C# Signature:

[DllImport("hhctrl.ocx", SetLastError=true)]
static extern IntPtr HtmlHelp(
        IntPtr hWndCaller,
        [MarshalAs(UnmanagedType.LPTStr)]
        string helpFile,
        HTMLHelpCommand command,
        int data );

User-Defined Types:

    [Flags()]
    public enum HTMLHelpCommand : uint
    {
        HH_DISPLAY_TOPIC = 0,
        HH_DISPLAY_TOC = 1,
        HH_DISPLAY_INDEX = 2,
        HH_DISPLAY_SEARCH = 3,
        HH_DISPLAY_TEXT_POPUP = 0x000E,
        HH_HELP_CONTEXT = 0x000F,
        HH_CLOSE_ALL = 0x0012
    }

VB Signature:

<DllImport("hhctrl.ocx", EntryPoint:="HtmlHelp", CharSet:=CharSet.Auto)> _
Function HTMLHelp( _
     ByVal hWndCaller As IntPtr, ByVal pszFile As String, _
     ByVal uCommand As Integer, ByVal dwData As Integer) As Integer
End Function

User-Defined Types:

Public Enum HTMLHelpCommand
     HH_DISPLAY_TOPIC = 0
     HH_DISPLAY_TOC = 1
     HH_DISPLAY_INDEX = 2
     HH_DISPLAY_SEARCH = 3
     HH_HELP_CONTEXT = &HF
     HH_CLOSE_ALL = &H12
End Enum

Notes:

None.

Tips & Tricks:

Article "How to use the unmanaged HTML Help API from a managed Visual C# application" on support.microsoft.com

Sample Code:

VB

HTMLHelp(Nothing, filePath, HTMLHelpCommand.HH_HELP_CONTEXT, contextID)

or

HTMLHelp(Nothing, filePath, HTMLHelpCommand.HH_DISPLAY_TOC, 0)

C#

HtmlHelp(IntPtr.Zero, filePath, HTMLHelpCommand.HH_HELP_CONTEXT, contextID)

or

HtmlHelp(IntPtr.Zero, filePath, HTMLHelpCommand.HH_DISPLAY_TOC, 0)

Alternative Managed API:

System.Windows.Forms.Help.ShowHelp()

C# Signature:

[DllImport("hhctrl.ocx", CharSet = CharSet.Auto)]
static extern int HtmlHelp(
        IntPtr hWndCaller,
        [MarshalAs(UnmanagedType.LPTStr)]
        string pszFile,
        HTMLHelpCommand uCommand,
        [MarshalAs(UnmanagedType.LPStruct)]
        HH_POPUP dwData);

User-Defined Types:

    [StructLayout(LayoutKind.Sequential), CLSCompliant(false)]
    struct COLORREF
    {
        uint _ColorRef;
        public COLORREF(Color aValue)
        {
            int lRGB = aValue.ToArgb();
            int n0 = (lRGB & 0xff) << 16;
            lRGB = lRGB & 0xffff00;
            lRGB = (lRGB | (lRGB >> 16 & 0xff));
            lRGB = (lRGB & 0xffff);
            lRGB = (lRGB | n0);
            _ColorRef = (uint)lRGB;
        }
        public COLORREF(int lRGB)
        {
            _ColorRef = (uint)lRGB;
        }
        public Color ToColor()
        {
            int r = (int)_ColorRef & 0xff;
            int g = ((int)_ColorRef >> 8) & 0xff;
            int b = ((int)_ColorRef >> 16) & 0xff;
            return Color.FromArgb(r, g, b);
        }
        public static COLORREF FromColor(System.Drawing.Color aColor)
        {
            return new COLORREF(aColor);
        }
        public static System.Drawing.Color ToColor(COLORREF aColorRef)
        {
            return aColorRef.ToColor();
        }
    }
    [StructLayout(LayoutKind.Sequential)]
    class POINT
    {
        public int x;
        public int y;
        public POINT()
        {
        }
        public POINT(int x, int y)
        {
            this.x = x;
            this.y = y;
        }
    }
    [StructLayout(LayoutKind.Sequential)]
    struct RECT
    {
        public int left;
        public int top;
        public int right;
        public int bottom;
        public RECT(int left, int top, int right, int bottom)
        {
            this.left = left;
            this.top = top;
            this.right = right;
            this.bottom = bottom;
        }
        public RECT(Rectangle r)
        {
            this.left = r.Left;
            this.top = r.Top;
            this.right = r.Right;
            this.bottom = r.Bottom;
        }
        public static RECT FromXYWH(int x, int y, int width, int height)
        {
            return new RECT(x, y, x + width, y + height);
        }
        public Size Size
        {
            get
            {
                return new Size(this.right - this.left, this.bottom - this.top);
            }
        }
    }
    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
    class HH_POPUP
    {
        internal int cbStruct = Marshal.SizeOf(typeof(HH_POPUP));
        internal IntPtr hinst = IntPtr.Zero;
        internal int idString;
        internal IntPtr pszText;
        internal POINT pt;
        internal COLORREF clrForeground = new COLORREF(-1);
        internal COLORREF clrBackground = new COLORREF(-1);
        internal RECT rcMargins = RECT.FromXYWH(-1, -1, -1, -1);
        internal IntPtr pszFont;
    }

Notes:

None.

Tips & Tricks:

Article "How to use the unmanaged HTML Help API from a managed Visual C# application" on support.microsoft.com

Sample Code:

C#

    string text_to_show_popup = "Without specifying the font instead of text obtain the abracadabra";
    string font_for_text_to_show_popup = "Tahoma,8,utf-8";
    Color back_сolor_for_popup_window = Color.FromArgb(255, 255, 192); // yellow background, as in windows
    Point current_cursor_location = Control.MousePosition;

    HH_POPUP param = new HH_POPUP();
    IntPtr ptrText = Marshal.StringToCoTaskMemAuto(text_to_show_popup);
    IntPtr ptrFont = Marshal.StringToCoTaskMemAuto(font_for_text_to_show_popup);
    param.pszText = ptrText;
    param.idString = 0;
    param.pt = new POINT(current_cursor_location.X, current_cursor_location.Y);
    param.clrBackground = COLORREF.FromColor(back_сolor_for_popup_window);
    param.pszFont = ptrFont;
    try
    {
        HtmlHelp(IntPtr.Zero, null, HTMLHelpCommand.HH_DISPLAY_TEXT_POPUP, param);
    }
    finally
    {
        Marshal.FreeCoTaskMem(ptrText);
        Marshal.FreeCoTaskMem(ptrFont);
    }

Alternative Managed API:

System.Windows.Forms.Help.ShowPopup()

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