Question

When Form2 is closed, via it’s X button, the Main form is sometimes hidden as well, but not always. Often times the Main form is hidden after initial ‘newForm’ button click and other times many open-close operations are required before the Main form gets hidden on Form2’s closing. Why is this happening? Why is it irregular?

This is a small test code for a larger application I’m working on. In that application a thread continuously reads the network stream and when a particular message is encountered a modal form is displayed. The user can close that modal form or it can be told to close itself by a different network message. In this event, to give the user some time to view the data that the form is displaying I implemented a delayed form closing for that form. When the form is running its delay closing code, another message can come in over the network that will open up a new instance of this form in which case, I observed, that once the timer of the original form runs out, the original form is left displayed until the new instance is closed. Calling Hide in the FormClosing event handler closes the original form if more than one instances of it are running, but it has this side effect of hiding the entire application (the Main form) when the last instance of this form is closed, either by the user or by the delayed closing code. And again, the entire application is not always hidden, but it does happen.

//Main form's 'newForm' button
private void btn_newForm_Click(object sender, EventArgs e)
{
        Form2 f = new Form2();
        f.ShowDialog();
}   

public partial class Form2 : Form
{
    private void Form2_FormClosing(object sender, FormClosingEventArgs e)
    {
        Hide();
    }
}

Update (from the application I’m working on):

The problem is shown visually below. The top part of the picture, labeled “A”, represents the situation where the first modal dialog (greyed out) was instantiated and it is in the process of being auto closed after 4 seconds have elapsed. The second instance (blue window heading) is active and awaiting input. In the lower part of the picture, labeled “B”, the counter to closing of the first instance has completed, yet the first instance remains visible. Adding Hide does not change picture “A” but picture “B” would only be showing the active modal dialog, which is what I want. If Hide is not used and we have the case shown in “B”, once the active modal dialog is closed the inactive dialog will disappear together with the active one, but no sooner. At this time my main form will be hidden as well, sometimes.

Answer 1

Your main form doesn’t get hidden, it disappears behind another window. The flaw in your code is that for a brief moment none of your windows can get the focus. Your main window can’t get the focus, it got disabled by your dialog and won’t get re-enabled until the dialog is fully closed. Your dialog can’t get the focus, you hide it. So Windows goes looking for another window to give the focus to and can only pick a window owned by another application. Like Visual Studio, nice and big so your main window is well covered by it.

Not sure what you are trying to do, it doesn’t make sense to call Hide() since the dialog will close a couple of microseconds later. Just delete the statement.