不多說(shuō)直接上代碼

@interface NSString (YXMethodExchange)

- (NSString *)yx_uppercaseString;
@end


@implementation NSString (YXMethodExchange)

- (NSString *)yx_uppercaseString{
    NSLog(@"執(zhí)行uppercaseString之前");
    //這里看似會(huì)遞歸，但實(shí)際并不會(huì)，因?yàn)閷?shí)際調(diào)用的是uppercaseString方法
    NSString *uppercaseString = [self yx_uppercaseString];
     NSLog(@"執(zhí)行uppercaseString之后 獲取到大寫(xiě):%@",uppercaseString);
    return uppercaseString;
}
@end

調(diào)用場(chǎng)景代碼

 Method up = class_getInstanceMethod([NSString class], @selector(uppercaseString));
 Method myUp = class_getInstanceMethod([NSString class], @selector(yx_uppercaseString));
 method_exchangeImplementations(up, myUp);
 [@"hellow" uppercaseString];

這樣就能在指定的方法調(diào)用前后加上輸出日志?？梢院芊奖愕膶?duì)IOS中沒(méi)有暴露的方法進(jìn)行日志打印，方便調(diào)試。這就是黑盒調(diào)試。