c# - 如何知道 RichTextBox 垂直滚动条是否达到最大值？

Question

使用richtextbox 方法“ScrollToCaret”时，我需要知道滚动条是否到达顶部/底部边距。

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，它会在控件中产生奇怪的视觉效果，因为它会尝试并重试向下滚动，但没有更多可以滚动的东西，我可以'不明白richtextbox控件的这种奇怪逻辑。

我希望你能理解我，原谅我的英语。

PS：我使用的是默认的richtextbox 垂直滚动条。

Answer 1

您必须稍微处理一下“Win32”。
“win32”中的“GetScrollInfo”方法就是你要找的。
使用“GetScrollInfo”方法，您可以获得以下 RichTextBox 滚动属性：

• 最大范围，
• 当前位置
• 拇指大小（即 RichTextBox“页面”大小）。

---

公式：

Max Position = Max Range - Thumb size

---

请参见下面的示例：

// 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@King King 版本，我已将其翻译为 VB.NET，还添加了更多功能，我认为它们都可以正常工作：

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