Doing something when a variable is changed

[abdul]

I have a CGButton class again and then I have four variables (left, top, width, height). When the user changes any of these variables, I want to move the button using API. Is it even possible or will I have to use a function like "Move", "Resize", or something else?

[Jop]

You can do it with MoveWindow I guess, look it up at MSDN...

[Jop]

Make sure you use Properties rather than just a public variable...
than you should be fine...
you know how to call MoveWindow right, so make a property like this:

property void set_Left (int value){
//MoveWindow with the new value of Left
} 

[abdul]

The keyword "property" doesn't exist.

[parksie]

__declspec(property) comes into it somewhere.

[twanvl]

You should make a class with get_variable(value) and set_variable(value).

The problem with __declspec(property) is that it is MSVC specific, and thus not portable.

You can use this macro, to make the code portable (and make it look a little more ugly):

#include <iostream>

// The PPLG macro allows you to 
//  make public memember variables
//  with custom get/let functions
#define PPLG(TYPE, VARNAME) \
private: \
    class VARNAME{ \
	public: \
        inline TYPE operator = (TYPE param) {return let(param);} \
		inline operator TYPE () {return get();}; \
	private: \
	    TYPE val; \
		TYPE let (TYPE param); \
		TYPE get (); \
	}; \
public: \
	VARNAME VARNAME;


// A test class
class a{ 
public:
	PPLG(int,b); //We have a member 'b', of type int
};


// The get & let functions
int a::b::get(){
	return val;
}
int a::b::let(int param){
	std::cout << "Variable set to " << param << std::endl;
	return val=param;
}

// A sample main function
int main(){
	a test_a;
	test_a.b = 10;
	test_a.b = test_a.b + 1;
	return 0;
}

[parksie]

I always found my preferred method (non-declspec) to be:

class test {
public:
    inline test() : m_propname(0) { }

    inline int propname() const { return m_propname; }
    void propname(int pn) { m_propname = pn; }

private:
    int m_propname;
}

[twanvl]

parksie: Something like that is probably better. My macro-using solution was only to show that it's posible to do it. It will make the program harder to understand, since it uses sub-classes hidden away in macros.

[parksie]

Anything is possible Whether you should do it is another matter

I think macros are "discouraged" in C++ for the reasons you gave.

[abdul]

Ok thanks. I guess I'll the use the method of set_property or get_property because it's pretty straight forward.

[Jop]

hmm I suggest Parksie's way to do it... that looks almost like a property...
the thing I suggested was for Managed C++ (.NET), I didn't realize it was the Managed version... don't use it