VFL简介

基本语法

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

举例

show code

- (void)viewDidLoad {

    [super viewDidLoad];
    self.view.backgroundColor = [UIColor whiteColor];


    [self.view addSubview:self.redView];
    [self.view addSubview:self.yellowView];
    self.redView.translatesAutoresizingMaskIntoConstraints = NO;
    self.yellowView.translatesAutoresizingMaskIntoConstraints = NO;
    NSDictionary *views = NSDictionaryOfVariableBindings(_redView,_yellowView);
    NSDictionary *metres = @{@"redWith":@100,@"leftArglin":@80,@"rightArglin":@50,@"yOffset":@100};
    NSArray *HContrains = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-leftArglin-[_redView(redWith)]-30-[_yellowView(redWith)]-rightArglin-|" options:0 metrics:metres views:views];
    NSArray *VContrains = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-yOffset-[_redView(redWith)]" options:0 metrics:metres views:views];
    NSArray *VContrainsT = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-yOffset-[_yellowView(_redView)]" options:0 metrics:metres views:views];
    [self.view addConstraints:HContrains];
    [self.view addConstraints:VContrains];
    [self.view addConstraints:VContrainsT];
}
-(UIView *)redView {
    if (!_redView) {
        _redView = [[UIView alloc]init];
        _redView.backgroundColor = [UIColor redColor];
    }
    return _redView;
}
-(UIView *)yellowView {
    if (!_yellowView) {
        _yellowView = [[UIView alloc]init];
        _yellowView.backgroundColor = [UIColor yellowColor];
    }
    return _yellowView;
}

图示：