CS0004: Introduction to Programming

1. CS0004: Introduction to Programming Events

2. Review • Event Procedure • A set of instructions to be executed when a certain event happens. • Many event-driven programs can be divided into three important sections or layers: • Presentation Layer • Anything the user sees and how the user interacts with a program. • Logic Layer • How the program acts when it receives events. • Data Access Layer • Allows simple access to persistent storage (like a database). We probably won’t be doing this in this course.

3. Review • When you run your Visual Basic program the following things happen: • Your program monitors the controls in the window to detect any event that a control can recognize (mouse movements, clicks, keystrokes, etc.) • When your program detects an event, it examines the code to see if you’ve written an even procedure for it. • If you have written an event procedure, the instructions in the procedure are executed and it goes back to step 1. • If you have not written an event procedure, it ignores the event and goes back to step 1.

4. Review • The naming (value of the name property) of controls should indicate what it is and what it does.

5. Events • Now that we have an interface, we can have our controls act on events. • For now, we will just change the properties of controls with our events • The basic form of setting a property of a control: controlName.property = setting • controlName– the name of the control whose property you want to change (ex. txtName) • property– the property you want to change (ex. ForeColor) • setting– value for which you want to set the property

6. Events • Examples: txtBox.Text = “Hello” • Displays “Hello” in the text box btnButton.Visible = True • Makes the button visible txtBox.ForeColor = Color.Red • Makes the text color in the text box red frmMain.Text = “My Form” • Will NOT work in the code for frmMain. You must use the word Me (because the form is referring to itself) Me.Text = “My Form” • These lines of code (statements) are called Assignment Statements.

7. Event Procedures • To give the controls function when events occur, we need to write our code in event procedures. • Note: I will often call event procedures, “event handlers”. • To view the code right click on the form and select “View Code” • To make an event procedure you can: • Double click on the control (creates the default event procedure for the control) • Click on the control then click the “Events” button at the top of the Properties Window • This will create the code for the event procedure.

8. Event Procedures • An event procedure looks something like this: Private Sub btnButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnButton.Click ‘Code goes here End Sub • Don’t worry about all the details of this code! • There’s only two parts you need to worry about: • btnButton_Click is the name of the event procedure • btnButton.Click tells the procedure to listen for the click event on the button btnButton. • The most of the rest are keywords used to describe the procedure • Keywords are words that have a particular meaning in VB • These are reserved, meaning they can’t be used for other purposes (this will be clearer when we talk about variables)

9. Event Procedures • A single event handler can listen for multiple different events. Private Sub btnButton_Click(…) Handles btnButton1.Click,btnButton2.Click ‘Code goes here End Sub • So the code inside of the procedure will be executed if either btnButton1 or btnButton2 is clicked.

10. IntelliSense • When you start typing code in Visual Studio, a system called IntelliSense will attempt to assist you by giving you options to complete your code. • This limits the amount of code you have to memorize. • When an item is highlighted in the drop-down supplied by IntelliSense, a tool tip is supplied next to it. • You can select an item in the menu by clicking on it, pushing enter, or tab. • If the IntelliSense drop-down gets in the way, you can hold down the control key to make it transparent.

11. Default Events • When double clicking on a control, you will get the event procedure for the control’s default event. • The some default events are as follows:

12. Some Events • Click– Useful for buttons. • DoubleClick – Not available for buttons, but can be used for labels, text boxes, etc. • Focus • Enter – Event raised when control first receives focus • Leave – Event raised when control first loses focus • Keys – Useful for text boxes. • KeyDown – Event raised when a key is first pressed • KeyUp – Event raised when a key is first released • Key Pressed – Event raised when the control has focus and a key is pressed and released. • Mouse • MouseDown – Event raised when the a mouse button is first pressed while over a control • MouseUp- Event raised when the a mouse button is first released while over a control • MouseEnter – Event raised when the mouse enters a visible part of the control • MouseLeave – Event raised when the mouse leaves a visible part of the control • MouseHover – Event raised when a mouse remains stationary over a control • Property Changed – When the programmer or the user changes a property of a control an event is raised • TextChanged – Event raised when the value of the “Text” property is changed

13. Opening a Project • To open a saved VB project: • Click on “Project/Solution” from the “File” menu under “Open”. • Navigate to where you saved your project. • Double Click on the folder that was created by Visual Studio when you saved (it should have the same name that you named you project) • Double click on the “.sln” file (it should have the same name that you named you project). • Also, if you successfully debug you program, it will create an executable file inside of your Debug directory. To get to it: • Double Click on the folder in the same folder as your “.sln” file. • Double Click on the “bin” folder. • Double Click on the “Debug” folder. • It is the “.exe” file in the “Debug” folder. • An executable file is a file for the specific purpose of running your program.