ios - Swift 中的 CGPointMakeWithDictionaryRepresentation

Question

我正在使用 AVCaptureSession在 Swift 应用程序中扫描二维码。我想在检测到的 QR 码周围画一个框，但我在转换 AVMetadataMachineReadableCodeObject 的“角”属性时遇到问题变成可用的东西。

var corners: [AnyObject]! { get }

The value of this property is an array of CFDictionary objects, each of which has been created from a CGPoint struct using the CGPointCreateDictionaryRepresentation function, representing the coordinates of the corners of the object with respect to the image in which it resides.

我试过这个(基于 project by werner77 )但我得到以下编译器错误 “'CGPoint?'与‘CGPoint’不同”

// MARK: - AVCaptureMetadataOutputObjectsDelegate
func captureOutput(captureOutput: AVCaptureOutput!, didOutputMetadataObjects metadataObjects: [AnyObject]!, fromConnection connection: AVCaptureConnection!) {

    let metadataObject = metadataObjects[0] as AVMetadataMachineReadableCodeObject;
    var corners = metadataObject.corners as Array<NSDictionary>;
    var topLeftDict = corners[0] as NSDictionary;
    var topLeft : CGPoint?

    // COMPILE ERROR: 'CGPoint?' is not identical to 'CGPoint'
    CGPointMakeWithDictionaryRepresentation(topLeftDict, &topLeft)   
}

如有任何帮助，我们将不胜感激。

Answer 1

了解可选项。

任何类型都可以附加?，这意味着它也可以是nil。这样做的好处是，您必须显式地处理或忽略 nil 对象，这与 Objective-C 不同，在 Objective-C 中，nil 对象可能会导致无法追踪的错误。

当从字典中获取对象时，它必须是可选的，因为字典中可能不存在该键。 CGPointMakeWithDictionaryRepresentation 需要一个非可选值，因此您必须使用初始化的非可选值。

// Playground:
var point = CGPointMake(1, 2)
var dictionary = CGPointCreateDictionaryRepresentation(point)
var aPoint = CGPointZero
CGPointMakeWithDictionaryRepresentation(dictionary, &aPoint)
aPoint // x 1, y 2