问为什么我的WinForms控件闪烁并缓慢调整大小？

EN

protected override void OnResizeBegin(EventArgs e) {
    SuspendLayout();
    base.OnResizeBegin(e);
}
protected override void OnResizeEnd(EventArgs e) {
    ResumeLayout();
    base.OnResizeEnd(e);
}

protected override void OnPaint(PaintEventArgs e)
{
    if (Visible)
    {
        Graphics gr = e.Graphics;
        Rectangle clipRectangle = new Rectangle(new Point(0, 0), this.Size);
        Size tSize = TextRenderer.MeasureText(Text, this.Font);
        Rectangle r1 = new Rectangle(0, (tSize.Height / 2), Width - 2, Height - tSize.Height / 2 - 2);
        Rectangle r2 = new Rectangle(0, 0, Width, Height);
        Rectangle textRect = new Rectangle(6, 0, tSize.Width, tSize.Height);

        GraphicsPath gp = new GraphicsPath();
        gp.AddRectangle(r2);
        gp.AddRectangle(r1);
        gp.FillMode = FillMode.Alternate;

        gr.FillRectangle(new SolidBrush(Parent.BackColor), clipRectangle);

        LinearGradientBrush gradBrush;
        gradBrush = new LinearGradientBrush(clipRectangle, SystemColors.GradientInactiveCaption, SystemColors.InactiveCaptionText, LinearGradientMode.BackwardDiagonal);
        gr.FillPath(gradBrush, RoundedRectangle.Create(r1, 7));

        Pen borderPen = new Pen(BorderColor);
        gr.DrawPath(borderPen, RoundedRectangle.Create(r1, 7));
        gr.FillRectangle(gradBrush, textRect);
        gr.DrawRectangle(borderPen, textRect);
        gr.DrawString(Text, base.Font, new SolidBrush(ForeColor), 6, 0);
    }

}

protected override void OnPaintBackground(PaintEventArgs pevent)
{
    if (this.BackColor == Color.Transparent)
        base.OnPaintBackground(pevent);
}

Public Class Form1

Public Sub New()
    Me.SetStyle(ControlStyles.UserPaint Or ControlStyles.OptimizedDoubleBuffer Or ControlStyles.AllPaintingInWmPaint Or ControlStyles.SupportsTransparentBackColor, True)
End Sub

Private Sub Form1_Resize(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Resize
    Me.Update()
End Sub

End Class

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        Resize += Form1_Resize;
        this.SetStyle(ControlStyles.UserPaint | ControlStyles.OptimizedDoubleBuffer | ControlStyles.AllPaintingInWmPaint | ControlStyles.SupportsTransparentBackColor, true);
    }

    private void Form1_Resize(object sender, System.EventArgs e)
    {
        this.Update();
    }

}