WinForm控件BeginInvoke/调用问题 [英] WinForm Control BeginInvoke/Invoke Issue

问题描述

我正在尝试使用VS2012在C ++/CLI应用程序中编写多线程WinForm.

I am trying to write a multithreaded WinForm in C++/CLI app using VS2012.

我知道只有UI线程可以更新控件，并且我一直在使用委托和invoke方法.但是，在使用BeginInvoke时遇到了内存访问问题，而在使用Invoke时却看不到.

I know that only the UI thread can update a control and I have been using delegates and the invoke methods. However, I have run into a memory access issue when using BeginInvoke that I do not see when using Invoke.

代理功能:

public: delegate void pictureboxShowDelegate(int tChannelNumber,System::Windows::Forms::PictureBox^,System::Drawing::Bitmap^ colorImage);

被调用函数:

void DrawCVImageShow(int tChannelNumber, System::Windows::Forms::PictureBox^ PBox, System::Drawing::Bitmap^ b)
{
    if(PBox->InvokeRequired)
    {
        pictureboxShowDelegate^ d = gcnew pictureboxShowDelegate(this,&MyForm::DrawCVImageShow);
        PBox->Invoke(d,tChannelNumber,PBox,b);
    }
    else
    {
        System::Drawing::Graphics^ graphics = PBox->CreateGraphics();
        System::Drawing::RectangleF rect(0,0,(float)PBox->Width,(float)PBox->Height);
    graphics->DrawImage(b,rect);
    }
}

如果以这种方式调用，则不会有任何问题. 如果我用BeginInvoke代替Invoke，则会得到一个AccessViolationException. 显然，这与参数的垃圾收集有关，但我根本无法弄清楚这一点.

If called this way, it works with no problem. If I substitute BeginInvoke for Invoke, I get an AccessViolationException. Clearly, this has to do with the garbage collection of the parameters but I simply can't figure this one out.

任何帮助都将不胜感激.

Any help greatly appreciated.

谢谢

推荐答案

在我看来，首先调用DrawCVImageShow的是

It sounds to me like whatever is calling DrawCVImageShow in the first place is Disposing the bitmap immediately after DrawCVImageShow returns.

如果是这种情况，有两种可能:

If that's the case, there are a couple possiblities:

• 进行配置，以使DrawCVImageShow是负责处理位图的对象，而不是调用DrawCVImageShow的对象. (简单的解决方案，尽管可能不是工程解决方案中最好的解决方案:创建位图的事物通常应负责处理它，这使DrawCVImageShow成为不太通用的方法.)
• 制作位图的克隆 ，并在使用后将其处置.我认为这是更合适的解决方案，但确实会使事情变得更加复杂.现在，您需要两个版本的DrawCVImageShow，一个版本处理位图(用于BeginInvoking)，另一个版本不处理(现在的方法).这也意味着当需要BeginInvoke时，您将在内存中拥有两个位图副本.希望这些位图不会太大而不会引起问题.

• Make it so that DrawCVImageShow is the one responsible for Disposing the bitmap, not whatever calls DrawCVImageShow. (Simple solution, though probably not the best from an engineering solution: The thing that created the bitmap should generally be responsible for disposing it, and it makes DrawCVImageShow a less general method.)
• Make a Clone of the bitmap, and dispose that one after it's been used. This is the more proper solution, in my opinion, but it does make things a little bit more complicated. You now need two versions of DrawCVImageShow, one that disposes the bitmap (for BeginInvoking), and one that doesn't (the method you have now). This also means you'll have two copies of the bitmap in memory when a BeginInvoke is needed; hopefully these bitmaps are not so large that this is an issue.

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