programming based on events -...

C# Programming: From Problem Analysis to Program Design

1

Programming

Based on

Events


4th Edition

10


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


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


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


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


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( )


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


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

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( ));

}


9


• These methods were associated (referenced) by

the ReturnsSimpleString ( ) delegate // Method that returns a string.

static string AHeading()

{

return "Your age will be ";

}

// Method that returns a string.

static string EndStatement( )

{

return " in 10 years.";

}


10



11

Figure 9-1 Windows-based form

Review DelegateExample


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


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


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


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


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

ListBox Control Properties


17

Table 10-2 ListBox properties


18

Adding a ListBox Control Object

Figure 10-2 String Collection Editor

Add ListBox

control, then

click on Items

property

(Collection) to

type entries

ListBox Control Methods


19

Table 10-3 ListBox methods

Events are

methods….

Default

event for

ListBox

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


20


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)

{

}


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


23

ListBox Control Objects (continued)

Figure 10-3 SelectedIndexChanged event fired


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;


25

ListBox Control Objects (continued)

Figure 10-4 Multiple selections within a ListBox object


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


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);

}


28

Figure 10-5 Add( ) method executed inside the buttonClick event

ListBoxExample

ListBoxExample

private void lstBxEvents_SelectedIndexChanged

(object sender, EventArgs e)

{

string result = " ";

foreach (string activity in lstBxEvents.SelectedItems)

result += activity + " ";

this.txtBxResult.Text = result;

}


29

Review ListBoxExample


30

ListBoxExample (continued)

Table 10-1 ListBoxExample property values


31

ListBoxExample (continued)

Table 10-1 ListBoxExample property values (continued)

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


32

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


33


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


35

Adding ComboBox Controls

Extra TextBox

object with

ComboBox – User selects

from list or

types new

value

Figure 10-6 ComboBox and ListBox objects


36

Adding ComboBox Controls (continued)

Top line left

blank in

ComboBox

when

DropDownStyle

property is set to

DropDown

(default setting)

Figure 10-7 ComboBox list of choices

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;


37

This line gets

added to

.designer.cs

Use .Text

property to

retrieve the

value


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 KeyPress( ) event-handler method

– BUT, event is fired with each and EVERY keystroke


39

Programming Event Handlers

(continued)

Figure 10-8 KeyPress and SelectedIndexChanged events fired

KeyPress( )

event-

handler

method

fired with

each

keystroke


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


41

Adding Menus

Figure 10-9 First step to creating a menu

Drag MenuStrip

control to form,

then click here to

display Menu

structure


42

MenuStrip Control Objects

• Ampersand (&) is typed between the F and o for the

Format option to make Alt+o shortcut for Format

Figure 10-10 Creating a shortcut for a menu item


43

MenuStrip Control Objects (continued)

• To create separators,

right-click on the text

label (below the

needed separator)

• Select Insert

Separator

Figure 10-11

Adding a separator

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

fro each selectable menu option

– Each has its own properties

– Each can have its own even handler method


44


45

MenuStrip Control Objects (continued)

Figure 10-12 Setting the Property for the ToolTip control

ToolTip

property sets

text that’s

displayed

when the

cursor is

rested on top

of the control


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

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");

}


47


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


Windows Dialog Boxes


49

Figure 10-13 Adding dialog controls to menu options


50


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 10-15

Font dialog box menu option


51


Windows Dialog Boxes – Color

private void menuColor_Click(object sender,

System.EventArgs e)

{

colorDialog1.Color = lblOutput.ForeColor;

if (colorDialog1.ShowDialog( ) != DialogResult.Cancel )

{

lblOutput.ForeColor = colorDialog1.Color;

}

}

Retrieves the

current ForeColor

property setting

for the Label

object

Checks to see

if Cancel

button clicked Set to

selection

made


52

Figure 10-14 Color dialog box menu option


Windows Dialog Boxes – Color

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


53

Review GardeningForm Example


54

GardeningForm Properties

Table 10-4 GardeningForm property values

Each entry

has an

associated

statement in

the

.Designer.cs

file


55

GardeningForm Properties (continued)

Table 10-4 GardeningForm property values (continued)


56





57


GardeningForm Events


58

Table 10-5 GardeningForm events

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


59


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


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

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) { }


62

Method name more generic so it can

be used with multiple controls


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


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


65

Adding RadioButton Objects

Figure 10-16 GroupBox and RadioButton objects added

Box drawn

around

RadioButton

objects is

from

GroupBox


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

Wiring One Event Handler to

Multiple Objects (continued)


67

Figure 10-17 Wired Click events

Each

CheckBox

and

RadioButton

wired to

same

method


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


69

ComputeCost_CheckChanged( ) and

Click( ) Events Raised

Figure 10-18 ComputeCost_CheckedChanged( ) and Click( )

events raised

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)


70


Foundation (WPF)


71

Figure 10-19 WPF design

RegistrationApp

was recreated

using WPF


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


72

Review WPF_Example


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


74

TabControl Controls (continued)

Figure 10-21 Tabbed controlled application


75


Figure 10-22 TabControl object stretched to fill form


76


• TabPage property

enables you to

format individual

tabs

• Clicking the

ellipsis beside the

Collection value

displays the

TabPage

Collection Editor

Figure 10-23 TabControl's TabPage Collection Editor


• 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


77

Review PizzaApp Example


78

DinerGUI

Application

Example

Figure 10-24 Problem specification for DinerGUI example


79

Table 10-6 Order class data fields

DinerGUI (continued)


80


Figure 10-25 Prototype for DinerGUI example


81

DinerGUI

(continued)

Figure 10-26 Class diagrams


82

Figure 10-27 Pseudocode for the Order class for DinerGUI



83

Figure 10-28

Pseudocode for

RadioButton,

CheckBox,

ListBox, and

ComboBox

object event

handlers

DinerGUI

(continued)


84

Figure 10-29 Pseudocode for menu object event handlers

DinerGUI

(continued)


85

Figure 10-30 Pseudocode for menu object event handlers and

ClearDrinks( ) method

DinerGUI

(continued)


86


Table 10-7 DinerGUI property values


87


Table 10-7 DinerGUI property values (continued)


88




89




90




91


Figure 10-31 Interface showing menu selections

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]);

}

}


92


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;

}


93


Review Diner Example


94


Figure 10-32 Message displayed from Place Order menu option


95

Figure 10-33 Message displayed from Current Order menu option



96


Figure 10-34 Special Requests click event fired


97


Figure 10-34 Clear Order click event fired


98


Table 10-8 DinerGUI events


99


Table 10-8 DinerGUI events

Coding Standards

• Follow a consistent naming standard for controls

• Before you register events, such as button click

events, name the associated control


100

Resources

Visual Studio 2012 - Getting Started Tutorials –

http://msdn.microsoft.com/en-us/library/dd492171.aspx

Visual C# Windows Forms Tutorials

http://visualcsharptutorials.com/windows-forms

C# Programmers Reference: Delegates Tutorial –

http://msdn.microsoft.com/en-

us/library/aa288459(VS.71).aspx


101







http://msdn.microsoft.com/en-us/library/aa288459(VS.71).aspx



Resources

Delegates and Events in C#/.NET –

http://www.akadia.com/services/dotnet_delegates_and_events

.html

Geekpedia - ListBox and CheckedListBox –

http://www.geekpedia.com/tutorial40_ListBox-and-

CheckedListBox.html

CodeGuru - Create a Dynamic Menu Using C# –

http://www.codeguru.com/csharp/csharp/cs_misc/designtechn

iques/article.php/c15661/


102

http://www.akadia.com/services/dotnet_delegates_and_events.html

http://www.akadia.com/services/dotnet_delegates_and_events.html

http://www.geekpedia.com/tutorial40_ListBox-and-CheckedListBox.html





http://www.codeguru.com/csharp/csharp/cs_misc/designtechniques/article.php/c15661/

http://www.codeguru.com/csharp/csharp/cs_misc/designtechniques/article.php/c15661/


103

Chapter Summary

• Delegates

• Event-handling procedures

– Registering an event

• ListBox control for multiple selections

• ComboBox versus ListBox objects


104

Chapter Summary (continued)

• Adding controls to save space

– MenuStrip controls

– TabControl

• Use of GroupBox controls

• RadioButton versus CheckBox objects

programming based on events -...

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