如何绘制选项卡控件边框

Question

I have a custom tab control but I wish to remove the Left, bottom and right big border like the picture bellow, I dont know how these variable work and searching didnt give me anything related to it. Sorry i just start to learn coding.

Here is the code, i tried to play around with it but it gave me weird borders all the time. Can you help me? Or please tell me how does it work. Thank you!

        public virtual void DrawBorder(Graphics g, Rectangle borderBounds)
        {
            if (Parent.SelectedIndex == -1)
            {
                using (Pen pen = new Pen(BorderColor))
                {
                    g.DrawRectangleFixed(pen, borderBounds);
                }
                return;
            }
            var tabBounds = Parent.GetTabBounds(Parent.SelectedTab);
            Point[] pt = new Point[8];
            if ((Parent.TabLocation & TabLocation.Top) != TabLocation.None)
            {
                pt[0] = borderBounds.GetBottomLeft().GetOffset(0, -1);
                pt[1] = borderBounds.GetBottomRight().GetOffset(-1, -1);
                pt[2] = borderBounds.GetTopRight().GetOffset(-1, 0);
                pt[3] = tabBounds.GetBottomRight().GetOffset(-1, -1);
                pt[4] = tabBounds.GetTopRight().GetOffset(-1, 0);
                pt[5] = tabBounds.GetTopLeft();
                pt[6] = tabBounds.GetBottomLeft().GetOffset(0, -1);
                pt[7] = borderBounds.GetTopLeft();
            }
            else if ((Parent.TabLocation & TabLocation.Bottom) != TabLocation.None)
            {
                pt[0] = borderBounds.GetBottomLeft().GetOffset(0, -1);
                pt[1] = tabBounds.GetTopLeft();
                pt[2] = tabBounds.GetBottomLeft().GetOffset(0, -1);
                pt[3] = tabBounds.GetBottomRight().GetOffset(-1, -1);
                pt[4] = tabBounds.GetTopRight().GetOffset(-1, 0);
                pt[5] = borderBounds.GetBottomRight().GetOffset(-1, -1);
                pt[6] = borderBounds.GetTopRight().GetOffset(-1, 0);
                pt[7] = borderBounds.GetTopLeft();
            }
            using (Pen pen = new Pen(BorderColor))
            {
                g.DrawPolygon(pen, pt);
            }
        }

Answer 1

I agree with others suggesting having a reproducible example makes helping easier. So please don't mind if I was doing the wrong guesses ...

First, what is the point to leave away the outside borders of your tab control? One of the UI purpose of a tab control is to group some and optically separate controls them from the rest of those in your UI.

Second, if you still like to do that, why are you (probably) creating your own TabControl subclass and take care of custom drawing at all? You can archive this in the XAML code directly by using the TabControl BorderThickness property:

<TabControl BorderThickness="0">
    <TabItem Header="Tab1">
        <TextBox Text="First Textbox"/>
    </TabItem>
    <TabItem Header="Tab2">
        <TextBox Text="Second Textbox"/>
    </TabItem>
</TabControl>

Finally, if you like to style any control rather than adding / changing its functionality, think about using XAML styling instead of creating a custom control.