Question

在我的应用程序中，您可以打开一个可以打开和关闭手电筒的站点。它第一次工作，但如果我尝试第二次切换手电筒，应用程序崩溃。

我认为这是AudioVideoCaptureDevice.OpenAsync的一个问题。如果我第二次调用它，则应用程序崩溃.Reflection.TargetInvocationException WinRT-Informationen：无法获取摄像头。您只能在前台使用此类。

有人知道这个问题吗？

protected AudioVideoCaptureDevice Device { get; set; }

public Page10()
{
    InitializeComponent();
}

async void tglSwitch_Checked(object sender, RoutedEventArgs e)
{
    var sensorLocation = CameraSensorLocation.Back;
    if (this.Device == null)
    {
        // get the AudioVideoCaptureDevice
        this.Device = await AudioVideoCaptureDevice.OpenAsync(sensorLocation,
        AudioVideoCaptureDevice.GetAvailableCaptureResolutions(sensorLocation).First());
    }
    var supportedCameraModes = AudioVideoCaptureDevice
        .GetSupportedPropertyValues(sensorLocation, KnownCameraAudioVideoProperties.VideoTorchMode);
    if (supportedCameraModes.ToList().Contains((UInt32)VideoTorchMode.On))
    {
        this.Device.SetProperty(KnownCameraAudioVideoProperties.VideoTorchMode, VideoTorchMode.On);

        // set flash power to maxinum
        this.Device.SetProperty(KnownCameraAudioVideoProperties.VideoTorchPower,
            AudioVideoCaptureDevice.GetSupportedPropertyRange(sensorLocation, KnownCameraAudioVideoProperties.VideoTorchPower).Max);

        this.tglSwitch.Content = "Light on";
        this.tglSwitch.SwitchForeground = new SolidColorBrush(Colors.Green);
    }
}

void tglSwitch_Unchecked(object sender, RoutedEventArgs e)
{
    var sensorLocation = CameraSensorLocation.Back;
    sensorLocation = CameraSensorLocation.Back;
    var supportedCameraModes = AudioVideoCaptureDevice
        .GetSupportedPropertyValues(sensorLocation, KnownCameraAudioVideoProperties.VideoTorchMode);
    if (this.Device != null && supportedCameraModes.ToList().Contains((UInt32)VideoTorchMode.Off))
    {
        this.Device.SetProperty(KnownCameraAudioVideoProperties.VideoTorchMode, VideoTorchMode.Off);
        this.tglSwitch.Content = "Light off";
    }
}

Answer 1

我建议在页面生命周期中使用OpenAsync ONE TIME初始化相机，例如在OnNavigatedTo事件中。只有让SetProperty()方法调用复选框事件中的代码才能控制光线。通过调用OnNavigatedFrom，正确处理相机然后离开页面也是非常重要的，例如在device.Dispose()事件中。此选项还可使您的手电筒更快地工作。

请记住，Windows Phone 8.1现在有专门用于火炬的API，效果很好，代码更漂亮。您也可以在Silverlight项目中使用，但必须迁移项目。以下是有关http://developer.nokia.com/community/wiki/Using_the_camera_light_in_Windows_Phone_7,_8_and_8.1和https://msdn.microsoft.com/en-us/library/windows/apps/windows.media.devices.torchcontrol的更多信息。

Windows Phone 8第二次无法调用AudioVideoCaptureDevice

1 个答案: