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Passing Object from Class to Windows Form

I've got four main files in play here: Form 1, which is called frmLogin, Form2, which is called frmUserHome, a class called DbConnector.cs and a class called BankAccount.cs
The program works as follows: Form1 calls method from DBConnector -> DB Connector method fills an object and it's variables which is instantiated in DBConnector. This object is of class BankAccount.cs
Then, after the method finishes and if successful, Form1 instantiates Form2 and it opens. In form2 is where I want to access the object that was created in the DBconnector class. How do I do this? I've tried instantiating new objects of BankAccount.cs in there, I've tried all these different constructor stuff I've seen on here. Nothing seems to be working.
For reference: the object is populated when it runs in Dbconnector. However, when I try to receive data when I use it in Form2, all of the fields are NULL.
I've made countless adjustments from reading different posts on here so the code is rightfully a mess now and probably extremely unorganised.
Here's the main portions of my code below:
Form1
namespace BankingSystem
{
public partial class frmLogIn : Form
{
public BankAccount myBankAccount = new BankAccount();
dbConnector newConnector;
public frmLogIn()
{
InitializeComponent();
timerMain.Enabled = true;
timerMain.Start();
}
private void btnLogIn_Click(object sender, EventArgs e)
{
try
{
newConnector.CheckDetailsLogin(accountNumTextBox.Text, pinNumTextBox.Text);
frmUserHome UserHome = new frmUserHome();
MessageBox.Show("Success! Happy Banking!");
UserHome.ShowDialog();
}
catch
{
MessageBox.Show("Failed - incorrect login details.");
}
}
}
}
DBConnector Class:
namespace BankingSystem
{
public class dbConnector
{
Boolean isCorrect = false;
private static SQLiteConnection sqlconnConnection;
public BankAccount myBankAccount = new BankAccount();
public DataSet myAppDataSet = new DataSet(); // created for you to use and push data into
public dbConnector(string strFilePath)
{
try
{
sqlconnConnection = new SQLiteConnection("Data Source=" + strFilePath);
}
catch (Exception ex)
{
throw new Exception("DbConnector initialisation unsuccessful:\n" + ex.Message);
}
}
public void CheckDetailsLogin(string strAccno, string strPin)
{
// this is where check ou the boiler plate code and adjst to my APP.
try
{
DataTable dtUser = new DataTable();
sqlconnConnection.Open();
string strQuery2 = #"SELECT * FROM Accounts WHERE Account_Number='"+ strAccno +"' AND PIN='"+ strPin +"';"; // example of a parametrised SQL statement.
SQLiteCommand sqlcomCommand2 = new SQLiteCommand(strQuery2, sqlconnConnection);
SQLiteDataAdapter sqldatadptAdapter = new SQLiteDataAdapter(sqlcomCommand2); // local SQL data Adaptor
try
{
sqldatadptAdapter.Fill(dtUser);
}
catch (Exception ex)
{
// Exception will the "thrown"/Raised when there was a problem
throw new Exception($"SELECT unsuccessful:\n{ex.Message}");
}
finally
{
sqlconnConnection.Close();
}
if (dtUser.Rows.Count == 0)
{
// the record set comes back with no records found, an empty Datatable with no rows
// means there was no data matching your query
throw new Exception("No Such Bank user found");
}
else
{
// change to your applications needs
// Rows[0] - we are expecting at least 1 row, and its basically an array so we address
// the first element with 0
// Rows[0]["fieldnamefromDB"] <- referencing the column in the DB
//this.strID = strUserID;
myBankAccount.AccountNumber = dtUser.Rows[0]["Account_Number"].ToString();
myBankAccount.AccountPin = dtUser.Rows[0]["PIN"].ToString();
myBankAccount.AccountBalance = Convert.ToDecimal(dtUser.Rows[0]["Balance"]);
myBankAccount.AccountHolder = dtUser.Rows[0]["First_Name"].ToString();
myBankAccount.AccountAddress = dtUser.Rows[0]["Home_Address"].ToString();
myBankAccount.MyAccountGUID = dtUser.Rows[0]["GUID"].ToString();
if (myBankAccount.AccountNumber == strAccno && myBankAccount.AccountPin == strPin)
{
isCorrect = true;
}
else
{
isCorrect = false;
}
//myLocalBankAccUsr
}
}
catch (Exception ex)
{
// exception thrown for the whole method or function
throw new Exception($"User(string):\n{ex.Message}");
}
}
BankAccount.cs class
namespace BankingSystem
{
public class BankAccount
{
private string accountNumber;
private decimal accountBalance;
private string accountHolder;
private string accountPhoneNumber;
private string accountAddress;
private string accountPin;
private string myAccountGUID;
// private string AccountHolderGUID;
// private string AccountTypeGUID;
public string AccountNumber
{
get { return accountNumber; }
set { accountNumber = value; }
}
public decimal AccountBalance
{
get { return accountBalance; }
set { accountBalance = value; }
}
public string AccountHolder
{
get { return accountHolder; }
set { accountHolder = value; }
}
public string AccountPhoneNumber
{
get { return accountPhoneNumber; }
set { accountPhoneNumber = value; }
}
public string AccountAddress
{
get { return accountAddress; }
set { accountAddress = value; }
}
public string AccountPin
{
get { return accountPin; }
set { accountPin = value; }
}
public string MyAccountGUID
{
get { return myAccountGUID; }
set { myAccountGUID = value; }
}
public Boolean CanWithDrawAmount(decimal AmountToTransfer)
{
if (AmountToTransfer > this.AccountBalance){
return false;
}else
{
return true;
}
}
public void UpdatePIN()
{
// connect to bank DB connector
// send it the new pin
// SQL update command
}
}
}
Here is Form2:
namespace BankingSystem
{
public partial class frmUserHome : Form
{
public frmUserHome()
{
InitializeComponent();
tabMainForm.Appearance = TabAppearance.FlatButtons;
tabMainForm.ItemSize = new Size(0, 1);
tabMainForm.SizeMode = TabSizeMode.Fixed;
timerMain.Enabled = true;
timerMain.Start();
}
private void frmUserHome_Load(object sender, EventArgs e)
{
labelWelcome.Text = "Welcome "; //newMainBank.AccountHolder;
}
The 'labelWelcome.Text = "Welcome" is where I want the name stored inside the object to be used. So it should ideally access the BankAccount class, access the AccountHolder field and use that field to concat onto the end of the 'Welcome' text. However, it just shows 'Welcome' and no name on the end, when I run the program (because all values get reset to null in form2.. for some reason)

Below I have updated the code for Form1 and Form2.
Form 1
namespace BankingSystem
{
public partial class frmLogIn : Form
{
dbConnector newConnector;
public frmLogIn()
{
InitializeComponent();
newConnector = new dbConnector(**pass str file path**);
timerMain.Enabled = true;
timerMain.Start();
}
private void btnLogIn_Click(object sender, EventArgs e)
{
try
{
newConnector.CheckDetailsLogin(accountNumTextBox.Text, pinNumTextBox.Text);
frmUserHome UserHome = new frmUserHome(newConnector.myBankAccount);
MessageBox.Show("Success! Happy Banking!");
UserHome.ShowDialog();
}
catch
{
MessageBox.Show("Failed - incorrect login details.");
}
}
}
}
Form 2
namespace BankingSystem
{
public partial class frmUserHome : Form
{ public BankAccount _bankAccount;
public frmUserHome(BankAccount bankAccount)
{
InitializeComponent(); _bankAccount = bankAccount;
tabMainForm.Appearance = TabAppearance.FlatButtons;
tabMainForm.ItemSize = new Size(0, 1);
tabMainForm.SizeMode = TabSizeMode.Fixed;
timerMain.Enabled = true;
timerMain.Start();
}
private void frmUserHome_Load(object sender, EventArgs e)
{
labelWelcome.Text = "Welcome "+ bankAccount.AccountHolder;
}

Display a logged in users info

I have a program where the user has to login, so they have a id and password. The database with the user login details are stored in a local .mdf file.
I would like to set it up so that whilst the user is logged in, the rest of the program shows their details in the top right corner, so for example their name and their id.
I unfortunately have no idea how to do this and all I have seen whilst I browsed around is people using the actual System login, which is not what I want.
Code for login form:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;
namespace InventoryManager
{
public partial class frmLogin : Form
{
public frmLogin()
{
InitializeComponent();
}
private void frmLogin_Load(object sender, EventArgs e)
{
this.AcceptButton = btnSubmit;
}
string cs = #"Data Source= (LocalDB)\v11.0;AttachDbFilename=|DataDirectory|Users.mdf;Integrated Security = True;";
private void btnSubmit_Click(object sender, EventArgs e)
{
if (txtUserID.Text == "" || txtPassword.Text == "")
{
MessageBox.Show("Please enter a User ID and Password");
return;
}
try
{
SqlConnection con = new SqlConnection(cs);
SqlCommand cmd = new SqlCommand("SELECT * FROM tbl_Login WHERE UserID = #userid AND Password = #password", con);
cmd.Parameters.AddWithValue("#userid", txtUserID.Text);
cmd.Parameters.AddWithValue("#password", txtPassword.Text);
con.Open();
SqlDataAdapter adapt = new SqlDataAdapter(cmd);
DataSet ds = new DataSet();
adapt.Fill(ds);
con.Close();
int count = ds.Tables[0].Rows.Count;
if (count == 1)
{
MessageBox.Show("Login Successful!");
this.Hide();
frmOverview fo = new frmOverview();
fo.Show();
}
else
{
MessageBox.Show("Login Failed");
txtPassword.Text = "";
}
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
}
}
}

You can make some static class like this one
public static class LoggedUser
{
public static string Name { get; set; }
public static string Username { get; set; }
}
after successful login, populate that class with data (in example):
if (count == 1)
{
MessageBox.Show("Login Successful!");
LoggedUser.Name = ds.Tables[0].Rows[1].ToString();
LoggedUser.Username = ds.Tables[0].Rows[2].ToString();
this.Hide();
frmOverview fo = new frmOverview();
fo.Show();
}
later, you can use data stored in LoggedUser class on every form in your project...

Using OpenFileDialog and StreamReader

There are two classes, one to cover the form (class 1) and the other to cover what gets displayed on the form (class 2). I'm trying to call a method in class 1 from class 2 to display certain information in a text box. I keep getting the error:
An object reference is required for the non-static field, method, or property
I've encountered this error before and been able to make it through, but nothing I've attempted so far has helped in this instance. I'm posting code for both the classes.
Class 1:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Forms;
namespace Project6
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
}
private void button1_Click(object sender, EventArgs e)
{
Stream myStream = null;
//Create an instance of the open file dialog box
OpenFileDialog ofd = new OpenFileDialog();
//Set parameters, filter options, and filter index
ofd.InitialDirectory = "c:\\";
ofd.Filter = "Text Files (.txt)|*.txt";
ofd.FilterIndex = 2;
ofd.Multiselect = false;
if (ofd.ShowDialog() == DialogResult.OK)
{
try
{
if ((myStream = ofd.OpenFile()) != null)
{
using (myStream = ofd.OpenFile())
{
StreamReader reader = new StreamReader(myStream);
string studentInformation = "";
string[] studentInformationArray = new string[11];
studentInformation = reader.ReadLine();
while ((studentInformation = reader.ReadLine()) != null)
{
studentInformationArray = studentInformation.Split(',');
Student newStudent = new Student(studentInformationArray);
}
}
}
}
catch (Exception ex)
{
MessageBox.Show("Error: Could not read file from disk. Original error: " + ex.Message);
}
}
}
private void textBox1_TextChanged(object sender, EventArgs e)
{
textBox1.Text = Student.GetName(); //This generates the compiler error
textBox1.Select(6, 5);
MessageBox.Show(textBox1.SelectedText);
}
}
}
Class 2:
using System;
using System.Windows.Forms;
namespace Project6
{
class Student
{
//Initialize variables
private string[] studentInformationArray;
//Constructor that accepts the studentInformationArray as an argument
public Student(string[] studentInformationArray)
{
this.studentInformationArray = studentInformationArray;
}
public Student()
{
string className = studentInformationArray[1];
string semester = studentInformationArray[2];
string picture = studentInformationArray[3];
int project1 = Convert.ToInt32(studentInformationArray[4]);
int project2 = Convert.ToInt32(studentInformationArray[5]);
int project3 = Convert.ToInt32(studentInformationArray[6]);
int project4 = Convert.ToInt32(studentInformationArray[7]);
int project5 = Convert.ToInt32(studentInformationArray[8]);
int project6 = Convert.ToInt32(studentInformationArray[9]);
int midtermExam = Convert.ToInt32(studentInformationArray[10]);
int finalExam = Convert.ToInt32(studentInformationArray[11]);
}
public string GetName()
{
string studentName;
studentName = studentInformationArray[0];
return studentName;
}
}
}

That's because that's not how you use the OpenFileDialog. Take a look at this example hosted by the MSDN here:
Edit: answering to your edited question. You will always get a NullReferenceException in the Student() constructor because you are never assigning something to your studentInformationArray. So you can fix it like this:
public Student()
{
studentInformationArray = new studentInformationArray[12];
string className = studentInformationArray[1];
// rest of your code...
}
However, you should take into account that studentInformationArray will be an empty array unless you assign something to it. Since you have a Student() overload that takes a string[], I'd suggest you that you either remove the default constructor or make it call the overloaded with default information, like this:
public Student(string[] studentInformationArray)
{
string className = studentInformationArray[1];
// rest of your code...
int project1 = int.Parse(studentInformationArray[4]); // always prefer int.Parse() instead of Convert.ToInt32()
// rest of your code...
this.studentInformationArray = studentInformationArray;
}
public Student()
{
string[] defaultInformation = new string[12];
// add information
defaultInformation[0] = "some information";
// ...
new Student(defaultInformation);
}
Some more points to take into account:
Class-level fields/properties should be spelled in Pascal Case (first letter of each word in uppercase, rest in lowercase)
Try to never use this.variableName = variableName.
Variables names should never include the type of the variable, that's redundant.
So, for example, change this:
private string[] studentInformationArray;
for this:
private string[] StudentInformation;
Answering your last question, regarding the compiler error, you need a reference to the Student read in order to get its name. You could do something like this:
public partial class Form1 : Form
{
private Student StudentRead;
// rest of your code...
// from your read method:
StudentRead = new Student(studentInformationArray);
// and finally:
private void textBox1_TextChanged(object sender, EventArgs e)
{
textBox1.Text = StudentRead.GetName();

ComboBox isnt displaying information from database

I have to create an automated teller machine app to access a database that contians sample customer records. I am having a problem displaying the account numbers from the accountInformation table (database), in my comboBox. I am pretty sure that I created the database connection correctly, and I thought that the code I have would dispay the numbers in the comboBox, so I'm not sure what the problem is. Is there something in comboBox properties that I need to change?
Here is my code:
using SQLDll;
namespace WindowsFormsApplication14
{
public partial class Form1 : Form
{
private Connection myConnection;
private Statement myStatement;
private ResultSet myResultSet;
String databaseURL = "http://www.boehnecamp.com/phpMyAdmin/razorsql_mysql_bridge.php";
public Form1()
{
InitializeComponent();
try
{
//connect to database
SQL sql = new SQL();
myConnection = sql.getConnection(databaseURL);
//create Statement for executing SQL
myStatement = myConnection.createStatement(databaseURL);
}
catch (Exception)
{
Console.WriteLine("Cannot connect to database server");
}
//close statement and database connection
myStatement.close();
myConnection.close();
}
private void Form1_Load(object sender, EventArgs e)
{
loadAccountNumbers();
}
public void setText(string text)
{
}
//load account numbers to ComboBox
private void loadAccountNumbers()
{
//get all account numbers from database
try
{
myResultSet = myStatement.executeQuery("SELECT accountNumber FROM accountInformation");
// add account numbers to ComboBox
while (myResultSet.next())
{
accountNumberComboBox.Items.Add(myResultSet.getString("accountNumber"));
}
myResultSet.close(); // close myResultSet
}//end try
catch (Exception)
{
Console.WriteLine("Error in loadAccountNumbers");
}
}//end method to loadAccountNumbers

I would recommend putting everything in one method. It is more readable and you can ensure everything gets closed even if an exception occurs.
public partial class Form1 : Form
{
private Connection myConnection;
private Statement myStatement;
private ResultSet myResultSet;
String databaseURL = "http://www.boehnecamp.com/phpMyAdmin/razorsql_mysql_bridge.php";
public Form1()
{
InitializeComponent();
loadAccountNumbers();
}
//load account numbers to ComboBox
private void loadAccountNumbers()
{
SQL sql = new SQL();
using (myConnection = sql.getConnection(databaseURL))
using (myStatement = myConnection.createStatement(databaseURL))
using (myResultSet = myStatement.executeQuery("SELECT accountNumber FROM accountInformation"))
{
// add account numbers to ComboBox
while (myResultSet.next())
accountNumberComboBox.Items.Add(myResultSet.getString("accountNumber"));
}
}

I found out what was wrong. I knew I had to call loadAccountNumbers() somewhere but I wasn't sure where. I placed it in public Form1() and that fixed my problem! Thanks for all the help.

Access TextBox from Static method in C#?

I have 2 classes: MyForm and Database
In MyForm I have a method to change a label text to show error:
public void printError(string text){
label1.Text = text;
}
My Database class needs to access that method too, so I make it static:
public static void printError(MyForm form, string text){
form.label1.Text = text;
}
Now the problem is, how do I call that method from Database class?
This question I found said that I need to pass MyForm into Database's contructor like this:
class MyForm : Form{
Database db;
public Form(){
db = new Database(this);
}
}
class Database{
MyForm form;
public Database(MyForm f){
form = f;
}
...
//then I can access the printError like this
MyForm.printError(form, "You got error");
}
I tried that and it freezes the form. Any other solution?
Thanks

Here is a very simple example of how you can achieve this without your data layer knowing about your UI:
class MyForm : Form
{
Database db;
public Form()
{
db = new Database(this);
}
public void DoSomething()
{
var errors = db.Login("", "");
if (errors.Any())
label1.Text = errors.First(); // Or you can display all all of them
}
}
class Database
{
public List<string> Login(string username, string password)
{
var errors = new List<string>();
if (string.IsNullOrEmpty(username))
errors.Add("Username is required");
if (string.IsNullOrEmpty(password))
errors.Add("Password is required");
[...]
return errors;
}
}

Like #Matthew Ferreira and others have stated the design is not idea, but here's something to get you started.
class MyForm : Form
{
public void SomeMethod()
{
var dataAccess = new Repository();
dataAccess.ExecuteQuery();
if (dataAccess.Exceptions.Any())
{
// display your error messages
form.label1.Text = dataAccess.Exceptions.Select(x => x.ToString());
}
}
}
class Repository
{
private readonly HashSet<Exception> _exceptions = new HashSet<Exception>();
public IEnumerable<Exception> Exceptions
{
get { return _exceptions; }
}
public int ExecuteQuery()
{
var numberOfRecordsAffected = 0;
try
{
// do something
}
catch (Exception ex)
{
// normall catching exceptions is a bad idea
// and you should really catch the exception at the
// layer best equiped to deal with it
_exceptions.Add(ex);
}
// but, for the purpose of this example we might want to add some logic to try the query on another database ????
try
{
// do something
}
catch (Exception ex)
{
_exceptions.Add(ex);
}
return numberOfRecordsAffected;
}
}

You need to look up "seperation of concerns". Its really bad to mix your UI code with you Database Access Layer (DAL). Better to bind the UI to business objects that are populated via a DAL.
To let the UI know about an error you could simply use a delegate.
namespace OperationErrorDelegate
{
public delegate void OperationErrorHandler(Exception ex);
public class DAL
{
public event OperationErrorHandler ReportError;
public void DoDALOperationThatCausesError()
{
try
{
int i = 1;
int j = 0;
int k = i/j;
}
catch (Exception ex)
{
ReportError(ex);
}
}
}
}
Add this code to the form:
using System ;
using System.Windows.Forms;
namespace OperationErrorDelegate
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
DAL DAL = new DAL();
DAL.ReportError += new OperationErrorHandler(DAL_OperationErrorProgress);
DAL.DoDALOperationThatCausesError();
}
private void DAL_OperationErrorProgress(Exception ex)
{
label1.Text = ex.Message;
}
}
}

Assuming the OP's requirement is to display an error message in a label, when the credentials are wrong:
private void btn_login_Click(object sender, EventArgs e)
{
MySqlConnection con = new MySqlConnection("server=localhost;uid=root;password=abc;database=mydb");
MySqlCommand cmd = new MySqlCommand("select * from emp where name='" + textBox1.Text + "'and pwd='" + textBox2.Text + "'",con);
con.Open();
MySqlDataReader dr = cmd.ExecuteReader();
if (dr.Read())
{ //successful
//navigate to next page or whatever you want
}
else
Label1.Text("Invalid userid or password");
con.Close();
}
And if you need error message for wrong data type (the user input string but the database column is Integer), then use validations at client side. You dont need to do it at backend, since that will be a burden.
You can use regular expressions for that in the button_click itself.