三 3. 自动布局之VFL

VFL

1. 什么是VFL语言

VFL全称是Visual Format Language，翻译过来是“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
也是很复杂，苹果出的

补充：重点是： 如果苹果出了新的知识，可以进入：xcode -- Window- api中进行搜索查看学习。

2.VFL示例

H:[cancelButton(72)]-12-[acceptButton(50)]
canelButton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，优先级越高的约束越先被满足）

V:[redBox][yellowBox(==redBox)]
竖直方向上，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左边缘默认间隔宽度，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右边缘的间距都是默认宽度。（竖线“|” 表示superview的边缘）

3. VFL的使用

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(...)

代码示例：

#import "ViewController.h"
@interface ViewController ()
@end

@implementation ViewController
- (void)viewDidLoad {
    [super viewDidLoad];

    UIView *blueView = [[UIView alloc] init];
    blueView.backgroundColor = [UIColor blueColor];
    // 不要将AutoresizingMask转为Autolayout的约束
    blueView.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:blueView];

    UIView *redView = [[UIView alloc] init];
    redView.backgroundColor = [UIColor redColor];
    // 不要将AutoresizingMask转为Autolayout的约束
    redView.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:redView];

    // 间距
    NSNumber *margin = @20;

    // 添加水平方向的约束
    // 宽度相等的写法：redView(==blueView)
    NSString *vfl = @"H:|-margin-[blueView]-margin-[redView(==blueView)]-margin-|";
    NSDictionary *views = NSDictionaryOfVariableBindings(blueView, redView);
    NSDictionary *mertrics = NSDictionaryOfVariableBindings(margin);
    NSArray *constraints = [NSLayoutConstraint constraintsWithVisualFormat:vfl options:NSLayoutFormatAlignAllTop | NSLayoutFormatAlignAllBottom metrics:mertrics views:views];
    [self.view addConstraints:constraints];

    // 添加竖直方向的间距
    NSNumber *height = @40;
    NSString *vfl2 = @"V:[blueView(height)]-margin-|";
    NSDictionary *mertrics2 = NSDictionaryOfVariableBindings(margin, height);
    NSArray *constraints2 = [NSLayoutConstraint constraintsWithVisualFormat:vfl2 options:kNilOptions metrics:mertrics2 views:views];// 用的同一个views字典:说明只要在字典中能找到这个view就可以了使用
    [self.view addConstraints:constraints2];

    // 添加红色剩余的约束  和原生的混合使用，其实VFL封装的就是原生的。主要是因为VFL有些约束不能设置，如倍数等,所以要混合使用  苹果api上有解释说有些情况不能用VFL
//    NSLayoutConstraint *redContraint1 = [NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:blueView attribute:NSLayoutAttributeTop multiplier:1.0 constant:0];
//    NSLayoutConstraint *redContraint2 = [NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:blueView attribute:NSLayoutAttributeBottom multiplier:1.0 constant:0];
//    [self.view addConstraint:redContraint1];
//    [self.view addConstraint:redContraint2];
}

- (void)test2
{
    UIView *blueView = [[UIView alloc] init];
    blueView.backgroundColor = [UIColor blueColor];
    // 不要将AutoresizingMask转为Autolayout的约束
    blueView.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:blueView];

    // 间距
    NSNumber *margin = @20;

    // 添加水平方向的约束
    NSString *vfl = @"H:|-margin-[blueView]-margin-|";
    //转成字典的宏 重点：
    NSDictionary *views = NSDictionaryOfVariableBindings(blueView);
    //字典里面只能放对象 所以用nsunmber类型 metrics就是转化间距的
    NSDictionary *mertrics = NSDictionaryOfVariableBindings(margin);
    NSArray *constraints = [NSLayoutConstraint constraintsWithVisualFormat:vfl options:kNilOptions metrics:mertrics views:views];
    [self.view addConstraints:constraints];

    // 添加竖直方向的间距
    NSNumber *height = @40;
    NSString *vfl2 = @"V:|-margin-[blueView(height)]";
    //转成字典的宏 重点：
    NSDictionary *mertrics2 = NSDictionaryOfVariableBindings(margin, height);
    NSArray *constraints2 = [NSLayoutConstraint constraintsWithVisualFormat:vfl2 options:kNilOptions metrics:mertrics2 views:views];
    [self.view addConstraints:constraints2];
}

- (void)test1
{
    UIView *blueView = [[UIView alloc] init];
    blueView.backgroundColor = [UIColor blueColor];
    // 不要将AutoresizingMask转为Autolayout的约束
    blueView.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:blueView];

    // 添加水平方向的约束
    NSString *vfl = @"H:|-20-[abc]-20-|";
    NSDictionary *views = @{@"abc" : blueView};
    NSArray *constraints = [NSLayoutConstraint constraintsWithVisualFormat:vfl options:kNilOptions metrics:nil views:views];
    [self.view addConstraints:constraints];

    // 添加竖直方向的间距
    NSString *vfl2 = @"V:|-20-[abc(40)]";
    NSDictionary *views2 = @{@"abc" : blueView};
    NSArray *constraints2 = [NSLayoutConstraint constraintsWithVisualFormat:vfl2 options:kNilOptions metrics:nil views:views2];
    [self.view addConstraints:constraints2];
}
@end