NS_OPTIONS简单用法

NS_OPTIONS  主要用于多选选项，表示一个选项集合

我们看下 UIView的声明

typedef NS_OPTIONS(NSUInteger, UIViewAutoresizing) {

    UIViewAutoresizingNone                =0,

    UIViewAutoresizingFlexibleLeftMargin  =1<<0,

    UIViewAutoresizingFlexibleWidth        =1<<1,

    UIViewAutoresizingFlexibleRightMargin  =1<<2,

    UIViewAutoresizingFlexibleTopMargin    =1<<3,

    UIViewAutoresizingFlexibleHeight      =1<<4,

    UIViewAutoresizingFlexibleBottomMargin =1<<5

};

使用的时候，可以联合使用，多选的 

// 以Iphone4（320， 480）为基础，设置各控件的位置// 注意：必须所有控件都按照Iphone4（320， 480）为基础初始化一次，不然按比例缩放时会发生错误！UIView *topView = [[UIView alloc] initWithFrame:CGRectMake(kMargin, kTopSpace, kTopViewWidth, kTopViewHeight)];

CGFloat textLabelTop = (topView.frame.size.width - kTextLabelWidth) /2;

CGFloat textLabelWidth = (topView.frame.size.height - kTextLabelHeight) /2;

UILabel *textLabel = [[UILabel alloc] initWithFrame:CGRectMake(textLabelTop, textLabelWidth, kTextLabelWidth, kTextLabelHeight)];// 设置文字及居中[textLabel setText:@"Garvey"];

[textLabel setTextAlignment:NSTextAlignmentCenter];// 分别设置样式[topView setBackgroundColor:[UIColor redColor]];

[textLabel setTextColor:[UIColor whiteColor]];// 设置文字控件的宽度按照上一级视图（topView）的比例进行缩放[textLabel setAutoresizingMask:UIViewAutoresizingFlexibleWidth];// 设置View控件的宽度按照父视图的比例进行缩放，距离父视图顶部、左边距和右边距的距离不变

NSUInteger  autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleBottomMargin | UIViewAutoresizingFlexibleRightMargin | UIViewAutoresizingFlexibleLeftMargin;

[topView setAutoresizingMask:autoresizingMask];

//通过 & 来判断是否包含:

if(autoresizingMask & :UIViewAutoresizingFlexibleWidth) {

包含 UIViewAutoresizingFlexibleWidth

}else{ //不包含UIViewAutoresizingFlexibleWidth }

//通过｜ 增加选项 

autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleBottomMargin;

//减少选项

autoresizingMask = autoresizingMask & (~UIViewAutoresizingFlexibleWidth);

扩展知识点：关于枚举的小知识

//typedef NS_OPTIONS(NSInteger, myType) {

//    type1 = 1 << 0,

//    type2 = 1 << 1,

//    type3 = 1 << 2,

//    type4 = 1 << 3,

//};

/**

type1 = 1 << 0 :值为1(2的0次方)

type2 = 1 << 1 :值为2(2的1次方)

type3 = 1 << 2 :值为4(2的2次方)

type4 = 1 << 3 :值为8(2的3次方)

*/