imageView.image = UIImage(ciImage：)不会第二次更新

Question

案例:我在视图中有一个UISwitch按钮。当开关关闭时，imageView将显示从字符串生成的QRCode映像。打开时，它将显示由字符串生成的条形码图像。我从https://www.hackingwithswift.com/和复制了https://www.hackingwithswift.com/和条形码生成函数--它们正在运行良好的。

问题是imageView第一次只显示生成的图像。在QRCode和条形码之间切换时，imageView将不再更新。我100%确信UISwitch正在工作，函数被调用并返回生成的映像。我已经测试了多次与断点和打印，功能是不返回零或空图像。

这里是QRCode生成代码

func generateQRCode(from string: String) -> UIImage? {
    let data = string.data(using: String.Encoding.ascii)

    if let filter = CIFilter(name: "CIQRCodeGenerator") {
        filter.setValue(data, forKey: "inputMessage")
        let transform = CGAffineTransform(scaleX: 3, y: 3)

        if let output = filter.outputImage?.transformed(by: transform) {
            return UIImage(ciImage: output) //<== it always returns this
        }
    }
    return nil
}

这里是条形码生成代码

func generateBarcode(from string: String) -> UIImage? {
    let data = string.data(using: String.Encoding.ascii)

    if let filter = CIFilter(name: "CICode128BarcodeGenerator") {
        filter.setValue(data, forKey: "inputMessage")
        let transform = CGAffineTransform(scaleX: 3, y: 3)

        if let output = filter.outputImage?.transformed(by: transform) {
            return UIImage(ciImage: output) //<== it always returns this
        }
    }
    return nil
}

这里是如何在QRCode和条形码之间切换，逻辑是正确的。

func toggleBarcode(isBarcode : Bool) {
    if isBarcode {
        qrImageView.image = generateBarcode(from: "Hacking with Swift")
    } else {
        qrImageView.image = generateQRCode(from: "Hacking with Swift")
    }
}

当测试的时候

qrImageView.image = UIImage(named: "myimage")

每次都管用。

imageView不只是用UIImage(ciImage：)更新

我甚至测试了几个不同版本的QR和条形码生成代码，它们都没有第二次更新imageView。

我试过了

qrImageView.setNeedsDisplay()

但没有运气。

Answer 1

快速搜索..。似乎要么是“窃听器”，要么是变化..。

将生成器代码更改为此似乎纠正了以下问题：

func generateQRCode(from string: String) -> UIImage? {
    let data = string.data(using: String.Encoding.ascii)

    let context = CIContext()

    if let filter = CIFilter(name: "CIQRCodeGenerator") {
        filter.setValue(data, forKey: "inputMessage")
        let transform = CGAffineTransform(scaleX: 3, y: 3)
        
        if let output = filter.outputImage?.transformed(by: transform) {
            if let retImg = context.createCGImage(output, from: output.extent) {
                return UIImage(cgImage: retImg)
            }
        }
    }
    return nil
}

func generateBarcode(from string: String) -> UIImage? {
    let data = string.data(using: String.Encoding.ascii)

    let context = CIContext()

    if let filter = CIFilter(name: "CICode128BarcodeGenerator") {
        filter.setValue(data, forKey: "inputMessage")
        let transform = CGAffineTransform(scaleX: 3, y: 3)
        
        if let output = filter.outputImage?.transformed(by: transform) {
            if let retImg = context.createCGImage(output, from: output.extent) {
                return UIImage(cgImage: retImg)
            }
        }
    }
    return nil
}