org.json.JSONException：类型java.lang.String的值连接无法转换为JSONArray

Question

我在android studio上尝试用户注册和登录活动。一切都很好。我的PHP脚本在输入数据或通过网页登录时响应。但是在Android应用程序中做同样的事情。我没有收到服务器响应字符串。但是，数据已成功添加到WAMP localhost服务器上的数据库中。

当我点击按钮时，我总是收到此错误;添加了数据，但没有响应，登录也一样。我的代码是：

    public class RegisterActivity extends AppCompatActivity {
    EditText etname,etusername,etemail,etpassword,etcnpassword;
    Button bregister;
    TextView signin;
    String name,username,email,password,cnpassword;
    AlertDialog.Builder builder;
    String reg_url="http://192.168.1.4/Register1.php";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_register);

    etname = (EditText) findViewById(R.id.name);
    etusername=(EditText) findViewById(R.id.username);
    etemail = (EditText) findViewById(R.id.email);
    etpassword = (EditText) findViewById(R.id.password);
    etcnpassword = (EditText) findViewById(R.id.cn_password);
    builder = new AlertDialog.Builder(RegisterActivity.this);

    bregister = (Button) findViewById(R.id.register_button);
    signin = (TextView) findViewById(R.id.tv_signin);

    signin.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent login = new Intent(RegisterActivity.this,      MainActivity.class);
            RegisterActivity.this.startActivity(login);
        }
    });

    bregister.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            name = etname.getText().toString();
            username=etusername.getText().toString();
            email = etemail.getText().toString();
            password = etpassword.getText().toString();
            cnpassword = etcnpassword.getText().toString();
            if (name.equals("") || username.equals("")||email.equals("") || password.equals("") || cnpassword.equals("")) {
                builder.setTitle("Error");
                builder.setMessage("Please fill all the fields");
                displayAlert("input_error");
            }
            else
            {
                if(!(password.equals(cnpassword))){
                    builder.setTitle("Error");
                    builder.setMessage("Passwords not matching.");
                    displayAlert("input_error");
                }
                else if(password.equals(cnpassword)){
                    StringRequest stringrequest=new StringRequest(Request.Method.POST, reg_url,
                            new Response.Listener<String>() {
                                @Override
                                public void onResponse(String response) {

                                    try {
                                        JSONArray jsonArray = new JSONArray(response);
                                        JSONObject jsonObject=jsonArray.getJSONObject(0);
                                        String code=jsonObject.getString("code");
                                        String message=jsonObject.getString("message");
                                        builder.setTitle("Server Response");
                                        builder.setMessage(message);
                                        displayAlert(code);
                                    } catch (JSONException e) {
                                        e.printStackTrace();
                                    }
                                }
                            }, new Response.ErrorListener() {
                        @Override
                        public void onErrorResponse(VolleyError error) {

                        }
                    }){
                        @Override
                        protected Map<String, String> getParams() throws AuthFailureError {
                            Map<String, String> params=new HashMap<String, String>();
                            params.put("name",name);
                            params.put("username",username);
                            params.put("email",email);
                            params.put("password",password);
                            return params;
                        }
                    };
                    mysingleton.getInstance(RegisterActivity.this).addtorequestqueue(stringrequest);
                }
                else
                    ;
            }
        }

    });
}

public void displayAlert(final String code){
    builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
            if (code.equals("input_error")) {
                etpassword.setText("");
                etcnpassword.setText("");
            } else if (code.equals("Registration success")) {
                finish();
             /*   Intent intent=new Intent(RegisterActivity.this,LoginActivity.class);
                startActivity(intent);*/
            } else if (code.equals("Registration failed")) {
                etname.setText("");
                etusername.setText("");
                etemail.setText("");
                etpassword.setText("");
                etcnpassword.setText("");
            }
        }
    });
    AlertDialog alertDialog=builder.create();
    alertDialog.show();
}
} 

php代码是 -

    <?php
require "init.php";
$name=$_POST["name"];
$username=$_POST["username"];
$email=$_POST["email"];
$password=$_POST["password"];

$sql="select * from login where email like '".$email."'; ";

$result=mysqli_query($con,$sql);
$response=array();

if(mysqli_num_rows($result)>0)
{
$code="Registration failed";
$message="User already exist";
array_push($response,array($code,$message));
echo json_encode($response);
}
else
{
$sql="insert into login(name,username,email,password) values('".$name."','".$username."','".$email."','".$password."');";
$result=mysqli_query($con,$sql);
$code="Registration success";
$message="Thank you for registering with us. Now you can log in.";
array_push($response,array($code,$message));
echo json_encode($response);
}

mysqli_close($con);

?>

错误是什么以及如何解决？