How to create a non-modal form but blocking?

Question

Should sound weird, but this is just for my hobby. I would want a (custom) messagebox to pop up with a YesNo buttons which should ideally block the code. But I should be able to click on the parent form so that I can dismiss the message box without having to specifically click on the messagebox buttons (equivalent to clicking No on the message box)..

something like this:

     void Foo()
     {
         CustomMsgBox.Show("do you really wanna delete?", CustomMsgBox.Buttons.YesNo);
         //block the code here, but user should be able to click on form, so that its equivalent to have clicked No;
         //if clicked No, return;

         //delete.
     }

So the solution I thought was make the custom message box non modal - so that user can click on form, but I'm not able to block code.. How can i do that?

It would look like this:

 void Foo()
 {
     NonModalMsgBox.Show("do you really wanna delete?", CustomMsgBox.Buttons.YesNo);
     //block thread till user clicks on form or messagebox buttons.
     //unblock when user clicks.
     //if No, return;

     //delete.
 }

Edit: I know this is not a standard practice and I know non modal forms do not block, while modal forms do. So please do not recommend to be content with either modal form's or non-modal form's behavior. My question would be is there any way to simulate the behaviour of ContextMenu with windows forms.

Answer 1

You can solve this quite easily. Create and use a modal dialog but override the WndProc of the dialog and process the WM_MOUSEDOWN event. Check the position of the mouse down and if it is over the parent window but not over the dialog itself then simply dismiss the dialog.

Answer 2

Essentially you can't do this in a 'blocking' call easily. What you could do easily enough is to either pass the information required to perform the delete, or a delegate to perform the operation, to the form. When they click Ok you simply perform the operation. If they activate the parent form, then just close the child.

Answer 3

Another way of handling this is by manually enabling the parent form when calling ShowDialog, from here

[DllImport("user32.dll")]
private static extern bool EnableWindow(IntPtr hWnd, bool enable);

internal static DialogResult ShowDialogSpecial(this Form formToBeShown, Form parent)
{
    parent.BeginInvoke(new Action(() => EnableWindow(parent.Handle, true)));
    formToBeShown.ShowDialog(parent);

    return formToBeShown.DialogResult;
}

Just call the extension method from any parent form like this:

var f = new Form();
f.ShowDialogSpecial(this);
//blocks but parent window will be active.

Of course you need to handle the clicks on parent form to close child form.

Answer 4

You want the user to be able to click the background window to cancel the dialog box? Add a handler to the background window so that when the user clicks on it you check to see if the non-modal window is displayed, if so close it.

Sounds easy, but you will need to be careful to handle every possible click on the background window and child windows. That sounds like a can of worms I wouldn't want to go down.

Perhaps instead you could detect if the non-modal dialog box loses focus and automatically close it. I can see this behavior making sense for a simple "confirm delete" dialog box, but as a user my first reaction is going to be to spam the ESC key to close the dialog box.

Answer 5

An easier way: set form's "TopMost" property to be True. Then it will act like blocking

Answer 6

You could do something like:

public void ShowMe() {
    Show();
    while (!_receivedDeactivateEvent)
        Application.DoEvents();
}

I'm not sure I'd recommend it, though -- I'm not sure how stable it would be, nor am I sure whether it would behave the way you want if you click the Delete button on the parent form while the 'dialog' is up (would it close the first dialog first, or leave it up? might be the latter, which could get messy).