c# - 如何使用手机摄像头作为背景？

Question

我正在尝试在 xamarin 表单中创建相机作为我的背景，我计划在我的共享代码中的 cameraview 顶部添加一些东西。

现在我正在为 iOS 设备做这件事。我现在在这行代码上遇到崩溃:Frame = liveCameraStream.Bounds 并出现错误:未将对象引用设置为对象的实例。

所以我的问题是如何调整我当前的代码以在 xamarin 表单中将相机作为背景？

这是我在 iOS 中的渲染器:

[assembly: ExportRenderer(typeof(ICameraBackground), typeof(CameraBackground_iOS))]
namespace project.iOS
{
public class CameraBackground_iOS : ViewRenderer
{
    AVCaptureSession captureSession;
    AVCaptureDeviceInput captureDeviceInput;
    AVCaptureStillImageOutput stillImageOutput;
    UIView liveCameraStream;

    protected override void OnElementChanged(ElementChangedEventArgs<View> e)
    {
        base.OnElementChanged(e);
        SetupLiveCameraStream();
    }

    protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        base.OnElementPropertyChanged(sender, e);
        SetupLiveCameraStream();
    }


    public async void SetupLiveCameraStream()
    {
        await AuthorizeCameraUse();
        captureSession = new AVCaptureSession();

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

        var captureDevice = AVCaptureDevice.DefaultDeviceWithMediaType(AVMediaType.Video);
        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.AddOutput(stillImageOutput);
        captureSession.AddInput(captureDeviceInput);
        captureSession.StartRunning();
    }


    public void ConfigureCameraForDevice(AVCaptureDevice device)
    {
        var error = new NSError();
        if (device.IsFocusModeSupported(AVCaptureFocusMode.ContinuousAutoFocus))
        {
            device.LockForConfiguration(out error);
            device.FocusMode = AVCaptureFocusMode.ContinuousAutoFocus;
            device.UnlockForConfiguration();
        }
        else if (device.IsExposureModeSupported(AVCaptureExposureMode.ContinuousAutoExposure))
        {
            device.LockForConfiguration(out error);
            device.ExposureMode = AVCaptureExposureMode.ContinuousAutoExposure;
            device.UnlockForConfiguration();
        }
        else if (device.IsWhiteBalanceModeSupported(AVCaptureWhiteBalanceMode.ContinuousAutoWhiteBalance))
        {
            device.LockForConfiguration(out error);
            device.WhiteBalanceMode = AVCaptureWhiteBalanceMode.ContinuousAutoWhiteBalance;
            device.UnlockForConfiguration();
        }
    }

    public async Task AuthorizeCameraUse()
    {
        var authorizationStatus = AVCaptureDevice.GetAuthorizationStatus(AVMediaType.Video);
        if (authorizationStatus != AVAuthorizationStatus.Authorized)
        {
            await AVCaptureDevice.RequestAccessForMediaTypeAsync(AVMediaType.Video);
        }
    }

Answer 1

Xamarin.Forms.Labs ，Xamarin.Forms 的 MVVM 框架，有一个 CameraView你可以使用。它也已在两个平台上实现。如果你不想安装整个包，你可以简单地获取源代码。但是，如果您决定这样做，请不要忘记为您的项目添加适当的许可证。

在 Xamarin.Forms 项目中可以很容易地使用 CameraView，如下所示:

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage x:Class="XLabs.Samples.Pages.Controls.CameraViewPage"
         xmlns="http://xamarin.com/schemas/2014/forms"
         xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
         xmlns:controls="clr-namespace:XLabs.Forms.Controls;assembly=XLabs.Forms">
<StackLayout>
    <controls:CameraView HorizontalOptions="FillAndExpand" VerticalOptions="FillAndExpand" />
</StackLayout>