Xamarin Community Toolkit CameraView拍照触发CAMERA_ERROR(3)问题求助

问题场景 #

使用Xamarin Community Toolkit的CameraView组件开发跨平台相机预览页，拍照时Debug输出显示"camera picture taken"，但MediaCaptured事件未触发，无该方法内的日志输出；拍照后出现错误：

[0:] CameraView: Error camera access
ErrorMessage: CAMERA_ERROR (3): The camera device has encountered a serious error.

已尝试重启应用、模拟器及更换设备，问题仍存在。

相关代码 #

XAML代码 #

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:xct="http://xamarin.com/schemas/2020/toolkit"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="Test.CameraPreview"
             
             NavigationPage.HasBackButton="True"
             NavigationPage.HasNavigationBar="False">
    <ContentPage.Content>
        <Grid x:Name="cameraGrid">
            <xct:CameraView x:Name="xctCameraView"
                            CaptureMode="Photo"
                            MediaCaptured="MediaCaptured"
                            HorizontalOptions="FillAndExpand"
                            VerticalOptions="FillAndExpand"/>
            <StackLayout VerticalOptions="EndAndExpand">
                <StackLayout Orientation="Horizontal" HorizontalOptions="CenterAndExpand" BackgroundColor="Transparent">
                    <Frame CornerRadius="15" x:Name="videoFrame" WidthRequest="48" Padding="7">
                        <Label Text="Video" HorizontalOptions="CenterAndExpand" x:Name="videoLabel" BackgroundColor="Transparent"/>
                    </Frame>
                    <Frame CornerRadius="15" x:Name="pictureFrame" WidthRequest="48" Padding="7">
                        <Label Text="Picture" HorizontalOptions="CenterAndExpand" x:Name="pictureLabel" BackgroundColor="Transparent"/>
                    </Frame>
                </StackLayout>
                <ImageButton Clicked="CapturePhoto" HeightRequest="120" WidthRequest="120"
                             HorizontalOptions="Center" x:Name="captureBtn" BackgroundColor="Transparent"/>
            </StackLayout>
        </Grid>
    </ContentPage.Content>
</ContentPage>

C#代码 #

private void CapturePhoto(object sender, EventArgs e)
{
    if (isPictureSelected)
    {
        if (xctCameraView != null)
        {
            Debug.WriteLine($"xctCameraView is not null");
            xctCameraView.Shutter();
            Debug.WriteLine($"camera picture taken");
        }
        else
        {
            DisplayAlert("Error", "Camera view is not available.", "OK");
        }
    }
}

private void MediaCaptured(object sender, MediaCapturedEventArgs e)
{
    switch (xctCameraView.CaptureMode)
    {
        default:
        case CameraCaptureMode.Default:
        case CameraCaptureMode.Photo:
            Debug.WriteLine($"media captured is passed");
            if (e.Image != null)
            {
                Debug.WriteLine($"e.Image is not null");
                var imageSource = (StreamImageSource)e.Image;
                using (var stream = imageSource.Stream(CancellationToken.None).Result)
                {
                    using (var memoryStream = new MemoryStream())
                    {
                        Debug.WriteLine($"var memoryStream = new MemoryStream() went through");
                        stream.CopyTo(memoryStream);
                        photoData = memoryStream.ToArray();
                        Debug.WriteLine($"navigating to EditPostPage");
                        Device.BeginInvokeOnMainThread(() =>
                        {
                            Navigation.PushAsync(new EditPostPage(userId, textId, photoData));
                        });
                    }
                }
            }
            break;
        case CameraCaptureMode.Video:
            break;
    }
}

排查原因及解决办法 #

1. 相机权限未正确配置 #

跨平台应用必须在各平台项目中声明相机权限，否则相机无法正常访问：

• Android：在AndroidManifest.xml中添加权限

  <uses-permission android:name="android.permission.CAMERA" />
  <uses-feature android:name="android.hardware.camera" />
  <uses-feature android:name="android.hardware.camera.autofocus" />
  

  同时在页面OnAppearing中动态请求权限（Android 6.0+）：

  protected override async void OnAppearing()
  {
      base.OnAppearing();
      var status = await Permissions.CheckStatusAsync<Permissions.Camera>();
      if (status != PermissionStatus.Granted)
      {
          status = await Permissions.RequestAsync<Permissions.Camera>();
          if (status != PermissionStatus.Granted)
          {
              DisplayAlert("权限不足", "需要相机权限才能使用拍照功能", "确定");
              return;
          }
      }
      xctCameraView.IsEnabled = true;
  }
  

• iOS：在Info.plist中添加相机权限描述

  <key>NSCameraUsageDescription</key>
  <string>需要访问相机进行拍照</string>
  

2. CameraView初始化时机问题 #

调用Shutter()时相机可能未完成初始化，导致拍照失败且事件不触发：

• 在页面OnAppearing中等待相机初始化完成：

  protected override async void OnAppearing()
  {
      base.OnAppearing();
      // 先执行权限检查
      xctCameraView.IsEnabled = true;
      await Task.Delay(500); // 等待相机资源加载
      if (!xctCameraView.IsAvailable)
      {
          DisplayAlert("错误", "相机初始化失败", "确定");
      }
  }
  

• 在CapturePhoto中增加可用状态检查：

  private void CapturePhoto(object sender, EventArgs e)
  {
      if (isPictureSelected && xctCameraView?.IsAvailable == true)
      {
          Debug.WriteLine($"xctCameraView is available");
          xctCameraView.Shutter();
          Debug.WriteLine($"camera picture taken");
      }
      else
      {
          DisplayAlert("Error", "Camera view is not available.", "OK");
      }
  }
  

3. 相机资源未正确释放 #

页面销毁时未释放相机资源，导致资源冲突触发错误：

• 在页面OnDisappearing中禁用相机：

  protected override void OnDisappearing()
  {
      base.OnDisappearing();
      xctCameraView.IsEnabled = false;
  }
  

4. 异步代码死锁问题 #

MediaCaptured中使用.Result会导致死锁，改用await处理：
修改为异步方法：

private async void MediaCaptured(object sender, MediaCapturedEventArgs e)
{
    switch (xctCameraView.CaptureMode)
    {
        default:
        case CameraCaptureMode.Default:
        case CameraCaptureMode.Photo:
            Debug.WriteLine($"media captured is passed");
            if (e.Image != null)
            {
                Debug.WriteLine($"e.Image is not null");
                var imageSource = (StreamImageSource)e.Image;
                using (var stream = await imageSource.Stream(CancellationToken.None))
                {
                    using (var memoryStream = new MemoryStream())
                    {
                        Debug.WriteLine($"var memoryStream = new MemoryStream() went through");
                        await stream.CopyToAsync(memoryStream);
                        photoData = memoryStream.ToArray();
                        Debug.WriteLine($"navigating to EditPostPage");
                        await Navigation.PushAsync(new EditPostPage(userId, textId, photoData));
                    }
                }
            }
            break;
        case CameraCaptureMode.Video:
            break;
    }
}

5. 版本兼容性问题 #

检查Xamarin Community Toolkit与Xamarin.Forms版本是否兼容，升级至最新稳定版：

• 更新NuGet包：确保Xamarin.CommunityToolkit和Xamarin.Forms都使用最新稳定版本，避免版本不匹配导致组件异常。

内容的提问来源于stack exchange，提问作者bluedra