В форме входа
public string UserName {get; private set;}
if (string.Compare(dbPassword, appPassword) == 0)
{
UserName = txtUser.Text;
//I need to pass username value to myForm...
DialogResult = DialogResult.OK;
}
else
{
//Show warning
}
в основной
DialogResult result;
using (var loginForm = new Login())
result = loginForm.ShowDialog();
if (result == DialogResult.OK)
{
var username = loginForm.UserName;
Application.Run(new myForm(username));
}