Ваш интерфейс ITaskBarList3 неверен. Вот правильный:
public enum TBPF
{
TBPF_NOPROGRESS = 0,
TBPF_INDETERMINATE = 0x1,
TBPF_NORMAL = 0x2,
TBPF_ERROR = 0x4,
TBPF_PAUSED = 0x8
}
public enum TBATF
{
TBATF_USEMDITHUMBNAIL = 0x1,
TBATF_USEMDILIVEPREVIEW = 0x2
}
public enum THB : uint
{
THB_BITMAP = 0x1,
THB_ICON = 0x2,
THB_TOOLTIP = 0x4,
THB_FLAGS = 0x8
}
public enum THBF : uint
{
THBF_ENABLED = 0,
THBF_DISABLED = 0x1,
THBF_DISMISSONCLICK = 0x2,
THBF_NOBACKGROUND = 0x4,
THBF_HIDDEN = 0x8
}
[StructLayout(LayoutKind.Sequential, Pack = 4, CharSet = CharSet.Auto)]
public struct THUMBBUTTON
{
public THB dwMask;
public uint iId;
public uint iBitmap;
public IntPtr hIcon;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = Windows.MAX_PATH)]
public string szTip;
public THBF dwFlags;
}
[ComImport]
[Guid("ea1afb91-9e28-4b86-90e9-9e9f8a5eefaf")]
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
public interface ITaskbarList3
{
// ITaskbarList
void HrInit();
void AddTab(IntPtr hwnd);
void DeleteTab(IntPtr hwnd);
void ActivateTab(IntPtr hwnd);
void SetActiveAlt(IntPtr hwnd);
// ITaskbarList2
void MarkFullscreenWindow(
IntPtr hwnd,
[MarshalAs(UnmanagedType.Bool)] bool fFullscreen);
// ITaskbarList3
void SetProgressValue(IntPtr hwnd, ulong ullCompleted, ulong ullTotal);
void SetProgressState(IntPtr hwnd, TBPF tbpFlags);
void RegisterTab(IntPtr hwndTab, IntPtr hwndMDI);
void UnregisterTab(IntPtr hwndTab);
void SetTabOrder(IntPtr hwndTab, IntPtr hwndInsertBefore);
void SetTabActive(IntPtr hwndTab, IntPtr hwndMDI, TBATF tbatFlags);
void ThumbBarAddButtons(
IntPtr hwnd,
uint cButtons,
[MarshalAs(UnmanagedType.LPArray)] THUMBBUTTON[] pButtons);
void ThumbBarUpdateButtons(
IntPtr hwnd,
uint cButtons,
[MarshalAs(UnmanagedType.LPArray)] THUMBBUTTON[] pButtons);
void ThumbBarSetImageList(IntPtr hwnd, IntPtr himl);
void SetOverlayIcon(
IntPtr hwnd,
IntPtr hIcon,
[MarshalAs(UnmanagedType.LPWStr)] string pszDescription);
void SetThumbnailTooltip(
IntPtr hwnd,
[MarshalAs(UnmanagedType.LPWStr)] string pszTip);
void SetThumbnailClip(
IntPtr hwnd,
[MarshalAs(UnmanagedType.LPStruct)] Rectangle prcClip);
}