Programming Interface Controls with VB.Net

User Interface Controls Form MessageBox, InputBox 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 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().

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

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 Dim counter = 0, sum = 0, myInt As Integer myInt = InputBox("Enter an integer") Do While counter <= myInt sum = sum + counter counter += 1 Loop MessageBox.Show("The sum is: " + sum.ToString)

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 Event 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 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)

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 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.

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

Structured Error Handling Dim result As Double Try result = CDbl(TextBox1.Text) / CDbl(TextBox2.Text) TextBox3.Text = result.ToString Catch except As Exception MessageBox.Show(except.Message) 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 property Note 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 Event private 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; }

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()

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. Form2 f2 = new Form2 (); Open Form2 as a Modeless form: f2.Show (); Open Form2 as a Modal form: f2.ShowDialog(); Demo: Problem with the Show method.

Interactive Input using VB’s InputBox Statement Add a reference to Microsoft Visual Baisc: 1. From the Solution Explorer, right-click the References node, then click Add Reference 2. From the.Net tab, select Microsoft Visual Baisc 3. Add this code to the form: using Microsoft.VisualBasic; int myint; myint= int.Parse(Interaction.InputBox("enter a number:")); MessageBox.Show(myint.ToString()); Example of using InputBox :

Accumulator Find the sum of all numbers between 1 and N. int N, Sum, Counter = 1; N = int.Parse(Interaction.InputBox("enter an integer:")); Sum = 0; while (Counter <= N) { Sum += Counter; ++Counter; } MessageBox.Show(Sum.ToString()); Method 1:

TextBox Validating Event Example: 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 the MyIsNumeric Function private void textBox1_Validating(object sender, CancelEventArgs e) { if (!MyIsNumeric(textBox1.Text)) { MessageBox.Show("Enter digit only"); e.Cancel=true; }

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) { counter+=1; 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; }