Mnemonics for hidden controls

21 Dec 2025

As you may know, you can switch between Windows controls using mnemonics. If you see an underlined character in any Windows application, you can press Alt + this character to set focus to this control or to click a button. For example, in this window, you can press:

• Alt+D to go to the Decoded JSON Web Token field,
• Alt+C to click the Copy button, or
• Alt+F to uncheck the Format JSON option.

The underlines become visible when you press the Alt key.

However, if a control is hidden in Win32 (using the ShowWindow function), the mnemonic for it still works. You can still press a hidden button if you know its mnemonic. Imagine you hide a button for unauthorized users, but these users can press it using the Alt+character keyboard shortcut, so this behavior can even create a security vulnerability.

If your application shows some controls and hides others depending on the state, you may have two controls with the same mnemonic. If one of them is hidden, it may be activated instead of the visible control with the same mnemonic. This happened to me when testing the previous version of Aba Search and Replace.

The fix is easy: you need to disable a control when you hide it and enable it when you show it. Each ShowWindow call should be paired with an EnableWindow call; you could create a small function that will call both and use it everywhere instead of ShowWindow.

This quirk applies only to the classic Win32 applications. I've tested with Windows Forms, WPF, and WinUI 3, and you cannot press a hidden button using its mnemonic there. Win32 provides an extra flexibility: you can create a mnemonic that does not correspond to any visible control, but this flexibility is usually not needed and can cause confusion.

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