Question

Basically; Form1 has 2 buttons, Form2 has 1 button.
When you click Form2’s button it checks which button on Form1 you clicked, opening Form3 or Form4 depending on which button you clicked (on Form1).

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So I’ve utilized Mark Halls first method of passing variables between forms. Now for the second half of my closed refinement.

Form1

private void btnLogin_Click(object sender, EventArgs e)
        {
            // Call function while storing variable info.
            Account("login");
        }

        private void btnRegister_Click(object sender, EventArgs e)
        {
            // Call function while storing variable info.
            Account("register");
        }

        // Function used to pass Variable info to Account form while opening it as instance.
        private void Account(string formtype)
        {
            // Generate/Name new instant of form.
            frontend_account frmAcc = new frontend_account();
            // Pass variable to instance.
            frmAcc.CheckButtonClick = formtype;
            // Show form instance.
            frmAcc.Show(this);
            // Hide this instance.
            this.Hide();
        }

Form2

// String Variable to store value from Login.
        public string CheckButtonClick { get; set; }

        private void btnContinue_Click(object sender, EventArgs e)
        {
            // If statement to open either Main form or Registration form, based on Login variable.
            if (CheckButtonClick == "login")
            {
                // Generate/Name new instant of form.
                frontend_main frmMain = new frontend_main();
                // Show form instant.
                frmMain.Show();
                // Close this instant.
                this.Close();
            }
            else if (CheckButtonClick == "register")
            {
                // Generate/Name new instant of form.
                frontend_register frmReg = new frontend_register();
                //  Show form instant.
                frmReg.Show();
                // Close this instant.
                this.Close();
            }
        }

On Form2 there are TWO radio buttons, can I adept that code to set the focus of a tab control when a form is opened? ie. if radClient is checked set focus on tabcontrol after opening winform, else if radStudent is checked set focus on tabcontrol (other page) after opening winform… and i guess don’t open a winform if no radio is checked.

I believe this will set the focus;

// Sets focus to first tab.
tabRegister.SelectedTab = tabRegister.TabPages[0];
// Sets focus to second tab.
tabRegister.SelectedTab = tabRegister.TabPages[1];

Answer 1

In your example the first problem I see is you are closing your parent form which closes your Form1 and disposes of Your Form2, What I would do is Hide Form1 instead of Closing it, I would then create a public property on Form2 to pass in the Button that was selected. But anytime you are opening and closing multiple Forms it can get messy, what I would do would be to create UserControls for your additional Forms and swap them out in a Panel. The first example is how to do it the way that you asked.

Form

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    private void btnLogin_Click(object sender, EventArgs e)
    {
        ShowForm2("login");
    }

    private void btnRegister_Click(object sender, EventArgs e)
    {
        ShowForm2("register");
    } 


    private void ShowForm2(string formtype)
    {
        Form2 f2 = new Form2(); // Instantiate a Form2 object.
        f2.CheckButtonClick = formtype;
        f2.Show(this); // Show Form2 and  
        this.Hide(); // closes the Form1 instance.  

    }
}

Form2

ublic partial class Form2 : Form
{
    public Form2()
    {
        InitializeComponent();
    }

    public string CheckButtonClick { get; set; }

    private void button1_Click(object sender, EventArgs e)
    {
        if (CheckButtonClick == "login")
        {
            Form3 f3 = new Form3(); // Instantiate a Form3 object.  
            f3.Show(); // Show Form3 and  
            this.Close(); // closes the Form2 instance.  
        }
        else if (CheckButtonClick == "register")
        {
            Form4 f4 = new Form4(); // Instantiate a Form4 object.  
            f4.Show(); // Show Form4 and  
            this.Close(); // closes the Form2 instance.  
        } 

    }
}

Form3 and Form4 note since Form1 is long forgotten to these forms I search for it to Open back up

public partial class Form3 : Form
{
    public Form3()
    {
        InitializeComponent();
    }

    private void Form3_FormClosed(object sender, FormClosedEventArgs e)
    {
        FormCollection frms = Application.OpenForms;
        foreach (Form f in frms)
        {
            if (f.Name == "Form1")
            {
                f.Show();
                break;
            }
        }
    }
}

The second Option with UserControls has one Form with a Panel on it. It uses events to signal the Form to Change Controls plus a public property on UserControl2

public partial class Form1 : Form
{
    string logonType;
    public Form1()
    {
        InitializeComponent();
    }

    private void userControl1_LoginOrRegisterEvent(object sender, LoginOrRegisterArgs e)
    {
        logonType = e.Value;
        userControl2.BringToFront();
    }


    private void userControl2_ControlFinshedEvent(object sender, EventArgs e)
    {
        if (logonType == "logon")
            userControl3.BringToFront();
        else if (logonType == "register")
            userControl4.BringToFront();
    }

    private void userControl3_ControlFinshedEvent(object sender, EventArgs e)
    {
        userControl1.BringToFront();
    }

    private void userControl4_ControlFinshedEvent(object sender, EventArgs e)
    {
        userControl1.BringToFront();
    }
}

UserControl1

public partial class UserControl1 : UserControl
{
   public delegate void LoginOrRegisterHandler(object sender, LoginOrRegisterArgs e);
   public event LoginOrRegisterHandler LoginOrRegisterEvent;

    public UserControl1()
    {
        InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        LoginOrRegisterArgs ea = new LoginOrRegisterArgs("logon");
        LoginOrRegisterEvent(sender, ea);
    }

    private void button2_Click(object sender, EventArgs e)
    {
        LoginOrRegisterArgs ea = new LoginOrRegisterArgs("register");
        LoginOrRegisterEvent(sender, ea);
    }
}

public class LoginOrRegisterArgs
{
    public LoginOrRegisterArgs(string s) {Value = s;}
    public string Value {get; private set;}
}

UserControl2

public partial class UserControl2 : UserControl
{
    public delegate void ControlFinishedHandler(object sender, EventArgs e);
    public event ControlFinishedHandler ControlFinshedEvent;
    public UserControl2()
    {
        InitializeComponent();
    }
    public string SetLogonType { get; set; }

    private void button1_Click(object sender, EventArgs e)
    {
        ControlFinshedEvent(sender, new EventArgs());
    }
}

UserControl3 & UserControl4 exactly the same except for different Class Name

public partial class UserControl3 : UserControl
{
    public delegate void ControlFinishedHandler(object sender, EventArgs e);
    public event ControlFinishedHandler ControlFinshedEvent;
    public UserControl3()
    {
        InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        ControlFinshedEvent(sender, new EventArgs());
    }
}