Creating a shortcode, but getting tied up with OOP and Classes?

I don’t see any issue with the OOP code that would cause it not to work.

I think the problem is with the shortcode itself. I don’t believe shortcodes can have spaces. Show Form is not a valid shortcode name. [Show Form] would be parsed as as a shortcode named Show with an attribute Form.

The conventional format for this shortcode would be show_form.