Creating Custom Controls

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.

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

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)

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.

Structured Error HandlingTry

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

Catch

• Catch ExceptionVar As ExceptionType– VB.Net Help provides information about a method’s

exceptions.– 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

User-Defined Application Exceptions

• System.ApplicationException• Throw• Code example:• Try• 'statements• Throw New ApplicationException("Test exception")

• Catch err As ApplicationException• MessageBox.Show(err.Message)• End Try

User-Defined Exception Class

Public Class JobCodeException

Inherits System.ApplicationException

Sub New(ByVal strMessage As String)

MyBase.New(strMessage)

End Sub

End Class

Using User-Defined Exception in Class

Private hiddenJobCode As Long

Public Property JobCode()

Set(ByVal Value)

If Value < 1 Or Value > 4 Then

Throw New JobCodeException("Invalide JobCode")

Else

hiddenJobCode = Value

End If

End Set

Get

JobCode = hiddenJobCode

End Get

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

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.UserControls class.

• 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

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

TimeZone Control CodePublic 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

Private Sub TimeZone_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load tmZone = tzone.Eastern 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 SubEnd Class

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

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

ValidDate Control CodePublic 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

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 < minDate Or enteredDate > maxDate Then

RaiseEvent InvalidDate("Date out of range")

Me.SelectAll()

e.Cancel = True

End If

End If

End Sub

End Class

Using DateTime Picker

• Properties:– MaxDate

– MinDate

– Value• One year appointment:

– DateTimePicker1.MaxDate = DateAdd(DateInterval.Year, 1, Now)

– DateTimePicker1.MinDate = Now

• Event:– ValueChanged

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

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

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.

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

Graphics ExamplePrivate 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

Creating an Array of ObjectsDim emps(2) As empDim i As IntegerFor i = 0 To emps.GetUpperBound(0) emps(i) = New emp()Nextemps(0).Eid = "e1"emps(0).Ename = "peter"emps(0).salary = 5000

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

Creating a MyGrid Control

• Properties:– Rows, Cols– Cell

• Methods:– AddRow– ReDimension

Assemblies

• An assembly is a logical grouping of functionality into a physical file. One or many business logic components can be reside in an assembly.

• This collection of components is compiled into a .DLL file.

• We can import this .DLL component to any VB projects.

Steps to Create An Assembly

• Create a class library with classes.– You can also use existing classes by Project/Add

Existing Item

• Select Build/Build Solution to compile the code.– When the class library is compiled successfully, an

assembly is created and stored in the project’s Bin folder.

• Demo: CustomerBackGroundCheck

Using the Assembly

• Reference the assembly: Project/Add Reference and use the Browse button to select the assembly.

• Import the assembly.

Code Using Assembly

Imports CustomerBackGroundCheck

Public Class Form1

Dim test As New CustomerBackGroundCheck.BackGroundCheck()

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

If test.CreditCheck("C1") = "good" Then

MessageBox.Show("good credit")

Else

MessageBox.Show("bad credit")

End If

End Sub

Adding Events to Controls Created with Code

• AddHandler object.event, AddressOf eventhandler

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

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.

Using One Event Handler to Handle Events Generated by Many Controls• Assume we have 3 buttons.• Use the Handles clause in the event

procedure to associate controls with the event procedure.

• We can assign a value for each control’s Tag property, or use control’s TabIndex property to determine which control generates the event.

Private Sub Button_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click, Button2.Click, Button3.Click

If sender.tag = "1" Then

MessageBox.Show("button 1 clicked")

ElseIf sender.tag = "2" Then

MessageBox.Show("button 2 clicked")

Else

MessageBox.Show("button 3 clicked")

End If

End Sub

Note: VB IntelliSense will not show the Tag property after you type sender.