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Summary

The GetScrollInfo API

C# Signature:

[DllImport("user32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
private static extern bool GetScrollInfo(IntPtr hwnd, int fnBar, ref SCROLLINFO lpsi);

VB Signature:

Declare Function GetScrollInfo Lib "user32" (ByVal hWnd As IntPtr, ByVal fnBar As ScrollBarDirection, ByRef lpsi As SCROLLINFO) As Integer

C# User-Defined Types:

[StructLayout(LayoutKind.Sequential)]
struct SCROLLINFO
{
    public uint cbSize;
    public uint fMask;
    public int nMin;
    public int nMax;
    public uint nPage;
    public int nPos;
    public int nTrackPos;
}

private enum ScrollBarDirection
{
    SB_HORZ = 0,
    SB_VERT = 1,
    SB_CTL = 2,
    SB_BOTH = 3
}

private enum ScrollInfoMask
{
    SIF_RANGE = 0x1,
    SIF_PAGE = 0x2,
    SIF_POS = 0x4,
    SIF_DISABLENOSCROLL = 0x8,
    SIF_TRACKPOS = 0x10,
    SIF_ALL = SIF_RANGE + SIF_PAGE + SIF_POS + SIF_TRACKPOS
}

VB User-Defined Types:

    <StructLayout(LayoutKind.Sequential)>Private Structure SCROLLINFO
    Public cbSize As Integer
    Public fMask As Integer
    Public nMin As Integer
    Public nMax As Integer
    Public nPage As Integer
    Public nPos As Integer
    Public nTrackPos As Integer
    End Structure

    Private Enum ScrollBarDirection
        SB_HORZ = 0
        SB_VERT = 1
        SB_CTL = 2
        SB_BOTH = 3
    End Enum

    Private Enum ScrollInfoMask
        SIF_RANGE = &H1
        SIF_PAGE = &H2
        SIF_POS = &H4
        SIF_DISABLENOSCROLL = &H8
        SIF_TRACKPOS = &H10
        SIF_ALL = (SIF_RANGE Or SIF_PAGE Or SIF_POS Or SIF_TRACKPOS)
    End Enum

Notes:

None.

Tips & Tricks:

Please add some!

C# Sample Code:

// Returns the width of a UserControl containing a RichTextBox
//  such that no horizontal scrollbar will be needed
public int PreferredWidth
{
    get
    {
      int MINWIDTH = 200;
      int BORDERWIDTH = SystemInformation.Border3DSize.Width;
      int SCROLLBARWIDTH = SystemInformation.VerticalScrollBarWidth;

      SCROLLINFO si = new SCROLLINFO();
      si.cbSize = Marshal.SizeOf( si );
      si.fMask = (int) ScrollInfoMask.SIF_RANGE;
      GetScrollInfo( RichTextBox1.Handle, (int) ScrollBarDirection.SB_HORZ, ref si );

      int iWidth = si.nMax - si.nMin + 2 * BORDERWIDTH + SCROLLBARWIDTH + 2;    
      return Math.Max( MINWIDTH, iWidth );
    }
}

VB Sample Code:

    Private Function GetScrollBarPageSize(ByVal hWnd As IntPtr, ByVal fnBar As Integer) As Integer
    Dim si As New SCROLLINFO
    With si
        .cbSize = Len(si)
        .fMask = SIF_PAGE
    End With
    Dim lRet As Integer = GetScrollInfo(hWnd, fnBar, si)
    If lRet <> 0 Then
        Return si.nPage
    Else
        Return -1
    End If
    End Function

Alternative Managed API:

Do you know one? Please contribute it!

Documentation

GetScrollInfo on MSDN