A Generic Calendar Application, pg.3 [AVDF Article]

The Calendar Application

Initializing the Calandar, Page 3

I wanted my Calendar application to be able to be passed a parameter of a date and then be able to load and display the calendar positioned at the desired date. To achieve this I use a hidden label control (lblLastDate) that will hold the value of the parameter that is passed to it. The Change event of this control triggers the Calendar_do function to position the calendar to the date in the Caption property of the lblLastDate control.

  Private Sub lblLastDate_Change()
    If Not IsDate(lblLastDate) Then
      lblLastDate = Date
    End If
    formisloading = True			  ' don't invoke combo Click events
    cboMonth.ListIndex = Month(lblLastDate) - 1
    cboYear.ListIndex = Year(lblLastDate) - Year(Date) + 10
    formisloading = False			  ' enable combo Click events
    Calendar_do Format(lblLastDate, "dd"), Str(cboMonth.ListIndex + 1),
  cboYear.Text, Me
  End Sub

The decision to change the caption property of the lblLastDate control (and therefore trigger its Change event) is made in the form's load event.

  Private Sub Form_Load()
  Screen.MousePointer = 11
    formisloading = True		          ' Prevent combo boxes from triggering Click events
  during loading
    cboYear_Init cboYear		          ' Fill the combo with a list of years
    cboMonth_Init cboMonth	                  ' Fill the combo with a list of months
    lblDay_Init			                  ' Set the names of the days of the week
    If IsDate(Command$) Then                      ' Test the command line for a date
        lblLastDate = Command$                    ' Trigger lblLastDate_Change

  ' Make sure the date passed is in Long Date format
    Else
        lblLastDate = Date                        ' Default to todays date
    End If
    formisloading = False
  Screen.MousePointer = 0
  End Sub

(You may want to change the highlighted code above depending upon how you want to implement the calendar component into you VB applications.)

Whereas Delphi uses a grid control to imitate the outline of a calendar in VB I chose to use a Command button array so that I would not have to include any OCX controls when I distributed the application. Nor would I need to add a grid OCX to a project that did not use a grid control in the first place just to add the functionality of a calendar to my application.

Add an array of command buttons (37 buttons arranged in row's of 7, one for each day of the week). The caption property will display the day numbers of the chosen date. All code that decides which buttons to display and what the value of their captions will be occurs in the subroutine Calendar_do :

  Sub Calendar_do(ByVal dy As String, ByVal m As String, ByVal Y As String, Frm
As Form)

  ' Calculates and sets the values of the calButton controls according
  ' the start day of the chosen month.
  Dim k As Integer
  Dim lmth As Integer
  Dim DayOne As Variant
  Dim Offset As Integer
  shaButton.Visible = False	                  ' hide the button highlight shape
  DayOne = DateValue("1/" & m & "/" & Y)          ' handles all date formats
  Offset = WeekDay(DayOne) - 2	                  ' find the first button that will be visible
  lmth = LenMonth(DayOne)		          ' find the number of buttons that will be displayed
  For k = 0 To 37
  If (k < 1 + Offset) Or k > Offset + lmth Then   ' are they in range
    Frm.CalButton(k).Caption = ""		  ' hide the button
    Frm.CalButton(k).Visible = False
  Else
    Frm.CalButton(k).Visible = True		  ' show the button
    Frm.CalButton(k).Caption = k - Offset	  ' set its caption value to the day number
  End If
  Next
  calButton_Click (Offset + Val(dy))		  ' Highlights the button of the selected date
  End Sub

(The function above includes a form control as an argument in order to maintain compatability with VBA implementations)

The completed Calendar form :

The Reload command button simply calls the form load event to refresh the combo and label initialization routines so that the calendar application could be tested when the international settings in the Control folder where changed without having to restart the Visual Basic session.

Users can navigate through dates by selecting the month and year from the dropdown lists or by clicking on the button corresponding to the day of the date.

The Click events of the combo boxes both call the Calendar_do utility to redisplay the button days in the correct order for the chosen Month/Year combination.

  Sub cboMonth_Click()
  If formisloading Then Exit Sub   ' don't do anything during form load event
  Screen.MousePointer = 11
  Calendar_do "1", Str(cboMonth.ListIndex + 1), cboYear.Text, Me
  Screen.MousePointer = 0
  End Sub

  Sub cboYear_Click()
  If formisloading Then Exit Sub
  Screen.MousePointer = 11
  Calendar_do "1", Str(cboMonth.ListIndex + 1), cboYear.Text, Me
  Screen.MousePointer = 0
  End Sub

[HOME] [TABLE OF CONTENTS] [SEARCH]