这是使用EM_GETLINE message来做，比较奇特的是lParam是指向一个字串所在的位置，
但是该字串传入时，前两个Byte要存该字串允许的最大长度。
'以下在Form需一个TextBox，并设定MultiLine = True, 一个Command Button
Private Sub Command1_Click()
Dim str5 As String
str5 = GetaLine(Text1,1) '取得第二行的字串，以0为基底
End Sub
'以下在.Bas
Option Explicit
Const EM_GETLINE = &HC4
Declare Function SendMessage Lib "user32" Alias "SendMessageA" _
(ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, _
lParam As Any) As Long
Public Function GetaLine(Text1 As TextBox, ByVal ntx As Long) As String
Dim str5(255) As Byte '如果您的字串 > 255 byte请自行增加该Byte Array
Dim str6 As String, i As Long
str5(0) = 255 '字串的前两个Byte存该字串的最大长度
str5(0) = 255
i = SendMessage(Text1.hwnd, EM_GETLINE, ntx, str5(0))
If i = 0 Then
GetaLine = ""
Else
str6 = StrConv(str5, vbUnicode)
GetaLine = Left(str6, InStr(1, str6, Chr(0)) - 1)
End If
End Function