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iOS学习之VFL语言简介

http://www.cnblogs.com/chars/p/5146607.html

什么是VFL语言

VFL(Visual Format Language),“可视化格式语言”。

VFL是苹果公司为了简化autolayout的编码而推出的抽象语言。

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语法说明

H:[cancelButton(72)]-12-[acceptButton(50)]
cancelButton宽72,acceptButton宽50,它们之间间距12
 
H:[wideView(>=60@700)]
wideView宽度大于等于60point,该约束条件优先级为700(优先级最大值为1000,优先级越高的约束条件越先被满足)
  
V:[redBox][yellowBox(==redBox)]
垂直方向上,先有一个redBox,其下方紧接一个高度等于redBox高度的yellowBox
  
H:|-10-[Find]-[FindNext]-[FindField(>=20)]-|
水平方向上,Find距离父view左边缘间隔10,之后是FindNext距离Find间隔默认宽度;再之后是宽度不小于20的FindField,它和FindNext以及父view右边边缘的间距都是默认宽度。(竖线“|”表示superview的边缘)。

使用方法

使用VFL来创建约束数组
+(NSArray *)constraintsWithVisualFormat:(NSString *)format options:(NSLayoutFormatOptions)opts metrics:(NSDictionary *)metrics views:(NSDictionary *)views;
  
format:VFL语句
opts:约束类型
metrics:VFL语句中用到的具体数值
views:VFL语句中用到的控件
  
创建一个字典(内部包含VFL语句中用到的控件)的快捷宏定义
NSDictionaryOfVariableBindings(...)

实例展示

效果图如下:

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实现代码:

-(void)horizontalLayout{
    //1.添加两个控件
    UIView *blueView = [[UIView alloc] init];
    blueView.backgroundColor = [UIColor blueColor];
    
    blueView.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:blueView];
    
    UIView *redView = [[UIView alloc] init];
    redView.backgroundColor = [UIColor redColor];
    redView.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:redView];
    
    //2.添加约束
    //2.1水平方向的约束
    NSString *hVFL = @"H:|-30-[blueView]-30-[redView(==blueView)]-30-|";
    NSArray *hCons = [NSLayoutConstraint constraintsWithVisualFormat:hVFL options:NSLayoutFormatAlignAllBottom | NSLayoutFormatAlignAllTop metrics:nil views:@{@"blueView":blueView, @"redView":redView}];
    [self.view addConstraints:hCons];
    
    //2.2垂直方向的约束
    NSString *vVFL = @"V:[blueView(50)]-30-|";
    NSArray *vCons = [NSLayoutConstraint constraintsWithVisualFormat:vVFL options:0 metrics:nil views:@{@"blueView":blueView}];
    [self.view addConstraints:vCons];
}

-(void)verticalLayout{
    //1.添加两个控件
    UIView *blueView = [[UIView alloc] init];
    blueView.backgroundColor = [UIColor blueColor];
    blueView.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:blueView];

    UIView *redView = [[UIView alloc] init];
    redView.backgroundColor = [UIColor redColor];
    redView.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:redView];

    //2.添加约束
    //2.1水平方向的约束
    NSString *hVFL = @"H:|-30-[blueView]-30-|";
    NSArray *hCons = [NSLayoutConstraint constraintsWithVisualFormat:hVFL options:0 metrics:nil views:@{@"blueView":blueView}];
    [self.view addConstraints:hCons];

    //2.2垂直方向的约束
    NSString *vVFL = @"V:|-30-[blueView(50)]-30-[redView(==blueView)]";
    NSArray *vCons = [NSLayoutConstraint constraintsWithVisualFormat:vVFL options:NSLayoutFormatAlignAllRight metrics:nil views:@{@"blueView":blueView, @"redView":redView}];
    [self.view addConstraints:vCons];
    NSLayoutConstraint *redLeftCon = [NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:blueView attribute:NSLayoutAttributeCenterX multiplier:1.0 constant:0];
    [self.view addConstraint:redLeftCon];
}

小结

最后对格式的字符串作一个总结介绍:

功能 表达式
水平方向 H:
垂直方向 V:
Views [view]
SuperView |
关系 >=,==,<=
空间,间隙 -
优先级 @value

iOS学习之VFL语言简介