Check if current application is not null in FocusElementManager Curre…

[gpetrou]

…nt_Exit method

[Dirkster99]

Hi, thanks a lot for the pull request - I'd realy like to merge it into the code and release a new version but I need to better understand what the problem is that we are fixing. I could off course be going off and be doing guess work but I prefer communication :-)

Would you be able to give me a short description for this fix? It would, for example, be enough if you give me a short list of test steps and an expectation to verify how the software behaves with and without your fix.

Thanks Dirk

[Dirkster99]

I gather from the links below that you want to improve non-WPF support, like WinForms, correct?

• Why Application.Current == null?

• AppDomain.CurrentDomain

...but if we use AppDomain.CurrentDomain.ProcessExit -= ... I am wondering how much sense this makes if we do not use AppDomain.CurrentDomain.ProcessExit += in other places, as well?

[gpetrou]

Sorry, I should have added a description here as well.
I was seeing an exception here on a WPF application because Exit was called and Application.Current was already null.
I will set it to draft for now as I need to have another look at this in case I missed something. Perhaps just having a null check should be enough.

[Dirkster99]

OK, if you see Application.Current == null on shutdown we should definitely fix this. I just never saw this problem and did not know its possible until I searched the net today.

I am just not sure about the AppDomain bit

• I think we should make the detach eventing consistent with the attaching bit (unless I am missing something)

So, we could either do the change below (and leave AppDomain to some other point in time) or also attach an AppDomain Exit event in SetupFocusManagement. (I hope I get this right since I have not used App.Domain so far):

private static void Current_Exit( object sender, EventArgs e )
{
      if (Application.Current != null)
         Application.Current.Exit -= Current_Exit;

      if( _windowHandler != null )
      {
        _windowHandler.FocusChanged -= new EventHandler<FocusChangeEventArgs>( WindowFocusChanging );
        //_windowHandler.Activate -= new EventHandler<WindowActivateEventArgs>(WindowActivating);
        _windowHandler.Detach();
        _windowHandler = null;
      }
}

[gpetrou]

I took another look at this and I only used a null check for now which seems enough.
Note that the problem does not always happen for me, but when it does the null check seems enough to fix it.

[Dirkster99]

This will be in the next release version 3.5.6 (most likely this weekend just because I don't want to build another release every day) but you could get the binaries from CI should you need it more urgent.

OK, thanks for your time and explaining it - I should have seen the point in the other PR (dah...) but I just hate to guess around critical fixes :-)