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  Visual Basic    (ActiveX/Controles/DLL)

Título da Dica:  como habilitar e desabilitar os itens Minimize, Maximize e Close do system menu
Postada em 5/4/2006 por Geronimo            
Esse exemplo mostra como habilitar e desabilitar os itens Minimize, Maximize e Close do system menu e por consequencia os botões do canto superior direito. Para testar crie um projeto com um MDIForm e um módulo e cole o código a seguir:

No módulo:

Option Explicit

Private Const SC_CLOSE As Long = &HF060&
Private Const SC_MAXIMIZE As Long = &HF030&
Private Const SC_MINIMIZE As Long = &HF020&

Private Const xSC_CLOSE As Long = -10&
Private Const xSC_MAXIMIZE As Long = -11&
Private Const xSC_MINIMIZE As Long = -12&

Private Const GWL_STYLE = (-16)
Private Const WS_MAXIMIZEBOX = &H10000
Private Const WS_MINIMIZEBOX = &H20000

Private Const hWnd_NOTOPMOST = -2
Private Const SWP_NOZORDER = &H4
Private Const SWP_NOSIZE = &H1
Private Const SWP_NOMOVE = &H2
Private Const SWP_FRAMECHANGED = &H20

Private Const MIIM_STATE As Long = &H1&
Private Const MIIM_ID As Long = &H2&
Private Const MFS_GRAYED As Long = &H3&
Private Const WM_NCACTIVATE As Long = &H86

Private Type MENUITEMINFO
    cbSize As Long
    fMask As Long
    fType As Long
    fState As Long
    wID As Long
    hSubMenu As Long
    hbmpChecked As Long
    hbmpUnchecked As Long
    dwItemData As Long
    dwTypeData As String
    cch As Long
End Type

Private Declare Function GetSystemMenu Lib "user32" (ByVal hWnd As Long, ByVal bRevert As Long) As Long
Private Declare Function GetMenuItemInfo Lib "user32" Alias "GetMenuItemInfoA" (ByVal hMenu As Long, ByVal un As Long, ByVal b As Boolean, lpMenuItemInfo As MENUITEMINFO) As Long
Private Declare Function SetMenuItemInfo Lib "user32" Alias "SetMenuItemInfoA" (ByVal hMenu As Long, ByVal un As Long, ByVal bool As Boolean, lpcMenuItemInfo As MENUITEMINFO) As Long
Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hWnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long
Private Declare Function IsWindow Lib "user32" (ByVal hWnd As Long) As Long
Private Declare Function GetWindowLong Lib "user32" Alias "GetWindowLongA" (ByVal hWnd As Long, ByVal nIndex As Long) As Long
Private Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal hWnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long
Private Declare Function GetParent Lib "user32" (ByVal hWnd As Long) As Long
Private Declare Function SetParent Lib "user32" (ByVal hWndChild As Long, ByVal hWndNewParent As Long) As Long
Private Declare Function SetWindowPos Lib "user32" (ByVal hWnd As Long, ByVal hWndInsertAfter As Long, ByVal X As Long, ByVal Y As Long, ByVal cx As Long, ByVal cy As Long, ByVal wFlags As Long) As Long

Public Function EnableCloseButton(ByVal hWnd As Long, Enable As Boolean) _

    EnableSystemMenuItem hWnd, SC_CLOSE, xSC_CLOSE, Enable, "EnableCloseButton"
    
End Function

Public Sub EnableMinButton(ByVal hWnd As Long, Enable As Boolean)

    Dim lngFormStyle As Long

    ' Enable / Disable System Menu Item
    EnableSystemMenuItem hWnd, SC_MINIMIZE, xSC_MINIMIZE, Enable, "EnableMinButton"
    
    ' Enable / Disable TitleBar button
    lngFormStyle = GetWindowLong(hWnd, GWL_STYLE)
    If Enable Then
        lngFormStyle = lngFormStyle Or WS_MINIMIZEBOX
    Else
        lngFormStyle = lngFormStyle And Not WS_MINIMIZEBOX
    End If
    SetWindowLong hWnd, GWL_STYLE, lngFormStyle
    
    ' Dirty, slimy, devious hack to ensure that the changes to the
    ' window's style take immediate effect before the form is shown
    SetParent hWnd, GetParent(hWnd)
    SetWindowPos hWnd, hWnd_NOTOPMOST, 0, 0, 0, 0, SWP_NOZORDER Or SWP_NOSIZE Or SWP_NOMOVE Or SWP_FRAMECHANGED
    
End Sub

Public Sub EnableMaxButton(ByVal hWnd As Long, Enable As Boolean)

    Dim lngFormStyle As Long

    ' Enable / Disable System Menu Item
    EnableSystemMenuItem hWnd, SC_MAXIMIZE, xSC_MAXIMIZE, Enable, "EnableMaxButton"
    
    ' Enable / Disable TitleBar button
    lngFormStyle = GetWindowLong(hWnd, GWL_STYLE)
    If Enable Then
        lngFormStyle = lngFormStyle Or WS_MAXIMIZEBOX
    Else
        lngFormStyle = lngFormStyle And Not WS_MAXIMIZEBOX
    End If
    SetWindowLong hWnd, GWL_STYLE, lngFormStyle
    
    ' Dirty, slimy, devious hack to ensure that the changes to the
    ' window's style take immediate effect before the form is shown
    SetParent hWnd, GetParent(hWnd)
    SetWindowPos hWnd, hWnd_NOTOPMOST, 0, 0, 0, 0, SWP_NOZORDER Or SWP_NOSIZE Or SWP_NOMOVE Or SWP_FRAMECHANGED

End Sub

Private Sub EnableSystemMenuItem(hWnd As Long, Item As Long, Dummy As Long, Enable As Boolean, FuncName As String)

    Dim hMenu As Long
    Dim MII As MENUITEMINFO
    Dim lngMenuID As Long
    
    If IsWindow(hWnd) = 0 Then
        Err.Raise vbObjectError, "modCloseBtn::" & FuncName, "modCloseBtn::" & FuncName & "() - Invalid Window Handle"
        Exit Sub
    End If
    
    ' Retrieve a handle to the window's system menu
    hMenu = GetSystemMenu(hWnd, 0)
    
    ' Retrieve the menu item information for the Max menu item/button
    MII.cbSize = Len(MII)
    MII.dwTypeData = String$(80, 0)
    MII.cch = Len(MII.dwTypeData)
    MII.fMask = MIIM_STATE
    
    If Enable Then
        MII.wID = Dummy
    Else
        MII.wID = Item
    End If
    
    If GetMenuItemInfo(hMenu, MII.wID, False, MII) = 0 Then
        Err.Raise vbObjectError, "modCloseBtn::" & FuncName, "modCloseBtn::" & FuncName & "() - Menu Item Not Found"
        Exit Sub
    End If
    
    ' Switch the ID of the menu item so that VB can not undo the action itself
    lngMenuID = MII.wID
    
    If Enable Then
        MII.wID = Item
    Else
        MII.wID = Dummy
    End If
    
    MII.fMask = MIIM_ID
    If SetMenuItemInfo(hMenu, lngMenuID, False, MII) = 0 Then
        Err.Raise vbObjectError, "modCloseBtn::" & FuncName, "modCloseBtn::" & FuncName & "() - Error encountered " & "changing ID"
        Exit Sub
    End If
    
    ' Set the enabled / disabled state of the menu item
    If Enable Then
        MII.fState = MII.fState And Not MFS_GRAYED
    Else
        MII.fState = MII.fState Or MFS_GRAYED
    End If
    
    MII.fMask = MIIM_STATE
    If SetMenuItemInfo(hMenu, MII.wID, False, MII) = 0 Then
        Err.Raise vbObjectError, "modCloseBtn::" & FuncName, "modCloseBtn::" & FuncName & "() - Error encountered " & "changing state"
        Exit Sub
    End If
    
    ' Activate the non-client area of the window to update the titlebar, and
    ' draw the Max button in its new state.
    SendMessage hWnd, WM_NCACTIVATE, True, 0
    
End Sub

No MDIForm:

Dim bMaxButton As Boolean
Dim bMinButton As Boolean
Dim bCloseButton As Boolean

Private Sub MDIForm_Load()

    bMaxButton = True
    bMinButton = True
    bCloseButton = True
    MsgBox "Clique com o Esquerdo para o Botão Minimizar" & vbCrLf & "Clique com o Direito para o Botão Maximizar" & vbCrLf & "Clique qualquer botão + CTRL para Botão Fechar", vbInformation
    
End Sub

Private Sub MDIForm_MouseUp(Button As Integer, Shift As Integer, X As Single, Y As Single)

    Select Case True
        Case (Button <> 0) And Shift = 2
            ' Click com qualquer botão + CTRL = Botão Fechar
            bCloseButton = Not bCloseButton
            EnableCloseButton Me.hWnd, bCloseButton
            
        ' Click com o esquerdo = Botão Minimizar
        Case Button = 1
            bMinButton = Not bMinButton
            EnableMinButton Me.hWnd, bMinButton
            
        Case Button = 2
            ' Click com o direito = Botão Maximizar
            bMaxButton = Not bMaxButton
            EnableMaxButton Me.hWnd, bMaxButton
            
    End Select
    
End Sub

PS.: Este exemplo deve funcionar com qualquer tipo de form, seja mdi, sdi ou mdichild


 


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