将一行从 Swift 转换为 Objective-C

Question

我正在尝试将扩展形式 Swift 转换为 Objective-C。需要确定 UIImage 的平均颜色。我几乎完成了所有工作，但坚持了一行：

var bitmap = [UInt8](repeating: 0, count: 4)

此扩展来自 https://www.hackingwithswift.com：

extension UIImage {
    var averageColor: UIColor? {
        guard let inputImage = CIImage(image: self) else { return nil }
        let extentVector = CIVector(x: inputImage.extent.origin.x, y: inputImage.extent.origin.y, z: inputImage.extent.size.width, w: inputImage.extent.size.height)

        guard let filter = CIFilter(name: "CIAreaAverage", parameters: [kCIInputImageKey: inputImage, kCIInputExtentKey: extentVector]) else { return nil }
        guard let outputImage = filter.outputImage else { return nil }

        var bitmap = [UInt8](repeating: 0, count: 4)
        let context = CIContext(options: [.workingColorSpace: kCFNull])
        context.render(outputImage, toBitmap: &bitmap, rowBytes: 4, bounds: CGRect(x: 0, y: 0, width: 1, height: 1), format: .RGBA8, colorSpace: nil)

        return UIColor(red: CGFloat(bitmap[0]) / 255, green: CGFloat(bitmap[1]) / 255, blue: CGFloat(bitmap[2]) / 255, alpha: CGFloat(bitmap[3]) / 255)
    }
}

这就是我在 Objective-C 中得到的：

- (UIColor *)averageColorWithUIImage:(UIImage *)image {
    CIImage *inputImage = [CIImage imageWithCGImage:(__bridge CGImageRef _Nonnull)(image)];
    if (!inputImage) {
        return nil;
    }
    CIVector *extentVector = [CIVector vectorWithX:inputImage.extent.origin.x Y: inputImage.extent.origin.y Z: inputImage.extent.size.width W: inputImage.extent.size.height];

    CIFilter *filter = [CIFilter filterWithName:@"CIAreaAverage" keysAndValues:kCIInputImageKey, inputImage, kCIInputExtentKey, extentVector, nil];
    if (!filter) {
        return nil;
    }
    CIImage *outputImage = filter.outputImage;
    if (!outputImage) {
        return nil;
    }

    NSSet *bitmap = [NSSet setWithObjects:0 count:4];
    CIContext *context = [[CIContext alloc] initWithOptions:@{kCIContextWorkingColorSpace : NSNull.null}];
    [context render:outputImage toBitmap:&bitmap rowBytes:4 bounds:CGRectMake(0, 0, 1, 1) format:kCIFormatRGBA8 colorSpace:nil];

        return [UIColor colorWithRed:(CGFloat)bitmap[0]/255.0
                   green:((CGFloat)bitmap[1])/255.0
                    blue:((CGFloat)bitmap[2])/255.0
                 alpha:((CGFloat)bitmap[3])/255.0];
}

我这里弄错了：

return [UIColor colorWithRed:(CGFloat)bitmap[0]/255.0
                   green:((CGFloat)bitmap[1])/255.0
                    blue:((CGFloat)bitmap[2])/255.0
                 alpha:((CGFloat)bitmap[3])/255.0];

错误是-

Expected method to read array element not found on object of type 'NSSet *'

Answer 1

以下是将 bitmap 变量转换为 Objective-C 的方法：

uint8_t bitmap[4] = {};

这是将其传递给渲染方法的方式：

[context render:outputImage toBitmap:bitmap
    rowBytes:4 bounds:CGRectMake(0, 0, 1, 1)
    format:kCIFormatRGBA8 colorSpace:nil];

请注意，您不是使用 & 运算符获取其地址！

将一行从 Swift 转换为 Objective-C

Convert a line from Swift to Objective-C

objective-c

swift