在登录表单上输入用户名和密码后，处理登录表单并显示主表单

Question

I run LoginForm using the code below:

[STAThread]
static void Main()
{
    Application.EnableVisualStyles();
    Application.SetCompatibleTextRenderingDefault(false);
    Application.Run(new LoginForm());
    //Application.Run(new MainForm());
}

When user presses the enter button, i want to dispose or close the LoginForm and want to run the MainForm but i got this exception: "InvalidOperationException was unhandled by user code"

Click handler of the enter button is given below:

private void LoginFormEnterButton_Click(object sender, EventArgs e)
{
    try
    {
        MainForm a = new MainForm();
        a.Show();
        this.Close();
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.ToString());
    }
}

What can i do to dispose the LoginForm and after that to run the MainForm successfully?

Answer 1

You can't dispose the Main window. You need to change the way.

First of all set MainForm as startup window.

Application.Run(new MainForm());

Load/show the LoginForm in constructor of MainForm,

public MainForm()
{
 LoginForm login=new LoginForm();
 login.ShowDialog();
 InitializeComponent();
}

and Click handler code in LoginForm,

private void LoginFormEnterButton_Click(object sender, EventArgs e)
{
   this.Close();
}

Answer 2

I think you should change your approach.

Start running your main form.
In the Load event of the main form, run the login form modally
Do the validation inside the login form and return DialogResult.OK.
In the Main form continue or exit depending on the return from Login form.

[STAThread] 
static void Main() 
{     
    Application.EnableVisualStyles();     
    Application.SetCompatibleTextRenderingDefault(false);     
    Application.Run(new MainForm()); 
} 

public void MainForm_Load(object sender, EventArgs e)
{
     // The using statement will take care of closing and disposing the login form
     using(LoginForm f = new LoginForm())
     {
         if(f.ShowDialog() != DialogResult.OK)
         {
              Application.Exit();
              return;
         }
     }

     // continue with main form processing
}

Answer 3

I think the main application loop is ending when close the login form. As an alternative, could you run the app with your mainform, and have it display the login form as a modal dialog. Then if the user doesn't log in successfully you can close the app

Answer 4

I use an ApplicationContext instead of passing a form.

   Application.Run(new TerminalApplicationContext());

in the ctor i show a form

public TerminalApplicationContext()
{
    login = new FormLogin();
    login.Logon += new FormLogin.LogonDelegate(login_Logon);
    login.Show();
}

Then in the delegate 'login_logon' i dispose the 'FormLogin' and show another one.