How to implement my own scrolling in windows form

I have an MdiClient derived from Form and I use the surface of this control for GDI+ drawing. I run into troubles implementing my own scrolling for this control. I set both AutoScroll and AutoSize properties to false and try to use form's own horizontal/vertical scrollbars instead of placing my own. Observed form's behavior is quite confusing. To begin with there are two properties (A) HScroll and (B) HorizontalScroll that also allows access to Visible attribute.

I ended up setting HorizontalScroll.Visible = true and leaving HScroll = false (same for vertical) but am curious why there are two of them. Documentation implies that both control visibility of horizontal scroll bar but they do not appear to access the same data. Besides, it looks like HScroll is being reset on every paint. At the moment I ignore existence of HScroll/VScroll. Is it OK for my application?

What is more critical for me is the ability control placement of the thumb on scroll bars. I set VerticalScroll attributes Minimum = 0, Maximum = 100, and Value = 50 but when form is displayed thumb is positioned at the start of scrollbar not in the middle. Why? Also when user clicks on horizontal scrollbar an event handler for horizontal scrolling is invoked but meanwhile form has already reset VerticalScroll.Value to 0 (without raising vertical scroll event). What is going on?

I probably don't understand how framework expects me to implement what I need. Can someone开发者_运维问答 shed some light.

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Credit goes to LarsTech who pointed me towards good solution. Setting large AutoScrollMinSize automatically does whatever needs to be done enabling and controlling form scrollbars. There is one potential trap to watch for. Be aware that programmatic attempts to set AutoScrollPosition will be ignored until form is shown. So if you want your form to open with scrollbars not in the default (0,0) position then place your code inside form_shown event handler.

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Just set the AutoScrollMinSize to your desired canvas.

Quick example:

using System.Drawing;
using System.Drawing.Drawing2D;

private void Form1_Load(object sender, EventArgs e)
{
  this.AutoScrollMinSize = new Size(1200, 1200);
}

private void Form1_Paint(object sender, PaintEventArgs e)
{
  e.Graphics.Clear(SystemColors.Window);
  using (Matrix mx = new Matrix(1, 0, 0, 1, this.AutoScrollPosition.X, this.AutoScrollPosition.Y))
  {
    e.Graphics.Transform = mx;
    e.Graphics.FillEllipse(Brushes.Red, new Rectangle(250, 250, 100, 100));
  }
}

See these links: Understanding Windows Forms AutoScroll and How to back-track the mouse to the virtual page.