相关疑难解决方法(0)

在Cocoa和Cocoa Touch框架中,枚举用作常量.我理解如何使用它,除了在一种情况下,您可以作为参数多个值传递给|操作符.像 :

pageControl.autoresizingMask = (UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleTopMargin);

枚举声明如下:

enum {
    UIViewAutoresizingNone                 = 0,
    UIViewAutoresizingFlexibleLeftMargin   = 1 << 0,
    UIViewAutoresizingFlexibleWidth        = 1 << 1,
    UIViewAutoresizingFlexibleRightMargin  = 1 << 2,
    UIViewAutoresizingFlexibleTopMargin    = 1 << 3,
    UIViewAutoresizingFlexibleHeight       = 1 << 4,
    UIViewAutoresizingFlexibleBottomMargin = 1 << 5
};
typedef NSUInteger UIViewAutoresizing;

如何定义自己这种类型的枚举(即什么<<意思)以及如何在作为参数传递时检查倍数值？