PencilKit无法同时满足约束

Question

我正在尝试实现铅笔工具包(一根铅笔，橡皮等)它出现在屏幕的底部。但是，在运行这行代码时：

guard let window = view.window, let toolPicker = PKToolPicker.shared(for: window)
else {return}

我在日志中看到以下错误，toolpicker没有出现：

    PDF Reader[926:85385] [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:0x60000191d450 UIView:0x7fdfb7376ff0.height == 75   (active)>",
    "<NSLayoutConstraint:0x60000191d4a0 V:|-(0)-[UIView:0x7fdfb7376ff0]   (active, names: '|':PKPaletteContainerView:0x7fdfb737b7e0 )>",
    "<NSLayoutConstraint:0x60000191dae0 V:|-(0)-[PKPaletteContainerView:0x7fdfb737b7e0]   (active, names: '|':UIView:0x7fdfb46181d0 )>",
    "<NSLayoutConstraint:0x60000191dc70 PKPaletteContainerView:0x7fdfb737b7e0.bottom == UIView:0x7fdfb46181d0.bottom   (active)>",
    "<NSLayoutConstraint:0x600001901ea0 V:|-(0)-[UIView:0x7fdfb46181d0]   (active, names: '|':PKPaletteView:0x7fdfb462d3e0 )>",
    "<NSLayoutConstraint:0x600001901ef0 UIView:0x7fdfb46181d0.bottom == PKPaletteView:0x7fdfb462d3e0.bottom   (active)>",
    "<NSLayoutConstraint:0x6000019fcf00 PKPaletteView:0x7fdfb462d3e0.height == 122   (active)>",
    "<NSLayoutConstraint:0x60000191d720 UIView:0x7fdfb7376ff0.bottom == PKPaletteContainerView:0x7fdfb737b7e0.bottom   (active)>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x60000191d450 UIView:0x7fdfb7376ff0.height == 75   (active)>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKitCore/UIView.h> may also be helpful.

我真的不确定如何处理PKPalette的约束，或者下面哪些约束是冲突的。我也尝试过禁用translatesAutoResizingMaskIntoConstraints，但它不起作用，因为我的应用程序的其他部分依赖它。感谢您的帮助，谢谢！

Answer 1

在iPhone上调用PKToolPicker时，我收到相同的日志消息。在iPad上，我没有得到约束错误。如果我仔细检查约束冲突，它似乎都是PKToolPicker内部的，与我的布局设置无关。

如果您运行相同的代码，但是在横向而不是纵向中使用iPhone，则不会发生冲突。因此，我怀疑PKPickerTool的限制存在某种限制，当屏幕太窄时，苹果需要修复这些限制。我去贴个雷达。

Answer 2

这并不是因为约束；您需要调用这些行：

toolPicker.setVisible(true, forFirstResponder: canvasView)
canvasView.becomeFirstResponder()

你可以在这里找到更多信息：

https://developer.apple.com/documentation/pencilkit/drawing_with_pencilkit https://developer.apple.com/videos/play/wwdc2019/221/

Answer 3

我也有同样的情况。如果你设置了布局断点，我可以看到涉及到的视图都是苹果自己的，它们甚至存在于一个私有的覆盖窗口中，而不是主窗口中。因此，框架中似乎存在一个合法的bug。

我发现对我来说，当我第一次尝试获取工具时，它会失败。为了解决这个问题，我现在只需在发布后很早的时候就得到一次工具。我不使用它们，但这会触发bug，所以当我真的需要这些工具时，它们就会工作。

if #available(iOS 13.0, *) {
    PKToolPicker.shared(for: view.window!)
}