The document discusses event driven programming using Visual Studio and VB.NET. It describes key aspects of event driven programming including event loops, GUI design using forms and controls, trigger functions, and event handlers. It provides examples of how to use these tools and techniques in Visual Studio and VB.NET, demonstrating the development process with code snippets and screenshots.

1. 1
What is Event Driven
Programming?
Visual Studio
and
VB.NET

2. 2
P1: Key Features of EDP
1. Event loops
2. GUI design (Forms & Controls
3. Trigger functions
4. Event handlers

3. 3
P2: Demonstrate the use of event
driven tools and techniques
Using Visual Studio and VB.NET language
Demonstrate the development process with screenshots
and code examples, to show the main choices available
IDE Tools inc:
GUI form design
Add & edit controls
Choice of triggers
Code colour & dropdown
Debugging tools
 Error list
 Breakpoints & step
through code
Coding Techniques inc:
Variables and Datatypes
 Const, Global, Local
 Integer, boolean, decimal,
string, date
Selection
 If...Else & Select...Case
Loops
 Fixed & Conditional

4. 4
Event Loops
Programmers are often not aware of these:
The Event loop keeps testing the user interface to see if
anything has happened e.g. a button click or a key
pressed. Open Task Manager to see which programs are running
When an event is detected, it is passed to the list of
identified trigger functions, which then launches a
response to the event.
The event handlers are the actual program code
modules that are executed when a particular trigger has
occurred.
Other (non user) activities can also cause an event to
trigger – typically used in networking and when reading
from or writing to files.

5. 5
Event Loop
1 User interacts with page
2 An ‘event’ is triggered
EVENT!
The page’s appearance is 3 A code handler runs in response
updated/modified as a result
4

6. 6
Forms and Controls
A GUI (graphical user interface) is what the user
sees when the program runs and usually consists of
one or several forms
Event driven programming is particularly suitable for
GUIs - uses WIMP system
Windows, Icons, Menus, Pointers
Programmer can assist user with intuitive interface,
restrict input to a limited range, provide visual
feedback and context-sensitive help
Event driven programs respond to events triggered
by the user via the mouse or keyboard

7. 7
Forms and Controls
Common methods for user interaction include clicking
the mouse or pressing a key
Each form contains various controls which allow the
user to interact with the program in different ways
e.g. Buttons, Textboxes, Labels, Menus, Pictureboxes, Timers
Wide choice of controls can be customised for use by
Select from toolbar and drop onto the form
change its properties in design view (text, image, visible)
Show form design in IDE and choice of controls in toolbox
Add different types controls to provide input and feedback
inc. visual and non-visual controls (timer)
Change the properties (inc Name) and explain purpose

8. 8
Trigger functions
Event driven programs respond to events
triggered by the user
The programmer chooses which event(s)
to respond to by selecting the appropriate
trigger function.
Every object has a range of trigger
functions – one for each possible event
Different controls have different events
(events for a text box not the same for a
button)
A Button has a Click event, a GotFocus event, a
MouseHover event etc
Button events

9. 9
Trigger Functions
Triggers can also come from unseen events e.g. Timer
Double clicking a control will select its default event
Timer1_Tick()
MenuItem1_Click()
Forms also have events inc:
Load (open for first time, set default values)
KeyDown (when the user presses a key)
Demonstrate how to create trigger functions for different controls
inc. mouse, keyboard and timer (control event)
Show how to select different triggers for the same control
Explain how trigger functions are used in your program

10. 10
Event Handlers
An event triggers the appropriate event handler
Event handlers contain the code that runs when an
event occurs
These event handlers are self-contained sections of
code – also called Procedures or Subroutines
VB.NET uses Sub/End Sub to start and end the code
This allows the programmer to work on one event of
one control at a time and makes testing easier

11. 11
Event Handlers
Demonstrate and explain different coding techniques
Variables
 Different datatypes
 Local and Global
Selection
 If...Else
 Select...Case
Loops
 Fixed loop e.g. For...Next
 Conditional loop e.g. Do...Loop While
Show how IDE assists with coding and debugging
 Pre-written code and drop-down lists showing choice of
possible commands
 Errors are highlighted and step through debugging

12. 12
Advantages
Flexibility:
Wide choice of controls and trigger functions -
programmer can decide what will happen when
Suitability for GUI:
WIMP system (Windows, Icons, Menus, Pointers)
Simplicity and Ease of development:
Programmers can add and code one object at a
time, using simple constructs
Pre-written code and drop-down lists showing
choice of possible commands
Errors are highlighted and step through debugging

13. 13
Disadvantages
Errors can be more difficult to spot than with
simpler, procedural programs
Programs with complex GUIs may be slower
to load and run than simpler programs –
particularly if RAM is insufficient
Programs with too many forms can be very
confusing and/or frustrating for the user

14. 14
Which control would a programmer
use to….?
Allow a Yes/ No answer only?
Allow a wide range of keyboard input?
Limit user input to the numbers 1, 2, 3 & 4?
Allow a user to subtly change the colour or
brightness selected in a graphics application
Allow a user to access commands without the
mouse, but using keyboard navigation only?