用api操作文本框的文本.frm

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VERSION 5.00
Begin VB.Form Form1 
   Caption         =   "计算TextBox的行数(不使用TextBox的消息)"
   ClientHeight    =   3120
   ClientLeft      =   60
   ClientTop       =   345
   ClientWidth     =   5760
   LinkTopic       =   "Form1"
   ScaleHeight     =   3120
   ScaleWidth      =   5760
   StartUpPosition =   3  'Windows Default
   Begin VB.CommandButton Command3 
      Caption         =   "读取第21行改良版"
      Height          =   615
      Left            =   4320
      TabIndex        =   3
      Top             =   1800
      Width           =   1335
   End
   Begin VB.CommandButton Command2 
      Caption         =   "读取第21行"
      Height          =   495
      Left            =   4320
      TabIndex        =   2
      Top             =   960
      Width           =   1335
   End
   Begin VB.CommandButton Command1 
      Caption         =   "计算行数"
      Height          =   495
      Left            =   4320
      TabIndex        =   1
      Top             =   120
      Width           =   1335
   End
   Begin VB.TextBox Text1 
      BeginProperty Font 
         Name            =   "PMingLiU"
         Size            =   12
         Charset         =   136
         Weight          =   400
         Underline       =   0   'False
         Italic          =   0   'False
         Strikethrough   =   0   'False
      EndProperty
      Height          =   2775
      Left            =   240
      MultiLine       =   -1  'True
      ScrollBars      =   3  'Both
      TabIndex        =   0
      Text            =   "用API操作文本框的文本.frx":0000
      Top             =   120
      Width           =   3975
   End
End
Attribute VB_Name = "Form1"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = False
Attribute VB_PredeclaredId = True
Attribute VB_Exposed = False
Option Explicit

Private Sub Command1_Click()
    Dim LineCount As Long
    
    LineCount = SendMessage(Text1.hwnd, EM_GETLINECOUNT, 0, ByVal 0&)
    MsgBox "行数=" & LineCount
End Sub

Private Sub Command2_Click()
    Dim S As String, Length As Integer
    
    Length = 80
    S = String(Length, Chr(0))
    RtlMoveMemory ByVal S, Length, 2
    SendMessage Text1.hwnd, EM_GETLINE, 21, ByVal S
    S = Left(S, InStr(S, Chr(0)) - 1)
    
    MsgBox S, , "第21行"
End Sub

Private Sub Command3_Click()
    Dim S As String, Length As Integer, pos As Long
    
    pos = SendMessage(Text1.hwnd, EM_LINEINDEX, 21, ByVal 0&)
    Length = SendMessage(Text1.hwnd, EM_LINELENGTH, pos, ByVal 0&)
    S = String(Length, Chr(0))
    RtlMoveMemory ByVal S, Length, 2
    SendMessage Text1.hwnd, EM_GETLINE, 21, ByVal S
    'S = Left(S, InStr(S, Chr(0)) - 1)
    
    MsgBox S, , "第21行"
End Sub