Question

I have two forms, mainForm and subForm. When mainForm loses focus I want subForm to disappear and then reappear as mainForm regains focus. I’m using the Activated and Deactivate events on the mainForm to keep track of whether mainForm has focus or not. When the Activated is fired I do subForm.Show() and the opposite for Deactivate. The problem I have is that when subForm gains focus mainForm disappear because I don’t know how to say programmatically “make subForm disappear when the mainForm’s Deactivate event fires except if it’s because the subForm gained focus. The whole point of what I’m doing is to make both windows disappear when the mainForm loses focus because the user clicked on another application or use ALT+TAB to switch. I don’t want to leave the subForm behind. Is there any way of checking as the Deactive fires whether it was because another form belonging to the application gained focus as opposed to some other application?

class MainForm : Form
{
    SubForm subForm = new SubForm();

    private void mainForm_Activated(object sender, EventArgs e)
    {
        this.subForm.Show();
    }

    private void mainForm_Deactivate(object sender, EventArgs e)
    {
        this.subForm.Hide()

        // I need some logic to make sure that it is only hidden
        // when the mainForm loses focus because the user clicked
        // some other application in the taskbar and not when the
        // subForm itself gains the focus.
    }
}

Answer 1

This works on my machine.

public partial class Form1 : Form {
    public Form1() {
        InitializeComponent();
    }

    private Form2 _form2;
    private void Form1_Load(object sender, EventArgs e) {
        _form2 = new Form2();
        _form2.Show();
        HandleFocusEvents();
    }

    private void HandleFocusEvents() {
        this.LostFocus += Form_LostFocus;
        _form2.LostFocus += Form_LostFocus;
        this.GotFocus += Form_GotFocus;
    }

    private void Form_LostFocus(object sender, EventArgs e) {
        if (!_form2.ContainsFocus && !this.ContainsFocus) {
            _form2.Hide();
        }
    }

    private void Form_GotFocus(object sender, EventArgs e) {
        if (!_form2.Visible) {
            _form2.Show();
        }
    }
}