1. Windows Desktop Applications
Windows Forms
Windows Forms
September 18, 2018

2. Windows Desktop Applications
Windows Desktop Applications are implemented in C# using Windows Forms
There are .NET classes that represent windows, buttons, text boxes, menus, list boxes, and so forth
With experience, they are very easy to use:
Drag and Drop from the “toolbox”
Set properties
Handle events
Windows Forms
September 18, 2018

3. Event Driven Programming
Console applications are essentially sequential code executed in the order specified by Main and whatever it calls
Windows programs are event-driven
Main instantiates a main window
Subsequently, the order of code execution is primarily determined by events, many of which are triggered from outside the code
User clicks a mouse
User presses a key, producing keystroke
User scrolls
Timer expires
I/O operation concludes
And so forth
Windows Forms
September 18, 2018

4. Events
During the execution of a Windows program, thousands of events typically occur
Every time the mouse is moved by one pixel over the window, a MouseMove event occurs, for example
Each time an event related to the program occurs, the program is notified by the system. It may
Take some action
Ignore the event and let Windows deal with it
Windows ignores most events but not all
It typically doesn’t ignore a CTRL-ALT-DELETE event, for example
Windows Forms
September 18, 2018

5. Dealing with Events Programs typically ignore most events
The events to which a program responds and the action it takes give the program its behavior
The program may provide one or more methods that execute actions to “do something” in response to the event
Such a method is called an event handler
An event handler is a method with a signature similar to this
private void HandlerName (Object sender, EventArgs e)
Windows Forms
September 18, 2018

6. Delegates
While it is not necessary to understand delegates to understand event-driven programming, the term delegate occurs frequently in the literature
The delegate is a type that defines a signature, that is, the return value type and parameter list types for a method
You can use the delegate type to declare a variable that can refer to any method with the same signature as the delegate
As indicated on the previous slide an EventHandler delegate has the signature:
public delegate void EventHandler(Object sender, EventArgs e);
Any method with the same signature can serve as an EventHandler
Windows Forms
September 18, 2018

7. Event Handlers
Registering an event-handler in C# is analogous to Adding a Listener in Java
Event handlers are “registered” for events to be handled
this.Load += new System.EventHandler (Form_Load);
Visual Studio generates the code to register most event handlers so that the programmer need not do so in most cases
Delegate
Event Handler method name which must have same signature as the EventHandler delegate
Load is the event name
Windows Forms
September 18, 2018

8. Windows Form Application
Create a Windows Forms Application …
… with an appropriate name
Windows Forms
September 18, 2018

9. Visual Editor for the Form – Form can be resized, etc.
Results
The Window
Driver Program
Rename the Form class
Visual Editor for the Form – Form can be resized, etc.
Rename Driver
Windows Forms
September 18, 2018

10. Main Program
No changes or additions to Main program are required for simple Windows Form applications
Windows Forms
September 18, 2018

11. Easily switch between the views
Design and Code Views
Code View
Windows derived from Form class like Java GUI window derived from JFrame
Easily switch between the views
Design View
Windows Forms
September 18, 2018

12. Design View and Toolbox
Controls in the Toolbox are represented by .NET classes
Dragging and dropping a control onto the form creates an object of the class in the code
The control may be placed at a desired location on the form and sized to suit your needs
Standard controls can be placed on a form
Windows Forms
September 18, 2018

13. Each Form has Two Code Files
Windows Forms
September 18, 2018

14. Each Form Has 3 Files
These represent the C# code, the designer code file, and the visual components of the form
In you plan to copy a form and paste it into another project, be sure to copy all 3 of the files
Windows Forms
September 18, 2018

15. Note the generated code for registering this event handler
Designer.cs
The designer code file contains VS-generated code that defines the controls dropped on the form and their properties, including their event handler registrations
Note the generated code for registering this event handler
Windows Forms
September 18, 2018

16. Properties of Controls
Each control has an extensive list of properties that allows the designer/programmer to manage many of the features of the control such as
Colors
Fonts
Size
Style
Object name
Caption (Text)
Many more
Windows Forms
September 18, 2018

17. Setting Properties of Controls
Properties can be set or retrieved
At design time in the Design View
Changes show up both in the visual editor and in the code files
Changes in the visual editor change the properties and change the code
Changes in the code may change the properties and the visual appearance in the editor (depending on whether the code is “definition” code or to be executed at run time)
At run time – via program code
Windows Forms
September 18, 2018

18. Design Time: Setting Properties of Controls
Object name in code
Button caption
Background color of Button
Text Alignment
Font Color
Is button visible?
Font
Windows Forms
September 18, 2018

19. Editing Properties: Example
Windows Forms
September 18, 2018

20. Properties in Code
After changing the properties, VS has added code to the Designer file to make the changes
Windows Forms
September 18, 2018

21. Making Simultaneous Changes to Multiple Controls
Drag a rectangle around desired controls
Change properties that are in common to the selected controls
Can see the results
All included controls are selected
The one with white handles is the “master”
Windows Forms
September 18, 2018

22. Controls Toolbar Send to Front or Back Windows Forms
September 18, 2018

23. Align and Size Controls
With all buttons selected, use the toolbar to align and resize them appropriately
The entire form also has properties to set
Made same size, aligned vertically, centered horizontally
Windows Forms
September 18, 2018

24. Form Properties
Windows Forms
September 18, 2018

25. Form Properties
Designate a button to be activated by pressing the <ENTER> key
Designate a button to be activated by pressing the <ESC> key
Windows Forms
September 18, 2018

26. Form Properties Specify where window appears on screen
Center the window on the screen
Neither maximized nor minimized originally
Windows Forms
September 18, 2018

27. Complete Form with More Controls
Textboxes – all set to right-aligned text because they are for numeric input; last is read-only
Align groups of controls to make the form look professional
Label controls
Windows Forms
September 18, 2018

28. Tab Order
For controls such as TextBoxes and Buttons that can have the keyboard focus, there is a tab order than one can set to control the order in which the controls receive focus as the tab key is pressed repeatedly
Windows Forms
September 18, 2018

29. Not clicked since focus cannot be on a read-only control
Tab Order
Click in the order you want focus to move. The Label for a TextBox should be clicked just before the TextBox
Not clicked since focus cannot be on a read-only control
Windows Forms
September 18, 2018

30. Cursor is here, right-justified initially
Tab Order
Run the application and this window will appear
Cursor is here, right-justified initially 2
If tab is pressed multiple times focus will move in the order of the numbers 3 4 5
Windows Forms
September 18, 2018

31. Current Status
At this point, the program runs successfully but does very little
We can see the form
We can type into the two input textboxes
We can click buttons
Nothing happens if we do these things
This is all of the “code behind” the form at this point
Windows Forms
September 18, 2018

32. Handling Some Events
Three primary events we need to handle are the click events for the 3 buttons
In the Design View, we double click each button
A skeleton of the Event Handler for each button is written in the “code behind” .cs file
Each Event Handler is registered in the designer.cs file
Windows Forms
September 18, 2018

33. Event Handler Skeletons
3 event handler skeletons added
Event Handler registered
Windows Forms
September 18, 2018

34. Add Event Handler Code
For the Quit button, we want to exit the program
For the Clear button, we want to make the text boxes empty and set the focus to the first text box
Run the program and observe how the Quit and Clear buttons work
Windows Forms
September 18, 2018

35. The Calculate Button Handler
When Calculate is pressed, we want to get the points and hours values from the form and divide to calculate GPA
Convert to decimal if possible
Calculate GPA
Else, show error message, reset form, and exit
If OK so far, display result
Windows Forms
September 18, 2018

36. Errors
The TryParse method takes care of some of the input errors a user may make
Empty input fields
Non-numeric input
It does not handle others such as
Entering 0 for the number of Hours Earned (divide by 0 error)
Producing a GPA of 57.2 or other invalid value
We must add code to handle the other anomalies
Windows Forms
September 18, 2018

37. Edited Handler
Windows Forms
September 18, 2018

38. Other Events
One may wish to display a “Goodbye” message when the application ends
Can be done in the btnQuit_Click handler for that approach to quitting the application but there are …
Other ways to quit
Red X
System Menu Close
Alt-F4
Use FormClosing event to catch them all at once
Windows Forms
September 18, 2018

39. Closing Event
In the Design View, click on the lightning bolt in Properties to get a list of all Events for the form
Double-Click FormClosing
Events
Windows Forms
September 18, 2018

40. Get current date and format it for display as “Thursday, June 5, 2014”
Load Event
Just before the window becomes visible for the first time, the Load event is recognized
It gives the programmer a chance to do some things at run time just before the window is shown
For example, we might want to do something like:
Display date and time
Display info about the application such as title, author, version, etc.
Give initial values to some controls
Set window caption
Get current date and format it for display as “Thursday, June 5, 2014”
Windows Forms
September 18, 2018