#pragma mark – 使用分类重写NSObject的load方法
+(void)load{
//只需要运行一次
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
Class class = [self class];
//交换viewWillAppear: 和 glt_viewWillAppear: 方法
SEL oriSelector = @selector(viewWillAppear:);
SEL swiSelctor = @selector(glt_viewWillAppear:);

//注意：导入头文件 #import <objc/message.h>
Method oriMethod = class_getInstanceMethod(class, oriSelector);
Method swiMethod = class_getInstanceMethod(class, swiSelctor);

BOOL success = class_addMethod(class, oriSelector, method_getImplementation(swiMethod), method_getTypeEncoding(swiMethod));

if (success) {
class_replaceMethod(class, swiSelctor, method_getImplementation(oriMethod), method_getTypeEncoding(oriMethod));
}else{
method_exchangeImplementations(oriMethod, swiMethod);
}
});
}

#pragma mark – 替换后的子类viewWillAppear
-(void)glt_viewWillAppear:(BOOL)animated{
[self glt_viewWillAppear:animated];
}