锚点样式自动布局约束的UIButtons未显示

Question

我有一个以这种方式添加的子视图：

dailyButtonView.translatesAutoresizingMaskIntoConstraints = false
dailyButtonView.backgroundColor = UIColor.redColor()


dailyWeeklyButtonViewContainer.addSubview(dailyButtonView)

let centerX_d = dailyButtonView.centerXAnchor.constraintEqualToAnchor(dailyWeeklyButtonViewContainer.centerXAnchor)
let centerY_d = dailyButtonView.centerYAnchor.constraintEqualToAnchor(dailyWeeklyButtonViewContainer.centerYAnchor)
let width_d = dailyButtonView.widthAnchor.constraintEqualToAnchor(dailyWeeklyButtonViewContainer.widthAnchor)
let height_d = dailyButtonView.heightAnchor.constraintEqualToAnchor(dailyWeeklyButtonViewContainer.heightAnchor)
dailyButtonViewCenterX = centerX_d
NSLayoutConstraint.activateConstraints([centerX_d,centerY_d,width_d,height_d])

之后，我想添加六个UIButton（相同的大小和相等的间距），所以我这样做了：

let dayButtonSide = self.dailyButtonView.frame.height * 0.6   
let dayDistance = (self.dailyButtonView.frame.width - dayButtonSide * 7) / 8.0
for index in 0...6{
    let temp = UIButton()
    temp.translatesAutoresizingMaskIntoConstraints = false
    temp.layer.cornerRadius = 5
    dailyButtonView.addSubview(temp)
    var test = CGFloat(index) * (dayButtonSide / 2)
    test += CGFloat(index + 1) * dayDistance - (dailyButtonView.bounds.width / 2)
    let centerX_t = temp.centerXAnchor.constraintEqualToAnchor(dailyButtonView.centerXAnchor, constant: test)
    let centerY_t = temp.centerYAnchor.constraintEqualToAnchor(dailyButtonView.centerYAnchor)
    let width_t = temp.widthAnchor.constraintEqualToAnchor(nil, constant: dayButtonSide)
    let height_t = temp.heightAnchor.constraintEqualToAnchor(nil, constant: dayButtonSide)
    NSLayoutConstraint.activateConstraints([centerX_t, centerY_t, width_t, height_t])

但是，即使日志中没有错误或警告，按钮也不会在模拟中显示。

Answer 1

我明白了。问题出在这一行：let dayButtonSide = self.dailyButtonView.frame.height * 0.6。因为我在viewDidLoad中调用了此函数，所以dailyButtonView没有列出这一点。