使用Volley+JSON连接SQL Server到Android Studio遇连接错误及图片显示求助

Hey there! Let's break down and fix your two core issues: the connection error stopping your ListView from loading data, and displaying varbinary(MAX) images from SQL Server in your ListView.

1. Troubleshooting the "Error in connection" Issue #

First, let's get your data loading working step by step:

Step 1: Verify Server & URL Reachability #

• Double-check that your URL http://myIP-Here/MSSQL/client.php works directly in your phone's browser. If it doesn't:
  • Replace myIP-Here with your computer's local network IP (e.g., 192.168.1.100) instead of localhost or 127.0.0.1 (your phone can't reach your computer's loopback address).
  • Ensure your computer and phone are on the same WiFi network.
  • Confirm the PHP file path is correct (no typos in /MSSQL/client.php).

Step 2: Add Critical Network Permissions #

Make sure your AndroidManifest.xml includes the internet permission (Volley can't send requests without this):

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

For Android 9+, you also need to allow cleartext HTTP (if you're not using HTTPS):

<application
    ...
    android:usesCleartextTraffic="true">
    ...
</application>

Step 3: Fix Adapter Initialization Order #

Your current code sets the adapter before adding data to rowItems—so the adapter never sees the new data. Here's the corrected subject() method:

public void subject(){
    String url = "http://your-local-ip/MSSQL/client.php";
    StringRequest stringRequest = new StringRequest(Request.Method.GET, url,
        new Response.Listener<String>() {
            @Override
            public void onResponse(String response) {
                Log.d("Raw Response", response);
                try {
                    JSONObject jsonObj = new JSONObject(response);
                    peoples = jsonObj.getJSONArray("json");
                    mylistview = findViewById(R.id.list);
                    
                    // Clear old data first
                    rowItems.clear();
                    
                    // Populate data into rowItems
                    for(int i=0;i<peoples.length();i++) {
                        JSONObject c = peoples.getJSONObject(i);
                        RowItem goodsItems = new RowItem();
                        goodsItems.setItem_id(c.getInt("item_id"));
                        goodsItems.setItem_name(c.getString("item_name"));
                        rowItems.add(goodsItems);
                    }
                    
                    // Initialize adapter AFTER data is ready
                    adapter = new CustomAdapter(MainActivity.this, rowItems);
                    mylistview.setAdapter(adapter);
                    mylistview.setOnItemClickListener(MainActivity.this);
                    
                } catch (JSONException e) {
                    e.printStackTrace();
                    Toast.makeText(MainActivity.this, "JSON Parse Error: " + e.getMessage(), Toast.LENGTH_LONG).show();
                }
            }
        }, 
        new Response.ErrorListener() {
            public void onErrorResponse(VolleyError error) {
                // Get detailed error info instead of generic message
                String errorMsg = "";
                if (error instanceof NetworkError) {
                    errorMsg = "Check your WiFi/data connection";
                } else if (error instanceof ServerError) {
                    errorMsg = "Server error - check PHP logs";
                    // Print server's error response (if available)
                    if (error.networkResponse != null) {
                        String serverError = new String(error.networkResponse.data);
                        Log.e("Server Error", serverError);
                    }
                } else if (error instanceof TimeoutError) {
                    errorMsg = "Request timed out - server might be slow";
                }
                Toast.makeText(MainActivity.this, errorMsg, Toast.LENGTH_LONG).show();
                Log.e("Volley Error", errorMsg, error);
            }
        }){
    @Override
    protected Map<String, String> getParams() {
        Map<String, String> params = new HashMap<>();
        return params;
    }
};
RequestQueue requestQueue = Volley.newRequestQueue(MainActivity.this);
requestQueue.add(stringRequest);
}

Step 4: Validate PHP JSON Output #

Ensure your client.php returns only valid JSON (no extra echo statements or HTML). A valid response should look like:

{"json":[{"item_id":1,"item_name":"Product 1"},{"item_id":2,"item_name":"Product 2"}]}

Use an online JSON validator to check the output.

2. Displaying varbinary(MAX) Images from SQL Server #

There are two reliable ways to handle this—pick the one that fits your image size:

Option 1: Base64 String in JSON (For Small Images) #

1. Modify your PHP code to convert varbinary data to a Base64 string:

   // Assuming your image column is named 'item_image'
   $item_image = base64_encode($row['item_image']);
   // Add this to your JSON output array
   

2. Update your RowItem class to hold the Base64 string:

   public class RowItem {
       public int item_id;
       public String item_name;
       public String item_image_base64; // New field
   
       public RowItem() {}
   
       // Getters and setters
       public int getItem_id() { return item_id; }
       public void setItem_id(int item_id) { this.item_id = item_id; }
       public String getItem_name() { return item_name; }
       public void setItem_name(String item_name) { this.item_name = item_name; }
       public String getItem_image_base64() { return item_image_base64; }
       public void setItem_image_base64(String item_image_base64) { this.item_image_base64 = item_image_base64; }
   }
   

3. Parse the Base64 field in your onResponse method:

   goodsItems.setItem_image_base64(c.getString("item_image"));
   

4. Load the image in CustomAdapter:

   @Override
   public View getView(int position, View convertView, ViewGroup parent) {
       if (inflater == null)
           inflater = (LayoutInflater) activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
       if (convertView == null)
           convertView = inflater.inflate(R.layout.list_item, null);
   
       TextView item_id = convertView.findViewById(R.id.item_id);
       TextView item_name = convertView.findViewById(R.id.item_name);
       ImageView image = convertView.findViewById(R.id.imView);
   
       final RowItem m = rowItems.get(position);
       item_id.setText(String.valueOf(m.getItem_id()));
       item_name.setText(m.getItem_name());
   
       // Load Base64 image
       if (m.getItem_image_base64() != null && !m.getItem_image_base64().isEmpty()) {
           byte[] decodedBytes = Base64.decode(m.getItem_image_base64(), Base64.DEFAULT);
           Bitmap bitmap = BitmapFactory.decodeByteArray(decodedBytes, 0, decodedBytes.length);
           image.setImageBitmap(bitmap);
       } else {
           // Set a default placeholder image
           image.setImageResource(R.drawable.default_image);
       }
   
       return convertView;
   }
   

Option 2: Separate Image Endpoint (For Large Images) #

This is better for bigger images since Base64 adds overhead.

1. Create a PHP endpoint (e.g., get_image.php) to return the image stream:

   <?php
   $item_id = $_GET['item_id'];
   // Connect to SQL Server, query the item_image column for this item_id
   header("Content-Type: image/jpeg"); // Adjust based on your image type (png, etc.)
   echo $row['item_image'];
   ?>
   

2. Use Picasso (a popular image loading library) to load the image in your adapter:
   • Add Picasso to your app-level build.gradle:

     implementation 'com.squareup.picasso:picasso:2.71828'
     

   • Update your CustomAdapter's getView method:

     @Override
     public View getView(int position, View convertView, ViewGroup parent) {
         // ... existing code ...
         ImageView image = convertView.findViewById(R.id.imView);
         final RowItem m = rowItems.get(position);
     
         // Load image from the endpoint
         Picasso.with(activity)
             .load("http://your-local-ip/MSSQL/get_image.php?item_id=" + m.getItem_id())
             .resize(300, 300)
             .placeholder(R.drawable.loading_image)
             .error(R.drawable.error_image)
             .into(image);
     
         return convertView;
     }
     

内容的提问来源于stack exchange，提问作者Emily