Question

I have custom tab control where OnPaint method is override.
Then strange growth of tabs occurs. Tabs getting bigger (padding getting bigger) and they width depends on length of the text.
When I use default Tab Control – padding is OK. How to avoid this situation when I use UserPaint?

partial class Tab : TabControl
{
    public Tab()
    {
        InitializeComponent();
        Init();
    }

     private void Init()
    {
        this.SetStyle(ControlStyles.UserPaint, true);
        this.SetStyle(ControlStyles.AllPaintingInWmPaint, true);
        this.SetStyle(ControlStyles.DoubleBuffer, true);
        this.SetStyle(ControlStyles.ResizeRedraw, true);
    }
    protected override void OnPaint(PaintEventArgs e)
    {
       DrawTabPane(e.Graphics);
    }

    private void DrawTabPane(Graphics g)
{
       if (!Visible)
      return;

       // here we draw our tabs
       for (int i = 0; i < this.TabCount; i++)
         DrawTab(g, this.TabPages[i], i);
    }
    internal void DrawTab(Graphics g, TabPage tabPage, int nIndex)
    {
        Rectangle recBounds = this.GetTabRect(nIndex);
        RectangleF tabTextArea = recBounds;

        Point[] pt = new Point[4];
        pt[0] = new Point(recBounds.Left + 1, recBounds.Bottom);
        pt[1] = new Point(recBounds.Left + 1, recBounds.Top + 1);
        pt[2] = new Point(recBounds.Right - 1, recBounds.Top + 1);
        pt[3] = new Point(recBounds.Right - 1, recBounds.Bottom);

        Brush br = new SolidBrush(clr_tab_norm);
        g.FillPolygon(br, pt);
        br.Dispose();

        StringFormat stringFormat = new StringFormat();
        stringFormat.Alignment = StringAlignment.Center;
        stringFormat.LineAlignment = StringAlignment.Center;
        br = new SolidBrush(clr_txt);

        g.DrawString(tabPage.Text, Font, br, tabTextArea, stringFormat);
    }

}

Answer 1

Turning on ControlStyles.UserPaint for controls that are built into Windows, like TabControl, is not the proper thing to do. I assume the bug is in GetTabRect(), it isn’t visible in the snippet.

Instead, you should use the TabControl.DrawMode property and implement the DrawItem event. There’s a good example in the MSDN Library.