VB User Interface Objects

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VB User Interface Objects
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VB User Interface Objects

• Form
• Menu
• DropDown menu, ToolTip
• InputBox, MsgBox, MessageBox
• Standard Controls
• Text Box, List Box, Option Button, Check Box,
  Command Button, GroupBox, etc.

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Form

• Methods
• Me.show(), Me.Hide, Me.Close
• Events
• Load, Activated, Closing, Closed
• Modeless form Other forms can receive input
  focus while this form remains active.
• Modal form No other form can receive focus while
  this form remains active.
• Formname.ShowDialog()

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Multiple Forms
Two forms Form1, Form2 To Open Form2 from
Form1 Dim f2 As New Form2()
f2.Show() Open Form2 as a Modal
form f2.ShowDialog() Note Form is defined as
a class. Must create an instance of the form
class by using the keyword New to access the form.
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SharingVariables Among Forms

• Define these variables with class-level scope
  using the Public keyword.
• Must use formName to qualify variables.
• Dim f2 As New Form2()
• TextBox1.Text f2.g2 g2 is declared in
  form2

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Variables Shared by Multiple Forms

• Define these variables with project-level scope
  in a module using the Public keyword
• Module Module1
• Public testVar As Integer
• End Module
• Note Use Project/Add Windows form to add a
  module.

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MsgBox

• MsgBox(prompt, other arguments)
• MsgBox can return a value representing the users
  choice of buttons displayed by the box. The
  return value has MsgBoxResult data type
• Dim RETurnVal As MsgBoxResult
• RETuranVal MsgBox("customer click cancel",
  MsgBoxStyle.AbortRetryIgnore)
• If RETurnVal MsgBoxResult.Abort Then
• MsgBox("YOU CLICK ABORT")
• End If

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MessageBox
MessageBox.Show(message) MessageBox.Show(message,
Caption) MessageBox.Show(message, Caption,
Buttons) Note 1. In each format, arguments are
positional and required. 2. This object returns a
DialogResult data type. To test the return
value Dim ReturnVal as DialogResult ReturnValM
essageBox(hello, ..) If ReturnValDialogResult
.OK
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InputBox
InputBox(Prompt ,Title , Default , Xpos ,
Ypos) Xpos is the distance from the left edge of
the screen, and Ypos is the distance from the top
of the screen. Both are measured in twips
(1/1440th of an inch). Note The arguments are
positional and optional. Enter a comma to skip
an argument. cityName InputBox("Please enter
city name, , SF) If cityName vbNullString
Then MessageBox.Show ("customer click
cancel") Else Text1.Text cityName End If
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Text Box

• Useful properties
• Locked read only
• Password Character
• Multiline
• ScrollBar
• Text
• Useful events
• TextChanged
• Validating

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Input Validation

• Numbers are checked to ensure they are
• Within a range of possible values
• Reasonableness
• Not causing problems such as division by 0.
• Containing only digits
• IsNumeric
• Textbox
• Set CauseValidation property to true.
• Use the Validating event
• Triggered just before the focus shifts to other
  control.

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TextBox Validating Event
Private Sub TextBox1_Validating(ByVal sender As
Object, ByVal e As System.ComponentModel.CancelEve
ntArgs) Handles TextBox1.Validating If
Not IsNumeric(TextBox1.Text) Then
e.Cancel True MsgBox("enter digits
only") Else MsgBox("good")
End If End Sub
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Group Box and Panel

• Controls in a Group Box should move with the
  boxs.
• A panel control can display scrollbars by setting
  the AutoScroll property to true.

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Radio Button

• Radio buttons must be grouped together inside a
  container such as a GroupBox or a form.
• When the user selects an option all other options
  in the same group are deselected.
• Checked property value True/False.
• Default button Set the Checked property to true
  at the design time.

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RadioButton Example 1
Private Sub RadioButton1_CheckedChanged(ByVal
sender As System.Object, ByVal e As
System.EventArgs) Handles RadioButton1.CheckedChan
ged If RadioButton1.Checked True Then
MsgBox("Check RadioButton1")
Else MsgBox("uncheck RadioButton1")
End If End Sub
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RadioButton Example 2
If radioButton1.Checkedtrue then textbox1.text
You select radio button 1 ElseIf
radioButton2.Checkedtrue then textbox1.textYou
select radio button 2 Else textbox1.textYou
select radio button 3 End If
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Check Box

• Check boxes do not belong to a group even when
  they are grouped in a Group Box.
• Checked property and checkedChangedevent

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Check Box Example 1
Private Sub CheckBox1_CheckedChanged(ByVal sender
As System.Object, ByVal e As System.EventArgs)
Handles CheckBox1.CheckedChanged If
CheckBox1.Checked True Then
MsgBox(check chk1") Else
MsgBox("uncheck chk1") End If End Sub
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Check Box Example 2
Dim msg as String MsgYou choose If
checkBox1.checkedtrue then msgmsg check box
1 End If If checkBox2.checkedtrue then msgmsg
check box 2 End If If checkBox3.checkedtrue
then msgmsg check box 3 End If
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List Box

• Useful properties
• Items The items in the listBox. It is a
  collection strcture. Items can be entered at the
  design time or entered in code.
• SelectionMode one or multi selection
• SelectedItem(s)
• Methods
• Add
• Clear
• Event SelectedIndexChange

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List Box Example
Private Sub Form1_Load(ByVal sender As Object,
ByVal e As System.EventArgs) Handles MyBase.Load
TextBox1.Clear() TextBox2.Clear()
ListBox1.Items.Clear()
ListBox1.Items.Add("Apple")
ListBox1.Items.Add("Orange")
ListBox1.Items.Add("Banana")
ListBox1.Items.Add("Strawberry")
TextBox2.Text ListBox1.Items.Count.ToString
End Sub Private Sub ListBox1_SelectedIndexCha
nged(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles ListBox1.SelectedIndexCh
anged TextBox1.Text ListBox1.SelectedIte
m End Sub
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ListBox Multiple Selections
Note The SelectionMode property must set to
multi selection. extBox2.Text
ListBox1.SelectedItems.Count.ToString Dim allSel
As String Dim i As Integer For i 0 To
ListBox1.SelectedItems.Count - 1 allSel
allSel ListBox1.SelectedItems.Item(i) Next
I Or use the For Each loop Dim item As
String For Each item In ListBox1.SelectedItems
allSel allSel item Next TextBox3.Text
allSel
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CheckedListBox

• ItemCheck event
• Private Sub CheckedListBox1_ItemCheck(ByVal
  sender As Object, ByVal e As System.Windows.Forms.
  ItemCheckEventArgs) Handles CheckedListBox1.ItemCh
  eck
• TextBox2.Text CheckedListBox1.SelectedIt
  em
• End Sub

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ToolTip
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Status Bar Timer

• Status Bar
• Panels
• Set ShowPanel property to true.
• StatusBar1.ShowPanels True
• StatusBarPanel1.Text System.DateTime.Now.ToStrin
  g
• Timer
• Private Sub Timer1_Tick(ByVal sender As
  System.Object, ByVal e As System.EventArgs)
  Handles Timer1.Tick StatusBarPanel1.Text
  System.DateTime.Now.ToString
• End Sub

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ImageList

• Manage a group of images. It is a repository of
  images that your program can use for various
  purposes.
• Use the Images property to create list.
• Controls with the ImageList and ImageIndex
  proerties , such as Button and Label, can use the
  images in the list.

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Arrays

• Declaring arrays
• Dim arrayName(upperBound) As dataType
• Ex. Dim myArray(5) as Integer
• This array has 6 elements starting from 0.
• Dynamic arrays
• Ability to change the size of an array at run
  time.
• Use dynamic arrays when the size is unknown at
  design time, or it varies from one time to
  another.

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Declaring Dynamic Arrays

• Declare the array without specifying upper bounds
  in the Dim statement.
• Later, when the program needs a certain number of
  elements in the array, use the ReDim statement to
  assign the array size.
• Each time a ReDim is executed, the values
  currently stored in the array are lost. To keep
  those data, use the Preserve keyword.
• Ex. ReDim Preserve arrayName(NewUpperbound)

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Dynamic Array Example
Dim StudentAge() . ReDim StudentAge(TotalStudents
)
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Control Arrays
Dim ctrlArray(1) As Button Private Sub
Form1_Load(ByVal sender As System.Object, ByVal e
As System.EventArgs) Handles MyBase.Load
ctrlArray(0) Button1 ctrlArray(1) Button2
TextBox1.Text ctrlArray(0).Text End
Sub
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Unstructured Error Handling

• On Error GoTo errorhandler (a label)
• Built-in Err object properties
• Number Error number
• Source Name of VB ile in which error occurred
• Description error message
• Continue the program execution
• Resume returns execution to the statement that
  caused the error.
• Resume Next
• Resume label Jumps to the line containing the
  label.
• Exit Sub
• Debug Debug.Print varName

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Error Handling Example
Private Sub cmdDivide_Click() On Error GoTo
DivideErrorHandler lalAnswer.CaptionCStr(CDbl(Tex
t1.text)/CDbl(Text2.Text)) Exit
Sub DivideErrorHandler MsgBox(CStr(Err.Number)
Err.Description) Exit Sub End Sub
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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
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Collections

• Collections are used to store lists of objects.
• More flexible than array
• No need to declare the number of objects in a
  collection, no need to ReDim.
• Objects can be added, deleted at any position.
• Object can be retrieved from a collection by a
  key.
• A collections name usually end with a s.

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Using Collections

• Define a collection
• Ex. Dim Pets as New Collection
• Methods
• ADD Add object to a collection
• Pets.Add(dog)
• Add an object with a key
• Pets.Add(Dog, D)
• Item Retrieve an object from a collection with a
  position index (base 1) or with a key.
• petName Pets.Item(1)
• petName Pets.Item(D)
• Count Return the number of objects in a
  collection.
• Remove Delete an object with a position index or
  key.

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Iterating Through a Collection
Dim Pets as New Collection Dim Indx as Long For
Indx 1 to Pets.Count operations Next
Indx For Each pet in Pets operations Next pet
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Enumerations

• Provide a way to associate meaningful names with
  a sequence of constant values.
• Define an enumeration using an Enum statement.
• Private Enum seasonOfYear
• Spring 1
• Summer 2
• Fall 3
• Winter 4
• End Enum
• Dim Sales(Spring to Winter) as Double

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Enumerations

• Provide a way to associate meaningful names with
  a sequence of constant values.

Enum enumTest spring 1 summer
fall winter End Enum Dim etest
As enumTest Private Sub Form1_Load(ByVal sender
As System.Object, ByVal e As System.EventArgs)
Handles MyBase.Load etest enumTest.summer
TextBox1.Text Val(etest).ToString
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More about Form

• A form must be instantiated in a variable
• Dim F1 as New Form1()
• Useful methods
• Show Loads and display a modeless form.
• Activate set focus to the form.
• BringToFront
• Hide
• ShowDialog
• Close Unloads the form (the forms instance
  variable no longer exists)

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Declare Forms Instance Variable in An Open Form
Event Procedure
Private Sub Button1_Click(ByVal sender As
System.Object, ByVal e As System.EventArgs)
Handles Button1.Click Dim f2 As New
Form2() f2.Show() End Sub Problem
This will create a new instance of the form every
time the button is clicked.
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Declare Forms Instance Variable in a Module as
Public Variable
Module Module1 Public f1 As New Form1()
Public f2 As New Form2() End Module It can be
accessed in a procedure Private Sub
Button1_Click(ByVal sender As System.Object,
ByVal e As System.EventArgs) Handles
Button1.Click f2.Show() End
Sub Problem Once the form is closed the
variable is no longer exists. Attempt to access
it again will trigger error.
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Close Form Or Hide Form
Use a forms Closing event to change Close to
Hide Private Sub Form2_Closing(ByVal sender As
Object, ByVal e As System.ComponentModel.CancelEve
ntArgs) Handles MyBase.Closing e.Cancel()
True Me.Hide() End Sub
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Main Menu Control

• Add MainMenu control and follow the TypeHere
  instruction.
• Each submenu and each item on a submenu is
  represented by a MenuItem control.
• Use an to specify an access key in the caption.
  Ex. File, Shos
• Write an event procedure for each menu item.

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Context Menu

• A context menu is a menu that displays when an
  object on the screen is right-clicked.
• Add the ContextMenu control (it is placed in a
  tray under the form). Right-click the control
  and choose Edit to create the menu.
• Use the objects ContextMenu property to bind the
  object to the context menu.