How to draw a control, without drawing the control.

Question

I've got a list of UserControl objects; when a menu option is clicked to go to another section of the application it does the following:

1. Set the currently displayed usercontrol to visible
2. Clear the main panel's Controls list
3. New up the requested control (if not already created in the list)
4. Add the new control to the main panels' Controls list
5. Dock the new control to fill
6. Set the new control to visible

I did this because, previously all of the areas of the application were not user controls and they were just collections of controls in a TabControl. The underlying code was monstrous (the code in frmMain was 13000+ lines).

It works well. All controls (what each tab page would have been before) manage their own behaviour, each control has a small code footprint. I can have a sexy menu. All good things.

However, obviously there's a problem. Before, the tabcontrol would load on startup, and all tabs would render (but weren't seen). One tab page in particular has a scheduling control on it and it takes a good 3-4 seconds to draw and adjust its layout. Now that controls are loaded and shown as they're needed, the first time you view this particular control, you see it load and adjust its size/formatting/etc. Which is hardly esthetically pleasing.

My question is, how can I load and render this control so that it'll render and figure out its layout, but without it actually showing the user?

I've tried simple things like:

ScheduleWindow scheduler = new ScheduleWindow() { Visible = false; }
mainPanel.Controls.Add(scheduler);
scheduler.Visible = true;

I've tried creating and loading the control on its own thread (with numerous difficulties) and it still didn't do anything...

Is there any way to achieve what I'm looking for?

Answer 1

Try calling scheduler.Handle.ToString() and/or scheduler.Refresh().

Answer 2

Try using the SuspendLayout() and ResumeLayout() methods on the main form? When you call SuspendLayout(), you can do whatever you need to do with the controls you are adding, such as docking, resizing, etc. When you call ResumeLayout(), all changes will be applied at once, and should happen instantaneously.

Alternatively, some controls have a BeginUpdate() and EndUpdate() method, which suspend redraws for that control, allowing you to do heavy work (such as adding thousands of items to a ListView) without seeing the updates happen live. This also improves performance, as rather than redrawing every time the control is changed, you batch changes, then redraw once.