SF 符号未加载到 UIImageView

Question

我正在创建一个用于跟踪健康信息的应用程序，我想使用 SF Symbols 中的两个箭头图像。不幸的是，无论我尝试什么，这些符号都不会出现。 我已经使用 Assets 文件夹中的图像测试了代码，这在我创建的 UIImageViews 中似乎没有问题。只有当我尝试使用 UIImage(systemName: ) 时才会遇到问题。

        self.calendarView = UIView(frame: CGRect(x: 0, y: self.getCurrentY(), width: UIScreen.main.bounds.width, height: 60))
        self.calendarView?.backgroundColor = .white
        self.calendarView?.layer.borderColor = UIColor.black.cgColor
        self.calendarView?.layer.borderWidth = 1

        self.currentDate = UILabel(frame: CGRect(x: self.calendarView!.bounds.width / 4, y: self.calendarView!.bounds.height / 2 - 20, width: self.calendarView!.bounds.width / 2, height: 40))
        self.currentDate!.text = "5/6/20"
        self.currentDate!.textColor = .black
        self.currentDate!.layer.borderColor = UIColor.black.cgColor
        self.currentDate?.layer.borderWidth = 1
        self.currentDate?.textAlignment = .center
        self.calendarView?.addSubview(currentDate!)

        //let testImage = UIImage(named: "logotest.jpg")!
        let image1 = UIImage(systemName: "arrow.left")!.withTintColor(.blue)
        let image2 = UIImage(systemName: "arrow.right")!.withTintColor(.blue)

        self.leftArrow = UIImageView(image: image1)
        self.rightArrow = UIImageView(image: image2)

        self.leftArrow?.frame = CGRect(x: 10, y: 10, width: 40, height: 40)
        self.rightArrow?.frame = CGRect(x: UIScreen.main.bounds.width - 50, y: 10, width: 40, height: 40)

        self.leftArrow?.layer.borderWidth = 1
        self.rightArrow?.layer.borderWidth = 1

        self.calendarView!.addSubview(self.leftArrow!)
        self.calendarView!.addSubview(self.rightArrow!)
        self.contentView.addSubview(self.calendarView!)

更奇怪的是，当我进入断点时，图像实际上显示了！我也附上了这张照片。对此我能得到的任何帮助表示赞赏。谢谢！

Answer 1

给你的 imageViews 着色将解决问题

leftArrow.tintColor = .blue 
leftArrow.tintColor = .blue

Answer 2

1) 您应该使用约束/自动布局而不是显式框架。

2) 你应该使用if let 和guard let 来避免所有那些! 和?

试试这样：

class ViewController: UIViewController {

    var leftArrow: UIImageView!
    var rightArrow: UIImageView!
    var calendarView: UIView!
    var currentDate: UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()

        //self.calendarView = UIView(frame: CGRect(x: 0, y: self.getCurrentY(), width: UIScreen.main.bounds.width, height: 60))
        self.calendarView = UIView()
        self.calendarView.backgroundColor = .white
        self.calendarView.layer.borderColor = UIColor.black.cgColor
        self.calendarView.layer.borderWidth = 1

        //self.currentDate = UILabel(frame: CGRect(x: self.calendarView!.bounds.width / 4, y: self.calendarView!.bounds.height / 2 - 20, width: self.calendarView!.bounds.width / 2, height: 40))
        self.currentDate = UILabel()
        self.currentDate.text = "5/6/20"
        self.currentDate.textColor = .black
        self.currentDate.layer.borderColor = UIColor.black.cgColor
        self.currentDate.layer.borderWidth = 1
        self.currentDate.textAlignment = .center

        //let testImage = UIImage(named: "logotest.jpg")!
        guard let imgLeft = UIImage(systemName: "arrow.left"),
            let imgRight = UIImage(systemName: "arrow.right") else {
                fatalError("Could not create arrow images!")
        }

        let image1 = imgLeft.withTintColor(.blue)
        let image2 = imgRight.withTintColor(.blue)

        self.leftArrow = UIImageView(image: image1)
        self.rightArrow = UIImageView(image: image2)

        //self.leftArrow.frame = CGRect(x: 10, y: 10, width: 40, height: 40)
        //self.rightArrow.frame = CGRect(x: UIScreen.main.bounds.width - 50, y: 10, width: 40, height: 40)

        self.leftArrow.layer.borderWidth = 1
        self.rightArrow.layer.borderWidth = 1

        self.calendarView.addSubview(currentDate)
        self.calendarView.addSubview(self.leftArrow)
        self.calendarView.addSubview(self.rightArrow)

        //self.contentView.addSubview(self.calendarView)
        self.view.addSubview(self.calendarView)

        [calendarView, currentDate, leftArrow, rightArrow].forEach {
            $0?.translatesAutoresizingMaskIntoConstraints = false
        }

        // respect safe area
        let g = view.safeAreaLayoutGuide

        NSLayoutConstraint.activate([

            // calendarView to view (safe area) Top / Leading / Trailing
            //  Height: 60
            calendarView.topAnchor.constraint(equalTo: g.topAnchor, constant: 0.0),
            calendarView.leadingAnchor.constraint(equalTo: g.leadingAnchor, constant: 0.0),
            calendarView.trailingAnchor.constraint(equalTo: g.trailingAnchor, constant: 0.0),
            calendarView.heightAnchor.constraint(equalToConstant: 60.0),

            // currentDate label to calendarView centerX & centerY
            //  Width: 1/2 of calendarView width
            //  Height: 40
            currentDate.centerXAnchor.constraint(equalTo: calendarView.centerXAnchor),
            currentDate.centerYAnchor.constraint(equalTo: calendarView.centerYAnchor),
            currentDate.heightAnchor.constraint(equalToConstant: 40.0),
            currentDate.widthAnchor.constraint(equalTo: calendarView.widthAnchor, multiplier: 0.5),

            // leftArrow to calendarView Leading: 10 Width: 40 Height: 40 centerY
            leftArrow.leadingAnchor.constraint(equalTo: calendarView.leadingAnchor, constant: 10.0),
            leftArrow.widthAnchor.constraint(equalToConstant: 40.0),
            leftArrow.heightAnchor.constraint(equalToConstant: 40.0),
            leftArrow.centerYAnchor.constraint(equalTo: calendarView.centerYAnchor),

            // rightArrow to calendarView Trailing: -10 Width: 40 Height: 40 centerY
            rightArrow.trailingAnchor.constraint(equalTo: calendarView.trailingAnchor, constant: -10.0),
            rightArrow.widthAnchor.constraint(equalToConstant: 40.0),
            rightArrow.heightAnchor.constraint(equalToConstant: 40.0),
            rightArrow.centerYAnchor.constraint(equalTo: calendarView.centerYAnchor),

        ])

    }
}

输出：

并且，通过自动布局和约束，它可以在需要时自动调整大小 - 例如在设备旋转时：