Drawing on Scrollable Containers

Creating a scrollable container is straightforward, since the control class inherits from System.Windows.Forms.ScrollableControl. This class exposes several useful properties

• AutoScroll This determines if scroll bars should be displayed if there is a control in the container that is outside the bounds of the client rectangle.
• AutoScrollMinSize This determines the minimum size of the client rectangle so that scroll bars do not appear. If the client rectangle is smaller than this, then there will be scroll bars.
• AutoScrollMargin This sets the minimum space between any child control and a scroll bar. It ensures that there will always be space between child controls and the scroll bar.
• DisplayRectangle This is a read-only property that returns the smallest rectangle that will contain all of the controls in the container. This is calculated by the size and location of the controls in the container. If the size or location are changed, then the DisplayRectangle will be recalculated. If there are no controls in the container, then the DisplayRectangle will equal the client rectangle.

Scrollable Forms

It is possible to make the main form a scrollable container, but there is a problem with adding scroll bars and a status bar: the scroll bars will be added below the status bar. This means that the status bar could be scrolled out of view. This is not the normal behaviour for a status bar.

Adding a Scrollable Panel

The next attempt is to add the status bar, then add a scrollable panel whose docking is set to full. Drawing to this panel has problems because the DisplayRectangle will always be the same as the ClientRectangle, so the scroll bars will never appear, unless additional controlls are added to the panel.

If this panel is undocked, then the scroll bars will hide the status bar.

Adding Another Panel

The final attempt is to add a new panel to the scrolling panel. Set the size of this panel to the size of the desired drawing area. The DisplayRectangle will be set to the size of this panel. Scroll bars will appear whenever the client rectangle is smaller than the panel. Be sure to send the status bar and toolbar to the back, so that they are behind the scrolling panel.

Scroll Increments

Line Scroll

The size of the line scroll is 5 pixels.

Page Scroll

The size of the page scroll is equal to the size of the client rectangle.