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When ResourceInfo encouters a resource of type 14 (RT_GROUP_ICON), it creates an object of type IconDirectoryResource. The latter creates an IconResource, which loads a DeviceIndependentBitmap.

  • An IconDirectoryResource represents a collection of icon resources.
  • An IconResource represents a single icon with many images of type DeviceIndependentBitmap.
  • A DeviceIndependentBitmap is not a resource per-se, but raw data embedded in the file at an offset defined by the icon resource and represents a single icon bitmap, for example in a BMP format.

Reading Icon Resources

The following example loads icon resources directly, without enumerating all resources.

string filename = Path.Combine(Environment.SystemDirectory, "regedt32.exe");
IconDirectoryResource rc = new IconDirectoryResource();
Console.WriteLine("IconDirectoryResource: {0}, {1}", rc.Name, rc.TypeName);
foreach (IconResource icon in rc.Icons)
  Console.WriteLine(" Icon {0}: {1} ({2} byte(s))",
      icon.Header.nID, icon.ToString(), icon.ImageSize);

Regedt32.exe contains a single 16-color, 32x32 icon. The following output is generated from the example above.

IconDirectoryResource: 1, RT_GROUP_ICON
Icon 1: 32x32 4-bit 16 Colors (744 byte(s))

Writing Icon Resources

In order to embed an existing icon from an .ico file into an executable (.exe or .dll) we load the .ico file and convert it to an IconDirectoryResource. The structure in an .ico file is similar to the structure of the icon in an executable. The only difference is that the executable headers store the icon Id, while an .ico header contains the offset of icon data.

IconFile iconFile = new IconFile("Icon1.ico");
IconDirectoryResource iconDirectoryResource = new IconDirectoryResource(iconFile);
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