php - 尝试初始化 JSONObject 时出现 Android ResponseListener JSON 错误

Question

我正在开发一个应用程序，它将存储到 MySQL 数据库并从中读取数据。目前，我能够成功获取 1 行，但是当我尝试获取 多行 时，它不起作用。当我尝试在 ResponseListener 中初始化 JSONObject(我在给出 error 的行上方添加注释)时，代码中断。为了与我的数据库通信，我使用了 volley 库。

这是错误输出:

08-23 17:27:12.853 22689-22689/com.example.www.myapp W/System.err:     at org.json.JSONTokener.syntaxError(JSONTokener.java:449)
08-23 17:27:12.853 22689-22689/com.example.www.myapp W/System.err:     at org.json.JSONTokener.nextValue(JSONTokener.java:97)
08-23 17:27:12.853 22689-22689/com.example.www.myapp W/System.err:     at org.json.JSONObject.<init>(JSONObject.java:156)
08-23 17:27:12.853 22689-22689/com.example.www.myapp W/System.err:     at org.json.JSONObject.<init>(JSONObject.java:173)
08-23 17:27:12.853 22689-22689/com.example.www.myapp W/System.err:     at com.example.www.myapp.DataActivity$2.onResponse(DataActivity.java:235)
08-23 17:27:12.853 22689-22689/com.example.www.myapp W/System.err:     at com.example.www.myapp.DataActivity$2.onResponse(DataActivity.java:229)
08-23 17:27:12.853 22689-22689/com.example.www.myapp W/System.err:     at com.android.volley.toolbox.StringRequest.deliverResponse(StringRequest.java:60)
08-23 17:27:12.853 22689-22689/com.example.www.myapp W/System.err:     at com.android.volley.toolbox.StringRequest.deliverResponse(StringRequest.java:30)
08-23 17:27:12.853 22689-22689/com.example.www.myapp W/System.err:     at com.android.volley.ExecutorDelivery$ResponseDeliveryRunnable.run(ExecutorDelivery.java:99)
08-23 17:27:12.853 22689-22689/com.example.www.myapp W/System.err:     at android.os.Handler.handleCallback(Handler.java:739)
08-23 17:27:12.853 22689-22689/com.example.www.myapp W/System.err:     at android.os.Handler.dispatchMessage(Handler.java:95)
08-23 17:27:12.853 22689-22689/com.example.www.myapp W/System.err:     at android.os.Looper.loop(Looper.java:158)
08-23 17:27:12.853 22689-22689/com.example.www.myapp W/System.err:     at android.app.ActivityThread.main(ActivityThread.java:7229)
08-23 17:27:12.853 22689-22689/com.example.www.myapp W/System.err:     at java.lang.reflect.Method.invoke(Native Method)
08-23 17:27:12.853 22689-22689/com.example.www.myapp W/System.err:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
08-23 17:27:12.853 22689-22689/com.example.www.myapp W/System.err:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)

到目前为止，这是我的代码:

响应监听器

private void getDataFromExternalDB(final String startid){
        id = Integer.parseInt(startid);
Response.Listener<String> responseListener = new Response.Listener<String>() {
            @Override
            public void onResponse(String response) {
                try {
                    //I get the error at the following line
                    JSONObject jsonResponse = new JSONObject(response);

                    while (jsonResponse.getJSONObject(""+id) != null){
                       jsonResponse.getJSONObject(""+id);
                        int user_id = jsonResponse.getInt("user_id");
                        String username = jsonResponse.getString("username");

                        Log.d("getDataFromExternalDB","user_id="+user_id + " username="+username);

                        id++;
                    }

                } catch (JSONException e) {
                    e.printStackTrace();
                }
            }
        };

        DataRequest dataRequest = new DataRequest (startid, responseListener);
        RequestQueue queue = Volley.newRequestQueue(DataActivity.this);
        queue.add(dataRequest );
}

DataRequest.java

 import com.android.volley.Response;
import com.android.volley.toolbox.StringRequest;

import java.util.HashMap;
import java.util.Map;

public class DataRequest extends StringRequest {
    private static final String DATA_REQUEST_URL = "http://192.168.178.17/getData.php";
    private Map<String, String> params;

    public DataRequest (String startid, Response.Listener<String> listener) {
        super(Method.POST, DATA_REQUEST_URL, listener, null);
        params = new HashMap<>();
        params.put("startid", startid);

    }

    @Override
    public Map<String, String> getParams() {
        return params;
    }
}

getData.php

 <?php

    $connect = mysqli_connect("localhost", "root", "pass", "db");

    $startid = $_POST["startid"];   

    function getData() {
        global $connect, $startid;
        $result = $connect->query("SELECT * FROM users WHERE user_id > " . $startid );
        $responses = array();
        $response = array();
        if ($result->num_rows > 0) {
            // output data of each row
            while($row = $result->fetch_assoc()) {

                $response["user_id"] = $row["user_id"]; 
                $response["username"] = $row["username"];


                $responses["" . $row["user_id"]]=$response;
            }
            echo json_encode($responses);
        }else {
            echo "0 results";
        } 

    }

    getData();  

    $connect->close();  

?>

Answer 1

请得到类似的回复

尝试{

                JSONObject json;
JSONArray jsonArray = null;
            if (json != null) {

                jsonArray = json.getJSONArray("mainTags");
                for (int i = 0; i < jsonArray.length(); i++) {
                    JSONObject c = jsonArray.getJSONObject(i);

                Sting name = c.getString("name");
                    Log.d("namee", name);


                }


            } else {
                // Log.d("Server Unreachable",
                // "Unable to Perform Your request.Server Is Unreachable! Please Try Later.");
            }
        } catch (JSONException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }