listView.setAdapter(listAdapter);

        // Set up Spinner with options and selection listener
        setupSpinner();

        // Initial data load with default URL
        fetchDataFromUrl("https://your-default-api-url.com/data");

        return view;
    }
}

2. Spinner Selection Listener #

Add a listener to trigger data refresh when a Spinner item is selected:

private void setupSpinner() {
    // Replace with your actual Spinner options
    List<String> spinnerOptions = Arrays.asList("Option 1", "Option 2", "Option 3");
    
    ArrayAdapter<String> spinnerAdapter = new ArrayAdapter<>(getContext(),
            android.R.layout.simple_spinner_item, spinnerOptions);
    spinnerAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
    spinner.setAdapter(spinnerAdapter);

    spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            String selectedValue = parent.getItemAtPosition(position).toString();
            // Build your dynamic URL using the selected value
            String dynamicUrl = "https://your-api-base-url.com/data?filter=" + selectedValue;
            // Fetch new data with the updated URL
            fetchDataFromUrl(dynamicUrl);
        }

        @Override
        public void onNothingSelected(AdapterView<?> parent) {
            // Optional: Handle empty selection case
        }
    });
}

3. Reusable Data Fetch Method #

Create a method that takes a URL, fetches JSON data, parses it, and updates the ListView:

private void fetchDataFromUrl(String url) {
    new FetchDataTask().execute(url);
}

// AsyncTask to handle background network operations (note: AsyncTask is deprecated in API 30+, consider Coroutines/RxJava for newer apps)
private class FetchDataTask extends AsyncTask<String, Void, List<YourDataModel>> {

    @Override
    protected List<YourDataModel> doInBackground(String... urls) {
        String targetUrl = urls[0];
        List<YourDataModel> newData = new ArrayList<>();

        try {
            // Establish connection and read JSON response
            URL apiUrl = new URL(targetUrl);
            HttpURLConnection connection = (HttpURLConnection) apiUrl.openConnection();
            connection.setRequestMethod("GET");

            BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
            StringBuilder responseBuilder = new StringBuilder();
            String line;

            while ((line = reader.readLine()) != null) {
                responseBuilder.append(line);
            }

            reader.close();
            connection.disconnect();

            // Parse JSON into your data model (adjust based on your JSON structure)
            String jsonResponse = responseBuilder.toString();
            JSONObject rootObj = new JSONObject(jsonResponse);
            JSONArray dataArray = rootObj.getJSONArray("your_data_array_key");

            for (int i = 0; i < dataArray.length(); i++) {
                JSONObject itemObj = dataArray.getJSONObject(i);
                YourDataModel item = new YourDataModel();
                item.setId(itemObj.getInt("id"));
                item.setTitle(itemObj.getString("title"));
                // Add other fields from your JSON
                newData.add(item);
            }

        } catch (IOException | JSONException e) {
            e.printStackTrace();
            // Show error message to user on UI thread
            getActivity().runOnUiThread(() -> 
                Toast.makeText(getContext(), "Failed to load data", Toast.LENGTH_SHORT).show()
            );
        }

        return newData;
    }

    @Override
    protected void onPostExecute(List<YourDataModel> result) {
        // Update data list and refresh ListView
        dataList.clear();
        dataList.addAll(result);
        listAdapter.notifyDataSetChanged();
    }
}

4. Data Model and Custom Adapter #

Define your data model and adapter to display the data in the ListView:

// Your data model class (match your JSON structure)
public static class YourDataModel {
    private int id;
    private String title;

    // Getters and Setters
    public int getId() { return id; }
    public void setId(int id) { this.id = id; }
    public String getTitle() { return title; }
    public void setTitle(String title) { this.title = title; }
}

// Custom adapter for ListView
public static class YourCustomAdapter extends ArrayAdapter<YourDataModel> {
    public YourCustomAdapter(Context context, List<YourDataModel> items) {
        super(context, 0, items);
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        // Reuse existing view if available
        if (convertView == null) {
            convertView = LayoutInflater.from(getContext())
                    .inflate(R.layout.your_list_item_layout, parent, false);
        }

        YourDataModel item = getItem(position);

        // Bind data to views in your list item layout
        TextView idTv = convertView.findViewById(R.id.item_id);
        TextView titleTv = convertView.findViewById(R.id.item_title);

        idTv.setText(String.valueOf(item.getId()));
        titleTv.setText(item.getTitle());

        return convertView;
    }
}

5. Required Permission #

Add the internet permission to your AndroidManifest.xml:

<uses-permission android:name="android.permission.INTERNET" />

Key Notes #

• AsyncTask Deprecation: For Android API 30+, consider using Kotlin Coroutines, RxJava, or ExecutorService instead of AsyncTask for background operations.
• JSON Parsing: Adjust the parsing logic to match your actual JSON response structure (e.g., different array keys, field names).
• Error Handling: Expand the error handling to cover cases like no internet connection, invalid URL, or empty responses.

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