DispatchQueue.main中的自动布局不工作

我有一个关于自动布局的问题。

background=>我希望在uiTableViewCell中排列uiImageView,使uiImageView异步获取图像,并通过图像的纵横比自动布局动态更改单元格的高度。 其中,uiImageView位于我的自定义uiView的顶部,而uiView又打开了单元格的ContentView。

自动布局与此代码一起工作良好,没有任何错误。

private var contentHeightConstraint = NSLayoutConstraint()

// this method called in constructor 
func setupAutolayout() {
  NSLayoutConstraint.activate([
    messageView.topAnchor.constraint(equalTo: contentView.topAnchor, constant: 8),
    messageView.rightAnchor.constraint(equalTo: contentView.rightAnchor, constant: 16),
    messageView.bottomAnchor.constraint(equalTo: contentView.bottomAnchor, constant: -8),
    messageView.widthAnchor.constraint(equalToConstant: 240),


    contentImageView.topAnchor.constraint(equalTo: messageView.topAnchor),
    contentImageView.leftAnchor.constraint(equalTo: messageView.leftAnchor),
    contentImageView.rightAnchor.constraint(equalTo: messageView.rightAnchor),
    contentImageView.bottomAnchor.constraint(equalTo: messageView.bottomAnchor)
  ])
}

// After view loaded, this method called
func something() {
  contentHeightConstraint = contentImageView.heightAnchor.constraint(equalToConstant: 150)
  contentHeightConstraint.isActive = true
}

但是,将dispatchqueue.main中的代码用作异步任务(将在主线程中执行)时,autolayout不能很好地工作。
这导致 [LayoutConstraints] Unable to simultaneously satisfy constraints 错误。

private var contentHeightConstraint = NSLayoutConstraint()

// this method called in constructor 
func setupAutolayout() {
  NSLayoutConstraint.activate([
    messageView.topAnchor.constraint(equalTo: contentView.topAnchor, constant: 8),
    messageView.rightAnchor.constraint(equalTo: contentView.rightAnchor, constant: 16),
    messageView.bottomAnchor.constraint(equalTo: contentView.bottomAnchor, constant: -8),
    messageView.widthAnchor.constraint(equalToConstant: 240),


    contentImageView.topAnchor.constraint(equalTo: messageView.topAnchor),
    contentImageView.leftAnchor.constraint(equalTo: messageView.leftAnchor),
    contentImageView.rightAnchor.constraint(equalTo: messageView.rightAnchor),
    contentImageView.bottomAnchor.constraint(equalTo: messageView.bottomAnchor)
  ])
}

// After view loaded, this method called
func something() {
  DispatchQueue.main.async {
    // of course, exec in MainThread
    self.contentHeightConstraint = contentImageView.heightAnchor.constraint(equalToConstant: 150)
    self.contentHeightConstraint.isActive = true
  }
}

这是错误消息(此错误消息仅在异步运行时出现)。

2019-03-31 13:10:06.791758+0900 app[42515:4243718] [LayoutConstraints] Unable to simultaneously satisfy constraints.
    Probably at least one of the constraints in the following list is one you don't want. 
    Try this: 
        (1) look at each constraint and try to figure out which you don't expect; 
        (2) find the code that added the unwanted constraint or constraints and fix it. 
(
    "<NSLayoutConstraint:0x600002a3dbd0 V:|-(8)-[UIView:0x7fe775f3f830]   (active, names: '|':UITableViewCellContentView:0x7fe775f3c210 )>",
    "<NSLayoutConstraint:0x600002a3f1b0 UIView:0x7fe775f3f830.bottom == UITableViewCellContentView:0x7fe775f3c210.bottom - 8   (active)>",
    "<NSLayoutConstraint:0x600002a32a80 V:|-(0)-[UIImageView:0x7fe775f40690]   (active, names: '|':UIView:0x7fe775f3f830 )>",
    "<NSLayoutConstraint:0x600002a32350 UIImageView:0x7fe775f40690.bottom == UIView:0x7fe775f3f830.bottom   (active)>",
    "<NSLayoutConstraint:0x600002a2c190 UIImageView:0x7fe775f40690.height == 150   (active)>",
    "<NSLayoutConstraint:0x600002a2d310 'UIView-Encapsulated-Layout-Height' UITableViewCellContentView:0x7fe775f3c210.height == 116   (active)>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x600002a2c190 UIImageView:0x7fe775f40690.height == 150   (active)>

点
需要注意的一点是,如果在uiImageView的heigtanchor之后正常添加约束,那么它将按预期工作,但是异步添加约束将不能正常工作。

附加信息
*表设置

table.estimatedRowHeight = 800
table.rowHeight = UITableView.automaticDimension