Android Volley获取带键名JSON数组元素方法求助

Let's get your Volley JSON array retrieval working—here's what's going wrong and how to fix it step by step.

1. Clarify the JSON Response Structure #

You mentioned the JSON has key names—this means the response is likely a JSON Object that contains your target array, not a root-level JSON Array. For example, a valid response might look like this (I fixed the comma typo in your example, since valid JSON uses dots for decimal separators):

{
  "values": [1579.39734, 2523679.59824966966, 4327116]
}

If you're using JsonArrayRequest but the root is a JSON Object, that's a major reason your code is failing. Let's adjust the request type accordingly.

2. Correct Volley Request Implementation #

Here are complete, working examples for both possible response structures:

Case A: Response is a root-level JSON Array #

If the server returns exactly [1579.39734, 2523679.59824966966, 4327116] (no outer object), use JsonArrayRequest with proper error handling:

private void loadJsonArray() {
    // Initialize progress dialog (finish your incomplete code here)
    ProgressDialog pDialog = new ProgressDialog(this);
    pDialog.setMessage("Loading...");
    pDialog.show();

    JsonArrayRequest jsArrayRequest = new JsonArrayRequest(
            Request.Method.POST, // Switch to GET if the server doesn't require POST
            new_url,
            null, // Add a JSONObject here if POST requires parameters
            new Response.Listener<JSONArray>() {
                @Override
                public void onResponse(JSONArray response) {
                    pDialog.dismiss();
                    double[] value = new double[response.length()];
                    try {
                        // Extract each element from the array
                        for (int i = 0; i < response.length(); i++) {
                            value[i] = response.getDouble(i);
                        }
                        // Use your value array (e.g., update UI or process data)
                        Log.d("Volley", "Loaded values: " + Arrays.toString(value));
                    } catch (JSONException e) {
                        e.printStackTrace();
                        Toast.makeText(getApplicationContext(), "Failed to parse JSON", Toast.LENGTH_SHORT).show();
                    }
                }
            },
            new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {
                    pDialog.dismiss();
                    // Debug the error to identify the root cause
                    String errorMessage;
                    if (error instanceof NetworkError) {
                        errorMessage = "Network error! Check your internet connection.";
                    } else if (error instanceof ParseError) {
                        errorMessage = "Invalid JSON response from server.";
                    } else if (error instanceof ServerError) {
                        errorMessage = "Server error. Try again later.";
                    } else {
                        errorMessage = error.getMessage() != null ? error.getMessage() : "Unknown error";
                    }
                    Toast.makeText(getApplicationContext(), errorMessage, Toast.LENGTH_SHORT).show();
                    Log.e("Volley Error", error.toString());
                }
            });

    // Add the request to Volley's request queue
    Volley.newRequestQueue(this).add(jsArrayRequest);
}

Case B: Response is a JSON Object containing the array #

If the response has a key (like "values"), use JsonObjectRequest instead to access the nested array:

private void loadJsonArray() {
    ProgressDialog pDialog = new ProgressDialog(this);
    pDialog.setMessage("Loading...");
    pDialog.show();

    JsonObjectRequest jsObjRequest = new JsonObjectRequest(
            Request.Method.POST,
            new_url,
            null,
            new Response.Listener<JSONObject>() {
                @Override
                public void onResponse(JSONObject response) {
                    pDialog.dismiss();
                    try {
                        // Retrieve the array using its key name (replace "values" with your actual key)
                        JSONArray jsonArray = response.getJSONArray("values");
                        double[] value = new double[jsonArray.length()];
                        for (int i = 0; i < jsonArray.length(); i++) {
                            value[i] = jsonArray.getDouble(i);
                        }
                        // Use your value array
                        Log.d("Volley", "Loaded values: " + Arrays.toString(value));
                    } catch (JSONException e) {
                        e.printStackTrace();
                        Toast.makeText(getApplicationContext(), "Failed to parse JSON", Toast.LENGTH_SHORT).show();
                    }
                }
            },
            new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {
                    pDialog.dismiss();
                    // Same error handling as above
                    String errorMessage;
                    if (error instanceof NetworkError) {
                        errorMessage = "Network error! Check your internet connection.";
                    } else if (error instanceof ParseError) {
                        errorMessage = "Invalid JSON response from server.";
                    } else if (error instanceof ServerError) {
                        errorMessage = "Server error. Try again later.";
                    } else {
                        errorMessage = error.getMessage() != null ? error.getMessage() : "Unknown error";
                    }
                    Toast.makeText(getApplicationContext(), errorMessage, Toast.LENGTH_SHORT).show();
                    Log.e("Volley Error", error.toString());
                }
            });

    Volley.newRequestQueue(this).add(jsObjRequest);
}

3. Key Fixes for Your Original Code #

• Added Error Handling: The missing ErrorListener was probably hiding why your code failed—now you'll get clear feedback on network issues, invalid JSON, or server errors.
• Proper JSON Parsing: Wrapped parsing in a try-catch block to handle exceptions like invalid indices or wrong data types.
• Handled Both Response Structures: Covered both root array and object-containing-array cases since you mentioned "key names" in the response.
• Cleaned Up Progress Dialog: Ensured the dialog is dismissed in both success and error cases to avoid memory leaks.

4. Additional Tips #

• Verify the JSON response using tools like Postman or curl to confirm its structure and validity.
• If using POST, make sure you're sending any required parameters (replace null with a JSONObject of key-value pairs if needed).
• Ensure your app has the INTERNET permission in AndroidManifest.xml:

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

内容的提问来源于stack exchange，提问作者Kah Hao