iOS开发-VFL(Visual format language)和Autolayout
AutoLayout不管是在StoryBorad还是在xib中都相对来说比较简单，VFL(Visual fromat language)可视化语言基本上用到的比较少，在xCode4时候自动布局的概念还没有，直接使用VFL会很方便，可视化语言依赖于oc运行时创建对应的约束，如果IBOutlet发生改变有的时候会造成莫名其妙的Bug。xCode5之后可视化语言用到的场景相对较少，但是作为一个工作的辅助还是可以稍微了解下。 基础知识 在StotyBoard中添加一个标签一个按钮，不适用自动布局，简单的控制它们之间的水平距离为80，如下图所示: 视图中添加约束: 1 2 NSLayoutConstraint *labelContraint=[ NSLayoutConstraint constraintWithItem: self .changeButton attribute: NSLayoutAttributeLeft relatedBy: NSLayoutRelationEqual toItem: self .descriptionLabel attribute: NSLayoutAttributeRight multiplier:1.0 constant:60]; [ self .view addConstraint:labelContraint]; 这个只是视图约束的一种方式，下面这种方式才是本文的主角: 1 2 3 4 //使用可视化语言添加约束 NSDictionary *viewDictionary= NSDictionaryOfVariableBindings (_descriptionLabel,_changeButton); NSArray *visualConstraint=[ NSLayoutConstraint constraintsWithVisualFormat:@ "[_descriptionLabel]-60-[_changeButton]" options:0 metrics: nil views:viewDictionary]; [ self .view addConstraints:visualConstraint]; 这里面用到的constraintsWithVisualFormat方法,具体参数说明如下: format:参数是vfl语句，语句的基本元素下面会详细解释一下； opts:枚举参数，默认写0； metrics:字典，当在format中使用了动态数据，会根据字典去匹配，接下来会具体有例子； views：字典，传入需要用到的视图集合； 具体format需要参考一下表达式的意思: 水平方向 H: 垂直方向 V: Views [需要定义的视图] SuperView | 关系 >=,==,<= 间隙 - 视图内部约束 （） Demo实战 通过VFL控制手动添加的标签的位置，具体效果如下: 代码实现如下: 1 2 3 4 5 6 7 8 9 10 11 UILabel *link=[[UILabel alloc]init]; link.text=@ "http://www.cnblogs.com/xiaofeixiang" ; link.translatesAutoresizingMaskIntoConstraints= NO ; [link setBackgroundColor:[UIColor greenColor]]; [ self .view addSubview:link]; NSArray *horizontal=[ NSLayoutConstraint constraintsWithVisualFormat:@ "H:|-40-[link]-20-|" options:0 metrics: nil views: NSDictionaryOfVariableBindings (link)]; NSArray *vertical=[ NSLayoutConstraint constraintsWithVisualFormat:@ "V:[_descriptionLabel]-100-[link(>=30)]" options:0 metrics: nil views: NSDictionaryOfVariableBindings (link,_descriptionLabel)]; [ self .view addConstraints:horizontal]; [ self .view addConstraints:vertical]; 第一个约束是控制标签距离父视图左右之间的距离，第二个控制标签和”博客园-FlyElephant"之间的垂直距离为100.当然如果你想通过字典控制垂直之间的距离可以按照下面这么做: 1 NSArray *vertical=[ NSLayoutConstraint constraintsWithVisualFormat:@ "V:[_descriptionLabel]-Vertical-[link(>=30)]" options:0 metrics:@{@ "Vertical" : @200 } views: NSDictionaryOfVariableBindings (link,_descriptionLabel)]; 最后的结果: 友情提示在添加约束的时候不要和StoryBoard中的冲突，如果添加的水平约束StoryBoard中也有的话，就会出现下面这种情况: 1 2 3 4 5 6 7 8 9 10 11 12 2015-07-01 10:54:13.537 VFLDemo[2358:60863] Unable to simultaneously satisfy constraints. Probably at least one of the constraints in the following list is one you don 't want. Try this: (1) look at each constraint and try to figure out which you don' t expect; (2) find the code that added the unwanted constraint or constraints and fix it. (Note: If you 're seeing NSAutoresizingMaskLayoutConstraints that you don' t understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) ( "<NSLayoutConstraint:0x7fc5e3732860 H:[UILabel:0x7fc5e372ef30'\U535a\U5ba2\U56ed-FlyElephant']-(15)-[UIButton:0x7fc5e372d550'\U7fa4:228407086']>" , "<NSLayoutConstraint:0x7fc5e37344e0 H:[UILabel:0x7fc5e372ef30'\U535a\U5ba2\U56ed-FlyElephant']-(60)-[UIButton:0x7fc5e372d550'\U7fa4:228407086']>" ) Will attempt to recover by breaking constraint < NSLayoutConstraint :0x7fc5e37344e0 H:[UILabel:0x7fc5e372ef30 '博客园-FlyElephant' ]-(60)-[UIButton:0x7fc5e372d550 '群:228407086' ]> Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger. The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful. 本文转自Fly_Elephant博客园博客，原文链接：http://www.cnblogs.com/xiaofeixiang/p/4612683.html，如需转载请自行联系原作者
