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 Forms Two forms: Form1, Form2 To 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() .

Demo: Problem with the Show method 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

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 (1/1440th 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 Note: vbNullString is a VB constant representing null value. All VB constants are listed in Constants collection.

Text Box Useful properties Useful events 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: Custom 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 If correct Then MessageBox.Show("perfect format") Else e.Cancel = True MessageBox.Show("not correct format") 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” If checkBox3.checked=true then msg=msg & “check box 3” Note: Cannot put these three conditions in a If …ElseIf block.

List Box Useful properties Methods Event: SelectedIndexChange 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

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 Multiple selections: CheckedItems 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 End If

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 = 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

Structured Error Handling Try result = Val(TextBox1.Text) / Val(TextBox2.Text) TextBox3.Text = result.ToString Catch except As DivideByZeroException MessageBox.Show(except.Message) Catch except As Exception 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 property Note 2: Late binding