Runtime详解（下）

- (void)viewDidLoad {
    [super viewDidLoad];
    // 方案一：先搞个分类，定义一个能加载图片并且能打印的方法+ (instancetype)imageWithName:(NSString *)name;
    // 方案二：交换 imageNamed 和 ln_imageNamed 的实现，就能调用 imageNamed，间接调用 ln_imageNamed 的实现。
    UIImage *image = [UIImage imageNamed:@"123"];
}

#import <objc/message.h>
@implementation UIImage (Image)
/**
 load方法: 把类加载进内存的时候调用,只会调用一次
 方法应先交换，再去调用
 */
+ (void)load {

    // 1.获取 imageNamed方法地址
    // class_getClassMethod（获取某个类的方法）
    Method imageNamedMethod = class_getClassMethod(self, @selector(imageNamed:));
    // 2.获取 ln_imageNamed方法地址
    Method ln_imageNamedMethod = class_getClassMethod(self, @selector(ln_imageNamed:));

    // 3.交换方法地址，相当于交换实现方式;「method_exchangeImplementations 交换两个方法的实现」
    method_exchangeImplementations(imageNamedMethod, ln_imageNamedMethod);
}

/**
 看清楚下面是不会有死循环的
 调用 imageNamed => ln_imageNamed
 调用 ln_imageNamed => imageNamed
 */
// 加载图片 且 带判断是否加载成功
+ (UIImage *)ln_imageNamed:(NSString *)name {

    UIImage *image = [UIImage ln_imageNamed:name];
    if (image) {
        NSLog(@"runtime添加额外功能--加载成功");
    } else {
        NSLog(@"runtime添加额外功能--加载失败");
    }
    return image;
}

/**
 不能在分类中重写系统方法imageNamed，因为会把系统的功能给覆盖掉，而且分类中不能调用super
 所以第二步，我们要 自己实现一个带有扩展功能的方法.
 + (UIImage *)imageNamed:(NSString *)name {

 }
 */
@end

@interface NSObject (Property)

// @property分类:只会生成get,set方法声明,不会生成实现,也不会生成下划线成员属性
@property NSString *name;
@property NSString *height;
@end

@implementation NSObject (Property)

- (void)setName:(NSString *)name {

    // objc_setAssociatedObject（将某个值跟某个对象关联起来，将某个值存储到某个对象中）
    // object:给哪个对象添加属性
    // key:属性名称
    // value:属性值
    // policy:保存策略
    objc_setAssociatedObject(self, @"name", name, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (NSString *)name {
    return objc_getAssociatedObject(self, @"name");
}

// 调用
NSObject *objc = [[NSObject alloc] init];
objc.name = @"123";
NSLog(@"runtime动态添加属性name==%@",objc.name);
//结果如下：

2016-02-17 19:37:10.530 runtime[12761:543574] runtime动态添加属性--name == 123

//关联对象
void objc_setAssociatedObject(id object, const void *key, id value, objc_AssociationPolicy policy)
//获取关联的对象
id objc_getAssociatedObject(id object, const void *key)
//移除关联的对象
void objc_removeAssociatedObjects(id object)

id object：被关联的对象
const void *key：关联的key，要求唯一
id value：关联的对象
objc_AssociationPolicy policy：内存管理的策略

typedef OBJC_ENUM(uintptr_t, objc_AssociationPolicy) {
    OBJC_ASSOCIATION_ASSIGN = 0,           /**< Specifies a weak reference to the associated object. */
    OBJC_ASSOCIATION_RETAIN_NONATOMIC = 1, /**< Specifies a strong reference to the associated object. 
                                            *   The association is not made atomically. */
    OBJC_ASSOCIATION_COPY_NONATOMIC = 3,   /**< Specifies that the associated object is copied. 
                                            *   The association is not made atomically. */
    OBJC_ASSOCIATION_RETAIN = 01401,       /**< Specifies a strong reference to the associated object.
                                            *   The association is made atomically. */
    OBJC_ASSOCIATION_COPY = 01403          /**< Specifies that the associated object is copied.
                                            *   The association is made atomically. */
};

#import "ViewController.h"
#import "objc/runtime.h"

@interface UIView (DefaultColor)

@property (nonatomic, strong) UIColor *defaultColor;

@end

@implementation UIView (DefaultColor)

@dynamic defaultColor;

static char kDefaultColorKey;

- (void)setDefaultColor:(UIColor *)defaultColor {
    objc_setAssociatedObject(self, &kDefaultColorKey, defaultColor, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (id)defaultColor {
    return objc_getAssociatedObject(self, &kDefaultColorKey);
}

@end

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    
    UIView *test = [UIView new];
    test.defaultColor = [UIColor blackColor];
    NSLog(@"%@", test.defaultColor);
}

@end

打印结果：
2018-04-01 15:41:44.977732+0800 ocram[2053:63739] UIExtendedGrayColorSpace 0 1

#import <Foundation/Foundation.h>
#import <objc/runtime.h>
@interface NSObject (Swizzling) 

+ (void)methodSwizzlingWithOriginalSelector:(SEL)originalSelector
                         bySwizzledSelector:(SEL)swizzledSelector;
@end

#import "NSObject+Swizzling.h"
@implementation NSObject (Swizzling)

+ (void)methodSwizzlingWithOriginalSelector:(SEL)originalSelector bySwizzledSelector:(SEL)swizzledSelector{
    Class class = [self class];
    //原有方法
    Method originalMethod = class_getInstanceMethod(class, originalSelector);
    //替换原有方法的新方法
    Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);
    //先尝试給源SEL添加IMP，这里是为了避免源SEL没有实现IMP的情况
    BOOL didAddMethod = class_addMethod(class,originalSelector,
                                        method_getImplementation(swizzledMethod),
                                        method_getTypeEncoding(swizzledMethod));
    if (didAddMethod) {//添加成功：说明源SEL没有实现IMP，将源SEL的IMP替换到交换SEL的IMP
        class_replaceMethod(class,swizzledSelector,
                            method_getImplementation(originalMethod),
                            method_getTypeEncoding(originalMethod));
    } else {//添加失败：说明源SEL已经有IMP，直接将两个SEL的IMP交换即可
        method_exchangeImplementations(originalMethod, swizzledMethod);
    }
}
@end

#import "UINavigationItem+Swizzling.h"
#import "NSObject+Swizzling.h"
static char *kCustomBackButtonKey;
@implementation UINavigationItem (Swizzling)
+ (void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        [self methodSwizzlingWithOriginalSelector:@selector(backBarButtonItem)
                               bySwizzledSelector:@selector(sure_backBarButtonItem)];

    });
}

- (UIBarButtonItem*)sure_backBarButtonItem {
    UIBarButtonItem *backItem = [self sure_backBarButtonItem];
    if (backItem) {
        return backItem;
    }
    backItem = objc_getAssociatedObject(self, &kCustomBackButtonKey);
    if (!backItem) {
        backItem = [[UIBarButtonItem alloc] initWithTitle:@"" style:UIBarButtonItemStylePlain target:nil action:NULL];
        objc_setAssociatedObject(self, &kCustomBackButtonKey, backItem, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    }
    return backItem;
}
@end