VB.NET Forms

1
VB.NET Forms

• ITE 370

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Forms Class

• Forms are part of the Windows Form class defined
  in the .NET Framework Class Library
• A form is a container for controls a form is
  used to design a GUI-based window in a Windows
  application
• A form displays information and receives input
  from the user
• Always orient a form at a task as defined by the
  user

Public Class Form1 Inherits
System.Windows.Forms.Form End Class Form1
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Form Properties

• Text defines the text to display in the caption
  bar
• StartPosition determines position of form when
  it first appears (eg. CenterScreen)
• Size.Width, Size.Height the 2D area occupied by
  the form, in units of pixels
• Location.X, Location.Y the relative position of
  the form on the screen
• FormBorderStyle determines the appearance and
  behavior of the borders of the form

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Displaying a Form at Startup

• Startup Form for project loads shows
  automatically
• Or, use a Sub Main in a separate module to show
  initial form
• Module Main
• Sub Main()
• ' declare form to display baseball teams
• Dim fTeam As fTeams
• fTeam New fTeams()
• Application.Run(fTeam)
• End Sub
• End Module

5
Form Display

• Showing a form
• Form1.Show() displays Form1
• Form1.ShowDialog() modally
• Closing a form in code
• Me.Close()

6
Cohesion and coupling

• Recall the principles of modular programming
• Cohesion is the degree to the which the parts
  (statements) of a module are interrelated, that
  is, they all contribute to doing one thing
• Coupling is the degree to which two modules
  interact, or are interrelated.
• High cohesion and low coupling are desirable
• To make software easy to maintain
• To reduce the possibility of errors
• For better fault detection and isolation

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Forms interaction and low coupling

• When one form calls (to display) another,
• Pass information back-and-forth through the
  constructor or public properties, not global
  variables, like control names
• Private Sub btnHello_Click(ByVal sender As
  System.Object, _
• ByVal e As System.EventArgs) Handles
  btnHello.Click
• ' declare and initialize a new form object,
  passing
• the user name to be displayed on the called
  form
• Dim fHello1 As New fHello(txtUserName.Text)
• fHello1.ShowDialog() ' display form
  fHello1 modally
• fHello1.Close()
• fHello1.Dispose()
• End Sub

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Form constructor

• Dim mUserName As String ' instance variable
• Public Sub New(ByVal UName As String)
• MyBase.New()
• 'This call is required by the Windows
  Form Designer.
• InitializeComponent()
• 'Add any initialization after the
  InitializeComponent() call
• mUserName UName
• lblUserName.Text "Hello, " mUserName
• End Sub

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User-defined property in form class

• Public Property UserName() As String
• Get
• Return mUserName
• End Get
• Set(ByVal Value As String)
• mUserName Value
• lblUserName.Text mUserName
• End Set
• End Property
• End Class

10
Form Visibility

• Make form visible
• fEdit.Visible True
• fMainMenu.Show
• Make form invisiblefMainMenu.Visible False
• Me.Visible False
• Me.Hide

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Form Enabling and Disabling

• Enable form
• fMain.Enabled True
• Disable form
• fMain.Enabled False
• Me.Enabled False

12
Form Events

• Form1_Load() - occurs before a form is displayed
  for the first time.
• Form1_Activated() -- ... Occurs form becomes the
  active window through code or by user
• Form1_Deactivate() - ... occurs when the form
  loses focus and is not the active form