The problem with the flickering of the buttons in the project

Question

Good time of day. The problem is very strange and incomprehensible. After successfully creating the button, and then using it, I noticed a very unpleasant bug, flickering buttons. Namely, it is played very easily, open the project, and press the ALT button. For some reason, the buttons blink once, and that's it. I don't understand why this happens and how to fix it. Please help.

using System;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Windows.Forms;

namespace TestProject
{
    public class RoundButton : Control
    {
        public Color BackColor2 { get; set; }
        public Color ButtonBorderColor { get; set; }
        public int ButtonRoundRadius { get; set; }

        public Color ButtonHighlightColor { get; set; }
        public Color ButtonHighlightColor2 { get; set; }
        public Color ButtonHighlightForeColor { get; set; }

        public Color ButtonPressedColor { get; set; }
        public Color ButtonPressedColor2 { get; set; }
        public Color ButtonPressedForeColor { get; set; }

        private bool IsHighlighted;
        private bool IsPressed;

        public RoundButton()
        {
            Size = new Size(100, 40);
            ButtonRoundRadius = 30;
            BackColor = Color.Gainsboro;
            BackColor2 = Color.Silver;
            ButtonBorderColor = Color.Black;
            ButtonHighlightColor = Color.Orange;
            ButtonHighlightColor2 = Color.OrangeRed;
            ButtonHighlightForeColor = Color.Black;

            ButtonPressedColor = Color.Red;
            ButtonPressedColor2 = Color.Maroon;
            ButtonPressedForeColor = Color.White;
        }

        protected override CreateParams CreateParams
        {
            get
            {
                CreateParams createParams = base.CreateParams;
                createParams.ExStyle |= 0x00000020; // WS_EX_TRANSPARENT
                return createParams;
            }
        }

        protected override void OnPaint(PaintEventArgs e)
        {
            e.Graphics.SmoothingMode = SmoothingMode.HighQuality;

            var foreColor = IsPressed ? ButtonPressedForeColor : IsHighlighted ? ButtonHighlightForeColor : ForeColor;
            var backColor = IsPressed ? ButtonPressedColor : IsHighlighted ? ButtonHighlightColor : BackColor;
            var backColor2 = IsPressed ? ButtonPressedColor2 : IsHighlighted ? ButtonHighlightColor2 : BackColor2;


            using (var pen = new Pen(ButtonBorderColor, 1))
                e.Graphics.DrawPath(pen, Path);

            using (var brush = new LinearGradientBrush(ClientRectangle, backColor, backColor2, LinearGradientMode.Vertical))
                e.Graphics.FillPath(brush, Path);

            using (var brush = new SolidBrush(foreColor))
            {
                var sf = new StringFormat { Alignment = StringAlignment.Center, LineAlignment = StringAlignment.Center };
                var rect = ClientRectangle;
                rect.Inflate(-4, -4);
                e.Graphics.DrawString(Text, Font, brush, rect, sf);
            }

            base.OnPaint(e);
        }

        protected override void OnPaintBackground(PaintEventArgs e)
        {
        }

        protected override void OnMouseEnter(EventArgs e)
        {
            base.OnMouseEnter(e);
            IsHighlighted = true;
            Parent.Invalidate(Bounds, false);
            Invalidate();
        }

        protected override void OnMouseLeave(EventArgs e)
        {
            base.OnMouseLeave(e);
            IsHighlighted = false;
            IsPressed = false;
            Parent.Invalidate(Bounds, false);
            Invalidate();
        }

        protected override void OnMouseDown(MouseEventArgs e)
        {
            base.OnMouseDown(e);
            IsPressed = true;
            Parent.Invalidate(Bounds, false);
            Invalidate();
        }

        protected override void OnMouseUp(MouseEventArgs e)
        {
            base.OnMouseUp(e);
            Parent.Invalidate(Bounds, false);
            Invalidate();
            IsPressed = false;
        }

        protected GraphicsPath Path
        {
            get
            {
                var rect = ClientRectangle;
                rect.Inflate(-1, -1);
                return GetRoundedRectangle(rect, ButtonRoundRadius);
            }
        }

        public static GraphicsPath GetRoundedRectangle(Rectangle rect, int d)
        {
            var gp = new GraphicsPath();

            gp.AddArc(rect.X, rect.Y, d, d, 180, 90);
            gp.AddArc(rect.X + rect.Width - d, rect.Y, d, d, 270, 90);
            gp.AddArc(rect.X + rect.Width - d, rect.Y + rect.Height - d, d, d, 0, 90);
            gp.AddArc(rect.X, rect.Y + rect.Height - d, d, d, 90, 90);
            gp.CloseFigure();

            return gp;
        }
    }
}

Answer 1

When pressing the ALT key the OnPaint() event gets called and the control is redrawn (if you put a breakpoint you will see it).
It comes from the base class of Control class.
you can solve this by adding this method to the parent form of the custom control:

protected override void WndProc(ref Message msg)
{
    if (msg.Msg == 0x128) return;
    base.WndProc(ref msg);
}

I guess the reason is that ALT key is used for other functionality of Control, for example, selecting a menu item from MenuStrip control.