iOS Swift UIImage 调整大小影响性能的问题；调整大小时出现意外尺寸[重复]

Question

我在 tableView（非常生涩）和几个视图控制器（加载缓慢）中遇到了性能问题。为了加快速度并使事情顺利进行，我尝试在初始加载时将传入图像的大小调整为它们各自 imageViews 的确切大小，而不是每次从 Core Data 加载时都在运行中。调整大小的图像将作为单独的属性存储在其父实体上。所有图片都是正方形的，即 1:1 的纵横比。

这是调整大小的代码：

extension UIImage {

    func resize(targetSize: CGSize) -> UIImage {

        print("Inside resize function")
        print("targetSize is \(targetSize)")

        return UIGraphicsImageRenderer(size:targetSize).image { _ in
            self.draw(in: CGRect(origin: .zero, size: targetSize))
        }
    }
}

这是调用调整大小函数并返回的函数：

    func difAndAssignPics() {

        guard let appDelegate =
            UIApplication.shared.delegate as? AppDelegate else {
                return
        }
// This is a copy of the original image, from which the smaller ones will be created

        print("bigToLittlePic size is \(bigToLittlePic?.size as Any)")

// These are the desired sizes of the three images I'm trying to create to facilitate performance

        let littlePicSize = CGSize(width: 110, height: 110)
        let mediumPicSize = CGSize(width: 160, height: 160)
        let displayPicSize = CGSize(width: 340, height: 340)

// This is the call to the resize function for each target size

        littlePic = bigToLittlePic?.resize(targetSize: littlePicSize)
        mediumPic = bigToLittlePic?.resize(targetSize: mediumPicSize)
        displayPic = bigToLittlePic?.resize(targetSize: displayPicSize)

// This code differentiates between front view and rear view of the item and prints out the size of each

        switch switchTag {
        case 1:
            newCoin.obversePic = (displayPic)!.pngData()! as NSData
            newCoin.obversePicThumb = (littlePic)!.pngData()! as NSData
            newCoin.obversePicMedium = (mediumPic)!.pngData()! as NSData

            selectIndicatorLabel.text = "Now select Reverse photo"
            appDelegate.saveContext()

            print("Inside switch case 1, difAndAssignPics")

            if let imageData = newCoin.obversePicThumb{
                let image = UIImage(data: imageData as Data)
                print("obversePicThumb size is \(image?.size as Any)")
            }
            if let imageData = newCoin.obversePicMedium{
                let image = UIImage(data: imageData as Data)
                print("obversePicMedium size is \(image?.size as Any)")
            }
            if let imageData = newCoin.obversePic{
                let image = UIImage(data: imageData as Data)
                print("obversePicBig size is \(image?.size as Any)")
            }


        case 2:
            newCoin.reversePic = (displayPic)!.pngData()! as NSData
            newCoin.reversePicThumb = (littlePic)!.pngData()! as NSData
            newCoin.reversePicMedium = (mediumPic)!.pngData()! as NSData

            selectIndicatorLabel.text = "Now select Obverse photo"
            appDelegate.saveContext()

            print("Inside switch case 2, difAndAssignPics")

            if let imageData = newCoin.reversePicThumb{
                let image = UIImage(data: imageData as Data)
                print("reversePicThumb size is \(image?.size as Any)")
            }
            if let imageData = newCoin.reversePicMedium{
                let image = UIImage(data: imageData as Data)
                print("reversePicMedium size is \(image?.size as Any)")
            }
            if let imageData = newCoin.reversePic{
                let image = UIImage(data: imageData as Data)
                print("reversePicBig size is \(image?.size as Any)")
            }
        default: break
        }
        reactivateDataButtons()
    }

以下是每张新图片介绍时控制台中打印的内容：

bigToLittlePic size is Optional((2320.0, 2320.0))

Inside resize function
targetSize is (110.0, 110.0)
Inside resize function
targetSize is (160.0, 160.0)
Inside resize function
targetSize is (340.0, 340.0)

好的，到目前为止一切顺利。但是，当图像返回到difAndAssignPics 时，这是打印输出：

reversePicThumb size is Optional((330.0, 330.0))
reversePicMedium size is Optional((480.0, 480.0))
reversePicBig size is Optional((1020.0, 1020.0))

为简洁起见，我只包含了反向图像的打印输出。正面给出相同的数字。

如您所见，不知何故，每个调整大小的图像的大小都膨胀了 3 倍。图片加载，质量很高，但性能仍然明显欠佳。我不知道如何核对这些数字。

有人有什么建议吗？

非常感谢！

编辑

我打印出在我的自定义单元格中被压缩到 110 x 110 imageViews 中的图像的大小。这些数字证实了调整大小功能中的某些东西被弄坏了。这是cellForRow中的数字：

obversePicThumb.size == Optional((330.0, 330.0))

reversePicThumb.size == Optional((330.0, 330.0))

编辑#2

post 回答了我的问题。非常感谢那些花时间看的人！

Answer 1

我不知道这是否会有所不同，但这是我的扩展来完成此操作：

extension UIImage {
    public func resizeToBoundingSquare(_ boundingSquareSideLength : CGFloat) -> UIImage {
        let imgScale = self.size.width > self.size.height ? boundingSquareSideLength / self.size.width : boundingSquareSideLength / self.size.height
        let newWidth = self.size.width * imgScale
        let newHeight = self.size.height * imgScale
        let newSize = CGSize(width: newWidth, height: newHeight)
        UIGraphicsBeginImageContext(newSize)
        self.draw(in: CGRect(x: 0, y: 0, width: newWidth, height: newHeight))
        let resizedImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext();
        return resizedImage!
    }
}

我的用法不是UITableView，也不是CoreData。 （我建议对类似的事情进行异步处理。）但是如果您的问题是调整大小，那么这应该具有可接受的性能。