1. C# Programming: From Problem Analysis to Program Design
Programming Based on Events 10
C# Programming: From Problem Analysis to Program Design
5th 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
Design and create a Windows Presentation Foundation (WPF) application
Work through a programming example that illustrates the chapter’s concepts
C# Programming: From Problem Analysis to Program Design

4. Delegates Delegates form the foundation for events in C#
Delegates store references (addresses) to methods
For events, it is the address of which method to invoke when an event is fired
Delegates enable you to pass methods as arguments (as opposed to data) to other methods
Delegate signature
Identifies what types of methods the delegate represents
C# Programming: From Problem Analysis to Program Design

5. Delegates (continued)
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
Recall signature for method includes only the name and the number and type of parameters – not the return type
C# Programming: From Problem Analysis to Program Design

6. Defining Delegates Delegate declaration example
delegate string ReturnsSimpleString( );
Above example represents methods that return a string and require no argument
Given the signature, the following methods could be associated or referenced by the delegate
static string EndStatement( )
static string ToString( )
static string ReturnSaying( )
C# Programming: From Problem Analysis to Program Design

7. Creating Delegate Instances
Think of the delegate as a way of defining or naming a method signature
Associate delegate with method(s) by creating delegate instance(s)
ReturnsSimpleString saying3 = new
ReturnsSimpleString(EndStatement);
Constructor for delegate of the delegate class always takes just parameter (method name)
Name of a method for the constructor to reference
C# Programming: From Problem Analysis to Program Design

8. Using Delegates
Delegate identifier references the method sent as argument to constructor
Any use of delegate identifier now calls that 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

9. Using Delegates (continued)
delegate string ReturnsSimpleString( );
static void Main ( ) {
int age = 18;
ReturnsSimpleString saying1 = new ReturnsSimpleString(AHeading);
ReturnsSimpleString saying2 = new
ReturnsSimpleString((age + 10).ToString);
ReturnsSimpleString saying3= new ReturnsSimpleString(EndStatement);
MessageBox.Show(saying1( ) + saying2( ) + saying3( )); }
C# Programming: From Problem Analysis to Program Design

10. Using Delegates (continued)
These methods were associated (referenced) by the ReturnsSimpleString ( ) delegate
// Method that returns a string.
static string AHeading() {
return "Your age will be "; }
static string EndStatement( )
return " in 10 years.";
C# Programming: From Problem Analysis to Program Design

11. Using Delegates (continued)
Review DelegateExample
C# Programming: From Problem Analysis to Program Design

12. Relationship of Delegates to Events
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 are 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

13. 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

14. Event-Handler Methods
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

15. 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
C# Programming: From Problem Analysis to Program Design

16. ListBox Control Includes number of properties and events
Items property
Used to set initial values
Click on (Collections) to add items
Name property
Useful to set if you are going to write program statements to manipulate the control
Sorted property
Set to true to avoid having to type values in sorted order
C# Programming: From Problem Analysis to Program Design

17. ListBox Control Properties
Table ListBox properties
C# Programming: From Problem Analysis to Program Design

18. Adding a ListBox Control Object
Add ListBox control, then click on Items property (Collection) to type entries
C# Programming: From Problem Analysis to Program Design

19. ListBox Control Methods
Events are methods….Default event for ListBox
Table ListBox methods
C# Programming: From Problem Analysis to Program Design

20. Registering A ListBox Event
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

21. ListBox Event Handlers
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

22. ListBox Control Objects
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

23. ListBox Control Objects (continued)
C# Programming: From Problem Analysis to Program Design

24. 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

25. ListBox Control Objects (continued)
C# Programming: From Problem Analysis to Program Design

26. 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
C# Programming: From Problem Analysis to Program Design

27. Adding Items to a ListBox
Add items at run time 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

28. ListBoxExample
C# Programming: From Problem Analysis to Program Design

29. Review ListBoxExample
private void lstBxEvents_SelectedIndexChanged
(object sender, EventArgs e) {
string result = " ";
foreach (string activity in lstBxEvents.SelectedItems)
result += activity + " ";
this.txtBxResult.Text = result; }
Review ListBoxExample
C# Programming: From Problem Analysis to Program Design

30. ListBoxExample (continued)
Table ListBoxExample property values
C# Programming: From Problem Analysis to Program Design

31. ListBoxExample (continued)
Table ListBoxExample property values (continued)
C# Programming: From Problem Analysis to Program Design

32. ComboBox Objects
In many cases, ListBox and ComboBox controls can be used interchangeably
ListBox control is usually used when you have all the choices available at design time
ComboBox facilitates displaying a list of suggested choices with an added feature
ComboBox objects contain their own text box field as part of the object
C# Programming: From Problem Analysis to Program Design

33. GardeningForm Example
New Project created
Includes ListBox and ComboBox Objects
Create Project like previous ones
Add Label
Change property values for form
Drag and drop ComboBox and ListBox onto form
C# Programming: From Problem Analysis to Program Design

34. Programming Event Handlers
For ListBox, use 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
Text ONLY gets the first one selected
C# Programming: From Problem Analysis to Program Design

35. Adding ComboBox Controls
Extra TextBox object with ComboBox – User selects from list or types new value
C# Programming: From Problem Analysis to Program Design

36. Adding ComboBox Controls (continued)
Top line left blank in ComboBox when DropDownStyle property is set to DropDown (default setting)
C# Programming: From Problem Analysis to Program Design

37. This line gets added to .designer.cs
ComboBox
Double clicking on ComboBox object registers it’s default event (SelectedIndexChanged( )
this.cmboFlowers.SelectedIndexChanged += new
System.EventHandler(this.cmboFlowers_SelectedIndexChanged);
this.txtBxResultFlowers.Text = this.cmboFlowers.Text;
This line gets added to .designer.cs
Use .Text property to retrieve the value
C# Programming: From Problem Analysis to Program Design

38. Handling ComboBox Events
ComboBox only allows a single selection to be made
ListBox allows multiple selections
Default event-handler method: SelectedIndexChanged( )
Same as ListBox control object
Could register TextChanged( ) event
Method is executed when new values are entered
C# Programming: From Problem Analysis to Program Design

39. Programming Event Handlers (continued)
C# Programming: From Problem Analysis to Program Design

40. 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

41. Adding Menus
Drag MenuStrip control to form, then click here to display Menu structure
C# Programming: From Problem Analysis to Program Design

42. MenuStrip Control Objects
Ampersand (&) is typed between the F and o for the Format option to make Alt+o shortcut for Format
C# Programming: From Problem Analysis to Program Design

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

44. Menu
To add tool tip, drag ToolTip control from Toolbox anywhere on the form
ToolTip, like MenuStrip rest in Component Tray below design surface
Separate ToolStripMenuItem objects are created from each selectable menu option
Each has its own properties
Each can have its own even handler method
C# Programming: From Problem Analysis to Program Design

45. MenuStrip Control Objects (continued)
ToolTip property sets text that’s displayed
when the cursor is rested on top of the control
C# Programming: From Problem Analysis to Program Design

46. 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

47. Menu Event Handler Methods
private void menuExit_Click(object sender, System.EventArgs e) {
Application.Exit( ); }
private void menuAbout_Click(object sender, System.EventArgs e)
MessageBox.Show("Gardening Guide Application\n\n\nVersion"
+ " 1.0", "About Gardening");
C# Programming: From Problem Analysis to Program Design

48. 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

49. Adding Predefined Standard Windows Dialog Boxes
C# Programming: From Problem Analysis to Program Design

50. 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 ; }
C# Programming: From Problem Analysis to Program Design

51. 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

52. Adding Predefined Standard Windows Dialog Boxes – Color
C# Programming: From Problem Analysis to Program Design

53. Review GardeningForm Example
GardeningForm App
Three separate source code files are created for this Windows application with ListBox and ComboBox
One file has Main( ) method – default name Program.cs
No changes made to this file
Other two files’ headings include partial class definition
.Designer.cs file has all autogenerated code from dragging and dropping controls and changing property values
.cs file has event handler methods
Review GardeningForm Example
C# Programming: From Problem Analysis to Program Design

54. GardeningForm Properties
Each entry has an associated statement in the .Designer.cs file
Table GardeningForm property values
C# Programming: From Problem Analysis to Program Design

55. GardeningForm Properties (continued)
Table GardeningForm property values (continued)
C# Programming: From Problem Analysis to Program Design

56. GardeningForm Properties (continued)
Table GardeningForm property values (continued)
C# Programming: From Problem Analysis to Program Design

57. GardeningForm Properties (continued)
Table GardeningForm property values (continued)
C# Programming: From Problem Analysis to Program Design

58. GardeningForm Events Table 10-5 GardeningForm events
C# Programming: From Problem Analysis to Program Design

59. CheckBox and RadioButton Objects
New Project is created
Windows Application
CheckBox and RadioButton objects added like other objects
Drag and drop controls
Set BackColor properties
Set Title bar using Text property
Name controls
C# Programming: From Problem Analysis to Program Design

60. 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

61. 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

62. Method name more generic so it can be used with multiple controls
CheckBox Control
Originally default event handler method for the Swim CheckBox object was:
private void ckBxSwim_CheckedChanged (object sender,
System.EventArgs e) { }
The heading for ckBxSwim_CheckedChanged( ) changed to ComputeCost_CheckedChanged ( )
private void ComputeCost_CheckedChanged (object sender, System.EventArgs e) { }
Method name more generic so it can be used with multiple controls
C# Programming: From Problem Analysis to Program Design

63. GroupBox Objects
GroupBox provides an identifiable group for controls – gives you a heading
Objects may be grouped together for visual appearance
Can move or set properties that impact the entire group
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

64. RadioButton Objects Appear as small circles
Give users a choice between two or more options
Not appropriate to select more than one RadioButton object (from a group)
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

65. Adding RadioButton Objects
Box drawn around RadioButton objects is from GroupBox
C# Programming: From Problem Analysis to Program Design

66. 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

67. Wiring One Event Handler to Multiple Objects (continued)
Each CheckBox and RadioButton wired to same method
C# Programming: From Problem Analysis to Program Design

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

69. ComputeCost_CheckChanged( ) and Click( ) Events Raised
C# Programming: From Problem Analysis to Program Design

70. Windows Presentation Foundation
WPF Application – one of options for Windows projects
Vector-based and resolution-independent → sharp graphics
As with WinForms, drag and drop controls from the Toolbox onto the window
Set property values and register events
Some of the names are different (Use Content instead of Text for buttons, labels, checkboxes and radio buttons)
C# Programming: From Problem Analysis to Program Design

71. Windows Presentation Foundation (WPF)
RegistrationApp was recreated using WPF
C# Programming: From Problem Analysis to Program Design

72. Windows Presentation Foundation (WPF)
Different files created
XAML
Resembles Hypertext Markup Language (HTML)
HTML for Windows application
Each control placed on design surface appears as a separate line in the XAML file
Beginning and ending tag for each control
No .Designer.cs file
.xaml.cs is the code behind file for event handlers
Review WPF_Example
C# Programming: From Problem Analysis to Program Design

73. 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

74. TabControl Controls (continued)
C# Programming: From Problem Analysis to Program Design

75. TabControl Controls (continued)
C# Programming: From Problem Analysis to Program Design

76. 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

77. TabControl Controls (continued)
To indicate tabPage2 should be on top
tabControl1.SelectedTab = tabPage2;
Can display images on tabs and change the background or foreground colors
Tabs can be displayed vertically instead of horizontally using the Alignment property
Can register Click events for each of the tabs
Review PizzaApp Example
C# Programming: From Problem Analysis to Program Design

78. DinerGUI Application Example
C# Programming: From Problem Analysis to Program Design

79. DinerGUI (continued) Table 10-6 Order class data fields
C# Programming: From Problem Analysis to Program Design

80. DinerGUI (continued)
C# Programming: From Problem Analysis to Program Design

81. DinerGUI (continued) Figure 10-26 Class diagrams
C# Programming: From Problem Analysis to Program Design

82. DinerGUI (continued)
Figure Pseudocode for the Order class for DinerGUI
C# Programming: From Problem Analysis to Program Design

83. DinerGUI (continued) Figure 10-28 Pseudocode for RadioButton,
CheckBox,
ListBox, and
ComboBox
object event
handlers
C# Programming: From Problem Analysis to Program Design

84. DinerGUI (continued)
Figure Pseudocode for menu object event handlers
C# Programming: From Problem Analysis to Program Design

85. DinerGUI (continued)
Figure Pseudocode for menu object event handlers and
ClearDrinks( ) method
C# Programming: From Problem Analysis to Program Design

86. DinerGUI (continued) Table 10-7 DinerGUI property values
C# Programming: From Problem Analysis to Program Design

87. DinerGUI (continued) Table 10-7 DinerGUI property values (continued)
C# Programming: From Problem Analysis to Program Design

88. DinerGUI (continued) Table 10-7 DinerGUI property values (continued)
C# Programming: From Problem Analysis to Program Design

89. DinerGUI (continued) Table 10-7 DinerGUI property values (continued)
C# Programming: From Problem Analysis to Program Design

90. DinerGUI (continued) Table 10-7 DinerGUI property values (continued)
C# Programming: From Problem Analysis to Program Design

91. DinerGUI (continued)
C# Programming: From Problem Analysis to Program Design

92. DinerGUI (continued)
C# Programming: From Problem Analysis to Program Design

93. DinerGUI (continued) private Order newOrder;
private void OrderGUI_Load(object sender,
System.EventArgs e) {
newOrder = new Order( );
for (int i = 0; i < newOrder.menuEntree.Length; i++)
this.lstBxEntree.Items.Add(newOrder.menuEntree[i]); }
C# Programming: From Problem Analysis to Program Design

94. DinerGUI (continued)
private void lstBxEntree_SelectedIndexChanged (object sender,System.EventArgs e) { newOrder.Entree = this.lstBxEntree.Text; } private void cmboSpecial_SelectedIndexChanged (object sender, System.EventArgs e) newOrder.SpecialRequest = this.cmboSpecial.Text;
Review Diner Example
C# Programming: From Problem Analysis to Program Design

95. DinerGUI (continued)
C# Programming: From Problem Analysis to Program Design

96. DinerGUI (continued)
C# Programming: From Problem Analysis to Program Design

97. DinerGUI (continued)
C# Programming: From Problem Analysis to Program Design

98. DinerGUI (continued) Table 10-8 DinerGUI events
C# Programming: From Problem Analysis to Program Design

99. DinerGUI (continued) Table 10-8 DinerGUI events
C# Programming: From Problem Analysis to Program Design

100. Coding Standards Follow a consistent naming standard for controls
Before you register events, such as button click events, name the associated control
C# Programming: From Problem Analysis to Program Design

101. Resources Visual Studio - Getting Started Tutorials –
Visual C# Windows Forms Tutorials
C# Programmers Reference: Delegates Tutorial –
C# Programming: From Problem Analysis to Program Design

102. Resources Delegates and Events in C#/.NET –
C# Programmers Reference: Delegates Tutorial –
Microsoft Virtual Academy - C# Fundamentals for Absolute Beginners – /
C# Programming: From Problem Analysis to Program Design

103. 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

104. 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