If the target window is owned by another process and has a caption, GetWindowText retrieves the window caption text. If the window does not have a caption, the return value is a null string. This behavior is by design. It allows applications to call GetWindowText without becoming unresponsive if the process that owns the target window is not responding. However, if the target window is not responding and it belongs to the calling application, GetWindowText will cause the calling application to become unresponsive. To retrieve the text of a control in another process, send a WM_GETTEXT message directly instead of calling GetWindowText.

C# Signature:

[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
static extern int GetWindowText(IntPtr hWnd, StringBuilder lpString, int nMaxCount);

VB.NET Signature:

'Imports System.Text
<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

VB.NET Signature Alternative:

'Imports System.Text

<DllImport("user32.dll", SetLastError:=True, CharSet:=CharSet.Ansi)> _
Public Function GetWindowText(hwnd As IntPtr, <MarshalAs(UnManagedType.LPStr)>lpString As System.Text.StringBuilder, cch As Integer) As Integer
End Function

VB Signature:

Public Declare Function GetWindowText Lib "user32.dll" Alias "GetWindowTextA" _
        (ByVal hWnd As Long, _
         ByVal prmstrString As String, _
         ByVal nMaxCount As Long) As Long

User-Defined Types:

None.

Notes:

Tips & Tricks:

Please add some!

Sample Code:

public static string GetText(IntPtr hWnd)
{
    // Allocate correct string length first
    int length       = GetWindowTextLength(hWnd);
    StringBuilder sb = new StringBuilder(length + 1);
    GetWindowText(hWnd, sb, sb.Capacity);
    return sb.ToString();
}

But, if you need to get text from a control in another process, GetWindowText() won't work. Use WM_GETTEXT instead.

Sample Code:

[DllImport("user32.dll", CharSet = CharSet.Auto)]
static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, IntPtr wParam, [Out] StringBuilder lParam);

public static string GetWindowTextRaw(IntPtr hwnd)
{
    // Allocate correct string length first
    int length = (int)SendMessage(hwnd, WM_GETTEXTLENGTH, IntPtr.Zero, IntPtr.Zero);
    StringBuilder sb = new StringBuilder(length + 1);
    SendMessage(hwnd, WM_GETTEXT, (IntPtr)sb.Capacity, sb);
    return sb.ToString();
}

vb.net sample

Public Function GetText(ByVal hWnd As IntPtr) As String
    Dim length As Integer
    If hWnd.ToInt32 = 0 Then
        Return Nothing
    End If
    length = GetWindowTextLength(hWnd)
    If length = 0 Then
        Return Nothing
    End If
    Dim sb As New System.Text.StringBuilder("", length + 1)

    GetWindowText(hWnd, sb, sb.Capacity)
    Return sb.ToString()
End Function

Alternative Managed API:

The ManagedWindowsApi project (http://mwinapi.sourceforge.net) provides a

class ManagedWinapi.SystemWindow that has a Title property.

Documentation

GetWindowText on MSDN

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