ios - UINavigationBar 底部边框消失

Question

我正在对 UINavigationBar 进行子类化，在界面生成器中，我使用 Identity Inspector 将其设置为我的 UINavigationController 的 NavigationBar 类>。问题是，当我覆盖 draw 方法时，我的 navigationBar 的底部边框消失了。这是我的代码:

class YC_NavigationBar: UINavigationBar {

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)

        self.backIndicatorImage = UIImage(named: "TopBar_Button_Back")!.withRenderingMode(.alwaysOriginal)
        self.backIndicatorTransitionMaskImage = UIImage(named: "TopBar_Button_Back")!.withRenderingMode(.alwaysOriginal)
        UIBarButtonItem.appearance().setBackButtonTitlePositionAdjustment(UIOffsetMake(0, -200.0), for: .default)

    }

    override func draw(_ rect: CGRect) {
        super.draw(rect)

        for i in self.subviews {
            if NSStringFromClass(i.classForCoder) == "_UINavigationBarContentView" {
                for j in i.subviews {
                    for constraint in j.constraints {
                        if constraint.firstAttribute == .leading && NSStringFromClass(constraint.firstItem!.classForCoder) == "_UIModernBarButton"  {
                            constraint.constant = 0
                            break
                        }
                    }
                    if NSStringFromClass(j.classForCoder) == "_UIButtonBarStackView" {
                        let ctr = NSLayoutConstraint(item: j, attribute: .trailing, relatedBy: .equal, toItem: i, attribute: .trailing, multiplier: 1, constant: 0)
                        i.addConstraint(ctr)
                    }
                }
                break
            }
        }
    }
}

仅仅覆盖该方法就发生了这种事情，这太荒谬了。我该如何解决这个问题？

Answer 1

这里有两个主要选项:

1. 像这样自己画一条线:

   override func draw(_ rect: CGRect) {
       super.draw(rect)
   
       // your other code here.
   
       if rect.maxY == self.bounds.maxY {
           if let context = UIGraphicsGetCurrentContext() {
               context.setStrokeColor(UIColor.red.cgColor)
               context.setLineWidth(1)
               context.move(to: CGPoint(x: 0, y: bounds.height))
               context.addLine(to: CGPoint(x: bounds.width, y: bounds.height))
               context.strokePath()
           }
       }
   }
   

2. 在 Interface Builder 的栏中添加一个 1px 高度的 subview 。

附言不要在 drawRect() 方法中执行布局代码。有一个特定的重写点正是为了这个目的而存在的:

open func layoutSubviews() // override point. called by layoutIfNeeded automatically. As of iOS 6.0, when constraints-based layout is used the base implementation applies the constraints-based layout, otherwise it does nothing.


    /* -layoutMargins returns a set of insets from the edge of the view's bounds that denote a default spacing for laying out content.
     If preservesSuperviewLayoutMargins is YES, margins cascade down the view tree, adjusting for geometry offsets, so that setting
     the left value of layoutMargins on a superview will affect the left value of layoutMargins for subviews positioned close to the
     left edge of their superview's bounds
       If your view subclass uses layoutMargins in its layout or drawing, override -layoutMarginsDidChange in order to refresh your 
     view if the margins change.
       On iOS 11.0 and later, please support both user interface layout directions by setting the directionalLayoutMargins property
     instead of the layoutMargins property. After setting the directionalLayoutMargins property, the values in the left and right
     fields of the layoutMargins property will depend on the user interface layout direction.
     */