在Objective-C iOS中增加/减少数字

Question

Im new in xcode and programming for iOS. I have follow this tutorial: http://www.thetutorialblog.com/cocoa-objective-c/creating-a-basic-ipad-application/

I got it working with one "- button", one label and one "+ button". But i want multiple of those, i have add the tutorial code and copy it like this:

IBOutlet UILabel *currentNumber2;

-(IBAction)incrementNumber2:(id)sender2;
-(IBAction)decrementNumber2:(id)sender2;


-(IBAction)incrementNumber2:(id)sender2 {
    number++;
    [currentNumber2 setText:[NSString stringWithFormat:@"%d", number]];
}


-(IBAction)decrementNumber2:(id)sender2 {
    number--;
    [currentNumber2 setText:[NSString stringWithFormat:@"%d", number]];
}

But when I press the first + button, it count up +1 in first label, then when I press the second + button, it continue counting from first button in label2 so it put in 2. Understand?

Answer 1

This is a quintessential behavior of object-oriented programming: that single instance of number is shared across every method call on that object. If you want to support multiple number instances, you have two choices: add more instance variables to your class and start adding more and more code as you make more instances, or simply spawn a new instance of your class.

Note that you will very quickly make a valuable realization: Sometimes the modeled domain has different object requirements than our application domain (ie you should be saying "But I shouldn't have to make more instances of my UIViewController !!", and you're right). This is the first step toward an architecture which iOS deeply supports: Model-View-Controller. Your Model, in this case number , should be decoupled from the controller, which should be capable of handling any quantity of them (not just as many as you happened to create ivars for).

It's a good path to be on :-)