Reliable way to check if control is running in VisualStudio Designer

[Muhomorik]

There seems to be no reliable way to detect that custom UserControl is running in Visual Studio Designer.

For years, this solution used to work, and still works for net framework .48

Unfortunately, with out of process designer and .net 8 it doesn't.

We need a better way to detect when user code is in VS designer.

1. Stop designer from running code it shouldn't run
2. Provide designer data (wpf style), so I can preview code without running it.

// Source - https://stackoverflow.com/a/2849244
// Posted by Jonathan, modified by community. See post 'Timeline' for change history
// Retrieved 2026-04-29, License - CC BY-SA 3.0

public MyUserControl()
{
    InitializeComponent();
    m_IsInDesignMode = (LicenseManager.UsageMode == LicenseUsageMode.Designtime);
}

private bool m_IsInDesignMode = true;
public bool IsInDesignMode { get { return m_IsInDesignMode; } }

Current workaround requires this solution everywhere.
Just make a method or property inside SDK

#10960 (comment)

Key problems with current soluitions

• Not developer friendly
• Silently kills designer without any clue what goes wrong.
• Silently removed failed controls from designer file when it fails to run code.

Related:

• Scenario where DesignMode is false from the NET WinForms OOP designer #7448
• .NET Core designer uses LicenseManager.UsageMode = LicenseUsageMode.Runtime instead of LicenseUsageMode.Designtime
• DesignMode with nested Controls