Programming Interface Controls ISYS 350

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

Working with Form To close a form: Events: this.Close(); Load, Activated, DeActivate, Closing, Closed

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; Note: sender – object that triggers the event; e – event argument that provides actions to handle the event.

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…

Text Box Useful properties Useful events 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.

Data Entered in Textbox1 Must Be between 10 and 30 private void textBox1_Validating(object sender, CancelEventArgs e) { double enteredData; enteredData = double.Parse(textBox1.Text); if (enteredData<10 || enteredData>30) MessageBox.Show("Pls enter a number between 10 and 30"); e.Cancel=true; }

Testing for digits only 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"); Note: VB has an IsNumeric function and Excel has an ISNumber function.

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)

Extract First Name and Last Name from Full Name in this format: FirstName LastName 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);

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

Example private void button1_Click(object sender, EventArgs e) { if (radioButton1.Checked) MessageBox.Show("Button 1 checked"); else if (radioButton2.Checked) MessageBox.Show("Button 2 checked"); else MessageBox.Show("Button 3 checked"); }

Tuition Rules For undergraduate: If total units <= 12, then tuition = 1200; Otherwise, tuition = 1200 + 200 per additional unit For graduate: If total units <= 9, then tuition = 1500; Otherwise, tuition = 1500 + 400 per additional unit

Nested Decision Structures You can create nested decision structures to test more than one condition. Nested means “one inside another” In C#, a generic format is: if (expression) { statements; } else statements

private void button1_Click(object sender, EventArgs e) { double units, tuition; units=double.Parse(textBox1.Text); if (radioButton1.Checked) if (units <= 12) tuition = 1200; else tuition = 1200 + 200 * (units - 12); } if (units <= 9) tuition = 1500; tuition = 1500 + 400 * (units - 9);

Check Box Check boxes do not belong to a group even when they are grouped in a Group Box. Checked property and checkedChanged event

Which CheckBoxes are cheked? private void button1_Click(object sender, EventArgs e) { string box=""; if (checkBox1.Checked) box += "box1"; if (checkBox2.Checked) box += "box2"; if (checkBox3.Checked) box += "box3"; MessageBox.Show(box); } Note: Cannot use if-else-if

Rules for Discount If total sales is greater than 1000, then the customer will get a 10% discount ; otherwise, the customer will get a 5% discount. If the customer is a club member, then applies 20% off the discounted charges.

private void button1_Click(object sender, EventArgs e) { try double totalSales, discountRate, netPay; string myMsg; totalSales = double.Parse(textBox1.Text); if (totalSales <= 1000) discountRate = .05; else discountRate = .1; netPay = totalSales * (1 - discountRate); if (checkBox1.Checked) netPay = netPay * (1 - .20); textBox2.Text = netPay.ToString("C"); } catch (Exception ex) MessageBox.Show(ex.Message);

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 SelectedIndex Methods Add Clear Event: SelectedIndexChange

ListBox 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

Adding Items Using Code private void Form11_Load(object sender, EventArgs e) { listBox1.Items.Add("Apple"); listBox1.Items.Add("Orange"); listBox1.Items.Add("Banana"); listBox1.Items.Add("Strawberry"); listBox1.Items.Add("Kiwi"); } private void listBox1_SelectedIndexChanged(object sender, EventArgs e) MessageBox.Show(listBox1.SelectedItem.ToString()); MessageBox.Show(listBox1.SelectedIndex.ToString());

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.

Create a Loan Payment Form

The switch Statement The switch statement lets the value of a variable or an expression determine which path of execution the program will take It is a multiple-alternative decision structure It can be used as an alternative to an if-else-if statement that tests the same variable or expression for several different values

Generic Format of switch Statement swtich (testExpression) { case value_1: statements; break; case value_2: … case value_n: default: } The testExpression is a variable or an expression that given an integer, string, or bool value. Yet, it cannot be a floating-point or decimal value. Each case is an individual subsection containing one or more statements, followed by a break statement The default section is optional and is designed for a situation that the testExpression will not match with any of the case

Sample switch Statement switch (month) { case 1: MessageBox.Show(“January”); break; case 2: MessageBox.Show(“February”); case 3: MessageBox.Show(“March”); default: MessageBox.Show(“Error: Invalid month”); } month Display “January” Display “February” Display “March” Display “Error: Invalid month”

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; case 2: rate = .07; case 3: rate = .08; case 4: rate = .09; default: rate = 0.05; 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 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;

Switch section’s ends with a break statement Example:Enter a digit and test its value int myInt = int.Parse(textBox1.Text); switch (myInt) { case 0: case 1: case 2: MessageBox.Show(" 0,1, or 2"); break; case 3: case 4: case 5: MessageBox.Show(" 3,4, or 5"); default: MessageBox.Show("between 6 and 9"); }

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?

Timer Tick Event 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(); }