From RAD Studio API Documentation
typedef void __fastcall (__closure *TKeyEvent)(System::TObject* Sender, System::Word &Key, System::WideChar &KeyChar, System::Classes::TShiftState Shift);
A TKeyEvent event handler must be called with the following parameters:
Sender--a pointer to the object that called this function.
Key--the key on the keyboard.
KeyChar--the character code.
Shift-- indicates which shift keys--SHIFT, CTRL, ALT, and CMD (only for Mac)--were down when the specified key was pressed with the control in focus.