How to Display the Main Form After Successful Login Without Closing the Application?

Show the main form after successful login without terminating the application

When trying to close the login form and display the main form after successful authentication, programmers often encounter problems where the main form does not appear and the application closes unexpectedly. To resolve this issue, it is important to understand the underlying mechanism that triggers application termination.

The Windows operating system uses a message pump to handle user input and UI updates. The message pump is associated with the startup form (in this case the login form). Closing the login form also kills the message pump, causing the entire application to shut down prematurely.

The recommended way to solve this problem is to separate the functionality of the login form from the main logic of the application. Create a separate method in the "Program.cs" file to handle the authentication process and display of the main form.

In this method:

1. Use the ShowDialog() method to create and display the login form as a modal dialog box. This will prevent the main logic from executing until the login dialog box is closed.
2. Check the login dialog's DialogResult property to determine the result of the authentication.
3. If authentication is successful, start the main form by calling Application.Run(new MainForm()); This will create a new message pump for the main form, allowing the application to continue running.
4. If authentication fails, use Application.Exit() to exit the application. This will prevent the main form from showing and avoid showing an empty window.

By implementing this method, you can successfully close the login form, authenticate the user, and display the main form without accidentally terminating the application.

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