Overview
This article shows how to set up and use a Class Module, as well as, more specifically, how to open forms such that they appear as a hierachical menu structure. Form A opens Form B and, while Form B is still open, remains hidden from view. As and when Form B terminates, Form A comes back into view and reassumes the focus.
The code for classForm below includes examples of setting class properties as well as various methods. Of particular interest among the methods is the encapsulated event handler frmCalled_Close (), which is able to be triggered due to the WithEvents keyword used in line #19 (See code below).
Module Code
Calling and Using Code
Line #4 indicates the declaration for the classForm object.
Line #7 indicates the basic setting up of the object. This tells the class which form is the caller for returning to after any called form terminates.
Line #11 indicates calling another form. At this point in the code the class takes over and hides the calling form as well as showing the called form.
Lines #18 through #20 indicate a stub of an event handler that must exist if the class is to be able to capture the called form terminating. This is necessary for the class to re-show the caller form.
This article shows how to set up and use a Class Module, as well as, more specifically, how to open forms such that they appear as a hierachical menu structure. Form A opens Form B and, while Form B is still open, remains hidden from view. As and when Form B terminates, Form A comes back into view and reassumes the focus.
The code for classForm below includes examples of setting class properties as well as various methods. Of particular interest among the methods is the encapsulated event handler frmCalled_Close (), which is able to be triggered due to the WithEvents keyword used in line #19 (See code below).
Module Code
Code:
Option Compare Database
Option Explicit
'21/1/2004 Added Private Set & Public Get code for frmTo.
'21/9/2004 Removed ResumeTo functionality. _
Now handled by the OnTimer() subroutine in the calling form _
checking for (Visible) which indicates the called form is finished.
'24/2/2005 Added function Uninitialised to show if instance of this object _
has yet been initialised with the callers info. _
It also checks this before it tries to open a new form.
'31/3/2008 Added varOpenArgs as optional parameter to ShowForm. Simply to be _
passed directly to the opened form using DoCmd.OpenForm(). _
Also set .OpenForm() to treat Cancel of the open as NOT an error.
Private Const conUnInitMsg As String = _
"Object uninitialised - unable to show form."
Private frmParent As Form
Private WithEvents frmCalled As Form
Public Property Set frmFrom(frmValue As Form)
Set frmParent = frmValue
End Property
Private Property Get frmFrom() As Form
Set frmFrom = frmParent
End Property
Private Property Set frmTo(frmValue As Form)
Set frmCalled = frmValue
End Property
Public Property Get frmTo() As Form
Set frmTo = frmCalled
End Property
'Uninitialised returns True if frmFrom not yet initialised.
Public Function Uninitialised() As Boolean
Uninitialised = (frmParent Is Nothing)
End Function
'ShowForm opens form strTo and hides the calling form. Returns True on success.
Public Function ShowForm(strTo As String, _
Optional strFilter As String = "", _
Optional varOpenArgs As Variant = Null) As Boolean
ShowForm = True
'Don't even try if caller hasn't initialised Form object yet
If Uninitialised() Then
ShowForm = False
Call ShowMsg(strMsg:=conUnInitMsg, strTitle:="classForm.ShowForm")
Exit Function
End If
Call DoCmd.Restore
'Handle error on OpenForm() only.
On Error GoTo ErrorSF
Call DoCmd.OpenForm(FormName:=strTo, _
WhereCondition:=strFilter, _
OpenArgs:=varOpenArgs)
On Error GoTo 0
Set frmTo = Forms(strTo)
frmFrom.Visible = False
Exit Function
ErrorSF:
ShowForm = False
' If open is cancelled (either by user or code) then simply exit
If Err.Number <> 2501 Then _
Call ErrorHandler(strName:=strTo, _
strFrom:=frmFrom.Name & ".ShowForm", _
lngErrNo:=Err.Number, _
strDesc:=Err.Description)
End Function
'************************* Contained Object Method(s) *************************
'For these subroutines to be activated the contained object must have the
''On Close' property set to a valid subroutine within the contained object.
Private Sub frmCalled_Close()
frmFrom.Visible = True
Call DoCmd.Restore
Set frmTo = Nothing
End Sub
'******************************************************************************
Calling and Using Code
Code:
Option Compare Database
Option Explicit
Private clsTo As New classForm
Private Sub Form_Open(Cancel As Integer)
Set clsTo.frmFrom = Me
End Sub
Private Sub cmdWhatever_Click()
Call clsTo.ShowForm(strTo:="frmWhatever")
End Sub
Private Sub cmdExit_Click()
Call DoCmd.Close
End Sub
Private Sub Form_Close()
'Method must exist in order for container to handle event.
End Sub
Line #7 indicates the basic setting up of the object. This tells the class which form is the caller for returning to after any called form terminates.
Line #11 indicates calling another form. At this point in the code the class takes over and hides the calling form as well as showing the called form.
Lines #18 through #20 indicate a stub of an event handler that must exist if the class is to be able to capture the called form terminating. This is necessary for the class to re-show the caller form.
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