OC底層探索(十七)自定義實作KVO

OC底層文章彙總

在OC底層探索(十六) KVO底層原理文章中分析了KVO的原理，我們實作自定義的KVO。

建立NSObject分類

• .h檔案

#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

typedef void(^QLJKVOBlock)(id observer,NSString *keyPath,id oldValue,id newValue);

@interface NSObject (QLJKVO)

- (void)QLJ_addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath block:(QLJKVOBlock)block;

- (void)QLJ_removeObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath;

@end

NS_ASSUME_NONNULL_END

           

• .m檔案

#import "NSObject+QLJKVO.h"
#import <objc/message.h>

static NSString *const kQLJKVOPrefix = @"QLJKVONotifying_";
static NSString *const kQLJKVOAssiociateKey = @"kQLJKVO_AssiociateKey";

@interface QLJInfo : NSObject
@property (nonatomic, weak) NSObject  *observer;
@property (nonatomic, copy) NSString    *keyPath;
@property (nonatomic, copy) QLJKVOBlock  handleBlock;
@end

@implementation QLJInfo

- (instancetype)initWitObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath handleBlock:(QLJKVOBlock)block{
    if (self=[super init]) {
        _observer = observer;
        _keyPath  = keyPath;
        _handleBlock = block;
    }
    return self;
}
@end

@implementation NSObject (QLJKVO)

//- (void)dealloc{
//    Class superClass = [self class];
//    object_setClass(self, superClass);
//}

+ (BOOL)kc_hookOrigInstanceMenthod:(SEL)oriSEL newInstanceMenthod:(SEL)swizzledSEL {
    Class cls = self;
    Method oriMethod = class_getInstanceMethod(cls, oriSEL);
    Method swiMethod = class_getInstanceMethod(cls, swizzledSEL);
    
    if (!swiMethod) {
        return NO;
    }
    if (!oriMethod) {
        class_addMethod(cls, oriSEL, method_getImplementation(swiMethod), method_getTypeEncoding(swiMethod));
        method_setImplementation(swiMethod, imp_implementationWithBlock(^(id self, SEL _cmd){ }));
    }
    
    BOOL didAddMethod = class_addMethod(cls, oriSEL, method_getImplementation(swiMethod), method_getTypeEncoding(swiMethod));
    if (didAddMethod) {
        class_replaceMethod(cls, swizzledSEL, method_getImplementation(oriMethod), method_getTypeEncoding(oriMethod));
    }else{
        method_exchangeImplementations(oriMethod, swiMethod);
    }
    return YES;
}


+ (void)load{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{

        [self kc_hookOrigInstanceMenthod:NSSelectorFromString(@"dealloc") newInstanceMenthod:@selector(myDealloc)];
    });
}

- (void)myDealloc{

    Class superClass = [self class];
    object_setClass(self, superClass);
    [self myDealloc];
}

- (void)QLJ_addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath block:(QLJKVOBlock)block{
    
    // 1: 驗證是否存在setter方法 : 不讓執行個體進來
    [self judgeSetterMethodFromKeyPath:keyPath];
    // 2: 動态生成子類
    Class newClass = [self createChildClassWithKeyPath:keyPath];
    // 3: isa的指向 : QLJKVONotifying_QLJPerson
    object_setClass(self, newClass);
    // 4: 儲存資訊
    QLJInfo *info = [[QLJInfo alloc] initWitObserver:observer forKeyPath:keyPath handleBlock:block];
    NSMutableArray *mArray = objc_getAssociatedObject(self, (__bridge const void * _Nonnull)(kQLJKVOAssiociateKey));
    if (!mArray) {
        mArray = [NSMutableArray arrayWithCapacity:1];
        objc_setAssociatedObject(self, (__bridge const void * _Nonnull)(kQLJKVOAssiociateKey), mArray, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    }
    [mArray addObject:info];
}

- (void)QLJ_removeObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath{
    
    NSMutableArray *observerArr = objc_getAssociatedObject(self, (__bridge const void * _Nonnull)(kQLJKVOAssiociateKey));
    if (observerArr.count<=0) {
        return;
    }
    
    for (QLJInfo *info in observerArr) {
        if ([info.keyPath isEqualToString:keyPath]) {
            [observerArr removeObject:info];
            objc_setAssociatedObject(self, (__bridge const void * _Nonnull)(kQLJKVOAssiociateKey), observerArr, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
            break;
        }
    }
    
    if (observerArr.count<=0) {
        // 指回給父類
        Class superClass = [self class];
        object_setClass(self, superClass);
    }
}

#pragma mark - 驗證是否存在setter方法
- (void)judgeSetterMethodFromKeyPath:(NSString *)keyPath{
    Class superClass    = object_getClass(self);
    SEL setterSeletor   = NSSelectorFromString(setterForGetter(keyPath));
    Method setterMethod = class_getInstanceMethod(superClass, setterSeletor);
    if (!setterMethod) {
        @throw [NSException exceptionWithName:NSInvalidArgumentException reason:[NSString stringWithFormat:@"老鐵沒有目前%@的setter",keyPath] userInfo:nil];
    }
}

#pragma mark -
- (Class)createChildClassWithKeyPath:(NSString *)keyPath{
    
    NSString *oldClassName = NSStringFromClass([self class]);
    NSString *newClassName = [NSString stringWithFormat:@"%@%@",kQLJKVOPrefix,oldClassName];
    Class newClass = NSClassFromString(newClassName);
    // 防止重複建立生成新類
    if (newClass) return newClass;
    /**
     * 如果記憶體不存在,建立生成
     * 參數一: 父類
     * 參數二: 新類的名字
     * 參數三: 新類的開辟的額外空間
     */
    // 2.1 : 申請類
    newClass = objc_allocateClassPair([self class], newClassName.UTF8String, 0);
    // 2.2 : 注冊類
    objc_registerClassPair(newClass);
    // 2.3.1 : 添加class : class的指向是QLJPerson
    SEL classSEL = NSSelectorFromString(@"class");
    Method classMethod = class_getInstanceMethod([self class], classSEL);
    const char *classTypes = method_getTypeEncoding(classMethod);
    class_addMethod(newClass, classSEL, (IMP)QLJ_class, classTypes);
    // 2.3.2 : 添加setter
    SEL setterSEL = NSSelectorFromString(setterForGetter(keyPath));
    Method setterMethod = class_getInstanceMethod([self class], setterSEL);
    const char *setterTypes = method_getTypeEncoding(setterMethod);
    class_addMethod(newClass, setterSEL, (IMP)QLJ_setter, setterTypes);
    // 2.3.3 : 添加dealloc
    SEL deallocSEL = NSSelectorFromString(@"dealloc");
    Method deallocMethod = class_getInstanceMethod([self class], deallocSEL);
    const char *deallocTypes = method_getTypeEncoding(deallocMethod);
    class_addMethod(newClass, deallocSEL, (IMP)QLJ_dealloc, deallocTypes);
  
//    Method m1 = class_getInstanceMethod([self class], NSSelectorFromString(@"dealloc"));
//    Method m2 = class_getInstanceMethod([self class], @selector(myDealloc));
//    method_exchangeImplementations(m1, m2);
//    method_exchangeImplementations(m1, m2);
    
    return newClass;
}

static void QLJ_dealloc(id self,SEL _cmd){
//    Class superClass = [self class];
//    object_setClass(self, superClass);
}

static void QLJ_setter(id self,SEL _cmd,id newValue){
    NSLog(@"來了:%@",newValue);
    NSString *keyPath = getterForSetter(NSStringFromSelector(_cmd));
    id oldValue = [self valueForKey:keyPath];
    // 4: 消息轉發 : 轉發給父類
    // 改變父類的值 --- 可以強制類型轉換
    void (*QLJ_msgSendSuper)(void *,SEL , id) = (void *)objc_msgSendSuper;
    // void /* struct objc_super *super, SEL op, ... */
    struct objc_super superStruct = {
        .receiver = self,
        .super_class = class_getSuperclass(object_getClass(self)),
    };
    //objc_msgSendSuper(&superStruct,_cmd,newValue)
    QLJ_msgSendSuper(&superStruct,_cmd,newValue);
    
    // 5: 資訊資料回調
    NSMutableArray *mArray = objc_getAssociatedObject(self, (__bridge const void * _Nonnull)(kQLJKVOAssiociateKey));
    
    for (QLJInfo *info in mArray) {
        if ([info.keyPath isEqualToString:keyPath] && info.handleBlock) {
            info.handleBlock(info.observer, keyPath, oldValue, newValue);
        }
    }
}

Class QLJ_class(id self,SEL _cmd){
    return class_getSuperclass(object_getClass(self));
}

#pragma mark - 從get方法擷取set方法的名稱 key ===>>> setKey:
static NSString *setterForGetter(NSString *getter){
    
    if (getter.length <= 0) { return nil;}
    
    NSString *firstString = [[getter substringToIndex:1] uppercaseString];
    NSString *leaveString = [getter substringFromIndex:1];
    
    return [NSString stringWithFormat:@"set%@%@:",firstString,leaveString];
}

#pragma mark - 從set方法擷取getter方法的名稱 set<Key>:===> key
static NSString *getterForSetter(NSString *setter){
    
    if (setter.length <= 0 || ![setter hasPrefix:@"set"] || ![setter hasSuffix:@":"]) { return nil;}
    
    NSRange range = NSMakeRange(3, setter.length-4);
    NSString *getter = [setter substringWithRange:range];
    NSString *firstString = [[getter substringToIndex:1] lowercaseString];
    return  [getter stringByReplacingCharactersInRange:NSMakeRange(0, 1) withString:firstString];
}


@end