Question

I'm getting this error

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String org.json.JSONObject.getString(java.lang.String)' on a null object reference at com.example.registerapp.RegisterActivity$1.onClick(RegisterActivity.java:65)

Here is my registerActivity.java class

public class RegisterActivity extends Activity {
Button btnRegister;
Button btnLinkToLogin;
EditText inputFullName;
EditText inputEmail;
EditText inputPassword;

// JSON Response node names
private static String KEY_SUCCESS = "success";
private static String KEY_ERROR = "error";
private static String KEY_ERROR_MSG = "error_msg";
private static String KEY_UID = "uid";
private static String KEY_NAME = "name";
private static String KEY_EMAIL = "email";
private static String KEY_CREATED_AT = "created_at";

@Override
public void onCreate(Bundle savedInstanceState) {

    int SDK_INT = android.os.Build.VERSION.SDK_INT;
    if (SDK_INT > 8) 
    {
        StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder()
                .permitAll().build();
        StrictMode.setThreadPolicy(policy);
        super.onCreate(savedInstanceState);
        setContentView(R.layout.register);
    // Importing all assets like buttons, text fields
    inputFullName = (EditText) findViewById(R.id.name);
    inputEmail = (EditText) findViewById(R.id.email);
    inputPassword = (EditText) findViewById(R.id.password);
    btnRegister = (Button) findViewById(R.id.btnRegister);
    btnLinkToLogin = (Button) findViewById(R.id.btnLinkToLoginScreen);

    // Register Button Click event

btnRegister.setOnClickListener(new View.OnClickListener() {         
        public void onClick(View view) {
            String name = inputFullName.getText().toString();
            String email = inputEmail.getText().toString();
            String password = inputPassword.getText().toString();
            UserFunctions userFunction = new UserFunctions();
            JSONObject json = userFunction.registerUser(name, email, password);

            // check for login response
            try {
                if (json.getString(KEY_SUCCESS) != null) {
                    String res = json.getString(KEY_SUCCESS); 
                    if(Integer.parseInt(res) == 1){
                        // user successfully registred
                        // Store user details in SQLite Database
                        DatabaseHandler db = new DatabaseHandler(getApplicationContext());
                        JSONObject json_user = json.getJSONObject("user");

                        // Clear all previous data in database
                        userFunction.logoutUser(getApplicationContext());
                        db.addUser(json_user.getString(KEY_NAME), json_user.getString(KEY_EMAIL), json.getString(KEY_UID), json_user.getString(KEY_CREATED_AT));                        
                        // Launch Dashboard Screen
                        Intent dashboard = new Intent(getApplicationContext(), MainActivity.class);
                        // Close all views before launching Dashboard
                        dashboard.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                        startActivity(dashboard);
                        // Close Registration Screen
                        finish();
                    }else{
                        // Error in registration
                    }
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }
        }
    });

    // Link to Login Screen
    btnLinkToLogin.setOnClickListener(new View.OnClickListener() {

        public void onClick(View view) {
            Intent i = new Intent(getApplicationContext(),
                    LoginActivity.class);
            startActivity(i);
            // Close Registration View
            finish();
        }
    });
}}

}

and this is the userfunctions.java class

public class UserFunctions {

private JSONParser jsonParser;

// Testing in localhost using wamp or xampp 
// use http://10.0.2.2/ to connect to your localhost ie http://localhost/
private static String loginURL = "http://10.0.2.2/login/";
private static String registerURL = "http://10.0.2.2/login/";

private static String login_tag = "login";
private static String register_tag = "register";

// constructor
public UserFunctions(){
    jsonParser = new JSONParser();
}

/**
 * function make Login Request
 * @param email
 * @param password
 * */
public JSONObject loginUser(String email, String password){
    // Building Parameters
    List params = new ArrayList();
    params.add(new BasicNameValuePair("tag", login_tag));
    params.add(new BasicNameValuePair("email", email));
    params.add(new BasicNameValuePair("password", password));
    JSONObject json = jsonParser.getJSONFromUrl(loginURL, params);
    // return json
    // Log.e(“JSON”, json.toString());
    return json;
}


 /**
 * function make Login Request
 * @param name
 * @param email
 * @param password
 * */
public JSONObject registerUser(String name, String email, String password){
    // Building Parameters
    List params = new ArrayList();
    params.add(new BasicNameValuePair("tag", register_tag));
    params.add(new BasicNameValuePair("name", name));
    params.add(new BasicNameValuePair("email", email));
    params.add(new BasicNameValuePair("password", password));

    // getting JSON Object
    JSONObject json = jsonParser.getJSONFromUrl(registerURL, params);
    // return json
    return json;
}

/**
 * Function get Login status
 * */
public boolean isUserLoggedIn(Context context){
    DatabaseHandler db = new DatabaseHandler(context);
    int count = db.getRowCount();
    if(count > 0){
        // user logged in
        return true;
    }
    return false;
}

/**
 * Function to logout user
 * Reset Database
 * */
public boolean logoutUser(Context context){
    DatabaseHandler db = new DatabaseHandler(context);
    db.resetTables();
    return true;
}

}

and here is the php script

  if (isset($_POST['tag']) && $_POST['tag'] != '') {
// get tag
$tag = $_POST['tag'];

// include db handler
require_once 'include/DB_Functions.php';
$db = new DB_Functions();

// response Array
$response = array("tag" => $tag, “success” => 0, “error” => 0);

// check for tag type
if ($tag == 'login') {
    // Request type is check Login
    $email = $_POST['email'];
    $password = $_POST['password'];

    // check for user
    $user = $db->getUserByEmailAndPassword($email, $password);
    if ($user != false) {
        // user found
         $response[“success”] = 1;
        $response["uid"] = $user["unique_id"];
        $response["user"]["name"] = $user["name"];
        $response["user"]["email"] = $user["email"];
        $response["user"]["created_at"] = $user["created_at"];
        $response["user"]["updated_at"] = $user["updated_at"];
        echo json_encode($response);
    } else {
        // user not found
        // echo json with error = 1
        $response[“error”] = 1;
        $response["error_msg"] = "Incorrect email or password!";
        echo json_encode($response);
    }
} else if ($tag == 'register') {
    // Request type is Register new user
    $name = $_POST['name'];
    $email = $_POST['email'];
    $password = $_POST['password'];

    // check if user is already existed
    if ($db->isUserExisted($email)) {
        // user is already existed - error response
         $response[“error”] = 2;
        $response["error_msg"] = "User already existed";
        echo json_encode($response);
    } else {
        // store user
        $user = $db->storeUser($name, $email, $password);
        if ($user) {
            // user stored successfully
             $response[“success”] = 1;
            $response["uid"] = $user["unique_id"];
            $response["user"]["name"] = $user["name"];
            $response["user"]["email"] = $user["email"];
            $response["user"]["created_at"] = $user["created_at"];
            $response["user"]["updated_at"] = $user["updated_at"];
            echo json_encode($response);
        } else {
            // user failed to store
             $response[“error”] = 1;
            $response["error_msg"] = "Error occured in Registartion";
            echo json_encode($response);
        }
    }
} else {
    echo "Unknow 'tag' value. It should be either 'login' or 'register'";

}
 } else {
echo "Required parameter 'tag' is missing!";

  }
  ?>

hope you will help me. Thank you :)

Answer 1

on java function registerUser I would System.out the name, email, and password to make sure they are being sent over correctly as params.
add a try catch in this registerUser function

public JSONObject registerUser(String name, String email, String password){
    try {
        // Building Parameters
        List params = new ArrayList();
        params.add(new BasicNameValuePair("tag", register_tag));
        params.add(new BasicNameValuePair("name", name));
        params.add(new BasicNameValuePair("email", email));
        params.add(new BasicNameValuePair("password", password));

       JSONObject json = jsonParser.getJSONFromUrl(registerURL, params);
       return json;

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


}

check your db to see if your user actually exists.
make sure your PHP doesn't have different quotation marks ( " and “ )
retry everything and check your logs... google getting a json object from php to java and how to read java / php logs if you don't know how.

take it easy hope that leads you to right path.

Attempt to invoke virtual method &#39;java.lang.String org.json.JSONObject.getString(java.lang.String)&#39; on a null object reference

1 个答案:

Attempt to invoke virtual method 'java.lang.String org.json.JSONObject.getString(java.lang.String)' on a null object reference