VB'NET Controls

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VB.NET Controls

• ITE 285

2
Topics

• Introduction to controls
• Control properties
• Control events
• Some common controls
• More controls

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Introduction to Controls

• Visual objects that are placed on a form to
  enable customized activities
• Built-in controls defined in Windows Form class
  library, and are defined
• with ToolBox and Form Designer
• or strictly with code
• Build your own controls (ITE 370)
• Windows Control Library project
• Add a control with Add Reference

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Categories of Controls w/Prefixes

• Text edit (TextBoxtxt___)
• Text display (Labeldefault name or lbl___)
• Selection from a list (ListBoxlst___,
  ComboBoxcbo___, )
• Graphic display (PictureBox)
• Graphic storage (ImageList)
• Value setting (CheckBoxchk___, CheckListBox,
  RadioButton,)
• Date setting (DateTimePicker, MonthCalendar)
• Dialog boxes (OpenFileDialog, PrintDialog)
• Menu controls (MainMenu, )
• Commands (Buttonbtn___, LinkLabel)
• Grouping other controls (GroupBox, TabControl,
  Panel)

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Control Properties

• Many controls share some common properties
• Name, Text
• Size.Height Width, Location.X Y, Dock
• CanFocus, ContainsFocus, Focused
• Visible Enabled determine availability to user
• Font properties affect text display in the
  control
• Font, size, bold, etc.
• Tab Index Tab Stop

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Control Events

• Many controls share a common set of events to
  which they can react
• Click DoubleClick
• MouseMove, MouseDown, MouseUp, MouseWheel,
  MouseHover, MouseLeave
• KeyPress, KeyDown, KeyUp
• Resize
• DragDrop

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Focus and Validation Event Sequence

• Enter
• GotFocus
• Leave
• Validating
• Validated
• LostFocus

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Adding Controls to Forms

• Double Click Control in Toolbox
• Click, Drag and Drop
• Copy and Paste Existing Controls

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Buttons

• Properties
• Text
• Cancel Cancel
• DialogResult
• Produces a click result when used in a modal form
• Ok, Cancel, etc.

• example event procedure
• Private Sub btnBack_Click( _
• ByVal sender As System.Object, _
• ByVal e As System.EventArgs) _ Handles
  btnBack.Click
• Exits this form.
• Me.Close()
• End Sub

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Labels and LinkLabels

• Use labels and link labels for text display
• Text property (no more Caption) defines text to
  display
• User cannot change a label
• LinkLabel enables hyperlinks
• Links.Add inserts a hyperlink into text
• Must write event-handler to invoke browser
• See example

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LinkLabel Example

• linkLabel1.Text "Click here to get more info."
• Create new link using Add method of
  LinkCollection class.
• 1st parameter is the start position of
  hyperlinked text
• 2nd parameter is no. of chars to hyperlink
• 3rd parameter is URL
• linkLabel1.Links.Add(6, 4, "www.microsoft.com")
• Private Sub linkLabel1_LinkClicked(sender As
  Object, _
• e As System.Windows.Forms.LinkLabelLinkClicke
  dEventArgs) _
• Handles LinkLabel1.LinkClicked
• Determine which link was clicked within
  the LinkLabel. linkLabel1.Links(linkLabel1.Links.I
  ndexOf(e.Link)).Visited True
• Display the appropriate link based on the
  value of the LinkData property
• of the Link object. System.Diagnostics.Proc
  ess.Start(e.Link.LinkData.ToString())
• End Sub linkLabel1_LinkClicked

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Text Boxes Text Edit and Display

• Text box allows user to enter or edit data
• Properties
• MaxLength, MultiLine
• AcceptsTab, AcceptsReturn, WordWrap
• ScrollBars

• Properties (cont)
• SelectionStart, SelectionLength, SelectedText
• Events
• TextChanged

Private Sub TextBox1_GotFocus(ByVal sender As
System.Object, _ ByVal e As System.EventArgs)
Handles TextBox1.GotFocus ' Select all
text in the text box TextBox1.SelectionSt
art 0 TextBox1.SelectionLength
TextBox1.Text.Length End Sub
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Text Box Example

• The following example creates a multiline TextBox
  control with vertical
• scroll bars. This example uses the AcceptsTab,
  AcceptsReturn, and
• WordWrap properties to make the multiline text
  box control useful for
• creating text documents.
• ' Create an instance of a TextBox control.
• Dim textBox1 As New TextBox()
• ' Set the Multiline property to true.
• textBox1.Multiline True
• ' Add vertical scroll bars to the TextBox
  control.
• textBox1.ScrollBars ScrollBars.Vertical
• ' Allow the RETURN key to be entered in the
  TextBox control.
• textBox1.AcceptsReturn True
• ' Allow the TAB key to be entered in the TextBox
  control.
• textBox1.AcceptsTab True
• ' Set WordWrap to allow text to wrap to the next
  line.
• textBox1.WordWrap True
• ' Set the default text of the control.
• textBox1.Text "Welcome!

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List Selection Controls

• ComboBox Properties
• Text
• DropDownStyle
• Simple
• Dropdown
• DropdownList
• Sorted
• Run Time Properties
• Items collection
• Methods
• Items.Clear
• .Add
• .Remove

• cboChoice.Items.Clear()
• cboChoice.Items.Add("First")
• cboChoice.Items.Add("Second")
• cboChoice.Items.Add("Third")
• cboChoice.Items.Add(TextBox1.Text)
• cboChoice.Items.Remove("Third")

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List Boxes Items and Selected__

• Items is an indexed collection of items
• in the list txtName.text (lstEmp.Items(2))
• SelectedIndex property is the zero-based number
  of the selected item in the list
• If user clicked the third item SelectedIndex will
  be 2
• Has value of -1 if nothing selected
• These two lines do the same thing
• txtName.text(cboChoice.SelectedItem)
• txtName.text(cboChoice.Items(cboChoice.SelectedInd
  ex))

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CheckBox Control

• CheckState property
• Checked
• Unchecked
• Indeterminate (checked but grayed)
• Checked property
• True or False
• Text property displays built-in caption

If chkMarried.checkState CheckState.checked
then code to execute End if If
chkMarried.checked true then code to
execute End if
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Radio Button

• Checked state
• True or False
• Text Property displays a built-in caption
• Should be contained inside a GroupBox Can
  select one option from available Radio Buttons
• If rdbAdult.checked True then
• code to execute
• Else If rdbChild checked True then
• code to execute
• Else if there is a third option
• code to execut
• End if

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Timer Control

• Executes code after a specified interval
• Timer Event
• Unique event that executes after the interval
  specified in the interval property expires
• Interval Property
• 0 - 65,535 milliseconds
• 0 - means disabled
• 60,000 milliseconds is one minute
• Enabled property must also be true for timer to
  work.
• Timer control is never visible at run time
• Stored in Component Tray at design time

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Best Control???

• Fewest Keystrokes
• Provides Essential Information
• Compensates for Limited Short-Term Memory
• Group Related Controls to Help User Understand
  what is needed
• TextBox is often the WORST Control
• Most Keystrokes
• User Must Remember
• Slow
• Prone to Data Entry Error

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VB.NET Controls

• ITE 285