为什么Autolayout不会更改视图框架

Question

我在其超级视图的函数中创建了一个视图

let black = NSView(frame: NSRect(x: 0, y: 0, width: 10, height: 10))

black.translatesAutoresizingMaskIntoConstraints = false
black.wantsLayer = true
black.layer?.backgroundColor = NSColor.black.cgColor
self.addSubview(black)

black.bottomAnchor.constraint(equalTo: self.bottomAnchor, constant: -15).isActive = true
black.leadingAnchor.constraint(equalTo: self.leadingAnchor, constant: 15).isActive = true
black.heightAnchor.constraint(equalToConstant: 115).isActive = true
black.widthAnchor.constraint(equalToConstant: 115).isActive = true

print ("origin (\(black.frame.origin.x),\(black.frame.origin.y)) size (\(black.frame.size.width),\(black.frame.size.height)) ")

输出为origin(0,0)，size(10,10)，这些是创建视图的值。 在屏幕上，黑色视图按预期定位origin:(15,15) size:(115,115)。

为什么框架没有更新？

Answer 1

设置约束后，您可以更新视图的框架，调用Cocoa的layoutIfNeeded函数：

black.layoutSubtreeIfNeeded()