將圖片儲存到沙盒下，首先獲取沙盒路徑，追加圖片名稱，將圖片轉換成NSData型別，寫到檔案裡。
persent引數：圖片質量引數，該值越大，表示圖片越清晰，圖片檔案也就越大

//儲存圖片至沙盒
    private func saveImage(currentImage: UIImage, persent: CGFloat, imageName: String){
        if let imageData = UIImageJPEGRepresentation(currentImage, persent) as NSData? {
            let fullPath = NSHomeDirectory().appending("/Documents/"
 
).appending(imageName)
            imageData.write(toFile: fullPath, atomically: true)
            print("fullPath=\(fullPath)")
        }
    }

也可以通過newSize自定義圖片的大小

private func saveImage(currentImage: UIImage, newSize: CGSize, imageName: String){
        //壓縮圖片尺寸
        UIGraphicsBeginImageContext(newSize)
        currentImage.draw(in
 
: CGRect(x: 0, y: 0, width: newSize.width, height: newSize.height))

        if let newImage = UIGraphicsGetImageFromCurrentImageContext() {
            //UIImageJPEGRepresentation此方法可將圖片壓縮，但是圖片質量基本不變，第二個引數即圖片質量引數。
            if let imageData = UIImageJPEGRepresentation(newImage, 1) as NSData? {
                let
 
 fullPath = NSHomeDirectory().appending("/Documents/").appending(imageName)
                imageData.write(toFile: fullPath, atomically: true)
                print("fullPath=\(fullPath)")
            }
        }
    }

從檔案中讀取圖片

if let savedImage = UIImage(contentsOfFile: fullPath) {
                self.imageView.image = savedImage
            } else {
                print("檔案不存在")
            }