SwiftUI-MJPEG視頻流不更新視圖中的影像

鑒于以下情況StreamView()：

struct StreamView: View {
    @StateObject var stream = MJPEGStream()

    var body: some View {
        MpegView(mjpegStream: self.stream)
            .background(.red)
            .frame(width: 200, height: 200)
    }
}

struct StreamView_Previews: PreviewProvider {
    static var previews: some View {
        StreamView()
    }
}

我有以下MpegView()實作ObservableObject：

class MJPEGStream: ObservableObject {
    @Published var stream = MJPEGStreamLib()
    
    init() {
        self.stream.play(url: URL(string: "http://192.168.1.120/mjpeg/1")!)
    }
}

struct MpegView: View {
    @ObservedObject var mjpegStream: MJPEGStream
    
    var body: some View {
        Image(uiImage: self.mjpegStream.stream.image)
            .resizable()
    }
}

基本上，以下類用var image = UIImage()MJPEG 流的更新影像替換了一個實體：

class MJPEGStreamLib: NSObject, URLSessionDataDelegate {
    enum StreamStatus {
        case stop
        case loading
        case play
    }
    
    var receivedData: NSMutableData?
    var dataTask: URLSessionDataTask?
    var session: Foundation.URLSession!
    var status: StreamStatus = .stop
    
    var authenticationHandler: ((URLAuthenticationChallenge) -> (URLSession.AuthChallengeDisposition, URLCredential?))?
    var didStartLoading: (() -> Void)?
    var didFinishLoading: (() -> Void)?

    var contentURL: URL?
    var image = UIImage()
    
    override init() {
        super.init()
        self.session = URLSession(configuration: URLSessionConfiguration.default, delegate: self, delegateQueue: nil)
    }
    
    convenience init(contentURL: URL) {
        self.init()
        self.contentURL = contentURL
        self.play()
    }
    
    deinit {
        self.dataTask?.cancel()
    }
    
    // Play function with url parameter
    func play(url: URL) {
        // Checking the status for it is already playing or not
        if self.status == .play || self.status == .loading {
            self.stop()
        }
        
        self.contentURL = url
        self.play()
    }
    
    // Play function without URL paremeter
    func play() {
        guard let url = self.contentURL, self.status == .stop else {
            return
        }
        
        self.status = .loading
        DispatchQueue.main.async {
            self.didStartLoading?()
        }
        
        self.receivedData = NSMutableData()
        
        let request = URLRequest(url: url)
        self.dataTask = self.session.dataTask(with: request)
        self.dataTask?.resume()
    }
    
    // Stop the stream function
    func stop() {
        self.status = .stop
        self.dataTask?.cancel()
    }
    
    // NSURLSessionDataDelegate
    func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive response: URLResponse, completionHandler: @escaping (URLSession.ResponseDisposition) -> Void) {
        // Controlling the imageData is not nil
        if let imageData = self.receivedData, imageData.length > 0,
            let receivedImage = UIImage(data: imageData as Data) {
            if self.status == .loading {
                self.status = .play
                DispatchQueue.main.async {
                    self.didFinishLoading?()
                }
            }
            
            // Set the imageview as received stream
            DispatchQueue.main.async {
                self.image = receivedImage
            }
        }
        
        self.receivedData = NSMutableData()
        completionHandler(.allow)
    }
    
    func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
        self.receivedData?.append(data)
    }
    
    // NSURLSessionTaskDelegate
    func urlSession(_ session: URLSession, task: URLSessionTask, didReceive challenge: URLAuthenticationChallenge, completionHandler: @escaping (URLSession.AuthChallengeDisposition, URLCredential?) -> Void) {
        var credential: URLCredential?
        var disposition: URLSession.AuthChallengeDisposition = .performDefaultHandling
        
        // Getting the authentication if stream asks it
        if challenge.protectionSpace.authenticationMethod == NSURLAuthenticationMethodServerTrust {
            if let trust = challenge.protectionSpace.serverTrust {
                credential = URLCredential(trust: trust)
                disposition = .useCredential
            }
        } else if let onAuthentication = self.authenticationHandler {
            (disposition, credential) = onAuthentication(challenge)
        }
        
        completionHandler(disposition, credential)
    }
}

然后在我的主要ContentView()我只有：

struct ContentView: View {
    var body: some View {
        StreamView()
    }
}

問題是Image中的MpegView()沒有使用從流中接收到的幀進行更新。我不確定這是否是我對類別庫@Published或@StateObject屬性的實作。

注意：我可以通過網路瀏覽器確認流是否有效，并且如果我除錯receivedImage它是來自流視頻的實際幀是什么。

uj5u.com熱心網友回復：

你觀察到的屬性的值stream中MJPEGStream是一個指向一個MJPEGStreamLib物件。

屬性更改的唯一時間，也是您ObservableObject將導致MpegView更新的唯一時間，是您第一次為指標賦值時 -MpegView首次創建時。之后，指向物件的指標永遠不會改變，即使它指向的物件正在快速生成影像。所以你的視圖永遠不會更新。

如果您希望您的 Swift 視圖在MJPEGStreamLib物件中的影像發生更改時更新，那么您需要MJPEGStreamLib將ObservableObject和 標記其image屬性為@Published。

uj5u.com熱心網友回復：

MJPEGStreamLib 包含靜態影像變數，因此影像視圖不會更新。您需要使用諸如@State 或@Published 之類的屬性包裝器來系結變數。仍然無法正常作業，請在此處發表評論。我會幫你

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