Why does MouseHover event only get called if a messagebox.show() or breakpoint occurs before it?

问题

I've got a boolean that keeps track of the state between a right-button MouseDown event on a FlowLayoutPanel and the corresponding subsequent MouseUpEvent:

    bool TextBoxesRespondingToMouseMoveEvents = false;

...Here's the code in the FlowLayoutPanel's MouseDown and MouseUp events, and a shared MouseHover handler that all TextBoxes on the FlowLayoutPanel share:

    private void flowLayoutPanelGreatGooglyMooglyMain_MouseDown(object sender, MouseEventArgs e) {
        if (e.Button == MouseButtons.Right) {
            TextBoxesRespondingToMouseMoveEvents = true;
            //MessageBox.Show("TextBoxesRespondingToMouseMoveEvents is now true");
            selectionStart = PointToClient(MousePosition);
        }
    }

    private void flowLayoutPanelGreatGooglyMooglyMain_MouseUp(object sender, MouseEventArgs e) {
        if (e.Button == MouseButtons.Right) {
            TextBoxesRespondingToMouseMoveEvents = false;
            selectionEnd = PointToClient(MousePosition);
        }
    }

    // This event is shared by all of the buttons on flowLayoutPanelGreatGooglyMooglyMain
    private void textBoxQH1_MouseHover(object sender, EventArgs e) {
        if (TextBoxesRespondingToMouseMoveEvents) {
            TextBox tb = (TextBox)sender;
            if (tb.BackColor.Equals(SystemColors.Window)) {
                tb.BackColor = System.Drawing.Color.Gainsboro;
            }
        }
    }

This WORKS as long as the MessageBox.Show() in the MouseDown event is not commented out, OR if I have a breakpoint in that event. If you just let the code run, though, with the MessageBox.Show() commented out, the MouseHover() event never fires.

Why, and how can I fix it?

回答1:

Have a look at the answers for this question; while they don't directly explain the difference in behavior between not/having the MessageBox (or breakpoint), it begins to explain that the textbox will be swallowing mouse events, and that you should hook the PreviewXXX events instead.

来源：https://stackoverflow.com/questions/10323824/why-does-mousehover-event-only-get-called-if-a-messagebox-show-or-breakpoint-o

标签

winforms

mouseevent

mouseover