Scrape text from textbox in Windows application

Question

Is it possible to scrape the text from a textbox that is contained within a separate executable? I have an application that has a debug window. The debug window generates a verbose log. However, the log never is saved anywhere and can only be viewed within the app. If the app generates an exception, I'd like to email myself knowing that an exception has been generated so I can hop in and check things out. There is also a button to copy the textbox so I was thinking of using Spy++ to get the command information. However, I don't know where to go from there. Any pointers are greatly appreciated.

I'd prefer to use C# in .NET, but if I need to use C++, I will.

UPDATE:

Based on the comments, I've tried doing the following:

Private Declare Function GETWINDOWTEXT Lib "user32" Alias "GetWindowTextA" (ByVal hwnd As Integer, ByVal lpString As String, ByVal cch As Integer) As Integer
Private Declare Function SetForegroundWindow Lib "user32.dll" (ByVal hwnd As Integer) As Integer
Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindow As String) As IntPtr
Private Declare Function FindWindowEx Lib "user32" Alias "FindWindowExA" (ByVal hWnd1 As Integer, ByVal hWnd2 As Integer, ByVal lpsz1 As String, ByVal lpsz2 As String) As Integer
Private Declare Ansi Function SendMessage Lib "user32.dll" Alias "SendMessageA" (ByVal hwnd As Integer, ByVal wMsg As Integer, ByVal wParam As Integer, ByVal lParam As String) As Integer
Private Const WM_GETTEXT As Short = &HDS
Private Const WM_GETTEXTLENGTH As Short = &HES

Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
    Dim hwnd As Integer = FindWindowEx(0, 0, "MyAppForm", "Hello World")

    If Not hwnd = 0 Then
        SetForegroundWindow(hwnd)

        'Dim LabelEx As Integer = FindWindowEx()
        Dim TextBoxEx As Integer = FindWindowEx(hwnd, 0, "MyAppTextBox", vbNullString)
        Dim txtLength As Long = SendMessage(TextBoxEx, WM_GETTEXTLENGTH, CInt(0), CInt(0)) + 1
        Dim txtBuff As String = Space(txtLength)
        Dim txtValue As Long = SendMessage(TextBoxEx, WM_GETTEXT, txtLength, txtBuff)

        MsgBox(txtBuff)
    End If
End Sub

However, I can't seem to find the handle of the textbox control. When I enumerate all of the windows, I only see one TextBox object, but I see the parent multiple times throughout the enumeration. How can I get the pointers to the controls within the window?

UPDATE 2:

I've uploaded a sample Windows app to show the type of app I'm trying to get access to. I'm trying to get the values of both labels in addition to the textbox. The textbox is the most important. The sample Win app is here: http://www.mediafire.com/file/172r2xapj7p4f2f/StatusSimulator.zip

Answer 1

Text scraping is done by accessibility interfaces. For managed code, you can use the classes in the System.Windows.Automation namespace. If you already have a window handle, then extracting the text is simple:

AutomationElement.FromHandle(hwnd)
                 .GetCurrentPropertyValue(ValuePattern.ValueProperty) as string;

(Kind of confused since the question is tagged C# and you ask for a C# solution, but your code sample is in VB.)

Answer 2

When you use the WM_GETTEXT message you provide a pointer to a buffer which receives the text. If you're sending this message to a window in another process then the pointer you provide will be in your process address space not the other process.

I've done something similar to this (scraping windows in another process) and what I did which worked was to use DLL injection. Basically you use SetWindowsHook and provide a callback inside a DLL. The OS then loads the DLL into other processes and you figure out when you've loaded into the desired target process. At that point your code is in that other process and you can get the window text.

Then there's the matter of getting it back to your app. I used a shared memory block to do it myself. Maybe there's a simpler way to do all this, though, but this worked for me in the past.

Answer 3

Your P/Invoke definition for GetWindowText isn't right. With P/Invoke String types are only marshalled in, and not out which is why you aren't getting any text back. If you change your lpString parameter to a StringBuffer it will work.

Note you also will need to set the capacity of the StringBuffer to 1000 before passing it to GetWindowText because it requires that an allocated buffer be passed to it - it won't size the StringBuffer itself.

See the definition and example and pinvoke.net.

<DllImport("user32.dll", SetLastError:=True, CharSet:=CharSet.Auto)> _
Private Shared Function GetWindowText(ByVal hwnd As IntPtr, ByVal lpString As StringBuilder, ByVal cch As Integer) As Integer
End Function

Private Declare Function SetForegroundWindow Lib "user32.dll" (ByVal hwnd As Integer) 

As Integer
Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindow As String) As IntPtr
Private Declare Function FindWindowEx Lib "user32" Alias "FindWindowExA" (ByVal hWnd1 As Integer, ByVal hWnd2 As Integer, ByVal lpsz1 As String, ByVal lpsz2 As String) As Integer
Private Declare Ansi Function SendMessage Lib "user32.dll" Alias "SendMessageA" (ByVal hwnd As Integer, ByVal wMsg As Integer, ByVal wParam As Integer, ByVal lParam As String) As Integer
Private Const WM_GETTEXT As Short = &HDS
Private Const WM_GETTEXTLENGTH As Short = &HES

Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
    Dim hwnd As Integer = FindWindowEx(0, 0, "MyAppForm", "Hello World")

    If Not hwnd = 0 Then
        SetForegroundWindow(hwnd)

        'Dim LabelEx As Integer = FindWindowEx()
        Dim TextBoxEx As Integer = FindWindowEx(hwnd, 0, "MyAppTextBox", vbNullString)
        Dim txtLength As Long = SendMessage(TextBoxEx, WM_GETTEXTLENGTH, CInt(0), CInt(0)) + 1
        Dim txtBuff As New System.Text.StringBuilder(txtLength + 1)
        GetWindowText(hWnd, txtBuff , txtBuff .Capacity)
        Dim txtValue As Long = SendMessage(TextBoxEx, WM_GETTEXT, txtLength, txtBuff)
        MsgBox(txtBuff.ToString())
    End If
End Sub