如何用SnapKit实现ContentView自适应内容尺寸？

我在使用AutoLayout时，通过以下代码实现布局，其中的bottomAnchor约束用于让contentView自适应内容尺寸：

let safeAreaLayoutGuide = contentView.safeAreaLayoutGuide
            
let bottomAnchor = userImage.bottomAnchor.constraint(equalTo: safeAreaLayoutGuide.bottomAnchor, constant: -16.0)
bottomAnchor.priority = .required - 1

NSLayoutConstraint.activate([
            userImage.topAnchor.constraint(equalTo: safeAreaLayoutGuide.topAnchor, constant: 16),
            userImage.leadingAnchor.constraint(equalTo: safeAreaLayoutGuide.leadingAnchor
                                               , constant: 16),
            userImage.widthAnchor.constraint(equalToConstant: 90),
            userImage.heightAnchor.constraint(equalToConstant: 90),
            
            userName.topAnchor.constraint(equalTo: safeAreaLayoutGuide.topAnchor, constant: 16),
            userName.leadingAnchor.constraint(equalTo: userImage.trailingAnchor, constant: 16),
            userName.trailingAnchor.constraint(equalTo: safeAreaLayoutGuide.trailingAnchor, constant: -16),
        
            userStatus.topAnchor.constraint(equalTo: userName.bottomAnchor, constant: 16),
            userStatus.leadingAnchor.constraint(equalTo: userImage.trailingAnchor, constant: 16),
            userStatus.trailingAnchor.constraint(equalTo: safeAreaLayoutGuide.trailingAnchor, constant: -16),

            textField.topAnchor.constraint(equalTo: userName.bottomAnchor, constant: 48),
            textField.leadingAnchor.constraint(equalTo: userImage.trailingAnchor, constant: 16),
            textField.trailingAnchor.constraint(equalTo: safeAreaLayoutGuide.trailingAnchor, constant: -16),
            textField.heightAnchor.constraint(equalToConstant: 32),
        
            showStatusButton.topAnchor.constraint(equalTo: textField.bottomAnchor, constant: 16),
            showStatusButton.leadingAnchor.constraint(equalTo: safeAreaLayoutGuide.leadingAnchor, constant: 16),
            showStatusButton.trailingAnchor.constraint(equalTo: safeAreaLayoutGuide.trailingAnchor, constant: -16),
            
            bottomAnchor
        ])

现在我尝试用SnapKit重构，已完成大部分控件的约束设置：

userImage.snp.makeConstraints { make in
            make.top.equalTo(self.safeAreaInsets.top).offset(16)
            make.left.equalTo(self.safeAreaInsets.left).offset(16)
            make.height.width.equalTo(userImage.layer.cornerRadius * 2)
        }
        
        userName.snp.makeConstraints { make in
            make.top.equalTo(self.safeAreaInsets.top).offset(16)
            make.left.equalTo(userImage.snp.right).offset(16)
            make.right.equalTo(self.safeAreaInsets.right).inset(-16)
        }
        
        userStatus.snp.makeConstraints { make in
            make.top.equalTo(userName.snp.bottom).offset(16)
            make.left.equalTo(userImage.snp.right).offset(16)
            make.right.equalTo(self.safeAreaInsets.right).offset(-16)
        }
        
        textField.snp.makeConstraints { make in
            make.top.equalTo(userStatus.snp.bottom).offset(40)
            make.left.equalTo(self.safeAreaInsets.left).offset(16)
            make.right.equalTo(self.safeAreaInsets.right).offset(-16)
            make.height.equalTo(32)
        }
        
        showStatusButton.snp.makeConstraints { make in
            make.top.equalTo(textField.snp.bottom).offset(16)
            make.left.equalTo(self.safeAreaInsets.left).offset(16)
            make.right.equalTo(self.safeAreaInsets.right).offset(-16)
        }

但不知道如何替代原来的bottomAnchor，实现contentView自适应内容（让其底部与showStatusButton的底部关联）。

解决方案 #

原来的bottomAnchor是一个低优先级约束，作用是兜底contentView的最小高度：当内部控件总高度不足时，让userImage底部距离safeArea底部保持16pt间距，避免contentView过矮；当内部控件（如showStatusButton）的高度足够撑高contentView时，这个约束会自动失效，contentView高度由最底部的控件决定。

在SnapKit中可以这样实现：

1. 给userImage添加低优先级的底部约束，对应原来的逻辑：

userImage.snp.makeConstraints { make in
    make.top.equalTo(contentView.snp.safeAreaLayoutGuideTop).offset(16)
    make.left.equalTo(contentView.snp.safeAreaLayoutGuideLeft).offset(16)
    make.height.width.equalTo(userImage.layer.cornerRadius * 2) // 保持你原来的设置，或者改为90和AutoLayout一致
    // 添加低优先级底部约束，效果等同于原来的bottomAnchor
    make.bottom.lessThanOrEqualTo(contentView.snp.safeAreaLayoutGuideBottom).offset(-16).priority(.required - 1)
}

2. 确保showStatusButton的布局能自然撑高contentView：
   不需要给showStatusButton额外加底部约束，因为它是布局中最靠下的控件，自动布局会根据它的位置计算contentView的高度。如果你的contentView是UITableViewHeaderFooterView或UICollectionReusableView，只要内部约束完整，系统会自动计算其高度。

另外，建议把代码中self.safeAreaInsets替换为contentView.snp.safeAreaLayoutGuideTop/contentView.snp.safeAreaLayoutGuideLeft等，这样更贴合AutoLayout中原先使用safeAreaLayoutGuide的逻辑，避免因视图层级问题导致的约束错误。

内容的提问来源于stack exchange，提问作者Philipp