我目前正在学习 Swift，并且正在为此上课。我们被告知要编写一段代码，将滤镜应用于示例图片，以在其参数中更改图像上给定的颜色强度，然后返回修改后的图像。

在我写的代码中，在最后几行，它指出了一个错误

missing return in a function expected to return 'UIImage'

我的类(class)代码:

import UIKit


let image = UIImage(named: "sample")!

class brightnessFilter {

func increaseContrast(image: UIImage) -> UIImage{
    var rgbaImage = RGBAImage(image: image)!

    let avgRed = 118
    let avgGreen = 98
    let avgBlue = 83

    for y in 0..<rgbaImage.height {
        for x in 0..<rgbaImage.width {
            let index = y * rgbaImage.width + x
            var pixel = rgbaImage.pixels[index]
            let redLum = Int(pixel.red) - avgRed
            let greenLum = Int(pixel.green) - avgGreen
            let blueLum = Int(pixel.blue) - avgBlue
            pixel.red = UInt8(max(min(255, avgRed + 2 * redLum), 0))
            pixel.blue = UInt8(max(min(255, avgBlue + 2 * blueLum), 0))
            pixel.green = UInt8(max(min(255, avgGreen + 2 * greenLum), 0))
            rgbaImage.pixels[index] = pixel

        }
    }
    let newImage1 = rgbaImage.toUIImage()!
    return (newImage1)
  }

}

let test = brightnessFilter()
let processedImg = test.increaseContrast(image)


class redFilter {


func increaseContrast(image: UIImage) -> UIImage{
    var rgbaImage = RGBAImage(image: image)!

    let avgRed = 118

    for y in 0..<rgbaImage.height {
        for x in 0..<rgbaImage.width {
            let index = y * rgbaImage.width + x
            var pixel = rgbaImage.pixels[index]
            let redDiff = Int(pixel.red) - avgRed
            if (redDiff > 0) {
                pixel.red = UInt8( max(0, min(255, avgRed + redDiff * 5)))
                rgbaImage.pixels[index] = pixel
            }
        }
        let newImage2 = rgbaImage.toUIImage()!
        return (newImage2)
    }
  }
}

let test2 = redFilter()

RGBA 类:

import UIKit

public struct Pixel {
public var value: UInt32

public var red: UInt8 {
    get {
        return UInt8(value & 0xFF)
    }
    set {
        value = UInt32(newValue) | (value & 0xFFFFFF00)
    }
}

public var green: UInt8 {
    get {
        return UInt8((value >> 8) & 0xFF)
    }
    set {
        value = (UInt32(newValue) << 8) | (value & 0xFFFF00FF)
    }
}

public var blue: UInt8 {
    get {
        return UInt8((value >> 16) & 0xFF)
    }
    set {
        value = (UInt32(newValue) << 16) | (value & 0xFF00FFFF)
    }
}

public var alpha: UInt8 {
    get {
        return UInt8((value >> 24) & 0xFF)
    }
    set {
        value = (UInt32(newValue) << 24) | (value & 0x00FFFFFF)
    }
  }
}

最佳答案

当一个方法声明写有返回值时，你必须确保它总是返回一个值。

我认为您的错误出在以下方法中:

func increaseContrast(image: UIImage) -> UIImage {
    var rgbaImage = RGBAImage(image: image)!

    let avgRed = 118
    let newImage2 = UIImage() //<-- Added         

    for y in 0..<rgbaImage.height {
        for x in 0..<rgbaImage.width {
            let index = y * rgbaImage.width + x
            var pixel = rgbaImage.pixels[index]
            let redDiff = Int(pixel.red) - avgRed
            if (redDiff > 0) {
                pixel.red = UInt8( max(0, min(255, avgRed + redDiff * 5)))
                rgbaImage.pixels[index] = pixel
            }
        }
        let newImage2 = rgbaImage.toUIImage()!
        return (newImage2) //<---NOTICE
    }// <---FIX
  }

注意:return 语句在for 循环中，这意味着该方法可能并不总是返回一个值。

修复:将返回语句放在代码中标记的大括号下。

新增:你必须返回一个值，因此，你必须创建一个

旁注:确保处理 nil

关于ios - instaFilter 处理器错误 - 预期返回的函数中缺少返回值，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/38320653/