VB.NET User Interface Controls

VB User Interface Objects• Form• InputBox, MessageBox• Standard Controls:

– TextBox, MaskedTextBox, List Box, Option Button, Check Box, CheckedListBox, Command Button, GroupBox, etc.

• Menu:– MenuStrip, ContextMenuStrip– ToolStrip

• ToolStripContainer– ToolTip

• Others:– Containers– Components– Dialogs

Form• Form is defined as a class. • Methods:

– Show, ShowDialog: Open a form

– Activate, Focus: Make an opened form get focus

– Hide, Close

– Ex.• Me.Hide, Me.Close

Note: Closing a form is equivalent to delete a form.• Events:

– Load, Activated, DeActivate, Closing, Closed

Multiple FormsTwo forms: Form1, Form2To Open Form2 from Form1:

Standard but troublesome way to open a form: Must create an instance of the form class by using the keyword New to access the form.

Dim f2 As New Form2()

f2.Show()

Open Form2 as a Modal form:

f2.ShowDialog()

.

• Modeless form: Other forms can receive input focus while this form remains active.– FormName.Show()

• Modal form: No other form can receive focus while this form remains active.– FormName.ShowDialog()

• Demo: Problem with the Show method

Using the Default Instances of Forms to Open a Form

• formName.Show, formName.ShowDialog

• Always bring up the same underlying default instance of the form.– Example: Form2.ShowDialog

MessageBoxMessageBox.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. Possible values for a DialogResult data type are: Abort, Cancel, Ignore, No, None, OK, ReTry, and Yes. To test the return value:

Dim ReturnVal as DialogResult

ReturnVal=MessageBox(“hello”, …..)

If ReturnVal=DialogResult.OK…

Form Closing Event Example

Private Sub Form10_FormClosing(ByVal sender As Object, ByVal e As System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing If MessageBox.Show("Are you sure?", "Warning", MessageBoxButtons.YesNo) = DialogResult.Yes Then e.Cancel = False Else e.Cancel = True End If End Sub

Note: Event procedure arguments: sender: object that triggers the event.e: event object

InputBoxInputBox(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 (1/1440 th 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

Note: vbNullString is a VB constant representing null value. All VB constants are listed in Constants collection.

Text Box

• Useful properties– BackColor, BorderStyle– ReadOnly– Enable– Visible– Password Character– Multiline– ScrollBar– Text

• Useful events– TextChanged: default event– Validating

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

• Texts are checked to ensure correct format.– Phone #, SSN.

• Required field• Textbox:

– Set CauseValidation property to true.– Use the Validating event:

• Triggered just before the focus shifts to other control.

TextBox Validating Event IsNumeric function

Private Sub TextBox1_Validating(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles TextBox1.Validating

If Not IsNumeric(TextBox1.Text) Then

e.Cancel = True

MessageBox.Show("enter digits only")

Else

MessageBox.Show("good")

End If

End Sub

Note: Why not use the TextChanged event?

MaskedTextBox

• To select a mask:– Click the smartTag and choose Set Mask, or– Use the mask property to choose a mask.

• Custom mask:– Search Help– Example:

• (???)-###

String Methods

• ToUpper, ToLower• Length – Number of characters• TrimStart, TrimEnd, Trim• Substring(Start), Substring(Start, length)• IndexOf(SearchString), IndexOf(SearchString, Start)

– 0 based index– Case-sensitive

• eName=“David”• Position=eName.IndexOf(“d”)

– Return –1 if the searchString is not found.

• Note: Text property of a Textbox has all the string methods.– Ex. TextBox1.Text.Substring(0,2)

Example: Extract the firstname and the lastname from a fullname • Dim indexSpace As Integer• Dim firstName, lastName As String• indexSpace = TextBox1.Text.IndexOf(" ")• firstName = TextBox1.Text.Substring(0, indexSpace)

• lastName = TextBox1.Text.Substring(indexSpace + 1)

• MessageBox.Show(firstName)• MessageBox.Show(lastName)

Validate SSN Format (Or Use MaskedTextbox)Private Sub TextBox1_Validating(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles TextBox1.Validating

Dim correct As Boolean = True

If Not IsNumeric(TextBox1.Text.Substring(0, 3)) Or _

Not IsNumeric(TextBox1.Text.Substring(4, 2)) Or _

Not IsNumeric(TextBox1.Text.Substring(7, 4)) Then

correct = False

End If

If TextBox1.Text.Substring(3, 1) <> "-" Or TextBox1.Text.Substring(6, 1) <> "-" Then

correct = False

End If

If correct Then

MessageBox.Show("perfect format")

Else

e.Cancel = True

MessageBox.Show("not correct format")

End If

End Sub

Group Box

• It is a container control.

• Controls in a Group Box should move with the box.

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.

• Properties:– Checked: True/False.

• Default button: Set the Checked property to true at the design time.

• Events: – CheckedChanged

RadioButton Example 1

Private Sub RadioButton1_CheckedChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles RadioButton1.CheckedChanged

If RadioButton1.Checked = True Then

MessageBox.Show("Check RadioButton1")

Else

MessageBox.Show("uncheck RadioButton1")

End If

End Sub

RadioButton Example 2

If radioButton1.Checked=true then

textbox1.text=“You select radio button 1”

ElseIf radioButton2.Checked=true then

textbox1.text=“You select radio button 2”

Else

textbox1.text=“You select radio button 3”

End If

Check Box

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

• Checked property and checkedChanged event

Check Box Example 1Private Sub CheckBox1_CheckedChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CheckBox1.CheckedChanged

If CheckBox1.Checked = True Then

MessageBox.Show(“check chk1")

Else

MessageBox.Show("uncheck chk1")

End If

End Sub

Check Box Example 2Dim msg as String

Msg=“You choose “

If checkBox1.checked=true then

msg=msg & “check box 1”

End If

If checkBox2.checked=true then

msg=msg & “check box 2”

End If

If checkBox3.checked=true then

msg=msg & “check box 3”

End If

Note: Cannot put these three conditions in a If …ElseIf block.

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.

• 0-based index– SelectionMode: one or multi selection– SelectedItem(s)– MultiColumn

• Methods– Add– Clear

• Event: SelectedIndexChange

List Box ExamplePrivate 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_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ListBox1.SelectedIndexChanged

TextBox1.Text = ListBox1.SelectedItem

End Sub

List Items Collections• Methods:

– ADD: ListBox1.Items.Add("Apple")

– Item: Retrieve an object from Items• ListBox1.Items.Item(Index) or ListBox1.Items(Index)

• 0-based index

– Insert: ListBox.Items.Insert(Index, item)

– Remove: Delete an object with a position index or key.• ListBox.Items.Remove(Item)

• ListBox.Items.RemoveAt(Index)

– Clear: ListBox.Items.Clear()

– Count: Return the number of objects in a collection.• ListBox.Items.Count

Selected Item’s Value

• Demo:– Select interest rate from a list box:

• 5% -> 0.05

– Dim intRate As Double– Select Case ListBox1.SelectedItem– Case "5% "– intRate = 0.05– Case “6%”– intRate = 0.06– Case “7%”– intRate = 0.07– End Select

CheckedListBox

• ItemCheck event– Private Sub CheckedListBox1_ItemCheck(ByVal sender As Object,

ByVal e As System.Windows.Forms.ItemCheckEventArgs) Handles CheckedListBox1.ItemCheck

– TextBox2.Text = CheckedListBox1.SelectedItem– End Sub

• Multiple selections:– CheckedItems– CheckedIndices– GetItemChecked

Using CheckedIndices and GetItemChecked Properties

Dim i As Integer For Each i In CheckedListBox1.CheckedIndices MessageBox.Show(CheckedListBox1.Items(i)) Next For i = 0 To CheckedListBox1.Items.Count - 1 If CheckedListBox1.GetItemChecked(i) = True Then MessageBox.Show(CheckedListBox1.Items(i)) End If Next

ComboBox• Allows the user to type text directly into the

combo box.• Use the Text property to get entered item:

– ComboBox1.Text– The index for an entered item is –1.– SelectedItem may be different from the Text property.

• Search an item in the list: ComboBox1.Items.IndexOf(“search text”)– Found: return the index of the search text.– Not found: return –1.

• How to add an entered item to the list?

Timer

• Timer– Properties:

• Enabled -- must set to True.• Interval

– Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick

label1.Text = System.DateTime.Now.ToString End Sub

Use a Timer to Close a Form

Dim counter As Integer = 0Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick counter = counter + 1 If counter > 100 Then Me.Close() End If End Sub

Structured Error HandlingTry

result = Val(TextBox1.Text) / Val(TextBox2.Text)

TextBox3.Text = result.ToString

Catch except As DivideByZeroException

MessageBox.Show(except.Message)

Catch except As Exception

MessageBox.Show(except.Message)

Finally

MessageBox.Show("I get exdecuted, no matter what")

End Try

MenuStrip Control

– Add MenuStrip control and follow the TypeHere instruction.

– Each submenu and each item on a submenu is represented by a MenuItem control.

– Write an event procedure for each menu item.

Using One Event Procedure to Handle Many Events

Private Sub BtnClick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click, Button2.Click, Button3.Click If sender.name = "Button1" Then MessageBox.Show("btn 1") ElseIf sender.name = "Button2" Then MessageBox.Show("Btn2") Else MessageBox.Show("btn3") End If End Sub

Note 1: Controls’ Tag propertyNote 2: Late binding