如何在Objective-C中使用覆盖方法临时定义子类？

Question

I want to define a method in a class A. The method should be over-writable for any i̶n̶s̶t̶a̶n̶c̶e̶ subclass of the class A. The instances of subclasses will be stored in a NSArray. I tried to use the delegate. But it didn't work. I checked a few articles posted online such as How do I create delegates in Objective-C? and http://www.tutorialspoint.com/ios/ios_delegates.htm But they seem not what I can use to achieve my goal. Could anyone who are familiar with this give me a hint please?

For example,

I create a base class called BaseClass for the UICollectionViewCell and inside the BaseClass there is a ActionMethod . Click different collection cell will result in a different action. So I will define a subclass for each cell that inherited from BaseClass to implement different action. Then how to overwrite the ActionMethod for each subclass?

Answer 1

You mean overriding , not over-writing methods. In Objective-C, you don't have to do anything other than put an implementation with the exact same method signature in the subclass.

Answer 2

Generally, you define a base class, such as Shape, which has a set of methods common to all shapes, such as, getEnclosingRectangle, getShapeArea, etc. Then you define separate subclasses of shapes, such as oval, polygon, rectangle and triangle. You can even define subclasses of those shapes, such as circle derived from oval. Then you could store all your ovals, rectangles and triangles (for example) in an NSArray, and call the getArea method for each of them. And each would have their particular getArea method defined in their class.

Answer 3

A delegate would work here. Another option is to use a callback block, eg

@interface Cell : NSObject

@property (nonatomic, copy) void(^onAction)();

- (void)actionMethod;

@end

@implementation Cell

- (void)actionMethod {
    self.onAction();
}

@end

Used as

Cell *cell1 = [[Cell alloc] init];
cell1.onAction = ^{
    NSLog(@"Action 1");
};

Cell *cell2 = [[Cell alloc] init];
cell2.onAction = ^{
    NSLog(@"Action 2");
};

As you can see, you don't need subclasses, you can just add that code to every cell dynamically.