Category关联属性

为一个对象设置关联对象，实现为其添加属性的效果，使用方法

objc_setAssociatedObject
objc_getAssociatedObject

UIView+LeoExtension.h

#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>
@interface UIView (LeoExtension)
@property (copy,nonatomic)NSString * leo_anaylizeTitle;
@end

UIView+LeoExtension.m

#import "UIView+LeoExtension.h"
#import <objc/runtime.h>
static const char kAnaylizeTitle;

@implementation UIView (LeoExtension)

-(NSString *)leo_anaylizeTitle{
    return objc_getAssociatedObject(self, &kAnaylizeTitle);
}
-(void)setLeo_anaylizeTitle:(NSString *)leo_anaylizeTitle{
    objc_setAssociatedObject(self, &kAnaylizeTitle,leo_anaylizeTitle, OBJC_ASSOCIATION_COPY_NONATOMIC);
}
@end

Method Swizzling

#import <objc/runtime.h>

@implementation UIViewController (Tracking)

+ (void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        Class class = [self class];
        SEL originalSelector = @selector(viewWillAppear:);
        SEL swizzledSelector = @selector(xxx_viewWillAppear:);
        Method originalMethod = class_getInstanceMethod(class, originalSelector);
        Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);

        // When swizzling a class method, use the following:
        // Class class = object_getClass((id)self);
        // ...
        // Method originalMethod = class_getClassMethod(class, originalSelector);
        // Method swizzledMethod = class_getClassMethod(class, swizzledSelector);

        BOOL didAddMethod =
            class_addMethod(class,
                originalSelector,
                method_getImplementation(swizzledMethod),
                method_getTypeEncoding(swizzledMethod));

        if (didAddMethod) {
            class_replaceMethod(class,
                swizzledSelector,
                method_getImplementation(originalMethod),
                method_getTypeEncoding(originalMethod));
        } else {
            method_exchangeImplementations(originalMethod, swizzledMethod);
        }
    });
}

#pragma mark - Method Swizzling

- (void)xxx_viewWillAppear:(BOOL)animated {
    [self xxx_viewWillAppear:animated];
    NSLog(@"viewWillAppear: %@", self);
}

@end

交叉后的Runtime顺序:

• 根据@selector(viewWillAppear:)找到自定义的xxx_viewWillAppear实现
• 自定义的xxx_viewWillAppear实现，向Self发送@selector(xxx_viewWillAppear)
• 根据@selector(xxx_viewWillAppear)，找到默认的SDK中viewWillAppear的实现
• 执行默认SDK中viewWillAppear代码
• 执行NSLog(@"viewWillAppear: %@", self);
• 结束