Sample Method Swizzle

UIImage-Addition.m

+ (void)initialize
{
    NSError *error = nil;
    [[self class] jr_swizzleClassMethod:@selector(imageNamed:) withClassMethod:@selector(gk_imageNamed:) error:&error];
}

+ (UIImage *)gk_imageNamed:(NSString *)str
{
    UIImage *image = [UIImage gk_imageNamed:str];
    if (!image && [str rangeOfString:@".jpg"].location == NSNotFound) {
        image = [UIImage gk_imageNamed:[NSString stringWithFormat:@"%@.jpg",str]];
    }
    return image;
}