如何知道富文本框垂直滚动条是否达到最大值

Question

当使用richtextbox方法"ScrollToCaret"时，我需要知道滚动条是否达到了上/下边距。

这是因为当垂直滚动条完全滚动到底部时，如果我再次使用"ScrollToCaret"方法，那么它会在控件中产生奇怪的视觉效果，因为它尝试重试向下滚动，但没有更多可滚动的，我无法理解富文本框控件的这种奇怪的逻辑。

我希望你能理解我，原谅我的英语。

PS：我使用的是默认的富文本框垂直滚动条。

Answer 1

你必须稍微

处理一下
"Win32"。"win32"中的"GetScrollInfo"方法就是您要查找的。
使用"GetScrollInfo"方法，您可以获得以下RichTextBox Scroll属性：

• 最大范围，
• 当前位置
• 拇指大小（即富文本框"页面"大小）。

---

公式：

Max Position = Max Range - Thumb size

---

请参阅以下示例：

// Add the reference:
// using System.Runtime.InteropServices;
// Define an extension method for this purpose:
public static class RichTextBoxExtension
{
    [DllImport("user32")]
    private static extern int GetScrollInfo(IntPtr hwnd, int nBar, 
                                            ref SCROLLINFO scrollInfo);
    public struct SCROLLINFO
    {
      public int cbSize;
      public int fMask;
      public int min;
      public int max;
      public int nPage;
      public int nPos;
      public int nTrackPos;
    }
    public static bool ReachedBottom(this RichTextBox rtb)
    {
       SCROLLINFO scrollInfo = new SCROLLINFO();
       scrollInfo.cbSize = Marshal.SizeOf(scrollInfo);
       //SIF_RANGE = 0x1, SIF_TRACKPOS = 0x10,  SIF_PAGE= 0x2
       scrollInfo.fMask = 0x10 | 0x1 | 0x2;
       GetScrollInfo(rtb.Handle, 1, ref scrollInfo);//nBar = 1 -> VScrollbar
       return scrollInfo.max == scrollInfo.nTrackPos + scrollInfo.nPage;
    }
}
//Usage:
if (!yourRichTextBox.ReachedBottom())
{
   yourRichTextBox.ScrollToCaret();
   //...
}

Answer 2

这是我@King王版本 我已经将其翻译成 VB.NET 并添加了更多功能，我认为它们都正常工作：

Public Class ScrollBarInfo
<System.Runtime.InteropServices.DllImport("user32")> _
Private Shared Function GetScrollInfo(hwnd As IntPtr, nBar As Integer, ByRef scrollInfo As SCROLLINFO) As Integer
End Function
Private Shared scrollInf As New SCROLLINFO()
Private Structure SCROLLINFO
    Public cbSize As Integer
    Public fMask As Integer
    Public min As Integer
    Public max As Integer
    Public nPage As Integer
    Public nPos As Integer
    Public nTrackPos As Integer
End Structure
Private Shared Sub Get_ScrollInfo(control As Control)
    scrollInf = New SCROLLINFO()
    scrollInf.cbSize = System.Runtime.InteropServices.Marshal.SizeOf(scrollInf)
    scrollInf.fMask = &H10 Or &H1 Or &H2
    GetScrollInfo(control.Handle, 1, scrollInf)
End Sub
Public Shared Function ReachedBottom(control As Control) As Boolean
    Get_ScrollInfo(control)
    Return scrollInf.max = scrollInf.nTrackPos + scrollInf.nPage
End Function
Public Shared Function ReachedTop(control As Control) As Boolean
    Get_ScrollInfo(control)
    Return scrollInf.nTrackPos < 0
End Function
Public Shared Function IsAtBottom(control As Control) As Boolean
    Get_ScrollInfo(control)
    Return scrollInf.max = (scrollInf.nTrackPos + scrollInf.nPage) - 1
End Function
Public Shared Function IsAtTop(control As Control) As Boolean
    Get_ScrollInfo(control)
    Return scrollInf.nTrackPos = 0
End Function
End Class