1. Creating Custom Controls

2. Overriding ToString Method Every class you create in VB.Net is derived from a built-in class named object. –Mscorlib/system/object The object class has a method named ToString method which returns a fully- qualified class name. This method is overridable.

3. Code Example Public Class Person Public SSN As String Public FirstName As String Public LastName As String Public BirthDate As Date Public Overrides Function ToString() As String toString = FirstName & " " & LastName & "'s birthday is " & BirthDate.ToString End Function

4. Overriding and Overloading GetHashCode Method Public Overloads Overrides Function GetHashCode() As Integer GetHashCode = CInt(SSN.Substring(0, 3)) Mod 10 End Function Public Overloads Function GetHashCode(ByVal M As Integer) As Integer GetHashCode = CInt(SSN.Substring(0, 3)) Mod M End Function Code Example: Dim myPerson As New Person() myPerson.SSN = TextBox1.Text TextBox2.Text = myPerson.GetHashCode TextBox3.Text = myPerson.GetHashCode(100)

5. Exception Exceptions signal errors or unexpected events that occur while an application is running. An error handler is a section of code that intercepts and responds to exceptions.

6. Structured Error Handling Try result = Val(TextBox1.Text) / Val(TextBox2.Text) TextBox3.Text = result.ToString Catch except As InvalidCastException MessageBox.Show(except.Message) Catch except As DivideByZeroException MessageBox.Show(except.Message) Catch except As Exception 'Handle everything else MessageBox.Show(except.Message) Finally MessageBox.Show("I get exdecuted, no matter what") End Try

7. Catch Catch ExceptionVar As ExceptionType –VB.Net Help provides information about a method’s exceptions. Ex. File class/Methods Ex. OleDbConnection class/Methods –Try – fileNumber = FreeFile() – FileOpen(fileNumber, "c:\stdata.txt", OpenMode.Input) – Catch err As FileNotFoundException – MessageBox.Show(err.Message) – MessageBox.Show("file not found") – Catch err As NotSupportedException – MessageBox.Show(err.Message) – End Try

8. User-Defined Application Exceptions System.ApplicationException Throw –Throw New ApplicationException("Test exception") Use Try block to catch the excaption –Try Statements –Catch err ApplicationException MessageBox.Show(err.Message) –End Try

9. Application Exception Example Public Class emp Public SSN As String Public Ename As String Public DateHired As Date Private hiddenJobCode As Long Public Property JobCode() Set(ByVal Value) If Value 4 Then Throw New ApplicationException("Invalide JobCode") Else hiddenJobCode = Value End If End Set Get JobCode = hiddenJobCode End Get End Property End Class

10. Catch Application Exception Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click Dim myEmp As New emp() Try myEmp.JobCode = TextBox1.Text MessageBox.Show(myEmp.JobCode) Catch err As ApplicationException MessageBox.Show(err.Message) TextBox1.Focus() End Try End Sub

11. User-Defined Exception Class Public Class JobCodeException Inherits System.ApplicationException Sub New(ByVal strMessage As String) MyBase.New(strMessage) End Sub End Class

12. Using User-Defined Exception in Class Private hiddenJobCode As Long Public Property JobCode() Set(ByVal Value) If Value 4 Then Throw New JobCodeException("Invalide JobCode") Else hiddenJobCode = Value End If End Set Get JobCode = hiddenJobCode End Get

13. Using User-Defined Exception in Program Dim myEmp As New Emp() Try myEmp.Eid = TextBox1.Text myEmp.Ename = TextBox2.Text myEmp.salary = CDbl(TextBox3.Text) myEmp.JobCode = TextBox4.Text Catch err As JobCodeException MessageBox.Show(err.Message) TextBox4.Focus() TextBox4.SelectAll() End Try

14. Class Events Events that are triggered in code in the class and can be detected by host program. To declare a event: –Public Event EventName(Argument list) –Ex. Public Event InvalidCode(ByVal message As String) To raise an event: –RaiseEvent EventName(Argument list)

15. Public Class Emp Public Event InvalidCode(ByVal message As String) Public Eid As String Public Ename As String Public salary As Double Private hiddenJobCode As Long Public Property JobCode() Set(ByVal Value) If Value 4 Then RaiseEvent InvalidCode("Invalide JobCode") Else hiddenJobCode = Value End If End Set Get JobCode = hiddenJobCode End Get End Property End Class

16. Handling Events Using WithEvents and Handles Declare the object variable using the WithEvents keyword: –Dim WithEvents myemp As New Emp() Event handler: –Sub HandlerName(Argumentlist) Handles event

17. Dim WithEvents myemp As New Emp() Private Sub InvalidCodeHandler(ByVal msg As String) Handles myemp.InvalidCode MessageBox.Show(msg) End Sub

18. Creating Custom Controls A customer control is a control that is designed by a programmer for a specific purpose. It is derived from the System.Windows.Forms.UserControl class. –Object Browser Two ways to create a control: –Windows Control Library Project Controls can be used in multiple projects. –Add a new UserControl to an existing project. Only in current project

19. Custom Control Example A form that displays time in the four time zones. Demo: TestTimeZone/TimeZoneAsProj

20. Creating TimeZone Control This control displays time in each time zone. It exposes a Zone property and a ShowTime method. New Project/Windows Control Library Design control’s appearance and add any functionality you want. Build the DLL: –The DLL is saved in project’s Bin folder. Create a Windows project to test the control. –Right Click Windows tab of the Tool Box and choose Customize ToolBox –Click.Net Framework component –Click Browse to select the DLL

21. TimeZone Control Code Public Class TimeZone Inherits System.Windows.Forms.UserControl Enum tzone Eastern = 1 Central Mountain Pacific End Enum Private sysTime As Date Private tmZone As tzone Public Property Zone() As tzone Get Zone = tmzone End Get Set(ByVal Value As tzone) tmzone = Value End Set End Property

22. Private Sub TimeZone_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load tmZone = tzone.Eastern‘Use control’s load event to assign initial value to control’s property End Sub Public Sub ShowTime() sysTime = Now If tmZone = tzone.Eastern Then lblE.Text = sysTime.ToLongTimeString lblC.Text = DateAdd(DateInterval.Hour, -1, sysTime).ToLongTimeString lblM.Text = DateAdd(DateInterval.Hour, -2, sysTime).ToLongTimeString lblP.Text = DateAdd(DateInterval.Hour, -3, sysTime).ToLongTimeString ElseIf tmZone = tzone.Central Then lblC.Text = sysTime.ToLongTimeString lblE.Text = DateAdd(DateInterval.Hour, 1, sysTime).ToLongTimeString lblM.Text = DateAdd(DateInterval.Hour, -1, sysTime).ToLongTimeString lblP.Text = DateAdd(DateInterval.Hour, -2, sysTime).ToLongTimeString ElseIf tmZone = tzone.Mountain Then lblM.Text = sysTime.ToLongTimeString lblE.Text = DateAdd(DateInterval.Hour, 2, sysTime).ToLongTimeString lblC.Text = DateAdd(DateInterval.Hour, 1, sysTime).ToLongTimeString lblP.Text = DateAdd(DateInterval.Hour, -1, sysTime).ToLongTimeString Else lblP.Text = sysTime.ToLongTimeString lblE.Text = DateAdd(DateInterval.Hour, 3, sysTime).ToLongTimeString lblC.Text = DateAdd(DateInterval.Hour, 2, sysTime).ToLongTimeString lblM.Text = DateAdd(DateInterval.Hour, 1, sysTime).ToLongTimeString End If End Sub End Class

23. Code Using TimeZone Control Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click TimeZone1.Zone = TimeZoneControlLibrary.TimeZone.tzone.Pacific TimeZone1.ShowTime() End Sub

24. Create an Inherited User Control Create a user control from an existing control such as TextBox, Label, etc. Example: Create a control, called ValidDate, that looks exactly like a textbox, but it will validate the entry for a valid date. –Inherits from System.Windows.Forms.TextBox –Properties: MaximumDate, MinimumDate with default value –Event: InvalidDate event

25. ValidDate Control Code Public Class ValidDate Inherits System.Windows.Forms.TextBox Public Event InvalidDate(ByVal message As String) Private maxDate As Date = Now.Date.AddYears(1) Private minDate As Date = Now.Date Public Property MaximumDate() As Date Get MaximumDate = maxDate End Get Set(ByVal Value As Date) maxDate = Value End Set End Property Public Property MinimumDate() As Date Get MinimumDate = minDate End Get Set(ByVal Value As Date) minDate = Value End Set End Property

26. Private Sub ValidDate_Validating(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles MyBase.Validating If Not IsDate(Me.Text) Then Me.SelectAll() e.Cancel = True RaiseEvent InvalidDate("Date not valid") Else Dim enteredDate As Date = CDate(Me.Text) If enteredDate maxDate Then RaiseEvent InvalidDate("Date out of range") Me.SelectAll() e.Cancel = True End If End Sub End Class

27. Using DateTime Picker Properties: –MaxDate –MinDate –Value: Selected date One year appointment: – DateTimePicker1.MaxDate = DateAdd(DateInterval.Year, 1, Now) – DateTimePicker1.MinDate = Now Event: –ValueChanged

28. Create an One-Year Appointment Date/Time Picker Control This control contains a DataTimePicker to choose appointment date up to one year in advance, and buttons to choose time. This control exposes two properties: –SelDate –SelTime Note: What is the purpose to have a Time1Available property?

29. MyCalendar Control Code Public Class testCalendar Inherits System.Windows.Forms.UserControl Private hiddenDate As Date Private hiddenTime As String Public WriteOnly Property time1Available() As Boolean Set(ByVal Value As Boolean) If Value Then Button1.Enabled = True Else Button1.Enabled = False End If End Set End Property Public ReadOnly Property selDate() As Date Get selDate = hiddenDate End Get End Property Public ReadOnly Property selTime() As String Get selTime = hiddenTime End Get End Property

30. Private Sub DateTimePicker1_ValueChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles DateTimePicker1.ValueChanged hiddenDate = DateTimePicker1.Value End Sub Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click hiddenTime = "10 am" TextBox1.Text = hiddenTime End Sub Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click hiddenTime = "12 pm" TextBox1.Text = hiddenTime End Sub Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click hiddenTime = "2 pm" TextBox1.Text = hiddenTime End Sub Private Sub Button4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button4.Click hiddenTime = "4 pm" TextBox1.Text = hiddenTime End Sub Private Sub testCalendar_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load DateTimePicker1.MaxDate = DateAdd(DateInterval.Year, 1, Now) DateTimePicker1.MinDate = Now End Sub End Class

31. Creating Form Controls With Code Use the name space: System.Windows.Forms –Ex. Define a textbox: –Dim tryTxt As New System.Windows.Forms.TextBox() Set property value: –tryTxt.Location = New System.Drawing.Point(70, 70) – tryTxt.Size = New System.Drawing.Size(144, 20) Add to form’s Controls collection: –Me.Controls.Add(tryTxt) –Form Controls example: Dim o As Object – For Each o In Me.Controls – MessageBox.Show(o.GetType.ToString) – Next

32. Example Private Sub Form11_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load Dim tryTxt As New System.Windows.Forms.TextBox() tryTxt.Location = New System.Drawing.Point(70, 70) tryTxt.Size = New System.Drawing.Size(144, 20) Me.Controls.Add(tryTxt) Dim tryButton As New System.Windows.Forms.Button() tryButton.Location = New System.Drawing.Point(70, 100) tryButton.Size = New System.Drawing.Size(100, 20) Me.Controls.Add(tryButton) End Sub

33. Graphics Basics Create a graphics object. Create a Pen or Brush object to draw with. Call the drawing methods from the Graphics object to draw.

34. Form’s Paint Event Each time a form is displayed, resized, moved, maximized, restored, the form’s Paint event is triggered. Use the Paint event’s EventArg or a form’s CreateGraphics method to create a graphics object. Objects: Point, Size, Shape

35. Graphics Example Private Sub Form2_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles MyBase.Paint Dim penBlk As New Pen(Color.Black, 10) Dim gr As Graphics = e.Graphics gr.DrawRectangle(penBlk, 50, 50, 100, 20) Dim gr1 As Graphics gr1 = Me.CreateGraphics Dim penRed As New Pen(Color.Red, 10) Dim startPoint As New Point(70, 10) Dim grSize As New Size(50, 20) Dim shapeRect As New Rectangle(startPoint, grSize) gr1.DrawRectangle(penRed, shapeRect) End Sub

36. Creating an Array of Objects Dim emps(2) As emp Dim i As Integer For i = 0 To emps.GetUpperBound(0) emps(i) = New emp() Next emps(0).Eid = "e1" emps(0).Ename = "peter" emps(0).salary = 5000

37. Creating an Array of Textbox with Code Dim test(1) As System.Windows.Forms.TextBox Dim pointX As Integer = 50 Dim pointY As Integer = 80 Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load Dim i As Integer For i = 0 To 1 test(i) = New System.Windows.Forms.TextBox() test(i).Location = New System.Drawing.Point(pointX, pointY) test(i).Name = "TextBox" & i.ToString test(i).Size = New System.Drawing.Size(144, 20) test(i).Text = test(i).Name test(i).Visible = True pointY += 50 Me.Controls.Add(test(i)) Next End Sub

38. Adding Events to Controls Created with Code AddHandler object.event, AddressOf eventhandler

39. Private pButton(2) As Windows.Forms.Button Private pointX As Integer = 0 Private pointY As Integer = 0 Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load Dim I As Integer For i = 0 To 2 pButton(i) = New System.Windows.Forms.Button() pButton(i).Location = New System.Drawing.Point(pointX, pointY) pButton(i).Name = "button" & i.ToString pButton(i).Size = New System.Drawing.Size(15, 20) pButton(i).Text = i.ToString Me.Controls.Add(pButton(i)) AddHandler pButton(i).Click, AddressOf ButtonClickHandler pointY += 20 Next End Sub Public Sub ButtonClickHandler(ByVal sender As Object, ByVal e As _ System.EventArgs) MessageBox.Show(sender.name) End Sub

40. Testing Custom Controls Create and build the control. Keep the custom control project open, and go to Windows desktop to open a second Visual Studio window. In the second Visual Studio window, open a project to test the custom control.

41. Keyboard-Related Events KeyDown: When a key is pressed. KeyUp: When a key is released. –The event procedure receives a KeyEventArgs argument. KeyPress: When a key is pressed and released (for regular keys-digits and letters). –The event procedure receives a KeyPressEventArgs.

42. Event Argument Properties KeyEventArgs: Alt Control Shift –Return a Boolean value indicating whether Alt/Ctrl/Shift was down. KeyCode: A member of Keys enumeration specifying the key that was pressed. KeyPressEventArgs KeyChar: The character of the key pressed. Handled: A Boolean indicating whether the event was handled by a KeyPressEvent procedure. If not handled, this event will be processed by the form as usual.

43. Filtering Textbox Input to Permit Only Digits and Hyphen Using the Handled Property Private Sub TextBox1_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles TextBox1.KeyPress Select Case e.KeyChar Case "0" To "9", "-" 'Do nothing - permitted character Case Else e.Handled = True End Select End Sub

44. Keys Enumeration Private Sub TextBox1_KeyDown(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles Textbox1.keydown If e.KeyCode = Keys.Delete Then …

45. Create 3 Buttons and Implement Delete Key TextMyGrid/Form2 Public Class Form2 Inherits System.Windows.Forms.Form Private pButton(2) As Windows.Forms.Button Private pointX As Integer = 0 Private pointY As Integer = 0 Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load pointX = 50 pointY = 50 Dim i, j As Integer For i = 0 To 2 pButton(i) = New System.Windows.Forms.Button() pButton(i).Location = New System.Drawing.Point(pointX, pointY) pButton(i).Name = "button" & i.ToString pButton(i).Size = New System.Drawing.Size(100, 50) pButton(i).Text = "Button" & i.ToString Me.Controls.Add(pButton(i)) AddHandler pButton(i).Click, AddressOf ButtonClickHandler AddHandler pButton(i).KeyDown, AddressOf Grid_KeyDown pointY += 70 Next End Sub

46. Private Sub Grid_KeyDown(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) If e.KeyCode = Keys.Delete Then Dim index As Integer index = sender.name.substring(6, 1) Me.Controls.Remove(pButton(index)) End If End Sub

47. Creating a MyGrid Control Properties: –Rows, Cols: Initialized to 2. –Cell(RowIndex, ColIndex) Methods: –AddRow –ReDimension KeyDown event: Delete a row by pressing the Delete key.