Question

I created a custom control which I want to use to overlay part of my form with status information on demand. It should display a text and have a background color depending on the type of information. Here is the still incomplete code.

public partial class StatusPanel : UserControl
{
    public enum PanelStyle
    {
        Info,
        Warning,
        Error
    }

    public PanelStyle Style { get; set; }

    public StatusPanel()
    {
        InitializeComponent();

        this.imgGreen = new Bitmap(256, 256, PixelFormat.Format32bppArgb);
        using(Graphics g = Graphics.FromImage(this.imgGreen))
        {
            g.Clear(Color.Transparent);
            Brush bg = new SolidBrush(Color.FromArgb(200, Color.Green));
            g.FillRectangle(bg, 0, 0, 256, 256);
        }

        this.imgYellow = new Bitmap(256, 256, PixelFormat.Format32bppArgb);
        using(Graphics g = Graphics.FromImage(this.imgYellow))
        {
            g.Clear(Color.Transparent);
            Brush bg = new SolidBrush(Color.FromArgb(10, Color.Yellow));
            g.FillRectangle(bg, 0, 0, 256, 256);
        }
    }

    protected readonly Font font = new Font("Arial", 12.0F);

    protected readonly Brush textBrush = new SolidBrush(Color.Black);

    protected readonly Image imgGreen;

    protected readonly Image imgYellow;

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

    protected override void OnPaintBackground(PaintEventArgs e)
    {
        // do not draw background
    }

    protected override void OnPaint(PaintEventArgs e)
    {
        e.Graphics.TextRenderingHint = System.Drawing.Text.TextRenderingHint.AntiAlias;
        e.Graphics.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBilinear;
        e.Graphics.PixelOffsetMode = System.Drawing.Drawing2D.PixelOffsetMode.HighQuality;
        e.Graphics.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

        Image img = GetImage();

        e.Graphics.DrawImage(img, 0, 0, this.Width, this.Height);

        e.Graphics.DrawString("ABC", this.font, this.textBrush, 1.0F, 1.0F);
    }

    protected Image GetImage()
    {
        return (this.Style == PanelStyle.Info) ? this.imgGreen : this.imgYellow;
    }
}

This works quite fine. But when I put some buttons on a form and one of this controls infront of them, they will “overdraw” when the mouse moves over the button and the highlight effects redraws them.

How will my component be notified that it needs to redraw because underlying control have redrawn?

Answer 1

register a paint-handler to all controls under Parent.Control and a handler for Parent.ControlAdded that registers your paint-handler

something like this:

private void myDummyUserControl_Load(object sender, EventArgs e)
{
    var uc = (DummyUserControl)sender;
    uc.Parent.ControlAdded += new ControlEventHandler(Parent_ControlAdded);
    foreach (Control c in uc.Parent.Controls)
    {
        if (uc == c)
            continue;
        c.Paint += new PaintEventHandler(c_Paint);
    }
}

void c_Paint(object sender, PaintEventArgs e)
{
    //checks & paint stuff here
}

void Parent_ControlAdded(object sender, ControlEventArgs e)
{
    e.Control.Paint += new PaintEventHandler(c_Paint);
}

//edit

not sure if you need to use recursion to go down the tree of child controls and need to add handlers on those too …