Visual Basic > Forms

Searching a window for a child window

Searching a window for a child window

The function below change be used to search a dialog for a specific child window (either by class name or caption).

Option Explicit

Private Declare Function GetWindow Lib "user32" (ByVal hwnd As Long, ByVal wCmd As Long) As Long
Private Declare Function GetClassName Lib "user32" Alias "GetClassNameA" (ByVal hwnd As Long, ByVal lpClassName As String, ByVal nMaxCount As Long) As Long
Private Declare Function GetWindowText Lib "user32" Alias "GetWindowTextA" (ByVal hwnd As Long, ByVal lpString As String, ByVal cch As Long) As Long

'Purpose     :  Enumerates all the child windows and returns the handle of a child window with
'               a matching caption or class name.
'Inputs      :  lParentHwnd             The handle to a parent window
'               [sClassName]            The class name to search for.
'               [sCaption]              The caption to search for.
'               [bSearchChildWindows]   Searchs within each child window for a matching window
'Outputs     :  Returns the handle of child window or zero if not found


Function FindChildWindow(ByVal lParentHwnd As Long, Optional ByVal sClassName As String, Optional ByVal sCaption As String, Optional bSearchChildWindows As Boolean = False) As Long
    Dim bClassMatches As Boolean, bCaptionMatches As Boolean
    Const clMaxName As Long = 255
    Const GW_CHILD = 5
    Const GW_HWNDNEXT = 2
    Const GW_HWNDFIRST = 0
    
    Dim lWinHwnd As Long, sTestName As String * clMaxName, lNumChars As Long
    
    'Ignore case
    sClassName = UCase$(sClassName)
    sCaption = UCase$(sCaption)

    'Find the first child window
    lWinHwnd = GetWindow(lParentHwnd, GW_CHILD)
    If lWinHwnd = 0 Then
        Exit Function
    End If
    Do
        bClassMatches = False
        bCaptionMatches = False
        lNumChars = clMaxName
        
        If Len(sClassName) Then
            'Get the child window classname
            lNumChars = GetClassName(lWinHwnd, sTestName, (clMaxName))
            If UCase(Left$(sTestName, lNumChars)) = sClassName Then
                'Found matching class name
                bClassMatches = True
            End If
        Else
            'No class name specified
            bClassMatches = True
        End If
        
        If Len(sCaption) Then
            lNumChars = GetWindowText(lWinHwnd, sTestName, (clMaxName))
            If UCase(Left$(sTestName, lNumChars)) = sCaption Then
                'Found matching caption
                bCaptionMatches = True
            End If
        Else
            'No caption specified
            bCaptionMatches = True
        End If
        
        If bClassMatches And bCaptionMatches Then
            'Found matching dialog, return handle
            FindChildWindow = lWinHwnd
            Exit Do
        ElseIf bSearchChildWindows Then
            'Search Child windows
            FindChildWindow = FindChildWindow(lWinHwnd, sClassName, sCaption, True)
            If FindChildWindow Then
                Exit Do
            End If
        End If
        
        'Try next next child
        lWinHwnd = GetWindow(lWinHwnd, GW_HWNDNEXT)
        If lWinHwnd = 0 Then
            'No more child windows
            Exit Do
        End If
    Loop While lWinHwnd     'Loop until there are no more child windows
End Function