#include <CtrlLib/CtrlLib.h>

using namespace Upp;


// subclass EditString, and define an Event(actually a Gate)
class MyEditString : public EditString
{
	bool Key(dword key, int rep)override
	{
		return (WhenKey && WhenKey(key, rep) ) ||
			this->EditString::Key(key, rep);
	}
public:
	Gate<dword, int> WhenKey;
};

// actually use it

class MyWin : public TopWindow
{
public:
	MyWin()
	{
		// the event handler will make the edit throw away key 'A';
		e.WhenKey = [=, this](dword key, int){
			return key == 'a' || key == 'A';
		};
		
		// the event handler will make the edit filter out digit key
		f.WhenKey = [=, this](dword key, int){
			return key >='0' && key <='9';
		};
		Add(e.TopPosZ(5).LeftPosZ(5));
		Add(f.TopPosZ(35).LeftPosZ(5));
	}
	
	MyEditString e, f;
};

GUI_APP_MAIN
{
	MyWin().Run();
}