3.2 VB.NET Events

1. 3.2 VB.NET Events • An Event Procedure • Properties and Event Procedures of the Form • Tab Order of Controls • Exercises

2. An Event Procedure • An event is an action, such as the user clicking on a button • Usually, nothing happens until the user does something and generates an event Demo – Sales Order app with no code

3. The three steps in creating a VB.NET program: • Create the interface; that is, generate, position, and size the objects. • Set properties; that is, configure the appearance of the objects. • Write the code that executes when events occur.

4. Changing Properties • Properties can be changed in code with the following: controlName.property = setting • This is an assignment statement txtBox.ForeColor = Color.Red Note: Right side is always assigned to left side Demo: blank sol’n

5. Object Properties • Some are values, some are string, some are boolean (true or false) • Strings always go in quotes!txtBox.text = “Enter a phrase” • Boolean and values do not have quotes

6. Control Name Prefixes Note: Can be named anything but this is a convention Ensure your naming is intuitive!

7. Most Common Errors • Misspelling the name of a control in code • VB editor will help you! • Renaming controls does not update in the body of an event procedure

8. Event Procedures Private SubobjectName_event(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles objectName.event Shown in the book as: Private SubobjectName_event(…) HandlesobjectName.event Each object has default event procedure – double click it you are unsure – try a label, textbox, button and listbox

9. Structure of an Event Procedure Private Sub objectName_event(...) Handles objectName.event statements End Sub Sometimes there are multiple actions that can trigger an event – e.g. Textbox.enter event

10. Program Region

11. IntelliSense Automatically pops up to give the programmer help. Demo: wrong spelling for a control

12. Code for Walkthrough Private Sub txtFirst_TextChanged(...) Handles txtFirst.TextChanged txtFirst.ForeColor = Color.Blue End Sub Private Sub btnRed_Click(...) Handles btnRed.Click txtFirst.ForeColor = Color.Red End Sub Private Sub txtFirst_Leave(...) Handles txtFirst.Leave txtFirst.ForeColor = Color.Black End Sub

13. Event Demo Private Sub txtBox_MouseHover …. txtBox.BackColor = Color.AliceBlue End Sub Private Sub txtBox_MouseLeave …. txtBox.BackColor = Color.White End Sub

14. Running Code • From menu – Debug – Run • Or F5 • Be careful – code is automatically saved when run

15. Assigning properties in code • The following won't work: Form1.Text = "Demonstration" • The form is referred to by the keyword Me. Me.Text = "Demonstration"

16. The Declaration Statement of an Event Procedure • A declaration statement for an event procedure: Private Sub btnOne_Click(...) Handles btnOne.Click • The name can be changed at will. For example Private Sub ButtonPushed(...) Handles btnOne.Click • Handling more than one event: Private Sub ButtonPushed(...) Handles btnOne.Click, btnTwo.Click

17. Tab Order of Controls • Determines which control gets the focus when you hit the Tab key • Order is initially established by the order controls are placed on the form • Controlled by tabindex property • Demo with Sales Order form

18. Exercises p. 69 to 74 Do #37 together & #38 aloneHomework - #46 – page 74 Solutions to odd numbers are in the back of text book – try some on your own!