How do you troubleshoot WPF UI problems?

Question

I'm working on a WPF application that sometimes exhibits odd problems and appears to hang in the UI. It is inconsistent, it happens in different pages, but it happens often enough that it is a big problem. I should mention that it is not a true hang as described below.

My first thought was that the animations of some buttons was the problem since they are used on most pages, but after removing them the hangs still occur, although seemingly a bit less often. I have tried to break into the debugger when the hang occurs; however there is never any code to view. No code of mine is running. I have also noticed that the "hang" is not complete. I have code that lets me drag the form around (it has no border or title) which continues to work. I also have my won close button which functions when I click it. Clicking on buttons appears to actually work as my code runs, but the UI simply never updates to show a new page.

I'm looking for any advice, tools or techniques to track down this odd problem, so if you have any thoughts at all, I will greatly appreciate it.

EDIT: It just happened again, so this time when I tried to break into the debugger I chose to "show disassembly". It brings me to MS.Win32.UnsafeNativeMethods.GetMessageW. The stack trace follows:

[Managed to Native Transition]

WindowsBase.dll!MS.Win32.UnsafeNativeMethods.GetMessageW(ref System.Windows.Interop.MSG msg, System.Runtime.InteropServices.HandleRef hWnd, int uMsgFilterMin, int uMsgFilterMax) + 0x15 bytes WindowsBase.dll!System.Windows.Threading.Dispatcher.GetMessage(ref System.Windows.Interop.MSG msg, System.IntPtr hwnd, int minMessage, int maxMessage) + 0x48 bytes WindowsBase.dll!System.Windows.Threading.Dispatcher.PushFrameImpl(System.Windows.Threading.DispatcherFrame frame = {System.Windows.Threading.DispatcherFrame}) + 0x8b bytes WindowsBase.dll!System.Windows.Threading.Dispatcher.PushFrame(System.Windows.Threading.DispatcherFrame frame) + 0x49 bytes WindowsBase.dll!System.Windows.Threading.Dispatcher.Run() + 0x4c bytes PresentationFramework.dll!System.Windows.Application.RunDispatcher(object ignore) + 0x1e bytes PresentationFramework.dll!System.Windows.Application.RunInternal(System.Windows.Window window) + 0x6f bytes PresentationFramework.dll!System.Windows.Application.Run(System.Windows.Window window) + 0x26 bytes PresentationFramework.dll!System.Windows.Application.Run() + 0x19 bytes WinterGreen.exe!WinterGreen.App.Main() + 0x5e bytes C# [Native to Managed Transition] [Managed to Native Transition] mscorlib.dll!System.AppDomain.nExecuteAssembly(System.Reflection.Assembly assembly, string[] args) + 0x19 bytes mscorlib.dll!System.Runtime.Hosting.ManifestRunner.Run(bool checkAptModel) + 0x6e bytes mscorlib.dll!System.Runtime.Hosting.ManifestRunner.ExecuteAsAssembly() + 0x84 bytes mscorlib.dll!System.Runtime.Hosting.ApplicationActivator.CreateInstance(System.ActivationContext activationContext, string[] activationCustomData) + 0x65 bytes mscorlib.dll!System.Runtime.Hosting.ApplicationActivator.CreateInstance(System.ActivationContext activationContext) + 0xa bytes mscorlib.dll!System.Activator.CreateInstance(System.ActivationContext activationContext) + 0x3e bytes Microsoft.VisualStudio.HostingProcess.Utilities.dll!Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssemblyDebugInZone() + 0x23 bytes mscorlib.dll!System.Threading.ThreadHelper.ThreadStart_Context(object state) + 0x66 bytes mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state) + 0x6f bytes mscorlib.dll!System.Threading.ThreadHelper.ThreadStart() + 0x44 bytes

Answer 1

Try removing the borderless behavior of your window and see if that helps. Also, are you BeginInvoke()'ing or Invoke()'ing any long running operations?

Another thing to look at: When you break into your code, try looking at threads other than your main thread. One of them may be blocking the UI thread.

Answer 2

One great tool is Snoop. Really nice for looking at what WPF objects are displayed on the visual tree at a given time. I'm not sure how much it will help, but it's possible you're jamming the UI thread with a lot of extra things it has to do. Snoop may be able to help you track down what is on the screen to give you an idea what to look for.

Answer 3

Your WPF app could be hanging due to performance issues. Try using Perforator to see if you have any parts that are software rendered or if you app is using too much video ram.

Answer 4

OK, more information. When the behavior occurs, I can get the window back to normal by minimizing and then maximizing, or at least it does it while using Perforator. This make it seem like it may be a window redraw issue, almost like the region isn't flagged as needing redrawn?

Answer 5

I have removed the borderless behavior as suggested by Bob King. To date, that seems to have gotten rid of the problem.

Now the question is, why and how can I fix the issue? The product is designed to have no border with some rounded corners and transparent parts.

Answer 6

Hurrah,... it seems that the problem isn't related to borderless windows (at least in my case).

There is a big performance hit when you set AllowsTransparency to true. So much of a hit it would seem, that the whole thing can hang the UI thread. Very strange behaviour. Could be related to this ticket