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. Event Procedure

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. 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

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 (1/1440 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.

Input Validation Example: Value entered in a textbox must be at least 50 Private Sub TextBox1_Validating(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles TextBox1.Validating If TextBox1.Text < 50 Then MessageBox.Show("Value must be at least 50.") e.Cancel = True End If End Sub

TextBox Validating Event: Using 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") 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 1 Private 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 2 Dim 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.

Lab: Create a form to compute tuition Two textboxes to enter name and total units. A group of two radiobuttons to choose resident or non- resident A checkbox to indicate Law School A textbox to display tuition A button to compute tuition: –State residents: Total units taken <=12, tuition = 1200 Total units taken > 12, tuition = per additional unit. –Non residents: Total units taken <= 9, tuition = 3000 Total units taken > 9, tuition = per additional unit. –All Law School students will pay $1000 special fee.

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 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_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

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 –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 = 0 Private 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

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 property Note 2: Late binding