c# - Safety of passing HBITMAP handle from unmanaged to managed code for created a System.Drawing.Bitmap -

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I'm very new to managed / unmanaged interop, so I'm looking to get some feedback about the following opinion To get a bitmap from unmanaged C ++ to manage, the # is the basic idea:

  1. C # call an interop function, FetchImage , which is unmanaged C In ++, it passes an out int param fetchImage is related to long * param.
  2. In C ++, FetchImage creates a CBitmap somewhere safe, that is not local, does some draws on it, bitmap's HBITMAP uses HandleToLong () to convert long to handle , stores it the ultimate for C #, and returns.
  3. Back in C #, the outside int param is converted to IntPtr and uses the system to copy the data Drawing.Image.FromHbitmap to create and System.Drawing.Bitmap objects.
  4. C # then calls another interop function, ReleaseImage .
  5. The resources associated with the C ++, release image in the CBITMAP have already been created.

    This is the abstract for impatient more specific code examples given below.

    C + interface definitions for functions: 

      namespace {std :: unique_ptr & lt; Cmtmap> Small; } HRESULT __stdcall Assistant: FetchImage (/ * [out] * / long * hBitmap) {bitty.reset (new CBitmap); // Call CreateBitmap and then draw something, // Make sure that it is not selected in DC when * hBitmap = HandleToLong (bitty-> GetSafeHandle ()); Return S_OK; } HRESULT __stdcall helper :: Release Image {bitty.reset (); Return S_OK; }   
     IDL prototype for interop functions, which are wrapped in the support group in C #:  [ID (1)] HRESULT FetchImage (Long * HBitmap); [Id (2)] HRESULT release image ();   
     In the affiliate category, these C # prototypes produce:  
      zero FetchImage (out int hibitmap); Zero release image ();   
     and C # who calls them looks like this:  
      int ret; Assistant. Fat image (outright); Bitmap b = image. FRHMP (IntPtr) ret Helper.ReleaseImage (); /   is a case of calling    or . If the release image is getting things out of sync somewhere else then maybe I will have a list of  CBITmap  instead of just one, then return the handle back to  release image  Send it on so that it only destroys one by matching. > FetchImage  Call.  
     Do not I have any information? I have to do this work, I just wanted to make sure that I am not doing anything dangerous because I do not know any better. You can only declare that it is the responsibility of releasing HBITMAP.   Since this simplifies your C ++ code, you can remove the ReleaseImage method. Example:    HRESULT __stdcall Assistant: FetchImage (/ * [out] * / HBITMAP * hBitmap) {* hBitmap = NULL; // Failure Exact_text & lt; Cgi.tap & gt; BMP (new CBITmap); // CreateBitmap call and then draw something, // Make sure that it is not selected in DC when * hBitmap = (HBITMAP) bmp- & gt; Apart (); Return S_OK; } // Delete the release image and delete all global variables ... // C # Example: IntPtr ret; Assistant. Fat image (outright); Try {bitmap b = image. FHMHMHMMMP (RT); } Finally {DeleteObject (ret); // Call in PinoWoK GDI}   
     Alternatively, you can check back using. Here are some benefits:  
       
    •  The caller frees the returned image using the standard COM reference calculation. Usually, the caller is free from being concerned about releasing the returned image (unless the caller is another C ++ program that requires manual callIUnknown :: Release).  
    •  Better compatibility with other COM-enabled languages, such as VBA / VB6 The iCutcher is the standard way of passing around a photo in COM.

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