在Camera.PictureCaptured之后重新启动Camera.StartStreamingBitmaps

Question

我有一个.Net小工具相机应用程序，它可以将位图从相机流到屏幕上。按一下按钮，它就会停止从相机中流式传输位图，拍摄一张照片，将其写入SD卡，然后重新开始流式传输。下面是代码的简化版本(不需要保存到SD卡中)：

using Microsoft.SPOT;
using GT = Gadgeteer;
using Gadgeteer.Modules.GHIElectronics;
namespace SimpleStopStreamingApp
{
    public partial class Program
    {
        void ProgramStarted()
        {
            camera.CameraConnected += new Camera.CameraConnectedEventHandler(camera_CameraConnected);
            camera.BitmapStreamed += new Camera.BitmapStreamedEventHandler(camera_BitmapStreamed);
            camera.PictureCaptured += new Camera.PictureCapturedEventHandler(camera_PictureCaptured);
            button.ButtonPressed += new Button.ButtonEventHandler(button_ButtonPressed);
        }
        void camera_CameraConnected(Camera sender)
        {
            camera.StartStreamingBitmaps(new Bitmap(camera.CurrentPictureResolution.Width, camera.CurrentPictureResolution.Height));
        }
        void camera_BitmapStreamed(Camera sender, Bitmap bitmap)
        {
            display_T35.SimpleGraphics.DisplayImage(bitmap, 0, 0);
        }
        void button_ButtonPressed(Button sender, Button.ButtonState state)
        {
            camera.StopStreamingBitmaps();
            camera.TakePicture();
        }
        void camera_PictureCaptured(Camera sender, GT.Picture picture)
        {
            camera.StartStreamingBitmaps(new Bitmap(camera.CurrentPictureResolution.Width, camera.CurrentPictureResolution.Height));
        }
    }
}

但是，当我尝试重新启动流(在PictureCaptured事件处理程序中)时，我得到了异常。

#### Exception System.Exception - 0xffffffff (1) ####
#### Message: 
#### GHI.Premium.USBHost.USBH_Webcam::StartStreaming_Internal [IP: 0000] ####
#### GHI.Premium.USBHost.USBH_Webcam::StartStreaming [IP: 0005] ####
#### Gadgeteer.Modules.GHIElectronics.Camera::StartStreamingBitmaps [IP: 007e] ####
#### Gadgeteer.Modules.GHIElectronics.Camera::OnPictureCapturedEvent [IP: 0037] ####
#### System.Reflection.MethodBase::Invoke [IP: 0000] ####
#### Gadgeteer.Program::DoOperation [IP: 001a] ####
#### Microsoft.SPOT.Dispatcher::PushFrameImpl [IP: 0054] ####
#### Microsoft.SPOT.Dispatcher::PushFrame [IP: 001a] ####
#### Microsoft.SPOT.Dispatcher::Run [IP: 0006] ####
#### Gadgeteer.Program::Run [IP: 0020] ####

A first chance exception of type 'System.Exception' occurred in GHI.Premium.USBHost.dll Error invoking method "Gadgeteer.Modules.GHIElectronics.Camera" (check arguments to Program.BeginInvoke are correct)

(注:如果我将位图存储为实例变量，并将其传递给StartStreamingBitmaps的两个调用，而不是每次都创建新的位图，则会得到相同的异常。)

到底怎么回事？如何停止摄像头流以捕获和图像，然后重新启动流媒体？

Answer 1

根据check arguments to Program.BeginInvoke are correct的说明，这听起来几乎像是希望在线程上运行StartStreamingBitmaps。

看看这个：

void camera_PictureCaptured(Camera sender, GT.Picture picture)
{
  camera.StartStreamingBitmaps(new Bitmap(camera.CurrentPictureResolution.Width, camera.CurrentPictureResolution.Height));
}

我对这个Gadgeteer模块一无所知，但是如果您正确地连接了它，我会认为您的新GT.Picture已经包含在传入的picture参数中。

它看起来就像是在相机完成拍摄后，您正在尝试从相机流式传输图像。

你能编辑你的帖子并提供更多细节吗？你能确认这个camera_PictureCaptured事件就是抛出异常的地方吗？只需将您的事件处理程序修改为：

void camera_PictureCaptured(Camera sender, GT.Picture picture)
{
  try
  {
    camera.StartStreamingBitmaps(new Bitmap(camera.CurrentPictureResolution.Width, camera.CurrentPictureResolution.Height));
  } catch (Exception err)
  {
    throw new Exception("PictureCaptured: " + err.Message);
  }
}

如果此事件处理程序不是引发异常的处理程序，请尝试在其他事件处理程序中放置类似的try...catch例程，直到发现问题的真正原因。

Answer 2

尝试在停止流式传输位图时删除回调：

void button_ButtonPressed(Button sender, Button.ButtonState state)
{
    camera.BitmapStreamed -= new Camera.BitmapStreamedEventHandler(camera_BitmapStreamed);
    camera.StopStreamingBitmaps();
    camera.TakePicture();
}

void camera_PictureCaptured(Camera sender, GT.Picture picture)
{
    camera.BitmapStreamed += new Camera.BitmapStreamedEventHandler(camera_BitmapStreamed);
    camera.StartStreamingBitmaps(new Bitmap(camera.CurrentPictureResolution.Width, camera.CurrentPictureResolution.Height));
}