How to show an extra character on the keyboard with a long press

Question

How to add an extra character with a long key press on the virtual keyboard, as in the following image:

I am using this library .

Answer 1

Apple provides a well-explained programming guide for custom keyboards here .

According to this guide:

Listed below are these features and others.

• Appropriate layout and functions based on the type of keyboard
• Auto Correction and Suggestion
• Automatic capitalization
• Double Span Auto Period

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Keycap Artwork.

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Update:

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