Question

我的UWP应用程序中有一个摄像头功能，该功能的一部分是实际检查是否有任何连接的摄像头设备。我按照这组示例开发了该功能：CameraStarterKit

当我在没有网络摄像头或摄像头的机器上测试代码时，将显示消息提示。但是我认为当我退出页面时检查是否有相机设备的代码仍在运行，因为当我最小化应用程序并再次打开它时，提示出现了。

当我导航到另一页时，我是否可以停止检查相机是否已连接的代码？

以下是检查相机是否已连接的代码：

private async Task InitializeCameraAsync()
    {
        Debug.WriteLine("InitializeCameraAsync");

        if (_mediaCapture == null)
        {


            // Attempt to get the back camera if one is available, but use any camera device if not
            var cameraDevice = await FindCameraDeviceByPanelAsync(Windows.Devices.Enumeration.Panel.Back);

            if (cameraDevice == null)
            {
                this.LoadProgressRing.IsActive = false;
                this.LoadProgressStackPanel.Visibility = Windows.UI.Xaml.Visibility.Collapsed;

                MessageDialog cameraError = new MessageDialog("Connection Problem. No camera device found. Please kindly contacct the administrator.");
                UICommand YesBtn = new UICommand("Ok", delegate (IUICommand command)
                {
                    idleTimer.Stop();
                    var rootFrame = (Window.Current.Content as Frame);
                    rootFrame.Navigate(typeof(HomePage));
                    rootFrame.BackStack.Clear();
                });
                cameraError.Commands.Add(YesBtn);
                await cameraError.ShowAsync();


                Debug.WriteLine("No camera device found!");
                return;
            }


            // Create MediaCapture and its settings
            _mediaCapture = new MediaCapture();


            var settings = new MediaCaptureInitializationSettings { VideoDeviceId = cameraDevice.Id };

            // Initialize MediaCapture
            try
            {
                await _mediaCapture.InitializeAsync(settings);
                _isInitialized = true;
            }
            catch (UnauthorizedAccessException)
            {
                Debug.WriteLine("The app was denied access to the camera");
            }

            // If initialization succeeded, start the preview
            if (_isInitialized)
            {
                // Figure out where the camera is located
                if (cameraDevice.EnclosureLocation == null || cameraDevice.EnclosureLocation.Panel == Windows.Devices.Enumeration.Panel.Unknown)
                {
                    // No information on the location of the camera, assume it's an external camera, not integrated on the device
                    _externalCamera = true;
                }
                else
                {
                    // Camera is fixed on the device
                    _externalCamera = false;

                    // Only mirror the preview if the camera is on the front panel
                    _mirroringPreview = (cameraDevice.EnclosureLocation.Panel == Windows.Devices.Enumeration.Panel.Front);
                }

                // Initialize rotationHelper
                _rotationHelper = new CameraRotationHelper(cameraDevice.EnclosureLocation);
                _rotationHelper.OrientationChanged += RotationHelper_OrientationChanged;

                await StartPreviewAsync();

                UpdateCaptureControls();


            }

            return;
        }

    }

修改

SetUpBasedOnStateAsync（）方法的代码：

private async Task SetUpBasedOnStateAsync()
    {
        // Avoid reentrancy: Wait until nobody else is in this function.
        while (!_setupTask.IsCompleted)
        {
            await _setupTask;
        }

        // We want our UI to be active if
        // * We are the current active page.
        // * The window is visible.
        // * The app is not suspending.
        bool wantUIActive = _isActivePage && Window.Current.Visible && !_isSuspending;

        if (_isUIActive != wantUIActive)
        {
            _isUIActive = wantUIActive;

            Func<Task> setupAsync = async () =>
            {
                if (wantUIActive)
                {
                    await SetupUiAsync();
                    await InitializeCameraAsync();
                }
                else
                {
                    await CleanupCameraAsync();
                    await CleanupUiAsync();
                }
            };
            _setupTask = setupAsync();
        }

        await _setupTask;
    }

Answer 1

当我导航到另一页时，我是否可以停止检查相机是否已连接的代码？

当您导航到另一个页面时，将调用OnNavigatingFrom处理程序方法，您可以看到将在其中调用SetUpBasedOnStateAsync方法。在此方法中，将调用InitializeCameraAsync方法。因此，您只需要在SetUpBasedOnStateAsync方法中更改一些行代码。

但我认为当我退出页面时检查是否有相机设备的代码仍然在运行，因为当我最小化应用程序并再次打开它时，提示出现。

这是正常行为。当您最小化并打开您的应用时，代码将进入此if块。如果您不想要此行为。我建议您可以创建一个新项目，而不是更改官方代码示例。因为你需要改变许多地方。

如何在导航到UWP应用程序中的其他页面时停止运行网络摄像头

1 个答案: