快速读取CFDictionary中的值 [英] reading value in CFDictionary with swift

问题描述

我只是从迅捷和可可开始.我正在尝试创建一个进行图像处理的基本应用.

I'm just starting with swift and cocoa. I'm trying to create a basic app that does image manipulation.

我已经准备好了图像的所有信息:

I've allready got all information of the image with this:

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

该词典包含以下信息:

{
    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，我想使用以下代码读取DPI的值，并且我不理解"__conversion"存在一些问题.

now I'd like to read the value for the DPI with following code and there is some problem with "__conversion" I don't understand.

let dpiH:NSNumber = CFDictionaryGetValue(imageDict, kCGImagePropertyDPIWidth)

我在做错什么，如何获得所需的字典值?

what am I doing wrong and how can I get to the desired values of the dictionary?

推荐答案

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

I've found it much easier to access the properties by 'converting' the CFDictionary to a Swift dictionary.

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(对所有if let都不好意思-我刚刚编写了这段代码):

---

Quick update for Swift 2.0 (excuse all the if lets - I just quickly crafted this code):

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)")
                }
            }
        }
    }
}

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