举例说明：创建一个grayView（宽150 高100 距上200 距左100）

方法一：原生API 

    UIView *grayView = [UIView new];
    grayView.backgroundColor = [UIColor lightGrayColor];
    // 禁止将 autoresizingmask 转换为 constraints
    grayView.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:grayView];
    
    // 添加 width 约束
    NSLayoutConstraint *widthConstraint = [NSLayoutConstraint constraintWithItem:grayView attribute:(NSLayoutAttributeWidth) relatedBy:(NSLayoutRelationEqual) toItem:nil attribute:(NSLayoutAttributeNotAnAttribute) multiplier:0.0 constant:150];
    // 添加 height 约束
    NSLayoutConstraint *heightConstraint = [NSLayoutConstraint constraintWithItem:grayView attribute:(NSLayoutAttributeHeight) relatedBy:(NSLayoutRelationEqual) toItem:nil attribute:(NSLayoutAttributeNotAnAttribute) multiplier:0.0 constant:100];
    // 添加 left 约束
    NSLayoutConstraint *leftConstraint = [NSLayoutConstraint constraintWithItem:grayView attribute:(NSLayoutAttributeLeft) relatedBy:(NSLayoutRelationEqual) toItem:self.view attribute:(NSLayoutAttributeLeft) multiplier:1.0 constant:100];
    // 添加 top 约束
    NSLayoutConstraint *topConstraint = [NSLayoutConstraint constraintWithItem:grayView attribute:(NSLayoutAttributeTop) relatedBy:(NSLayoutRelationEqual) toItem:self.view attribute:(NSLayoutAttributeTop) multiplier:1.0 constant:200];
    
    
    [grayView addConstraint:widthConstraint];
    [grayView addConstraint:heightConstraint];
    [self.view addConstraint:leftConstraint];
    [self.view addConstraint:topConstraint];

方法二：VFL(Visual Format Language)

    UIView *grayView = [UIView new];
    grayView.backgroundColor = [UIColor lightGrayColor];
    grayView.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:grayView];

    // format参数
    NSString *Hvfl = @"H:|-left-[grayView(150)]";
    NSString *Vvfl = @"V:|-top-[grayView(100)]";

    // 设置 margin 数值
    NSDictionary *metrics = @{@"top":@200,@"left":@100};

    // 把要添加约束的view 转成字典
    NSDictionary *views = NSDictionaryOfVariableBindings(grayView);// 这个方法会自动把传入的参数椅子垫的形式返回，字典的key就是其本身的名字，如@{@"grayView":grayView}

    // 添加对齐方式
    NSLayoutFormatOptions ops = NSLayoutFormatAlignAllLeft | NSLayoutFormatAlignAllTop;// 左边与顶部

    
    NSArray *Hconstraints = [NSLayoutConstraint constraintsWithVisualFormat:Hvfl options:ops metrics:metrics views:views];

    NSArray *Vconstraints = [NSLayoutConstraint constraintsWithVisualFormat:Vvfl options:ops metrics:metrics views:views];


    [self.view addConstraints:Hconstraints];
    [self.view addConstraints:Vconstraints];

运行如下：

本篇博客只是针对基础知识点的整理归纳与简单应用 详细代码解析请参考如下博客：

史上比较用心的纯代码实现 AutoLayout

iOS Autolayout之VFL