声明仅在文件范围内有效（不知道这意味着什么）

Question

我正在开发一款试图为照片制作可自定义边框大小的应用。所以边框中的所有边都不会是相同的宽度。我在线获得扩展ca层，并被告知它允许我创建一个边框，每边都有一个可自定义的宽度。我只是不知道代码ca层在哪里。

import UIKit

class x1ViewController: UIViewController, UIImagePickerControllerDelegate, UINavigationControllerDelegate, UITextFieldDelegate {



@IBOutlet weak var imageDisplay: UIImageView!
     var screenView: UIImageView!




    extension CALayer {

        func addBorder(edge: UIRectEdge, color: UIColor, thickness: CGFloat) {

            let border = CALayer();

            switch edge {
            case UIRectEdge.top:
                border.frame = CGRect(x: 0, y: 0, width: self.frame.width, height: thickness)
                break
            case UIRectEdge.bottom:
                border.frame = CGRect(x:0, y:self.frame.height - thickness, width:self.frame.width, height:thickness)
                break
            case UIRectEdge.left:
                border.frame = CGRect(x:0, y:0, width: thickness, height: self.frame.height)
                break
            case UIRectEdge.right:
                border.frame = CGRect(x:self.frame.width - thickness, y: 0, width: thickness, height:self.frame.height)
                break
            default:
                break
            }

            border.backgroundColor = color.cgColor;

            self.addSublayer(border)
        }

    }


@IBAction func camera(_ sender: AnyObject) {
    if UIImagePickerController.isSourceTypeAvailable(UIImagePickerControllerSourceType.camera){
        let imagePicker = UIImagePickerController()
        imagePicker.delegate = self




        imageDisplay.layer.borderColor = UIColor(red: 0, green: 1.0, blue: 0, alpha: 1).cgColor
        imageDisplay.layer.cornerRadius = 1
        imageDisplay.contentMode = .scaleAspectFit
        imageDisplay.layer.borderWidth = 1


        imagePicker.sourceType = UIImagePickerControllerSourceType.camera;
        imagePicker.allowsEditing = false
        self.present(imagePicker, animated: true, completion: nil)}}

func imagePickerController(_ picker: UIImagePickerController, didFinishPickingImage image: UIImage!, editingInfo: [NSObject: AnyObject]!){
    imageDisplay.image = image
    self.dismiss(animated: true, completion: nil);
    screenView = UIImageView()

    screenView.frame = CGRect(x:0, y: 0, width: self.view.frame.width, height: self.view.frame.height)




    let text = "#HAPPY"
    let label = UILabel(frame: CGRect(x: 125, y: 700, width: self.view.frame.width, height: 300))
    label.font = UIFont(name: label.font.fontName, size: 122)

    label.textColor = UIColor.blue
    label.alpha = 1.0
    label.text = text


    self.view.addSubview(screenView)
    self.view.addSubview(label)


    UIGraphicsBeginImageContext(self.imageDisplay.frame.size)
    self.view.drawHierarchy(in: self.view.frame, afterScreenUpdates: true)

}
@IBAction func save(_ sender: AnyObject) {

    let alert = UIAlertController(title: "Image Saved", message: "Image is in photo gallery", preferredStyle: .alert)
    let okay = UIAlertAction(title: "OK", style: .default, handler: nil)
    alert.addAction(okay)
    present(alert, animated: true, completion: nil)



    let photo = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    UIImageWriteToSavedPhotosAlbum(photo!, nil, nil, nil)

}


}