什么是Swizzling Method
method Swizzling是OC runtime机制提供的一种可以动态替换方法的实现的技术，我们可以利用它替换系统或者自定义类的方法实现，来满足我们特别的需求
建立在Runtime之上的Swizzling Method
在此
Swizzling Method的实现原理
OC中的方法在runtime.h中的定义如下：
struct objc_method{ SEL method_name OBJC2_UNAVAILABLE; char *method_types OBJC2_UNAVAILABLE; IMP method_imp OBJC2_UNAVAILABLE; } OBJC2_UNAVAILABLE; } method_name: 方法名 method_types: 方法类型,主要存储着方法的参数类型和返回值类型 method_imp: 方法的实现，函数指针 由此，我们也可以发现OC中的方法名是不包括参数类型的，也就是在runtime中方法名相同参数不同的方法会被视为同一个方法 原则上，方法的名称method_name和方法的实现method_imp是一一对应的，而Swizzling Method的原理就是动态的改变他们的对应关系，以达到替换方法的目的。Runtime中和方法替换相关的函数
class_getInstanceMethod
OBJC_EXPORT Method _Nullableclass_getInstanceMethod(Class _Nullable cls, SEL _Nonnull name);复制代码
作用：获取一个类的实例方法
cls : 方法所在的类name: 选择子的名称(选择子就是方法名称)class_getClassMethod
OBJC_EXPORT Method _Nullableclass_getClassMethod(Class _Nullable cls, SEL _Nonnull name);复制代码
作用：获取一个类的类方法
cls : 方法所在的类name: 选择子名称method_getImplementation
OBJC_EXPORT IMP _Nonnullmethod_getImplementation(Method _Nonnull m);复制代码
作用: 根据方法获取方法的指针
m : 方法method_getTypeEncoding OBJC_EXPORT const char * _Nullable method_getTypeEncoding(Method _Nonnull m); 复制代码 作用: 获取方法的参数和返回值类型描述 m : 方法
class_addMethod
OBJC_EXPORT BOOLclass_addMethod(Class _Nullable cls, SEL _Nonnull name, IMP _Nonnull imp, const char * _Nullable types);复制代码
作用: 给类添加一个新方法和该方法的实现
返回值： yes,表示添加成功; No,表示添加失败cls： 将要添加方法的类name: 将要添加的方法名imp: 实现这个方法的指针types: 要添加的方法的返回值和参数method_exchangeImplementations
OBJC_EXPORT voidmethod_exchangeImplementations(Method _Nonnull m1, Method _Nonnull m2);复制代码
作用：交换两个方法 class_replaceMethod
OBJC_EXPORT IMP _Nullableclass_replaceMethod(Class _Nullable cls, SEL _Nonnull name, IMP _Nonnull imp, const char * _Nullable types) ;复制代码
作用： 指定替换方法的实现 cls : 将要替换方法的类 name: 将要替换的方法名 imp: 新方法的指针 types: 新方法的返回值和参数描述
Swizzling Method的常见应用场景
- 替换一个类的实例方法
eg：替换UIViewController中的viewDidLoad方法
//将方法替换包装成函数待调用void MethodSwizzle(Class c, SEL oriSEL, SEL overrideSEL){ Method originMethod = class_getInstanceMethod(c, oriSEL); Method swizzleMethod = class_getInstanceMethod(c, overrideSEL); BOOL did_add_method = class_addMethod(c, oriSEL, method_getImplementation(swizzleMethod), method_getTypeEncoding(swizzleMethod));//添加Method，其键值为originSelector，值为swizzleMethod的实现 if (did_add_method) { NSLog(@"debugMsg: ViewController类中没有viewDidLoad方法(可能在其父类h中)，所以先添加后替换"); class_replaceMethod(c, overrideSEL, method_getImplementation(originMethod), method_getTypeEncoding(originMethod)); } else { NSLog(@"debugMsg: 直接交换方法"); method_exchangeImplementations(originMethod, swizzleMethod); }}//调用load方法+ (void)load{ static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ MethodSwizzle([self class], @selector(viewDidLoad), @selector(wn_viewDidLoad)); });}//替换方法的实现- (void)wn_viewDidLoad{ NSLog(@"调用了wn_viewDidLoad"); [self wn_viewDidLoad];}复制代码 - 替换一个类的实例方法到另一个类中去实现 这种情况一般用在当我们不清楚私有库的具体实现，只知道该类名称和该类的一个方法，此时我们需要hook这个类的方法到另一个新类中。 eg: 我们
hook Animal类中的有一个eat:方法\
//Animal.h@interface Animals : NSObject- (void)eat:(NSString *)food;@end//Animal.m@implementation Animals- (void)eat:(NSString *)food{ NSLog(@"food Name = %@",food);}复制代码 然后新建一个类Dog, hook eat:方法到Dog中。如下：
//Dog.m//方法替换的函数实现void SwizzleMethod(Class oriClass, Class overClass, SEL oriSEL, SEL overSEL){ Method origin_method = class_getInstanceMethod(oriClass, oriSEL); Method swizzle_method = class_getInstanceMethod(overClass, overSEL); //判断oriClass是否已经存在overSEL方法，若已存在，则return BOOL exit_overSel = class_addMethod(oriClass, overSEL, method_getImplementation(swizzle_method), method_getTypeEncoding(swizzle_method)); if (!exit_overSel) return; //获取oriClass的overSEL的Method实例 swizzle_method = class_getInstanceMethod(oriClass, overSEL); if (!swizzle_method) return; BOOL exit_origin = class_addMethod(oriClass, oriSEL, method_getImplementation(swizzle_method), method_getTypeEncoding(swizzle_method)); if (exit_origin) { class_replaceMethod(oriClass, overSEL, method_getImplementation(origin_method), method_getTypeEncoding(origin_method)); } else { method_exchangeImplementations(origin_method, swizzle_method); }}//调用替换方法+ (void)load{ static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ SwizzleMethod(NSClassFromString(@"Animals"), [self class], NSSelectorFromString(@"eat:"), NSSelectorFromString(@"dog_eat:")); });}//替换方法的实现- (void)dog_eat:(NSString *)food{ if ([food isEqualToString:@"dogFood"]) { [self dog_eat:food]; } else { NSLog(@"不是狗粮"); }}复制代码 我们来测试一下，在viewController中输出
- (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view. Animals *animal = [[Animals alloc] init]; [animal eat:@"dogFood"]; [animal eat:@"pigFood"];}复制代码 打印结果为：
Test[9442:2104359] food Name = dogFoodTest[9442:2104359] 不是狗粮复制代码
- 替换类方法 尝试替换Animals的类方法：
run:
//Animals.h+ (void)run:(NSInteger)kilo;//Animals.m+ (void)run:(NSInteger)kilo{ NSLog(@"胜利了！！跑了 %ld kilo",(long)kilo);}//Animals (Run)void ExchangeMethod(Class class, SEL oriSEL, SEL exchangeSEL){ Method origin_method = class_getClassMethod(class, oriSEL); Method exchange_method = class_getClassMethod(class, exchangeSEL); if (!origin_method || !exchange_method) return; IMP origin_imp = method_getImplementation(origin_method); IMP swizzle_imp = method_getImplementation(exchange_method); const char *origin_type= method_getTypeEncoding(origin_method); const char *swizzle_type = method_getTypeEncoding(exchange_method); Class metaClass = objc_getMetaClass(class_getName(class)); class_replaceMethod(metaClass, oriSEL, swizzle_imp, swizzle_type); class_replaceMethod(metaClass, exchangeSEL, origin_imp, origin_type);}+ (void)load{ static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ ExchangeMethod([self class], @selector(run:), @selector(ex_run:)); });}+ (void)ex_run:(NSInteger)kilo{ if (kilo >= 10) { [self ex_run:kilo]; } else { NSLog(@"失败了！！=_= ，只跑了%ld kilo",kilo); }}//ViewConroller.m- (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view. [Animals run:11]; [Animals run:7];}复制代码 输出结果为：
Test[9494:2117807] 胜利了！！跑了 11 kiloTest[9494:2117807] 失败了！！=_= ，只跑了7 kilo复制代码
注意:
类方法的替换有个需要特别注意的地方:若把以下部分代码：
IMP origin_imp = method_getImplementation(origin_method);IMP swizzle_imp = method_getImplementation(exchange_method);const char *origin_type= method_getTypeEncoding(origin_method);const char *swizzle_type = method_getTypeEncoding(exchange_method); Class metaClass = objc_getMetaClass(class_getName(class));class_replaceMethod(metaClass, oriSEL, swizzle_imp, swizzle_type);class_replaceMethod(metaClass, exchangeSEL, origin_imp, origin_type);复制代码
换成：
Class meta_class = objc_getMetaClass(class_getName(class));class_replaceMethod(meta_class, origin_selector, method_getImplementation(swizzle_method), swizzle_type = method_getTypeEncoding(swizzle_method));class_replaceMethod(meta_class, swizzle_selector, method_getImplementation(origin_method), method_getTypeEncoding(origin_method));复制代码
运行会直接crash，因为方法替换未成功，调用方法是导致了死循环。具体原因未知，但猜测肯定和MetaClass有关
- 替换类簇中的方法
//MutableDictionary.m//方法实现void ExchangeDicMethod(Class oriClass, Class curClass, SEL oriSEL, SEL curSEL){ Method origin_method = class_getInstanceMethod(oriClass, oriSEL); Method current_method = class_getInstanceMethod(curClass, curSEL); if (!origin_method || !current_method) return; class_replaceMethod(oriClass, curSEL, method_getImplementation(origin_method), method_getTypeEncoding(origin_method)); class_replaceMethod(oriClass, oriSEL, method_getImplementation(current_method), method_getTypeEncoding(current_method));}@implementation MutableDictionary//方法调用+ (void)load{ static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ ExchangeDicMethod(NSClassFromString(@"__NSDictionaryM"), [self class], @selector(setObject:forKey:), @selector(ex_setObject:forKey:)); });}//替换方法实现- (void)ex_setObject:(id)obj forKey:(id )key{ if (obj && key) { NSLog(@"方法安全执行"); [self ex_setObject:obj forKey:key]; } else { NSLog(@"setObject:forKey:方法未执行，obj或者key未空"); }}@end复制代码 常见的Method Swizzling应用事例
- 防止数组取值时越界crash
+ (void)load{ static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ [NSClassFromString(@"__NSArrayI") jr_swizzleMethod:@selector(objectAtIndex:) withMethod:@selector(SF_ObjectAtIndex_NSArrayI:) error:nil]; [NSClassFromString(@"__NSArrayI") jr_swizzleMethod:@selector(objectAtIndexedSubscript:) withMethod:@selector(SF_ObjectAtIndexedSubscript_NSArrayI:) error:nil]; [NSClassFromString(@"__NSArrayM") jr_swizzleMethod:@selector(objectAtIndex:) withMethod:@selector(SF_ObjectAtIndex_NSArrayM:) error:nil]; [NSClassFromString(@"__NSArrayM") jr_swizzleMethod:@selector(objectAtIndexedSubscript:) withMethod:@selector(SF_ObjectAtIndexedSubscript_NSArrayM:) error:nil];}- (id)SF_ObjectAtIndex_NSArrayI:(NSUInteger)index{ @autoreleasepool { if (index >= self.count || index < 0 || !self.count) { @try { return [self SF_ObjectAtIndex_NSArrayI:index]; } @catch (NSException *exception) { NSLog(@"%@", [NSThread callStackSymbols]); return nil; } @finally { } } else { return [self SF_ObjectAtIndex_NSArrayI:index]; } }}- (id)SF_ObjectAtIndexedSubscript_NSArrayI:(NSUInteger)index{ @autoreleasepool { if (index >= self.count || index < 0 || !self.count) { @try { return [self SF_ObjectAtIndexedSubscript_NSArrayI:index]; } @catch (NSException *exception) { NSLog(@"%@", [NSThread callStackSymbols]); return nil; } @finally { } } else { return [self SF_ObjectAtIndexedSubscript_NSArrayI:index]; } }}- (id)SF_ObjectAtIndex_NSArrayM:(NSUInteger)index{ @autoreleasepool { if (index >= self.count || index < 0 || !self.count) { @try { return [self SF_ObjectAtIndex_NSArrayM:index]; } @catch (NSException *exception) { NSLog(@"%@", [NSThread callStackSymbols]); return nil; } @finally { } } else { return [self SF_ObjectAtIndex_NSArrayM:index]; } }}- (id)SF_ObjectAtIndexedSubscript_NSArrayM:(NSUInteger)index{ @autoreleasepool { if (index >= self.count || index < 0 || !self.count) { @try { return [self SF_ObjectAtIndexedSubscript_NSArrayM:index]; } @catch (NSException *exception) { NSLog(@"%@", [NSThread callStackSymbols]); return nil; } @finally { } } else { return [self SF_ObjectAtIndexedSubscript_NSArrayM:index]; } }}复制代码 此处使用到了流行的包装库：, 也可以在中找到JRSwizzle源码
- 改变某类视图的大小，例如盖面app中所有UIButton的大小 我们就可以这样实现:\
#import "UIButton+Size.h"#import@implementation UIButton (Size)+ (void)load{ static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ // 增大所有按钮大小 Method origin_method = class_getInstanceMethod([self class], @selector(setFrame:)); Method replaced_method = class_getInstanceMethod([self class], @selector(miSetFrame:)); method_exchangeImplementations(origin_method, replaced_method); });}- (void)miSetFrame:(CGRect)frame{ frame = CGRectMake(frame.origin.x, frame.origin.y, frame.size.width+20, frame.size.height+20); NSLog(@"设置按钮大小生效"); [self miSetFrame:frame];}@end复制代码
- 处理按钮重复点击\
如果重复过快的点击同一个按钮，就会多次触发点击事件。我们可以这么解决：
//UIButton+QuickClick.h@interface UIButton (QuickClick)@property (nonatomic,assign) NSTimeInterval delayTime;@end//UIButton+QuickClick.m@implementation UIButton (QuickClick)static const char* delayTime_str = "delayTime_str";+ (void)load{ static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ Method originMethod = class_getInstanceMethod(self, @selector(sendAction:to:forEvent:)); Method replacedMethod = class_getInstanceMethod(self, @selector(miSendAction:to:forEvent:)); method_exchangeImplementations(originMethod, replacedMethod); });}- (void)miSendAction:(nonnull SEL)action to:(id)target forEvent:(UIEvent *)event{ if (self.delayTime > 0) { if (self.userInteractionEnabled) { [self miSendAction:action to:target forEvent:event]; } self.userInteractionEnabled = NO; dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(self.delayTime * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{ self.userInteractionEnabled = YES; }); }else{ [self miSendAction:action to:target forEvent:event]; }}- (NSTimeInterval)delayTime{ NSTimeInterval interval = [objc_getAssociatedObject(self, delayTime_str) doubleValue]; return interval;}- (void)setDelayTime:(NSTimeInterval)delayTime{ objc_setAssociatedObject(self, delayTime_str, @(delayTime), OBJC_ASSOCIATION_RETAIN_NONATOMIC);}@end复制代码 项目在此 Swizzling Method的使用注意事项
后续补充...
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