Question

I’m porting a C++ SDK from a USB device to use in C# through pinvoke and and I’m having good progress so far, and the problem now is with a function that builds an image list that I can use to attach to other controls using functions like SetImageList.

What I would like to do is save all the images from this list to the disk and use them later.

There are other functions that returns the index of a paraticular image inside this list, so I could pass this index and then save the image to the disk.

Answer 1

With the CImageList class instance (which you get by calling to the Detach method on the GetImageList method on the CListCtrl instance that you have), you can get the HIMAGELIST handle by calling the Detach method.

From there you can call the underlying Windows API through the Platform Invocation Services (P/Invoke) layer.

The following assumes you have this HIMAGELIST pointer in an IntPtr:

IntPtr imageList = ...;

First, you’ll need to declare the ImageList_GetImageCount function in .NET:

[DllImport("Comctl32.dll", SetLastError = true)]
static extern int ImageList_GetImageCount(IntPtr himl);

And of course, store the result of that call in a variable:

int imageCount = ImageList_GetImageCount(imageList);

You’ll also need to be able to get the details about each image, so you’ll need the call to ImageList_GetImageInfo:

[StructLayout(LayoutKind.Sequential)]
struct RECT
{
    public int left, top, right, bottom;
}

[StructLayout(LayoutKind.Sequential)]
struct IMAGEINFO
{
    public IntPtr hbmImage;
    public IntPtr hbmMask;
    public int Unused1;
    public int Unused2;
    public RECT rcImage;
}

[DllImport("Comctl32.dll", SetLastError = true)]
static extern bool ImageList_GetImageInfo(IntPtr himl, int i,
    ref IMAGEINFO pImageInfo);

With these, you can start your loop to get the information about the image:

for (int i = 0; i < imageCount; ++i)
{
    // The image info.
    var imageInfo = new IMAGEINFO();

    // Get the call to ImageList_GetImageInfo.
    if (!ImageList_GetImageInfo(imageList, i, ref imageInfo)
        throw new System.ComponentModel.Win32Exception();

Notice that in the IMAGEINFO structure has a field that contains the pointer to the bitmap (the hbmImage field).

This is a handle to an HBITMAP handle, which has an equivalent in .NET in the Bitmap class. You can translate between the two by calling the static FromHbitmap method on the Image class (yes, it’s strange it’s not on the Bitmap class):

    using (Bitmap bitmap = Image.FromHbitmap(imageInfo.hbmImage))
    {

Once you have the Bitmap instance, you can call the Save method on each instance to dump them to disk:

        bitmap.Save("<need to generate a filename>.<and extension>");
    }
}

Note that there is the ImageList class in .NET, but there’s no way to pass the HIMAGELIST handle to the managed implementation (which would have made this much easier).