区分用户关闭表单和用户关闭应用程序

Question

I am dealing with the following scenario:

• When user is trying to close one particular form in my application (via Ctrl + F4 or via dedicated button) I need him to log out when certain conditions are met,
• Therefore I overrode OnFormClosed method, check the conditions, if they are met I display a message box and once user clicks OK, he is logged out of my application,
• I am investigating FormClosedEventArgs.CloseReason and only apply this logic in situation of UserClosing ,
• However, when user tries to close the entire application (via Alt + F4 or Close button in upper right corner), the CloseReason is still UserClosing , so instead of shutting down the application, he is presented the messagebox and logged out of application afterwards. This is not desired because application shutdown is obviously stronger than log out.

So my question - is there a nice way to distiguish between user closing a form or user closing an entire application? I could probably set some bool flags by overriding ProcessCmdKey to distinguish between Alt + F4 and Ctrl + F4 , but that is not very nice and also doesn't solve this issue when clicking the close button.

Answer 1

There is no nice way, you have to detect the user closing your main window before the FormClosing events starts firing. Not a capability that's exposed in Winforms, but you can easily add it by overriding the WndProc() method in your main window's Form class. You're interested in the WM_SYSCOMMAND message, SC_CLOSE command:

    public static bool MainWindowClosing;

    protected override void WndProc(ref Message m) {
        if (m.Msg == 0x112 && (m.WParam.ToInt32() & 0xfff0) == 0xf060) {
            MainWindowClosing = true;
        }
        base.WndProc(ref m);
    }

Now you can test that variable in your other classes:

    protected override void OnFormClosing(FormClosingEventArgs e) {
        if (!Form1.MainWindowClosing && e.CloseReason == CloseReason.UserClosing) {
            // Display your dialog
            //...
        }
        base.OnFormClosing(e);
    }

You need to set MainWindowClosing back to false if you do anything to prevent the user from closing your app. And I would remiss to not mention that adding a login procedure beyond the highly secure Windows login is a grave mistake that is likely to expose passwords.

Answer 2

I don't think there's any built-in method to do what you want (other than preprocessing system keystrokes). Any closing initiated by the user in the application (except for MDI forms) is going to be ÙserClosing .

One workaround could be having your form embedded in another form (with the Owner set to the outer form) and check if the inner form closing is with a FormOwnerClosing reason (that'd happen if you click the 'X' on the outer form), and check for UserClosing on the parent form, instead of the actual form (the inner one), but I'd say that's even less elegant and would split your code around two different forms.