C# ASPX: Cannot read properties of undefined (reading 'keydown') - c#

I am not that familiar with ASPX. Once I save a form on my page, application keeps working as expected, except that I receive this exception in console. Exception
I am not able to find the source of the problem or any place where this exception may occur related to keydown event. Also when I click on the underlined title on the right side, it takes me to console and I can see these strange stack traces. Stacktrace
Can anyone guide me on how to approach? Also can this problem be related to some config keys in Web.Config not specifically the code itself?
Thank you
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Related

WPF default behavior on exceptions

Please note that I'm aware of possible solution and have read some other SO posts which will answer the question how to handle unhandled exceptions globally and I'm not asking if it is good practice or not.
What I'm asking is:
Why do WPF applications close on exceptions?
I always thought that it is the expected behaviour, however when researching how to implement the exception handling globally in WPF, I encountered this sentence on the Microsoft documentation page:
By default, Windows Presentation Foundation catches unhandled exceptions, notifies users of the exception from a dialog box (from which they can report the exception), and automatically shuts down an application.
But my experience is different, the application just exits without any warning, so any unhandled exception will be a total mystery for the user and me as a developer.
My question is really: Am I missing something, or is Microsoft wrong about their own framework?
The docs seems to be wrong.
By default, a WPF application exits without any dialog box when an unhandled exception is thrown on the dispatcher thread.
You may consider to edit the docs and submit a PR on GitHub by clicking on the "Edit" button in the top right corner of the page.

Exception Unhandled: System.OutOfMemoryException: 'Out of memory.'

Basically, it has been 3 days since I'm trying to resolve this issue. I'm coding a sort of Mail Client in C# - everything was working pretty much good, while I started getting this unhandled exception... I would like to post a code section, but I do not know exactly what it causing this problem. A good fact is that the project is pushed over Github. Over internet it is said that maybe some variables used on some loops may cause the problem; I've already tried to edit some parts, but unluckily nothing worked...
Latest edit:
Added a Bunifu.Framework.UI.BunifuFlatButton over a UserControl. On click event, this happens:
MessageBox.Show(settingsControl.FLAG.ToString());
- I was testing if this would print me the int FLAG variable taken from another UserControl called settingsControl.
Every suggestion is appreciated. Thanks!

Object already in use elsewhere

When I am drag picture Box in Windows form it's showing as Object already in use elsewhere.
I searched over Stack overflow and other website says that error is Threads, Coding oriented and GDI+. But I didn't write any coding in that. I just drag the picture box. Then it shows “already in use elsewhere”.
Anyone Explain?
This is usually an indicator that something else, potentially some other thread in your own application, already has the target file that you're trying to save locked at the file system level. If you look at the inner exception I believe it should mention this. If it's not directly in the InnerException Another way to confirm this (or discover what it might really be instead) is to turn on first chance exceptions in the debugger and watch for what exception is being thrown "underneath" Save and then being turned into this generic exception.
A Generic Error occured at GDI+ in asp.net mostly because of missing target folder / access permissions.

winform application exception DragDrop occurs outside of IDE

My winform application is failing when run outside of the IDE with a dragdrop exception. The error does not occur while being run from inside the ide (VS2008). How can I trace this. I have seen mention of using JIT in the error box that is displayed post error - will this help me trace my problem?
Don't know if this will be helpful, but...awhile ago I was getting DragDropException when my WinForms app was being run on a thumb drive, not a full system. The form generating the error had no drag-and-drop feature. I never figured out the problem, but I saw that a UserControl on that form had defaulted AllowDrop=true unnecessarily. Once I turned that off, the problem went away.
If your form is intended to support drag-and-drop, I'd look into on what thread the form generating the exception is instantiated. My understanding is that Microsoft's implementation of drag-and-drop is COM-based, which must be initialized in an STA thread. Putting the [STAThread] attribute before your program's entry point will accomplish this.

Viewing XAML file in the VisualStudio UI Designer executes the code behind file?

Please humor me as I might be crazy.
Does viewing xaml in the Visual Studio UI designer execute the code-behind file?
For the past while whenever I try to view the main xaml file of my WPF application it throws an exception, but because I've been busy with other things I never really looked into it until today. Now I notice that in the exception's call stack it's calling many of the code-behind's methods, including methods like Window_Loaded (!). It's like it's trying to run my application while I'm designing it and obviously failing.
So I'm also wondering why it does this.
I'm also wondering how exactly I'm supposed to debug this as it's doing all this behind my back.
The actual exception comes from the fact that my application uses an unmanaged dll that it tries to use but somehow can't find it for some reason.
[Edit]
I've tried moving my unmanaged DLL to Windows/System32, but I still get the same exception.
Thanks!
Yes, there are things (like constructors) that get evaluated at design time. If your code is throwing an exception in the designer you can add this:
if (DesignerProperties.GetIsInDesignMode(this))
{
return;
}

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