1. Programming Based on Events9
C# Programming: From Problem Analysis to Program Design
2nd Edition
C# Programming: From Problem Analysis to Program Design

2. Chapter Objectives
Define, create, and use delegates and examine their relationship to events
Explore event-handling procedures in C# by writing and registering event-handler methods
Create applications that use the ListBox control object to enable multiple selections from a single control
Contrast ComboBox to ListBox objects by adding both types of controls to an application
C# Programming: From Problem Analysis to Program Design

3. Chapter Objectives (continued)
Add Menu and TabControl control options to Window forms and program their event-handler methods
Wire multiple RadioButton and CheckBox object events to a single event-handler method
Work through a programming example that illustrates the chapter’s concepts
C# Programming: From Problem Analysis to Program Design

4. Delegates
Delegates store references (addresses) to methods, as opposed to storing actual data
Delegates form the foundation for events in C#
Declaration for a delegate looks more like a method declaration than a class definition
Except, delegate declaration has no body
Declaration begins with the keyword delegate
Declaration ends with a parenthesized list of parameters
Unlike a method, the return type of a delegate becomes part of its identifying signature
C# Programming: From Problem Analysis to Program Design

5. Delegates (continued)
Delegate declaration example
delegate string ReturnsSimpleString( );
Delegate signature
Identifies what types of methods the delegate represents
Above Example represents methods that return a string and require no argument
static string EndStatement( )
static string ToString( )
static string ReturnSaying( )
C# Programming: From Problem Analysis to Program Design

6. Delegates (continued)
Associate delegate with method(s) by creating delegate instance(s)
Example
ReturnsSimpleString saying3 = new
ReturnsSimpleString(EndStatement);
Constructor for delegate of the delegate class always takes just parameter
Name of a method for the constructor to reference
C# Programming: From Problem Analysis to Program Design

7. Delegates (continued)
Delegate identifier references the method sent as argument to constructor
Any use of delegate identifier now calls the method
Methods are said to be wrapped by the delegate
Delegate can wrap more than one method, called a multicast delegate
+= and -= operators are used to add/remove methods to/ from the delegate chain or invocation list
Multicast delegates must have a return type of void
C# Programming: From Problem Analysis to Program Design

8. Relationship of Delegates to Events
Delegates are used for event-driven application
Delegate acts as intermediary between objects that are raising or triggering an event
During compilation, the method or methods that will be called are not determined
Events as special forms of delegates
Place a reference to event-handler methods inside a delegate
Once reference is made, or event is registered, delegate is used to call event-handler method when an event like a button click is fired
C# Programming: From Problem Analysis to Program Design

9. Event Handling in C#
Form Designer in Visual Studio did much of the work for you
Double-clicked on a Button control object during design
1) Click event is registered as being of interest
2) An event-handler method heading is generated
Two steps form event wiring process
Wire an event: associate (identify) a method to handle its event
C# Programming: From Problem Analysis to Program Design

10. Event Handling in C# (continued)
Code associates the methods with a delegate
this.button1.Click += new System.EventHandler(this.button1_Click);
this.button2.Click += new System.EventHandler(this.button2_Click);
System.EventHandler is a delegate type
button1.Click and button2.Click are methods
Keyword this is added to all code generated by Visual Studio to indicate the current instance of a class
C# Programming: From Problem Analysis to Program Design

11. ListBox Control Objects
Displays list of items for single or multiple selections
Scroll bar is automatically added when total number of items exceeds the number that can be displayed
Can add or remove items at design time or dynamically at run time
Includes number of properties and events
The Items property used to set initial values
Click on (Collections) to add items
C# Programming: From Problem Analysis to Program Design

12. Adding a ListBox Control Object
Add ListBox control, then click on Items property (Collection) to type entries
Figure 9-2 String Collection Editor
C# Programming: From Problem Analysis to Program Design

13. ListBox Control Objects (continued)
Name property
Useful to set for program statements
Sorted property
Set to true to avoid having to type values in sorted order
Register an event for the ListBox
Might want to know when the item selection changes
Double-clicking on any control registers its default event for the control
SelectedIndexChanged: default event for ListBox
C# Programming: From Problem Analysis to Program Design

14. ListBox Control Objects (continued)
Register its event with the System.EventHandler delegate
this.lstBoxEvents.SelectedIndexChanged += new System.EventHandler (this.listBox1_SelectedIndexChanged);
Visual Studio adds event-handler method
private void listBox1_SelectedIndexChanged
(object sender, System.EventArgs e) { }
C# Programming: From Problem Analysis to Program Design

15. ListBox Control Objects (continued)
To retrieve string data from ListBox use Text property
this.txtBoxResult.Text = this.lstBoxEvents.Text;
Place in method body
When event fires, selection retrieved and stored in TextBox object
C# Programming: From Problem Analysis to Program Design

16. ListBox Control Objects (continued)
Figure 9-3 SelectedIndexChanged event fired
C# Programming: From Problem Analysis to Program Design

17. Multiple Selections with a ListBox
SelectionMode Property has values of MultiSimple, MultiExtended, None, and One
MultiSimple: use the spacebar and click the mouse
MultiExtended can also use Ctrl key, Shift key, and arrow keys
foreach(string activity in lstBoxEvents.SelectedItems) {
result += activity + " "; }
this.txtBoxResult.Text = result;
C# Programming: From Problem Analysis to Program Design

18. ListBox Control Objects (continued)
Figure 9-4 Multiple selections within a ListBox object
C# Programming: From Problem Analysis to Program Design

19. ListBox Control Objects (continued)
SelectedItem and SelectedItems return objects
Store numbers in the ListBox, once retrieved as objects, cast the object into an int or double for processing
Adding items to a ListBox at run time by using Add( ) method with the Items property
lstBoxEvents.Items.Add("string value to add");
private void btnNew_Click(object sender, System.EventArgs e) {
lstBoxEvents.Items.Add(txtBoxNewAct.Text); }
C# Programming: From Problem Analysis to Program Design

20. ListBoxExample
Figure 9-5 Add( ) method executed inside the buttonClick event
C# Programming: From Problem Analysis to Program Design

21. C# Programming: From Problem Analysis to Program Design

22. ListBox Control Properties
C# Programming: From Problem Analysis to Program Design

23. ListBox Control Methods
C# Programming: From Problem Analysis to Program Design

24. ListBox Control Methods (continued)
Note that ListBox control inherits members from Control class
C# Programming: From Problem Analysis to Program Design

25. ComboBox Controls Figure 9-6 ComboBox and ListBox objects
Extra TextBox object with ComboBox – User selects from list or types new value
Figure 9-6 ComboBox and ListBox objects
C# Programming: From Problem Analysis to Program Design

26. ComboBox Controls (continued)
Top line left blank in ComboBox when DropDownStyle property is set to DropDown (default setting)
Figure 9-7 ComboBox list of choices
C# Programming: From Problem Analysis to Program Design

27. Handling ComboBox Events
ComboBox only allows a single selection to be made
Default event-handler method: SelectedIndexChanged( )
Same as ListBox control object
Could register KeyPress( ) event-handler method
BUT, event is fired with each and EVERY keystroke
C# Programming: From Problem Analysis to Program Design

28. Programming Event Handlers
Since ListBox object allows multiple selections, Text property cannot be used
Text ONLY gets the first one selected
Use the SelectedItems, SelectedIndices, or Items to retrieve a collection of items selected
Zero-based structures
Access them as you would access an element from an array
SelectedIndices is a collection of indexes
C# Programming: From Problem Analysis to Program Design

29. Programming Event Handlers (continued)
KeyPress( ) event-handler method fired with each keystroke
Figure 9-8 KeyPress and SelectedIndexChanged events fired
C# Programming: From Problem Analysis to Program Design

30. MenuStrip Controls Offers advantage of taking up minimal space
Drag and drop MenuStrip object from toolbox to your form
Icon representing MenuStrip placed in Component Tray
Select MenuStrip object to set its properties
To add the text for a menu option, select the MenuStrip icon and then click in the upper-left corner of the form
C# Programming: From Problem Analysis to Program Design

31. MenuStrip Controls (continued)
Drag MenuStrip control to form, then click here to display Menu structure
Figure 9-9 First step to creating a menu
C# Programming: From Problem Analysis to Program Design

32. MenuStrip Control Objects
Ampersand (&) is typed between the F and o for the Format option to make Alt+o shortcut for Format
Figure 9-10 Creating a shortcut for a menu item
C# Programming: From Problem Analysis to Program Design

33. MenuStrip Control Objects (continued)
To create separators, right-click on the text label (below the needed separator)
Select Insert Separator
Figure 9-11 Adding a separator
C# Programming: From Problem Analysis to Program Design

34. MenuStrip Control Objects (continued)
Set the text to be displayed
when the cursor is rested on top of the control
Figure 9-12 Setting the Property for the ToolTip control
C# Programming: From Problem Analysis to Program Design

35. Wire Methods to Menu Option Event
Set the Name property for each menu option
Do this first, then wire the event
Click events are registered by double-clicking on the Menu option
When the menu option is clicked, the event triggers, happens, or is fired
C# Programming: From Problem Analysis to Program Design

36. Adding Predefined Standard Windows Dialog Boxes
Included as part of .NET
Dialog boxes that look like standard Windows dialog boxes
File Open, File Save, File Print, and File Print Preview
Format Font
Format Color dialogs
C# Programming: From Problem Analysis to Program Design

37. Adding Predefined Standard Windows Dialog Boxes – Color
Retrieves the current ForeColor property setting for the Label object
private void menuColor_Click(object sender,
System.EventArgs e) {
colorDialog1.Color = lblOutput.ForeColor;
if (colorDialog1.ShowDialog( ) != DialogResult.Cancel )
lblOutput.ForeColor = colorDialog1.Color; }
Checks to see if Cancel button clicked
Set to selection made
C# Programming: From Problem Analysis to Program Design

38. Adding Predefined Standard Windows Dialog Boxes – Color (continued)
Figure 9-14 Color dialog box menu option
C# Programming: From Problem Analysis to Program Design

39. Adding Predefined Standard Windows Dialog Boxes – Font
private void menuFont_Click (object sender, System.EventArgs e) {
fontDialog1.Font =
lblOutput.Font;
if (fontDialog1.ShowDialog( )
!= DialogResult.Cancel )
lblOutput.Font =
fontDialog1.Font ; }
Figure 9-15 Font dialog box menu option
C# Programming: From Problem Analysis to Program Design

40. CheckBox Objects Appear as small boxes
Allow users to make a yes/no or true/false selection
Checked property set to either true or false depending on whether a check mark appears or not
Default false value
CheckChanged( ) – default event-handler method
Fired when CheckBox object states change
Can wire one event handler to multiple objects
C# Programming: From Problem Analysis to Program Design

41. Wiring One Event Handler to Multiple Objects
Using Properties window, click on the Events Icon
Click the down arrow associated with that event
Select method to handle the event
Follow the same steps for other objects
C# Programming: From Problem Analysis to Program Design

42. Wiring One Event Handler to Multiple Objects (continued)
Figure 9-16 Wiring the event-handler method
C# Programming: From Problem Analysis to Program Design

43. CheckBox Object
Figure 9-17 ComputeCost_CheckedChanged( ) method raised
C# Programming: From Problem Analysis to Program Design

44. GroupBox Objects
CheckBox objects may be grouped together for visual appearance
Can move or set properties that impact the entire group
A GroupBox control should be placed on the form before you add objects
GroupBox control adds functionality to RadioButton objects
Allow only one selection
C# Programming: From Problem Analysis to Program Design

45. RadioButton Objects Appear as small circles
Give users a choice between two or more options
Not appropriate to select more than one CheckBox object with RadioButton objects
Group RadioButton objects by placing them on a Panel or GroupBox control
Setting the Text property for the GroupBox adds a labeled heading over the group
C# Programming: From Problem Analysis to Program Design

46. RadioButton Objects (continued)
Figure 9-18 GroupBox and RadioButton objects added
C# Programming: From Problem Analysis to Program Design

47. RadioButton Objects (continued)
Turn selection on
this.radInterm.Checked = true;
Raise a number of events, including Click( ) and CheckedChanged( ) events
Wire the event-handler methods for RadioButton objects, just like CheckBox
C# Programming: From Problem Analysis to Program Design

48. RadioButton Objects (continued)
Register ComputeCost_CheckedChanged( ) method
Figure 9-19 Wired Click event
C# Programming: From Problem Analysis to Program Design

49. RadioButton Objects (continued)
ComputeCost_CheckedChanged( ) method
if (this.radBeginner.Checked) {
cost +=10;
this.lblMsg.Text =
"Beginner “ +
“-- Extra $10 charge"; }
else
// more statements
C# Programming: From Problem Analysis to Program Design

50. ComputeCost_CheckChanged( ) and Click( ) Events Raised
Figure 9-20 ComputeCost_CheckedChanged( ) and Click( ) events raised
C# Programming: From Problem Analysis to Program Design

51. TabControl Controls
Sometime an application requires too many controls for a single screen
TabControl object displays multiple tabs, like dividers in a notebook
Each separate tab can be clicked to display other options
Add a TabControl object to the page by dragging the control from the Container section of the Toolbox
C# Programming: From Problem Analysis to Program Design

52. TabControl Controls (continued)
Figure 9-21 Tabbed controlled application
C# Programming: From Problem Analysis to Program Design

53. TabControl Controls (continued)
Figure 9-22 TabControl object stretched to fill form
C# Programming: From Problem Analysis to Program Design

54. TabControl Controls (continued)
TabPage property enables you to format individual tabs
Clicking the ellipsis beside the Collection value displays the TabPage Collection Editor
C# Programming: From Problem Analysis to Program Design

55. DinerGui Application Example
Figure 9-24 Problem specification for DinerGUI example
C# Programming: From Problem Analysis to Program Design

56. DinerGui Application Example (continued)
C# Programming: From Problem Analysis to Program Design

57. DinerGui Application Example (continued)
Figure 9-25 Prototype for DinerGUI example
C# Programming: From Problem Analysis to Program Design

58. DinerGui Application Example (continued)
Figure 9-26
Class diagrams
C# Programming: From Problem Analysis to Program Design

59. DinerGui Application Example (continued)
Figure 9-35 Clear Order click event fired
C# Programming: From Problem Analysis to Program Design

60. Chapter Summary Delegates Event-handling procedures
Registering an event
ListBox control for multiple selections
ComboBox versus ListBox objects
C# Programming: From Problem Analysis to Program Design

61. Chapter Summary (continued)
Adding controls to save space
MenuStrip controls
TabControl
Use of GroupBox controls
RadioButton versus CheckBox objects
C# Programming: From Problem Analysis to Program Design