Programming Interface Controls with VB.Net

User Interface Controls• Form• MessageBox• Common Controls:

– Button, TextBox, MaskedTextBox, List Box, Option Button, Check Box, CheckedListBox, numericUpDown

• Container controls:– GroupBox, etc.

• Others:– Timer– ToolTip– Components

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

Control StartUp Form

• Click:– Project/Properties/Application/StartUp Form– Then select the form

SharingVariables Among 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 Module to add a module.

Modules

• A file contains code such as:– Variable declarations– Procedures and functions

• Variables and procedures used by more than one form should store in a module.

• Global variables: Public

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

Text Box

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

• Useful events– TextChanged: default event– Validating – useful for validating data entered in the box

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 EventPrivate 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

MessagBox.Show("enter digits only")

Else

MessageBox.Show("good")

End If

End Sub

Note: Why not use the TextChanged event?

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 FormatPrivate 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

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

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

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

Programming Interface Controls with C#

Working with Form

• To close a form:– this.Close();

• To choose the startup form:Change the code in Program.cs– Example, to start from form2 instead of form1,

use this code:• Application.Run(new Form2());

Form Closing Eventprivate void Form2_FormClosing(object sender, FormClosingEventArgs e) { if (MessageBox.Show("Are you sure?", "Warning", MessageBoxButtons.YesNo) == DialogResult.Yes) { e.Cancel = false; } else { e.Cancel = true; } }

TextBox Validating EventExample: Testing for digits only

There is no equivalent IsNumeric function in C#. This example uses the Double.Parse method trying to convert the data entered in the box to double. If fail then it is not numeric.

private void textBox1_Validating(object sender, CancelEventArgs e) { try { Double.Parse(textBox1.Text); e.Cancel = false; } catch { e.Cancel = true; MessageBox.Show("Enter digits only"); } }

Extract First Name and Last Name

int indexSpace;string firstName, lastName ;indexSpace = textBox2.Text.IndexOf(" ");firstName = textBox2.Text.Substring(0, indexSpace);lastName = textBox2.Text.Substring(indexSpace + 1);MessageBox.Show(firstName);MessageBox.Show(lastName);

Creating a Boolean MyIsNumeric Function

private Boolean MyIsNumeric(string s) { try { Double.Parse(s); return true; } catch { return false; } }

Using MyIsNumeric Function to Vaidate SSN Format

private void button3_Click(object sender, EventArgs e){ bool correct = true; if (! MyIsNumeric(textBox2.Text.Substring(0, 3)) || ! MyIsNumeric(textBox2.Text.Substring(4, 2)) || ! MyIsNumeric(textBox2.Text.Substring(7, 4)) ) { correct = false; } if (textBox2.Text.Substring(3, 1) != "-" || textBox2.Text.Substring(6, 1) != "-" ) { correct = false; } if (correct) { MessageBox.Show("perfect format"); } else { MessageBox.Show("not correct format"); }}

Working with Radiobuttons, Listbox• Create a form with 2 radiobuttons. When radiobutton1

is selected, populate a listbox with fruit names.; otherwise populate the listbox with vegetable names. Then, dsplay the fruit or vegetable’s name in a textbox when user select an item from the listbox.

private void radioButton1_CheckedChanged(object sender, EventArgs e) { if (radioButton1.Checked) { listBox1.Items.Clear(); listBox1.Items.Add("Apple"); listBox1.Items.Add("Orange"); listBox1.Items.Add("Banana"); listBox1.Items.Add("Strawberry"); listBox1.Items.Add("Papaya"); } if (radioButton2.Checked) { listBox1.Items.Clear(); listBox1.Items.Add("Spinach"); listBox1.Items.Add("Brocoli"); listBox1.Items.Add("Tomato"); listBox1.Items.Add("Lettuce"); listBox1.Items.Add("Cabbage"); } }

private void listBox1_SelectedIndexChanged(object sender, EventArgs e) { textBox1.Text = listBox1.SelectedItem.ToString(); }

Create a Loan Payment Form

Using VB.Net’s PMT Function

• Add a reference to Microsoft Visual Baisc– From the Solution Explorer, right-click the

References node, then click Add Reference– From the .Net tab, select Microsoft Visual

Baisc– Add this code to the form:

• using Microsoft.VisualBasic;

private void button1_Click(object sender, EventArgs e) { double loan, term, rate, payment; loan = Double.Parse(textBox1.Text); if (radioButton1.Checked) { term = 15; } else { term = 30; } switch (listBox1.SelectedIndex) { case 0: rate=.05; break; case 1: rate=.06; break; case 2: rate = .07; break; case 3: rate = .08; break; case 4: rate = .09; break; default: rate = 0.05; break; } payment = Financial.Pmt(rate / 12, term * 12, -loan); textBox2.Text = payment.ToString(); }

How to Use VB’s IsNumeric Function

• Add a reference to Microsoft VisualBasic Compatibility namespace.

• Then, add this code to the form:– using Microsoft.VisualBasic;

• Microsoft.VisualBasic.Information class contains the IsNumeric function

if (! Information.IsNumeric(textBox1.Text)) { e.Cancel = true; MessageBox.Show("Enter digits only"); } else { e.Cancel=false; }

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.

• 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?

ToolTip

• Add ToolTip to form.

• Use controls’ ToolTipOn property to enter tip.

Timer• Properties:

• Enabled -- must set to True.• Interval

• Tick Event

private void timer1_Tick(object sender, EventArgs e) { textBox1.Text = System.DateTime.Now.ToString(); }

Use a Timer to Close a Form

int counter = 0; private void timer1_Tick(object sender, EventArgs e) { if (counter > 50) { this.Close(); } }

Using One Event Procedure to Handle Many Events

private void buttonClick(object sender, EventArgs e) { if (sender.ToString().Contains("0")) { Phone = Phone + "0"; } else if (sender.ToString().Contains("1")) { Phone = Phone + "1"; } else { Phone = Phone + "2"; } textBox1.Text = Phone; }