Autolayout自动布局实现的方法二：VFL语言实现约束

什么是VFL语言

• VFL全称是VisualFormatLanguage，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

  
  
  

    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
    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];
    [self.view addConstraints:constraints2];

• 最终效果：

竖屏效果

横屏效果