Question

我正在尝试在缓存目录中保存带有叠加层的地图快照，并在存在时检索它。但是，尽管创建了文件，但当我尝试检索它时，UIImage（contentsOfFile :)返回nil。我已经打印了写入和读取的文件路径，它们是相同的，并且通过下载容器并检查目录并且文件肯定存在来验证文件是否存在。

知道这里的问题是什么吗？

let cachesDirectory: URL = {
    let urls = FileManager.default.urls(for: .cachesDirectory, in: .userDomainMask)
    return urls[urls.endIndex - 1]
}()

let mapCachesDirectory = cachesDirectory.appendingPathComponent("map-snapshots", isDirectory: true)

func configureMap(data: NSSet?) {
    mapView.isZoomEnabled = false
    mapView.isScrollEnabled = false
    mapView.isUserInteractionEnabled = false

    guard let data = data as? Set<SessionData>, data.count > 0 else { return }

    activityIndicatorView.isHidden = false
    activityIndicatorView.startAnimating()

    DispatchQueue.global(qos: .userInitiated).async {
        var points = [CLLocationCoordinate2D]()
        for object in data {
            guard object.locationLatitude != 0, object.locationLatitude != 0 else { continue }
            points.append(CLLocationCoordinate2DMake(object.locationLatitude, object.locationLongitude))
        }
        DispatchQueue.main.async(execute: {
            self.createOverlay(points: points)
            self.activityIndicatorView.stopAnimating()
            self.activityIndicatorView.isHidden = true
            self.cacheMapImage(view: self.mapView)
        })
    }
}

func cacheMapImage(view: UIView) {
    UIGraphicsBeginImageContextWithOptions(view.bounds.size, true, 0)
    view.drawHierarchy(in: view.bounds, afterScreenUpdates: true)
    let compositeImage = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    DispatchQueue.global(qos: .userInitiated).async {
        if let compositeImage = compositeImage, let info = self.info {
            let data = UIImagePNGRepresentation(compositeImage)
            do {
                var isDirectory: ObjCBool = false
                let fileManager = FileManager.default
                if fileManager.fileExists(atPath: self.mapCachesDirectory.absoluteString, isDirectory: &isDirectory) == false {
                    try fileManager.createDirectory(at: self.mapCachesDirectory, withIntermediateDirectories: true, attributes: nil)
                }
                let fileURL = self.mapCachesDirectory.appendingPathComponent(info.uid).appendingPathExtension("png")
                try data?.write(to: fileURL)
                print("\(fileURL.absoluteString) Saved")
            } catch {
                log.error(error)
            }
        }
    }
}

func cachedMapImage() -> UIImage? {
    guard let info = info else { return nil }
    let filePath = mapCachesDirectory.appendingPathComponent(info.uid).appendingPathExtension("png").absoluteString
    let image = UIImage(contentsOfFile: filePath)
    print("\(filePath): \(image)")
    return image
}

func createOverlay(points: [CLLocationCoordinate2D]) {
    guard points.count > 0 else { return }

    let overlay = MKGeodesicPolyline(coordinates: points, count: points.count)
    mapView.add(overlay)

    let inset: CGFloat = 50.0
    mapView.setVisibleMapRect(overlay.boundingMapRect, edgePadding: UIEdgeInsetsMake(inset,inset,inset,inset), animated: true)
}

Answer 1

问题是您正在使用URL属性absoluteString，您应该使用path属性。 absoluteString和path属性之间的区别在于absoluteString包含文件url方案（＆＃34; file：//＆＃34;），这是它找不到文件的原因应该是它的路径，但它实际上是它的绝对字符串。

尽管文件存在于caches目录中，UIImage（contentsOfFile :)返回nil

1 个答案: