WPF performance issue when resizing the window with lots of controls

Question

I have a WPF window that contains a fancy image with roughly 200 controls (derived from buttons), all of which use one of my 5 templates (paths, shadow effects, etc). Agreed, it is a heavy window to draw. I can live with that.

My problem comes from resizing the window. Maximize/Restore take about 1-2 seconds, but manually dragging the bottom-left corner causes the system to hang for about 5-10 seconds. In that delay, the window is black & contains partial leftovers until the final result is shown. It looks amateurish and that, I can't live with.

Remote connection : using a remote account, I found that the window resize always takes 1-2 seconds, but doesn't draw the "intermediate" stages while I'm dragging the window borders. The result is as snappy as I would expect.

My conclusion is this: It's the redraws during the resize that are bottlenecks.

The inevitable question is this : how can I prevent redrawing the window until the resize is finished?

Thanks in advance for any ideas...

Answer 1

@Seb: I'm beginning to think WPF is not designed for interfaces that go beyond 2-3 controls at a time

Visual Studio 2010 and Expression Blend should be good counterexamples. Though Visual Studio sometimes freezes the bottleneck is definitely not in the WPF rendering.

@Seb: The inevitable question is this : how can I prevent redrawing the window until the resize is finished?

Simply set the window's content visibility to Visibility.Collapsed before the resize/maximize and make it visible afterwards. Though I think you asked the wrong question. Here is the right one

How to make my controls measure/arrange extremely fast?

And to answer it you should take a look at your code. Maybe you intensively use dependency properties in the measuring/arrange algorithm? Or maybe you picked wrong panels (e.g. Grid is slower than Canvas)? Or maybe... I stop guessing here :).

By the way, it's always better to launch your app under profiler and prove the bottleneck rather than assuming the place where it might be. Check Eqatec Profiler it's free yet powerful enough. VS 2010 also offers nice profiling features, though it's far from being free. And you may want to check WPF Performance Suite.

Hope this helps.

Answer 2

Let me know how this works... I am assuming that your root visual item is stretching to horizontally and vertically to fill your window with auto height/width. Get rid of the Auto height/width. On app start up set the dimensions of the root element. There is a FrameworkElements have a size changed event. Register for this on your Application.Current.MainWindow (maybe be a typo, that was from memory). Whenever this event fires, start a timer with a small interval. If you get another resize while the timer is running, ignore it and reset the timer. Once the timer fires, you now know the new size the user desires and that they have (at least for a short period) stopped resizing the window.

Hope that helps!