为什么在 iOS 上使用 Xamarin Forms 的实时摄像头捕获控件会冻结？

Question

我将 Xamarin Moments from GitHub and now I'm trying to convert the CameraPage renderer 的源代码从 Page 下载到 ContentView

然后我重构了代码，使其成为 ContentView 渲染器。实时预览和图像捕获的大部分实际设置来自 Moments 应用程序，其中 needed/preferred.

显示实时预览，但当我按下按钮拍照时，应用程序无一例外地冻结，甚至在 Xcode 的控制台视图中也没有。

//this is how it's called: 
btnTakePicture.Clicked += (s,e)=> { GetCameraImage().Wait(); };

// this method freezes
public async Task<byte[]> GetCameraImage()
{
    byte[] imageBuffer = null;

    if (captureDeviceInput != null)
    { 
        var videoConnection = stillImageOutput.ConnectionFromMediaType(AVMediaType.Video);
        Console.WriteLine("[HASFIQWRPPOA] This message shows up");

// this is where the app freezes, even though the live preview still moves.
        var sampleBuffer = await stillImageOutput.CaptureStillImageTaskAsync(videoConnection);
        Console.WriteLine("[CLKJFADSFQXW] THIS DOESN'T SHOW UP");

        // var jpegImageAsBytes = AVCaptureStillImageOutput.JpegStillToNSData (sampleBuffer).ToArray ();
        var jpegImageAsNsData = AVCaptureStillImageOutput.JpegStillToNSData(sampleBuffer);
        Console.WriteLine("[ROIAJDGNQWTG]");
        // var image = new UIImage (jpegImageAsNsData);
        // var image2 = new UIImage (image.CGImage, image.CurrentScale, UIImageOrientation.UpMirrored);
        // var data = image2.AsJPEG ().ToArray ();
        imageBuffer = jpegImageAsNsData.ToArray();
        Console.WriteLine("[FIOUJGAIDGUQ] Image buffer: "+imageBuffer.Length);
    } 

    if (imageBuffer != null && imageBuffer.Length > 100)
    {
        using (var ms = new MemoryStream(imageBuffer))
        {
            var uiimg = UIImage.LoadFromData(NSData.FromStream(ms)); 
            this.Add(new UIImageView(uiimg)); 
        }
    }

    return imageBuffer;
}

下面是我设置实时预览的方法

// This method runs fine and the camera preview is started as expected
    public void SetupLiveCameraStream()
    {
        try
        {   
// add a UIView to the renderer
            liveCameraStream = new UIView()
            { 
                Frame = new CGRect(0f, 0f, Element.Width, Element.Height),  
            };   

            this.Add(liveCameraStream);  
// find a camera
            var captureDevice = AVCaptureDevice.DefaultDeviceWithMediaType(AVMediaType.Video);

            if (captureDevice != null)
            { 
                Console.WriteLine("[ZKSDJGWEHSY] Capture device found"); // not the case on simulator

                captureSession = new AVCaptureSession(); 

                videoPreviewLayer = new AVCaptureVideoPreviewLayer(captureSession)
                {
                    Frame = liveCameraStream.Bounds
                };

                liveCameraStream.Layer.AddSublayer(videoPreviewLayer);

                ConfigureCameraForDevice(captureDevice);

                captureDeviceInput = AVCaptureDeviceInput.FromDevice(captureDevice);

                var dictionary = new NSMutableDictionary();
                dictionary[AVVideo.CodecKey] = new NSNumber((int)AVVideoCodec.JPEG);
                stillImageOutput = new AVCaptureStillImageOutput()
                {
                    OutputSettings = new NSDictionary()
                };

                captureSession.AddInput(captureDeviceInput);
                captureSession.AddOutput(stillImageOutput);
                captureSession.StartRunning();
                Console.WriteLine("[OIGAJGUWRJHWY] Camera session started"); 
            }
            else
            {
                Console.WriteLine("[OASDFUJGOR] Could not find a camera device");
            } 
        }
        catch (Exception x)
        {
            Console.WriteLine("[QWKRIFQEAHJF] ERROR:" + x);
        }
    }

Answer 1

我遇到了这个问题，结果我陷入了僵局，因为结合使用了 async/await 和 Task.Result。猜测您可能会遇到与使用 Task.Wait().

类似的情况

两段代码：

btnTakePicture.Clicked += await (s,e) => { GetCameraImage().Wait(); };

并且：

var sampleBuffer = await stillImageOutput.CaptureStillImageTaskAsync(videoConnection);

为什么在 iOS 上使用 Xamarin Forms 的实时摄像头捕获控件会冻结？

Why does live camera capture control with Xamarin Forms on iOS freeze?

xamarin.ios

xamarin

xamarin.forms