如何在不关闭应用程序的情况下关闭登录表单并显示主表单？

Question

I have two forms in my project (Login and Main).

What I'm trying to accoomplish is, if the login is successful, I must show the Main form and close the Login form.

I have this method in Login form that closes the Login form when the login is successful. But the Main form doesn't show.

public void ShowMain()
{
    if(auth()) // a method that returns true when the user exists.
    {             
        var main = new Main();
        main.Show();
        this.Close();
    }
    else
    {
        MessageBox.Show("Invalid login details.");
    }         
}

I tried hiding the Login form if the login process is successful. But it bothers me because I know while my program is running the login form is still there too, it should be closed right?

What should be the right approach for this? Thanks...

Answer 1

The reason your main form isn't showing is because once you close the login form, your application's message pump is shut down, which causes the entire application to exit. The Windows message loop is tied to the login form because that's the one you have set as the startup form in your project properties. Look in your "Program.cs" file, and you'll see the responsible bit of code: Application.Run(new LoginForm()) . Check out the documentation for that method here on MSDN , which explains this in greater detail.

The best solution is to move the code out of your login form into the "Program.cs" file. When your program first starts, you'll create and show the login form as a modal dialog (which runs on a separate message loop and blocks execution of the rest of your code until it closes). When the login dialog closes, you'll check its DialogResult property to see if the login was successful. If it was, you can start the main form using Application.Run (thus creating the main message loop); otherwise, you can exit the application without showing any form at all. Something like this:

static void Main()
{
    LoginForm fLogin = new LoginForm();
    if (fLogin.ShowDialog() == DialogResult.OK)
    {
        Application.Run(new MainForm());
    }
    else
    {
        Application.Exit();
    }
}

Answer 2

I would do this the other way round.

In the OnLoad event for your Main form show the Logon form as a dialog. If the dialog result of that is OK then allow Main to continue loading, if the result is authentication failure then abort the load and show the message box.

EDIT Code sample(s)

private void MainForm_Load(object sender, EventArgs e)
{
    this.Hide();

    LogonForm logon = new LogonForm();

    if (logon.ShowDialog() != DialogResult.OK)
    {
        //Handle authentication failures as necessary, for example:
        Application.Exit();
    }
    else
    {
        this.Show();
    }
}

Another solution would be to show the LogonForm from the Main method in program.cs, something like this:

static void Main()
{
    Application.EnableVisualStyles();
    Application.SetCompatibleTextRenderingDefault(false);

    LogonForm logon = new LogonForm();

    Application.Run(logon);

    if (logon.LogonSuccessful)
    {
        Application.Run(new MainForm());
    }
}

In this example your LogonForm would have to expose out a LogonSuccessful bool property that is set to true when the user has entered valid credentials

Answer 3

It's simple.

Here is the code.

 private void button1_Click(object sender, EventArgs e)
 {  
        //creating instance of main form
        MainForm mainForm = new MainForm();

        // creating event handler to catch the main form closed event
        // this will fire when mainForm closed
        mainForm.FormClosed += new FormClosedEventHandler(mainForm_FormClosed);
        //showing the main form
        mainForm.Show();
        //hiding the current form
        this.Hide();
  }

  // this is the method block executes when main form is closed
  void mainForm_FormClosed(object sender, FormClosedEventArgs e)
  {
       // here you can do anything

       // we will close the application
       Application.Exit();
  }

Answer 4

This is my solution. Create ApplicationContext to set mainform of application and change mainform when you want to open new form and close current form.

Program.cs

static class Program
{
    static ApplicationContext MainContext = new ApplicationContext();

    /// <summary>
    /// The main entry point for the application.
    /// </summary>
    [STAThread]
    static void Main()
    {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);

        MainContext.MainForm = new Authenticate();
        Application.Run(MainContext);
    }

    public static void SetMainForm(Form MainForm)
    {
        MainContext.MainForm = MainForm;
    }

    public static void ShowMainForm()
    {
        MainContext.MainForm.Show();
    }
}

When login process is complete.

private void BtLogin_Click(object sender, EventArgs e)
    {
        //Login Process Here.

        Program.SetMainForm(new Portal());
        Program.ShowMainForm();

        this.Close();
    }

I hope this will help you.

Answer 5

static class Program
{
    [STAThread]
    static void Main()
    {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        Login();
    } 

    private static bool logOut;

    private static void Login()
    {
        LoginForm login = new LoginForm();
        MainForm main = new MainForm();
        main.FormClosed += new FormClosedEventHandler(main_FormClosed);
        if (login.ShowDialog(main) == DialogResult.OK)
        {
            Application.Run(main);
            if (logOut)
                Login();
        }
        else
            Application.Exit();
    }

    static void main_FormClosed(object sender, FormClosedEventArgs e)
    {
        logOut= (sender as MainForm).logOut;
    }
}

public partial class MainForm : Form
{
    private void btnLogout_ItemClick(object sender, ItemClickEventArgs e)
    {
        //timer1.Stop();
        this.logOut= true;
        this.Close();
    }
}

Answer 6

This is the most elegant solution.

private void buttonLogin_Click(object sender, EventArgs e)
{
    MainForm mainForm = new MainForm();
    this.Hide();
    mainForm.ShowDialog();
    this.Close();
}

;-)

Answer 7

Here's a simple solution, your problem is that your whole application closes when your login form closes right? If so, then go to your projects properties and on the Application Tab change the shutdown mode to "When last form closes" that way you can use Me.close without closing the whole program

Answer 8

Evan the post is too old i like to give you a trick to do this if you wants to show splash/login screen and when the progress bar of splash screen get certain value/or successful login happen and closed the splash/login then re show the main form, frm-main will be the startup form not frm-spalash

in frm-main

public partial class frmMain : Form
{
    public frmMain()
    { 
        frmSplash frm = new frmSplash();
        frm.Show(); // new splash screen will shows
        this.Opacity=0; // will hide your main form
        InitializeComponent();
    }
 }

in the frm-Splash

private void timer1_Tick(object sender, EventArgs e)
{
 int cnt = progressBar1.Value;

    switch (cnt)
    {
        case 0:
                //Do sum stuff
            break;
        case 100:

            this.Close(); //close the frm-splash
            frmMain.ActiveForm.Opacity = 100; // show the frm-main

            break;
    }

    progressBar1.Value = progressBar1.Value+1;
}

if you use it for login form

private void btlogin_Click(object sender, EventArgs e)
{
 bool login = false;

    //try your login here 
    //connect your database or whatever
    //and then when it success update login variable as true

        if(login == true){

            this.Close(); //close the frm-login
            frmMain.ActiveForm.Opacity = 100; // show the frm-main

        }else{
              //inform user about failed login
        }
}

note that i use a timer and a progress bar to manipulate the actions you don't need those two it just for sake of complete answer only, hope this helps

Answer 9

you should do it the other way round:

Load the mainform first and in its onload event show your loginform with showdialog() which will prevent mainform from showing until you have a result from the loginform

EDIT : As this is a login form and if you do not need any variables from your mainform ( which is bad design in practice ), you should really implement it in your program.cs as Davide and Cody suggested.

Answer 10

我认为更好的方法是在通常具有Application.Run（form1）的Program.cs文件中执行此操作，以这种方式获得更简洁的方法，Login表单不需要与Main表单耦合，您只需显示登录名，如果返回true，则显示主表单，否则显示错误。

Answer 11

Try this:

public void ShowMain()
    {
        if(auth()) // a method that returns true when the user exists.
        { 
            this.Close();
            System.Threading.Thread t = new System.Threading.Thread(new System.Threading.ThreadStart(Main));
            t.Start();
        }
        else
        {
            MessageBox.Show("Invalid login details.");
        }         
    }
   [STAThread]
   public void Main()
   {
      Application.EnableVisualStyles();
      Application.SetCompatibleTextRenderingDefault(false);
      Application.Run(new Main());

   }

You must call the new form in a diferent thread apartment, if I not wrong, because of the call system of windows' API and COM interfaces.

One advice: this system is high insecure, because you can change the if condition (in MSIL) and it's "a children game" to pass out your security. You need a stronger system to secure your software like obfuscate or remote login or something like this.

Hope this helps.

Answer 12

public void ShowMain()
  {
       if(auth()) // a method that returns true when the user exists.
       {        
         this.Hide();
         var main = new Main();
         main.Show();
       }
      else
       {
              MessageBox.Show("Invalid login details.");
        }         
   }

Answer 13

best way for show login for and close login form before login successfully put login form in FrmMain after InitializeComponent.

 public FrmMain()
 {
      FrmSplash FrmSplash = new FrmSplash();
      FrmSplash.ShowDialog();

      InitializeComponent();
      //Login Section
 {

Answer 14

try this

 private void cmdLogin_Click(object sender, EventArgs e)
    {
        if (txtUserName.Text == "admin" || txtPassword.Text == "1")
        {

            FrmMDI mdi = new FrmMDI();
            mdi.Show();
            this.Hide();
        }
        else {

            MessageBox.Show("Incorrect Credentials", "Library Management System", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
        }
    }

and when you exit the Application you can use

 Application.Exit();

Answer 15

1.Go to MainMenu Design properties> Go to my events

2.Click MainMenu event Shown and show LoginForm

3.Leave MainMenu as the First run in Program.cs