Question

I have a class that extends TabControl, basically to have one with the tabs down the left hand side instead of along the top. To do I have set it to be custom drawn.

The problem is when this is put onto a form via the designer, it easily makes the designer loose track of itself and just give up and display nothing. To fix it I have to close the designer and re-open it and then everything is fine until I hit debug, or I go to a code window for a while and come back, where it gives up again.

Is there anything I can do to help visual studio a bit? As while its not throwing errors, it is getting a little tedious now. I’m using visual studio 2008.

Here is the code that extends the tab control, if anyone sees any issues that could be causing this it’d be very appreciated.

public class VerticalTabControl : TabControl
{
    private Color tabColour1 = Color.AliceBlue;

    public Color TabColour1
    {
        get { return tabColour1; }
        set { tabColour1 = value; this.Refresh(); }
    }

    private Color tabColour2 = Color.White;

    public Color TabColour2
    {
        get { return tabColour2; }
        set { tabColour2 = value; this.Refresh(); }
    }

    private Color selectedTabColor1 = Color.AliceBlue;

    public Color SelectedTabColor1
    {
        get { return selectedTabColor1; }
        set { selectedTabColor1 = value; this.Refresh(); }
    }

    private Color selectedTabColor2 = Color.White;

    public Color SelectedTabColor2
    {
        get { return selectedTabColor2; }
        set { selectedTabColor2 = value; this.Refresh(); }
    }

    private Color backgroundColour = Color.White;

    public Color BackgroundColour
    {
        get { return backgroundColour; }
        set { backgroundColour = value; this.Refresh(); }
    }

    private Color tabTextColour = Color.Black;

    public Color TabTextColour
    {
        get { return tabTextColour; }
        set { tabTextColour = value; this.Refresh(); }
    }

    protected override void OnParentChanged(EventArgs e)
    {
        base.OnParentChanged(e);
        this.Parent.Resize += new EventHandler(Parent_Resize);
    }

    void Parent_Resize(object sender, EventArgs e)
    {
        this.Refresh();
    }


    public VerticalTabControl()
        : base()
    {
        this.Alignment = TabAlignment.Left;
        this.SizeMode = TabSizeMode.Fixed;
        this.ItemSize = new Size(50, 120);
        this.DrawMode = TabDrawMode.OwnerDrawFixed;
        this.DrawItem += new DrawItemEventHandler(VerticalTabControl_DrawItem);          
    }

    void VerticalTabControl_DrawItem(object sender, DrawItemEventArgs e)
    {
        Graphics g = e.Graphics;
        TabControl ctrl = sender as TabControl;
        String sText = ctrl.TabPages[e.Index].Text;

        Rectangle r = new Rectangle(e.Bounds.Left, e.Bounds.Top, e.Bounds.Width, e.Bounds.Height);

        if (e.Index == ctrl.SelectedIndex)
        {
            using (LinearGradientBrush gb = new LinearGradientBrush(r, this.selectedTabColor1, this.selectedTabColor2, LinearGradientMode.Horizontal))
            {
                e.Graphics.FillRectangle(gb, r);
            }
        }
        else
        {
            using (LinearGradientBrush gb = new LinearGradientBrush(r, this.tabColour1, this.tabColour2, LinearGradientMode.Horizontal))
            {
                e.Graphics.FillRectangle(gb, r);
            }
        }

        // Set up the page and the various pieces.
        TabPage page = ctrl.TabPages[e.Index];

        // Set up the offset for an icon, the bounding rectangle and image size and then fill the background.
        int iconOffset = 0;
        Rectangle tabBackgroundRect = e.Bounds;

        // If we have images, process them.
        if (this.ImageList != null)
        {
            // Get sice and image.
            Size size = this.ImageList.ImageSize;
            Image icon = null;
            if (page.ImageIndex > -1)
              icon = this.ImageList.Images[page.ImageIndex];
            else if (page.ImageKey != "")
              icon = this.ImageList.Images[page.ImageKey];

            // If there is an image, use it.
            if (icon != null)
            {
             Point startPoint = new Point(tabBackgroundRect.X + 6,
                   tabBackgroundRect.Y + 2 + ((tabBackgroundRect.Height - size.Height) / 2));
               e.Graphics.DrawImage(icon, new Rectangle(startPoint, size));
                iconOffset = size.Width + 4;
            }
        }

        // Draw out the label.
        SizeF sizeText = g.MeasureString(sText, ctrl.Font);
        int iX = e.Bounds.Left + 6 + iconOffset;
        int iY = e.Bounds.Top + (e.Bounds.Height / 2) - (int)(sizeText.Height / 2);

        using (Brush ForeBrush = new SolidBrush(tabTextColour))
        {
            g.DrawString(sText, ctrl.Font, ForeBrush, iX, iY);
        }

        Rectangle rec = ctrl.GetTabRect(ctrl.TabPages.Count - 1);
        Rectangle recF = new Rectangle(0, rec.Bottom, this.ItemSize.Height, ctrl.Height - rec.Bottom);
        using (SolidBrush bb = new SolidBrush(backgroundColour))
        {
            g.FillRectangle(bb, recF);
        }
    }

}

Answer 1

turns out this was the offending bit of code

protected override void OnParentChanged(EventArgs e)
{
    base.OnParentChanged(e);
    this.Parent.Resize += new EventHandler(Parent_Resize);
}

‘this.Parent’ was sometimes null and so an exception would have been thrown which would have caused the designer to fail.

Have now fixed this and also tidied up the event hooking so I didn’t leave hooks everywhere. Seems to work fine now. Thanks for your help whoever answered this and deleted their answer for some reason.