Question

I have always found it hard to decide when I should create a single object and pass it to every object that needs it, or create a new object for every object which needs that item.

Some cases are so obvious, like entity objects which are readonly after allocation and instantiation. You can pass the same object anywhere and not worry about another object modifying it, which ruins the other objects holding a reference to it.

My problem mainly lies with objects that represent themselves to the user. Objects like CCSprite in cocos2d, NSMenuItem in Cocoa (AppKit) and other objects with visual representation..

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Examples:

In cocoa, i know that I have to create an NSMenu for each NSPopUpButton, so that the selection for a specific button does not affect the rest. But, what about the NSMenuItems contained within? Can I create a single set and pass them to all the menus? What are your grounds, or how did you come to such a conclusion?

Other example:

In cocos2d, and almost all GUI based applications, you can pass to a button two images/sprites/…etc. such that one is for the normal state, and the other is for the selected (highlighted, pressed, clicked) state. Can I pass the same image/sprite/…etc. to both, making them point to the same object?

I hope this is not an implementation related issue (that it ultimately depends on the implementation) , since I face it in a lot of my programming projects, in cocoa, cocos2d, Java … etc.

PS: I need help with choosing the proper tags

Answer 1

I suggest creating new instances unless doing this causes a performance problem. Sharing an NSMenuItem instance among many NSMenu makes it more difficulty to maintain control over that instance, which increases the risk of errors.