Adding Smart Tags to Windows Forms Controls : Page 2

Programming the User Control
With the design of the user control completed, you can now start coding. Switch to the code behind file for the user control (UserControl1.vb) and add the following namespace:

   Imports System.ComponentModel

The System.ComponentModel namespace provides classes that are used to implement the run-time and design-time behavior of components and controls. In this case, you'll be adding attributes to the control class and its properties to customize its behavior. You will see the effects of these attributes shortly.

Next, declare the Formats and Months enumerations to represent the format and months, respectively:

   Public Enum Formats
      DDMMYYYY  '---e.g. 29 02 2006---
      DDMmmYYYY '---e.g. 12 Jan 2006---
      MMDDYYYY  '---e.g. 02 25 2006---
      MmmDDYYYY '---e.g. Jan 15 2006---
   End Enum
   Public Enum Months
      Jan = 1
      Feb = 2
      Mar = 3
      Apr = 4
      May = 5
      Jun = 6
      Jul = 7
      Aug = 8
      Sep = 9
      Oct = 10
      Nov = 11
      Dec = 12
   End Enum

Defining the Member Variables
Change the default class name from UserControl1 to DateControl and declare the member variables as shown below:

   <DefaultEvent("Err")> _
      Public Class DateControl
      '---member variables---
      Private _Format As Formats = Formats.DDMMYYYY
      Private _Day As Integer
      Private _Month As Integer
      Private _year As Integer
      Private _MinYear As Integer = 1918
      Private _MaxYear As Integer = 2050
      Private _DayControl As New ComboBox
      Private _MonthControl As New ComboBox
      '---event handler for error---
      <Category("Date Settings"), _
         DescriptionAttribute("Error event handler.")> _
         Public Event Err(ByVal str As String)
   End Class

You use the ControlDesigner class to extend the design mode behavior of user controls.

Notice the following:

• The control fires the Err event if a validation error occurs, providing the control with a way to communicate the error to the user.
• The Category attribute causes the Err event to appear under the Date Settings category in the VS Properties window. The DescriptionAttribute specifies the message VS displays at the bottom of the properties window.
• The DefaultEvent attribute indicates the default event handler for this control. When you drop this control on the design surface of a Windows Form, double-clicking it will automatically cause VS 2005 to insert stub code for the Err event handler.
• The _DayControl and the _MonthControl reference the respective ComboBox controls representing the day and month.

Next, add a Format property to the class so users can select the date format. Depending on the format selected, the control uses the _DayControl and _MonthControl variables to reference the actual ComboBox controls representing the day and month. Also, when a user selects a format, the control calls the InitDates() method (defined shortly) to refresh the control dynamically to reflect the selected format:

   <Category("Date Settings"), _
      DescriptionAttribute( _
      "Sets the display format for " & _
      "the control.")> _
   Public Property Format() As Formats
      Get
         Return _Format
      End Get
      Set(ByVal value As Formats)
         _Format = value
         Select Case Me.Format
            Case Formats.DDMmmYYYY, Formats.DDMMYYYY
               _DayControl = cbbField1
               _MonthControl = cbbField2
            Case Formats.MMDDYYYY, Formats.MmmDDYYYY
               _DayControl = cbbField2
               _MonthControl = cbbField1
         End Select
         _DayControl.BackColor = Color.White
         _MonthControl.BackColor = Color.White
         InitDates()
      End Set
   End Property

The Day property lets users set the day of the date individually, using a numeric value from 1 to 31. Notice that if the day value is set to an invalid value, the control raises the Err event:

   <Category("Date Settings"), _
      DescriptionAttribute( _
      "Sets the day value for the control.")> _
   Public Property Day() As Integer
      Get
         Return _Day
      End Get
      Set(ByVal value As Integer)
         If value >= 1 And value <= 31 Then
            _Day = value
            _DayControl.Text = _Day
         Else
            RaiseEvent Err("Day is out of range.")
         End If
      End Set
   End Property

The Month property lets users set the month to a numeric value from 1 to 12. While it is similar to the Day property, you need to take special care when users select a format that displays the month alphabetically (such as Jan or Feb), because you must convert the numeric value of the month into its corresponding enumeration value:

   <Category("Date Settings"), _
      DescriptionAttribute( _
      "Sets the month value for the control.")> _
   Public Property Month() As Integer
      Get
         Return _Month
      End Get
      Set(ByVal value As Integer)
         If value >= 1 And value <= 12 Then
            _Month = value
            If Me.Format = Formats.DDMMYYYY Or _
               Me.Format = Formats.MMDDYYYY Then
                  _MonthControl.Text = _Month
            Else
               _MonthControl.Text = _
                  [Enum].GetName( _
                  GetType(Months), _Month)
            End If
         Else
            RaiseEvent Err( _
                "Month is out of range.")
         End If
      End Set
   End Property

Creating the Year property is much more straightforward:

   <Category("Date Settings"), _
       DescriptionAttribute( _
       "Sets the year value for the control.")> _
      Public Property Year() As Integer
         Get
            Return _year
         End Get
      Set(ByVal value As Integer)
         _year = value
         cbbYear.Text = _year
      End Set
   End Property

In addition to properties for setting the day, month, and year, the control has a [Date] (the square brackets are because Date is a reserved word in VB) property to let users set the date using the Date class:

   <Category("Date Settings"), _
      DescriptionAttribute( _
      "Gets or sets the date for the control.")> _
   Public Property [Date]() As Date
      Get
         Try
            Dim d As New Date( _
               Me.Year, Me.Month, Me.Day)
            Return d
         Catch ex As Exception
            Return Nothing
         End Try
      End Get
      Set(ByVal value As Date)
         Me.Day = value.Day
         Me.Month = value.Month
         Me.Year = value.Year
      End Set
   End Property

The MinYear and MaxYear properties set the first and last years to display:

   <Category("Date Settings"), _
      DescriptionAttribute( _
      "Sets the start year for the control.")> _
   Public Property MinYear() As Integer
      Get
         Return _MinYear
      End Get
      Set(ByVal value As Integer)
         _MinYear = value
      End Set
   End Property
   
   <Category("Date Settings"), _
      DescriptionAttribute( _
      "Sets the end year for the control.")> _
   Public Property MaxYear() As Integer
      Get
         Return _MaxYear
      End Get
      Set(ByVal value As Integer)
         _MaxYear = value
      End Set
   End Property

As mentioned previously, the InitDates() method refreshes the control so it reflects the currently selected format:

   Private Sub InitDates()
      '---day---
      _DayControl.Items.Clear()
      For i As Integer = 1 To 31
         _DayControl.Items.Add(i)
      Next
      '---month---
      _MonthControl.Items.Clear()
      For i As Integer = 1 To 12
         If Me.Format = _
            Formats.DDMMYYYY Or Me.Format = _
            Formats.MMDDYYYY Then
               _MonthControl.Items.Add(i)
         Else
            _MonthControl.Items.Add( _
               [Enum].GetName( _
               GetType(Months), i))
         End If
      Next
      '---year---
      cbbYear.Items.Clear()
      For i As Integer = Me.MinYear To Me.MaxYear
         cbbYear.Items.Add(i)
      Next
      '---display the set date---
      _DayControl.SelectedIndex = Me.Day - 1
      _MonthControl.SelectedIndex = Me.Month - 1
      cbbYear.Text = Me.Year
   End Sub

The preceding method simply populates the ComboBox controls with the various dates so that the user can choose from them, and sets them to display the currently selected date.

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