Programming Interface Controls

1. Programming Interface Controls ISYS 350

2. 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

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

4. 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.

5. 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…

6. 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

7. 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.

8. 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; } }

9. 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.

10. 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)

11. 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);

12. Group Box • It is a container control. • Controls in a Group Box should move with the box.

13. 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

14. 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"); }

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

16. 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) { if (expression) { statements; } else { statements; } } else { statements }

17. 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); } else { if (units <= 9) tuition = 1500; else tuition = 1500 + 400 * (units - 9); } }

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

19. 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

20. 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.

21. 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); } }

22. 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 • SelectedIndex • Methods • Add • Clear • Event: SelectedIndexChange

23. 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

24. 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()); }

25. 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.

26. Create a Loan Payment Form

27. 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

28. Generic Format of switch Statement • 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 swtich (testExpression) { case value_1: statements; break; case value_2: statements; break; … case value_n: statements; break; default: statements; break; }

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

30. 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;

31. 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(); }

32. 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; }

33. Switch section’s ends with a break statementExample: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"); break; default: MessageBox.Show("between 6 and 9"); break; }

34. 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?

35. Timer • Properties: • Enabled -- must set to True. • Interval • Tick Event private void timer1_Tick(object sender, EventArgs e) { textBox1.Text = System.DateTime.Now.ToString(); }

36. 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(); } }

37. Close a form after 10 seconds:Set interval to 1000 int counter = 0; private void timer1_Tick(object sender, EventArgs e) { label2.Text= System.DateTime.Now.ToString(); ++counter; if (counter > 10) this.Close(); }