在重写类方法中调用super

Question

我想通过类似UIButtonType的UIButton类添加一个新的自定义:

enum {
    UIButtonTypeMatteWhiteBordered = 0x100
};

@interface UIButton (Custom)

+ (id)buttonWithType:(UIButtonType)buttonType;

@end

是否有可能以super某种方式获得该重写方法的实现？

+ (id)buttonWithType:(UIButtonType)buttonType {
    return [super buttonWithType:buttonType];
}

上面的代码无效,因为在此上下文中super引用UIControl.

Answer 1

您可以在运行时使用自己的自定义方法替换方法,如下所示:

#import <objc/runtime.h>

@implementation UIButton(Custom)

// At runtime this method will be called as buttonWithType:
+ (id)customButtonWithType:(UIButtonType)buttonType 
{
    // ---Add in custom code here---

    // This line at runtime does not go into an infinite loop
    // because it will call the real method instead of ours. 
    return [self customButtonWithType:buttonType];
}

// Swaps our custom implementation with the default one
// +load is called when a class is loaded into the system
+ (void) load
{
    SEL origSel = @selector(buttonWithType:);

    SEL newSel = @selector(customButtonWithType:);

    Class buttonClass = [UIButton class];

    Method origMethod = class_getInstanceMethod(buttonClass, origSel);
    Method newMethod = class_getInstanceMethod(buttonClass, newSel);
    method_exchangeImplementations(origMethod, newMethod);
}

请注意如何使用它,请记住它取代了您的应用使用的每个UIButton的默认实现.此外,它确实覆盖+加载,因此它可能不适用于已经具有+ load方法并依赖它的类.

在你的情况下,你可能最好只是继承UIButton.

编辑:正如Tyler在下面所说,因为你必须使用类级方法来创建一个按钮,这可能是覆盖创建的唯一方法.