macos - 使用 swift 读取 CFDictionary 中的值

Question

我刚开始使用 swift 和 cocoa。我正在尝试创建一个进行图像处理的基本应用。

我已经得到了图像的所有信息:

let imageRef:CGImageSourceRef = CGImageSourceCreateWithURL(url, nil).takeUnretainedValue()
let imageDict:CFDictionaryRef = CGImageSourceCopyPropertiesAtIndex(imageRef, 0, nil).takeUnretainedValue()

字典包含以下信息:

{
    ColorModel = Gray;
    DPIHeight = 300;
    DPIWidth = 300;
    Depth = 1;
    Orientation = 1;
    PixelHeight = 4167;
    PixelWidth = 4167;
    "{Exif}" =     {
        ColorSpace = 65535;
        DateTimeDigitized = "2014:07:09 20:25:49";
        PixelXDimension = 4167;
        PixelYDimension = 4167;
    };
    "{TIFF}" =     {
        Compression = 1;
        DateTime = "2014:07:09 20:25:49";
        Orientation = 1;
        PhotometricInterpretation = 0;
        ResolutionUnit = 2;
        Software = "Adobe Photoshop CS6 (Macintosh)";
        XResolution = 300;
        YResolution = 300;
    };
}

现在我想用下面的代码读取 DPI 的值，“__conversion”有一些我不明白的问题。

let dpiH:NSNumber = CFDictionaryGetValue(imageDict, kCGImagePropertyDPIWidth)

我做错了什么，我怎样才能得到字典的期望值？

Answer 1

我发现通过将 CFDictionary“转换”为 Swift 字典来访问属性要容易得多。

let imageSource = CGImageSourceCreateWithURL(imageURL, nil)
let imageProperties = CGImageSourceCopyPropertiesAtIndex(imageSource, 0, nil) as Dictionary
let dpiWidth = imageProperties[kCGImagePropertyDPIWidth] as NSNumber

---

Swift 2.0 的快速更新(请原谅所有的 if let - 我只是快速制作了这段代码):

import UIKit
import ImageIO

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        if let imagePath = NSBundle.mainBundle().pathForResource("test", ofType: "jpg") {
            let imageURL = NSURL(fileURLWithPath: imagePath)
            if let imageSource = CGImageSourceCreateWithURL(imageURL, nil) {
                if let imageProperties = CGImageSourceCopyPropertiesAtIndex(imageSource, 0, nil) as Dictionary? {
                    let pixelWidth = imageProperties[kCGImagePropertyPixelWidth] as! Int
                    print("the image width is: \(pixelWidth)")
                }
            }
        }
    }
}