ios中遇到一些難解的問(wèn)題用swizz確實(shí)會(huì)比較方便的解決，比如批量換系統(tǒng)字體，比如AOP方式實(shí)現(xiàn)埋點(diǎn)，比如想為AB都有一個(gè)共同的基類C的方法，但是又因C沒(méi)有公開(kāi)方法，此時(shí)想為AB新增一個(gè)方法fun1，或修改C中的某一個(gè)方法，此時(shí)swizz可以解決這個(gè)問(wèn)題。

要注意幾點(diǎn)

1. 方法重復(fù)，比如如果本來(lái)在其他的catalog分類中已經(jīng)有了一個(gè)方法fun1，此時(shí)想替換改類的fun2，這時(shí)候就容易出現(xiàn)混亂，導(dǎo)致無(wú)法預(yù)知執(zhí)行的是那個(gè)fun1

2. 被實(shí)現(xiàn)的方法必須是當(dāng)前類方法，不能是父類方法，否則就不會(huì)執(zhí)行父類方法了

3. 交換的方法如果用到了cmd(當(dāng)前方法的一個(gè)SEL指針)，當(dāng)cmd發(fā)生了變化，就無(wú)法保證系統(tǒng)方法內(nèi)沒(méi)有使用到cmd

4. 在+load方法中替換，難保證其他方法是否也在執(zhí)行，不會(huì)發(fā)生線程沖突導(dǎo)致失敗

文章完，大家自己可以做個(gè)試驗(yàn)看看效果吧

@implementation ViewController(swizzz222)
 
-(void)xxx_viewDidLoad{ 
    NSLog(@"xxx__222_viewDidLoad..."); 
    [self xxx_viewDidLoad]; 
}
 
@end
 
@implementation ViewController(swizz)
 
-(void)xxx_viewDidLoad{ 
    NSLog(@"xxx_viewDidLoad..."); 
    [self xxx_viewDidLoad]; 
}

 
-(void)yyy_viewDidLoad{
 
    NSLog(@"yyy_viewDidLoad...");
    [self yyy_viewDidLoad];
}
 
@end



@implementation AppDelegate
 
+ (void)ht___replaceMethod:(Class)aClass originalSelector:(SEL)originalSelector swizzledSelector:(SEL)swizzledSelector
{
    Method originalMethod = class_getInstanceMethod(aClass, originalSelector);
    Method swizzledMethod = class_getInstanceMethod(aClass, swizzledSelector);
    BOOL didAddMethod =

    class_addMethod(aClass,

                    originalSelector,

                    method_getImplementation(swizzledMethod),

                    method_getTypeEncoding(swizzledMethod));
 

    if (didAddMethod) {

        NSLog(@"已經(jīng)添加了 添加方法 class_replaceMethod %@",NSStringFromSelector(swizzledSelector));

        class_replaceMethod(aClass,

                            swizzledSelector,

                            method_getImplementation(originalMethod),

                            method_getTypeEncoding(originalMethod));

    } else {

        NSLog(@"沒(méi)有添加成功，交換方法 method_exchangeImplementations %@",NSStringFromSelector(swizzledSelector));

        method_exchangeImplementations(originalMethod, swizzledMethod);

    }

}
 

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

    // Override point for customization after application launch.
 
//    [self.class htv___replaceMethod:ViewController.class originalSelector:@selector(viewDidLoad) swizzledSelector:@selector(xxx_viewDidLoad)];

//    [self.class htv___replaceMethod:ViewController.class originalSelector:@selector(viewDidLoad) swizzledSelector:@selector(yyy_viewDidLoad)];

    [self.class htv___replaceMethod:ViewController.class originalSelector:@selector(viewDidAppear:) swizzledSelector:@selector(viewWillAppear:)];

    return YES;
} 
@end