'需要导入3个命名空间导入方法为，在文件最前面写以下内容
'VB.NET code
Imports System.Runtime.InteropServices
Imports System.Text
Imports System.Threading

'以下方法测试通过。有效。获得文本框内容。
'VB.NET code
<DllImport("user32.dll",EntryPoint:="FindWindowEx")> _
Public Shared Function FindWindowEx(ByVal hWnd1 As IntPtr,_
ByVal hWnd2 As Integer,ByVal lpsz1 As String,_
ByVal lpsz2 As String) As Integer
End Function
<DllImport("User32 ")>
Public Shared Function SendMessage(ByVal hWnd As Integer,_
ByVal Msg As Integer,ByVal wParam As Integer,_
ByVal lParam As IntPtr) As Boolean
End Function

Public Const WM_GETTEXT As Integer = &HD
Private Shared Sub Test04()
Dim running As Boolean = True
Dim process_array As Process() = Process.GetProcesses()
For Each p As Process In process_array
If p.MainWindowTitle.IndexOf("记事本") <> -1 Then
Dim hEdit As Integer = FindWindowEx(p.MainWindowHandle,"Edit","")
Dim w As String = " "
Dim ptr As IntPtr = Marshal.StringToHGlobalAnsi(w)
If SendMessage(hEdit,WM_GETTEXT,100,ptr) Then
MessageBox.Show(Marshal.PtrToStringAnsi(ptr))
End If
End If
Next
End Sub

using System.Runtime.InteropServices;
using System.Text;
using System.Threading;

[DllImport("user32.dll",EntryPoint = "FindWindowEx")]
public static extern int FindWindowEx(IntPtr hWnd1,
int hWnd2,string lpsz1,
string lpsz2);
[DllImport("user32.dll",EntryPoint = "GetWindowText")]
public static extern int GetWindowText(int hwnd,StringBuilder
lpString,int cch);
[DllImport("User32 ")]
public static extern bool SendMessage(int hWnd,
int Msg,int wParam,
IntPtr lParam);

public const int WM_GETTEXT = 0xD;
private static void Test04()
{
bool running = true;
new Thread(() =>
{
while (running)
{
Process[] process_array = Process.GetProcesses();
foreach (Process p in process_array)
{
if (p.MainWindowTitle.IndexOf("记事本") != -1)//找到了
{
int hEdit = FindWindowEx(p.MainWindowHandle,"");
string w = " ";
IntPtr ptr = Marshal.StringToHGlobalAnsi(w);
if (SendMessage(hEdit,ptr))

Console.WriteLine(Marshal.PtrToStringAnsi(ptr)); } } int tick = Environment.TickCount; while (running && Environment.TickCount - tick < 10000) { Thread.Sleep(10); } } Console.WriteLine("run over"); }).Start(); while (Console.ReadLine().ToLower() != "quit") ; running = false;}