如果这确实是您需要了解的有关RichTextBox的ScrollBars状态的信息，请使用GetScrollBarInfo()获取此信息，然后测试存储在返回的SCROLLBARINFO结构的rgstate组件中的值。

• 当ScrollBar被禁用时，rgstate[0]被设置为STATE_SYSTEM_UNAVAILABLE;在这种情况下，索引2处值（页面元素）应设置为STATE_SYSTEM_INVISIBLE。
• 当ScrollBar不存在时，相同的值为STATE_SYSTEM_INVISIBLE
• 否则为0（此处设置为SBIdObj.STATE_SYSTEM_AVAILABLE = 0x00000000）

可用于测试ScrollBars的示例方法。将其称为，例如：

var result = GetScrollBarsState(myRichTextBox.Handle);

它返回一个命名元组，其中两个ScrollBar的状态都设置为当前的SBIdObj值

public (SBRgState Vertical, SBRgState Horizontal) GetScrollBarsState(IntPtr controlHandle)
{
    var sbi = new SCROLLBARINFO() { cbSize = Marshal.SizeOf<SCROLLBARINFO>() };

    bool result = GetScrollBarInfo(controlHandle, SBIdObj.OBJID_VSCROLL, ref sbi);
    if (!result) throw new Exception("Failed to retrieve vertical ScrollBar info");
    var vert = (SBRgState)sbi.rgstate[0];

    result = GetScrollBarInfo(controlHandle, SBIdObj.OBJID_HSCROLL, ref sbi);
    if (!result) throw new Exception("Failed to retrieve horizontal ScrollBar info");
    var horz = (SBRgState)sbi.rgstate[0];
    return (vert, horz);
}

声明：

[DllImport("User32.dll", CharSet = CharSet.Auto, SetLastError = true)]
internal static extern bool GetScrollBarInfo(IntPtr hWnd, SBIdObj idObject, ref SCROLLBARINFO psbi);

[StructLayout(LayoutKind.Sequential)]
public struct SCROLLBARINFO {
    public int cbSize;
    public Rectangle rcScrollBar;
    public int dxyLineButton;
    public int xyThumbTop;
    public int xyThumbBottom;
    public int reserved;
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 6)]
    public int[] rgstate;
}

// GetScrollBarInfo idObject
public enum SBIdObj : uint {
    OBJID_HSCROLL = 0xFFFFFFFA,
    OBJID_VSCROLL = 0xFFFFFFFB,
    OBJID_CLIENT = 0xFFFFFFFC
}

// SCROLLBARINFO rgstate flags
[Flags]
public enum SBRgState {
    STATE_SYSTEM_AVAILABLE = 0x00000000,
    STATE_SYSTEM_UNAVAILABLE = 0x00000001,
    STATE_SYSTEM_PRESSED = 0x00000008,
    STATE_SYSTEM_INVISIBLE = 0x00008000,
    STATE_SYSTEM_OFFSCREEN = 0x00010000,
}