自动布局方法1

/**
 创建约束
 
 @param view1 被约束视图view1
 @param attr1 被约束视图的布局属性
 @param relation 关系属性
 @param view2 参照视图view2
 @param attr2 参照视图view2的布局属性
 @param multiplier 倍数
 @param c 常数
 @return 约束
 */
+(instancetype)constraintWithItem:(id)view1
                        attribute:(NSLayoutAttribute)attr1
                        relatedBy:(NSLayoutRelation)relation
                           toItem:(nullable id)view2
                        attribute:(NSLayoutAttribute)attr2
                       multiplier:(CGFloat)multiplier
                         constant:(CGFloat)c;

依据的公式是：view1.attr1 = view2.attr2 * multiplier + constant

NSLayoutAttribute（布局属性）

NSLayoutRelation（关系属性）

代码提示

<#被约束视图#>.translatesAutoresizingMaskIntoConstraints = NO;
    [<#view的父视图#> addConstraint:[NSLayoutConstraint constraintWithItem:<#被约束视图#> attribute:(NSLayoutAttribute<#被约束视图的布局属性#>) relatedBy:(NSLayoutRelation<#布局属性的布局关系#>) toItem:<#参照视图#> attribute:NSLayoutAttribute<#参照视图的布局属性#> multiplier:<#倍数#> constant:<#常数#>]];

代码示例

- (void)codeLayoutConstraint {
   
   //创建背景图
   UIView *backgroundView = [[UIView alloc] init];
   backgroundView.backgroundColor = [UIColor yellowColor];
   [self.view addSubview:backgroundView];
   backgroundView.translatesAutoresizingMaskIntoConstraints = NO;
   
   //和父视图等宽
   [self.view addConstraint:[NSLayoutConstraint constraintWithItem:backgroundView attribute:(NSLayoutAttributeWidth) relatedBy:(NSLayoutRelationEqual) toItem:self.view attribute:NSLayoutAttributeWidth multiplier:1 constant:0]];
   
   //二分之一高
   [self.view addConstraint:[NSLayoutConstraint constraintWithItem:backgroundView attribute:(NSLayoutAttributeHeight) relatedBy:(NSLayoutRelationEqual) toItem:self.view attribute:NSLayoutAttributeHeight multiplier:0.5 constant:0]];
   
   //垂直对齐
   [self.view addConstraint:[NSLayoutConstraint constraintWithItem:backgroundView attribute:(NSLayoutAttributeCenterX) relatedBy:(NSLayoutRelationEqual) toItem:self.view attribute:NSLayoutAttributeCenterX multiplier:1 constant:0]];
   
   //水平对齐
   [self.view addConstraint:[NSLayoutConstraint constraintWithItem:backgroundView attribute:(NSLayoutAttributeCenterY) relatedBy:(NSLayoutRelationEqual) toItem:self.view attribute:NSLayoutAttributeCenterY multiplier:1 constant:0]];
   
   
   
   //创建橙色视图
   UIView *orangeView = [[UIView alloc] init];
   orangeView.backgroundColor = [UIColor orangeColor];
   [backgroundView addSubview:orangeView];
   orangeView.translatesAutoresizingMaskIntoConstraints = NO;

   //上边距离父视图上边20
   [backgroundView addConstraint:[NSLayoutConstraint constraintWithItem:orangeView attribute:(NSLayoutAttributeTop) relatedBy:(NSLayoutRelationEqual) toItem:backgroundView attribute:NSLayoutAttributeTop multiplier:1 constant:20]];
   
   //下边距离父视图下边减20
   [backgroundView addConstraint:[NSLayoutConstraint constraintWithItem:orangeView attribute:(NSLayoutAttributeBottom) relatedBy:(NSLayoutRelationEqual) toItem:backgroundView attribute:NSLayoutAttributeBottom multiplier:1 constant:-20]];
   
   if (/* DISABLES CODE */ (YES)) {//if和else效果一样
       //前边距离父视图前边20
       [backgroundView addConstraint:[NSLayoutConstraint constraintWithItem:orangeView attribute:(NSLayoutAttributeLeading) relatedBy:(NSLayoutRelationEqual) toItem:backgroundView attribute:NSLayoutAttributeLeading multiplier:1 constant:20]];
       
       //后边距离父视图后边减100
       [backgroundView addConstraint:[NSLayoutConstraint constraintWithItem:orangeView attribute:(NSLayoutAttributeTrailing) relatedBy:(NSLayoutRelationEqual) toItem:backgroundView attribute:NSLayoutAttributeTrailing multiplier:1 constant:-100]];
   } else {
       //左边距离父视图前边20
       [backgroundView addConstraint:[NSLayoutConstraint constraintWithItem:orangeView attribute:(NSLayoutAttributeLeft) relatedBy:(NSLayoutRelationEqual) toItem:backgroundView attribute:NSLayoutAttributeLeft multiplier:1 constant:20]];
       //右边距离父视图后边减100
       [backgroundView addConstraint:[NSLayoutConstraint constraintWithItem:orangeView attribute:(NSLayoutAttributeRight) relatedBy:(NSLayoutRelationEqual) toItem:backgroundView attribute:NSLayoutAttributeRight multiplier:1 constant:-100]];
   }
   
   
   
   
   
   //创建红色视图
   UIView *redView = [[UIView alloc] init];
   redView.backgroundColor = [UIColor redColor];
   [backgroundView addSubview:redView];
   redView.translatesAutoresizingMaskIntoConstraints = NO;
   
   //上边距离父视图上边20
   [backgroundView addConstraint:[NSLayoutConstraint constraintWithItem:redView attribute:(NSLayoutAttributeTop) relatedBy:(NSLayoutRelationEqual) toItem:backgroundView attribute:NSLayoutAttributeTop multiplier:1 constant:20]];
   
   //高度44
   [backgroundView addConstraint:[NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:44]];
   
   //自身宽高比1:1
   [backgroundView addConstraint:[NSLayoutConstraint constraintWithItem:redView attribute:(NSLayoutAttributeHeight) relatedBy:(NSLayoutRelationEqual) toItem:redView attribute:NSLayoutAttributeWidth multiplier:1 constant:0]];
   
   if (/* DISABLES CODE */ (NO)) {//if和else效果一样
       //左边距离橙色视图右边20
       [backgroundView addConstraint:[NSLayoutConstraint constraintWithItem:redView attribute:(NSLayoutAttributeLeft) relatedBy:(NSLayoutRelationEqual) toItem:orangeView attribute:NSLayoutAttributeRight multiplier:1 constant:20]];
   } else {
       //前边距离橙色视图后边20
       [backgroundView addConstraint:[NSLayoutConstraint constraintWithItem:redView attribute:(NSLayoutAttributeLeading) relatedBy:(NSLayoutRelationEqual) toItem:orangeView attribute:NSLayoutAttributeTrailing multiplier:1 constant:20]];
   }
}

自动布局方法2(了解即可)

     @param format 使用VFL格式化的字符串，可以参见官方的帮助文档；
     @param opts 指定VFL中所有对象的布局属性和方向。举例：有2个视图使用VFL进行布局，可以使用NSLayoutFormatAlignAllLeft，就让两个视图左对齐；
     @param metrics 度量或者指标的字典，字典里面有相关的键值对来控制相关的度量指标，通过key获取；
     @param views 指定约束的视图：一个或多个。
    + (NSArray<__kindof NSLayoutConstraint *> *)constraintsWithVisualFormat:(NSString *)format
                                                                    options:(NSLayoutFormatOptions)opts
                                                                    metrics:(nullable NSDictionary<NSString *,id> *)metrics
                                                                      views:(NSDictionary<NSString *, id> *)views;

VFL字符串说明：

VFL字符串说明.png

代码示例

- (void)codeLayoutConstraint2 {
    
    UIView *yellowView = [[UIView alloc] init];
    yellowView.backgroundColor = [UIColor yellowColor];
    [self.view addSubview:yellowView];
    yellowView.translatesAutoresizingMaskIntoConstraints = NO;
    
    UIView *orangeView = [[UIView alloc] init];
    orangeView.backgroundColor = [UIColor orangeColor];
    [self.view addSubview:orangeView];
    orangeView.translatesAutoresizingMaskIntoConstraints = NO;
    
    UIView *redView = [[UIView alloc] init];
    redView.backgroundColor = [UIColor redColor];
    [self.view addSubview:redView];
    redView.translatesAutoresizingMaskIntoConstraints = NO;
    
    
    //创建VFL约束字符串
    
    //水平顺序：父视图，space个距离，黄色宽100，5个距离，橙色视图，space1个距离，父视图
    NSString *hVFL = @"H:|-space-[yellowView(100)]-5-[orangeView]-space1-|";
    
    //水平顺序：父视图，space个距离，红色视图宽和橙色视图相等
    NSString *hVFL1 = @"H:|-space-[redView(==orangeView)]";
    
    //垂直顺序：父视图，100个距离，橙色视图高100
    NSString *vVFL = @"V:|-100-[orangeView(==100)]";
    
    //垂直顺序：父视图，100个距离，黄色视图高100，5个距离，红色视图和橙色视图高相等
    NSString *vVFL1 = @"V:|-100-[yellowView(==100)]-5-[redView(==orangeView)]";
    
    
    //度量值
    NSDictionary *metircs = @{@"space":@15,@"space1":@30};
    //views
    NSDictionary *views = NSDictionaryOfVariableBindings(yellowView,orangeView,redView);
    
    //创建约束
    NSArray *hconstraint = [NSLayoutConstraint constraintsWithVisualFormat:hVFL options:NSLayoutFormatDirectionLeadingToTrailing metrics:metircs views:views];
    
    NSArray *hconstraint1 = [NSLayoutConstraint constraintsWithVisualFormat:hVFL1 options:NSLayoutFormatAlignAllLeft | NSLayoutFormatAlignAllTop metrics:metircs views:views];
    
    NSArray *vconstraint = [NSLayoutConstraint constraintsWithVisualFormat:vVFL options:NSLayoutFormatDirectionLeadingToTrailing metrics:metircs views:views];
    
    NSArray *vconstraint1 = [NSLayoutConstraint constraintsWithVisualFormat:vVFL1 options:NSLayoutFormatDirectionLeadingToTrailing metrics:metircs views:views];
    
    //添加约束
    [self.view addConstraints:hconstraint];
    
    [self.view addConstraints:hconstraint1];
    
    [self.view addConstraints:vconstraint];
    
    [self.view addConstraints:vconstraint1];
    
}