如何使用手機相機作爲背景？

Question

我想創建相機作爲我的背景在Xamarin形式，我打算在我的共享代碼中的cameraview頂部添加的東西。

現在我正在做iOS設備。我現在碰到這行代碼：Frame = liveCameraStream.Bounds帶有錯誤：對象引用未設置爲對象的實例。

所以我的問題是我怎樣才能調整我的當前代碼來獲取相機作爲背景在Xamarin形式？

這是我在iOS的渲染：

[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，爲Xamarin.Forms一個MVVM框架，具有CameraView，您可以使用。它也已在兩個平臺上實現。如果你不想安裝整個軟件包，你可以簡單地獲取源代碼。但是，如果您決定這麼做，不要忘記將適當的許可證添加到您的項目中。

的CameraView可以在Xamarin.Forms項目很容易被消耗掉，像這樣：

<?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>