When the helpNamespace property in helpProvider is blank after delete the previous saved URL, project exit from runtime automatically when press F1

[Liv-Goh]

.NET version

.NET 9.0 SDK build: 9.0.100-preview.7.24321.3

Did it work in .NET Framework?

Yes

Did it work in any of the earlier releases of .NET Core or .NET 5+?

Yes, this is a regression issue. Not reproduced on .NET 8.0

Issue description

Current Behavior (.NET 9.0): When the helpNamespace property in helpProvider is blank after delete the previous saved URL, project exit from runtime automatically when press F1 and no error exception popped out.

https://github.com/dotnet/winforms/assets/169347065/fb053321-b64c-4e64-ab81-9c72b4d5ffcf

Expected Behavior (.NET 8.0): When the helpNamespace property in helpProvider is blank after delete the previous saved URL, error exception popped out when press F1.

Steps to reproduce

1. Create a WinForms .NET 9.0 project
2. Add a button and helpProvider to form designer
3. Set button "showHelpOnHelpProvider1" property to True
4. Add a random URL (e.g. https://github.com/dotnet/winforms) to helpProvider "HelpNamespace" property, save
5. Delete URL in "HelpNamespace", save
6. Run the project and press F1

[elachlan]

Issue is here: https://github.com/dotnet/winforms/blob/5ba64aeb545308babc843c8d4ecee1e069e85ead/src/System.Windows.Forms/src/System/Windows/Forms/Help/HelpProvider.cs#L130-L144

It should be:

if (!string.IsNullOrEmpty(HelpNamespace))

[elachlan]

@Liv-Goh two things:

• What is the value of the HelpNamespace in the designer.cs?
• What is the stack trace from .NET 8? (we should see what argument exception is thrown.)

[Liv-Goh]

@elachlan the test results are as below

• What is the value of the HelpNamespace in the designer.cs?

HelpNamespace value is empty string in both .NET 8 and 9

• What is the stack trace from .NET 8? (we should see what argument exception is thrown.)

System.ArgumentException HResult=0x80070057 Message=Help URL '' is not valid. (Parameter 'url') Source=System.Windows.Forms StackTrace: at System.Windows.Forms.Help.ShowHTMLFile(Control parent, String url, HelpNavigator command, Object param) at System.Windows.Forms.HelpProvider.OnControlHelp(Object sender, HelpEventArgs hevent) at System.Windows.Forms.Control.OnHelpRequested(HelpEventArgs hevent) at System.Windows.Forms.Control.WmHelp(Message& m) at System.Windows.Forms.Control.WndProc(Message& m) at System.Windows.Forms.ButtonBase.WndProc(Message& m) at System.Windows.Forms.NativeWindow.Callback(HWND hWnd, MessageId msg, WPARAM wparam, LPARAM lparam)

[elachlan]

https://github.com/dotnet/winforms/blob/5ba64aeb545308babc843c8d4ecee1e069e85ead/src/System.Windows.Forms/src/System/Windows/Forms/Help/Help.cs#L53-L64

https://github.com/dotnet/winforms/blob/5ba64aeb545308babc843c8d4ecee1e069e85ead/src/System.Windows.Forms/src/System/Windows/Forms/Help/Help.cs#L290-L309

https://github.com/dotnet/winforms/blob/5ba64aeb545308babc843c8d4ecee1e069e85ead/src/System.Windows.Forms/src/System/Windows/Forms/Help/Help.cs#L194-L196

Help.GetHelpFileType probably needs to check for empty string instead of a standard null check. We also should probably throw ArugementNullException in ShowHTML10Help, like we do in ShowHTMLFile.

[merriemcgaw]

@elachlan would you like to work on this one, or should I assign a team member? This is definitely one I want to take for .NET 9.

[elachlan]

@merriemcgaw happy for someone else to take this on.

[Tanya-Solyanik]

@LeafShi1 - could your teams please take a look?