Desktop Applications: Core Concepts

1
Chapter 2

• Desktop ApplicationsCore Concepts

2
Objectives (1)

• Explore the types of VB .NET applications
• Understand the organization of a VB .NET
  application
• Examine the windows that comprise the Visual
  Studio .NET IDE
• Work with a form module
• Understand the basic operation of Windows forms
• Learn how to manage forms

3
Objectives (2)

• Understand the purpose of VB .NET controls,
  create control instances, and set properties for
  those control instances
• Set the tab order for controls
• Understand the operation of VB .NET event
  handlers
• Dynamically create event handlers and control
  instances at runtime
• Understand the collections of controls

4
Previewing the Completed Solution

• Most chapters, including this one, present a
  completed solution at the beginning of the
  chapter
• The completed solution has numerous comments
• Each chapter contains a startup solution
• By completing hands-on steps corresponding to the
  startup solution, you end up with the completed
  solution
• For brevity, the startup solution does not
  contain comments

5
Types of Visual Basic .NET Applications (1)

• Chapter 1 introduced the Console Application
• Applications are called projects
• This chapter introduces the Windows Application
  and other Visual Studio .NET project types
• Project types
• Windows Application run directly by the end
  user
• Class Library contain components (namespaces)
  intended for use by other developers
• Windows Control Library contain custom controls

6
Types of Visual Basic .NET Applications (2)

• Project types
• ASP.NET Web Application applications that run
  on the Internet or an intranet
• ASP.NET Web Service Web applications having
  different clients other than a Web browser
• Web Control Library contains custom controls
  designed for use on the Web
• Console Application run from a Command Prompt
  window
• Windows Service applications with which the
  user has no interaction

7
Creating a New Project
Project types pane
Application templates
Solution name
Solution folder
8
Organization of a Visual Basic .NET Application

• Applications are organized into solutions
• Solution file has a file suffix of .sln
• Solution file is a text file
• All elements of a solution are stored in a
  separate directory called a solution directory
• Solution directory (folder) is created when the
  solution is created
• Cannot create a solution in an existing directory

9
The Solution Explorer
Show All Files button
Click to expand or collapse folders
10
Project Files

• Each solution contains one or more projects
• Project files are XML documents
• Project file contains
• The type of project
• References to namespaces and assemblies
• Compilation information specific to a project
• Module files make up the forms and other classes
  in the project

11
Solution, Project, and Module Relationships
12
Summary of the IDE Windows

• The Visual Studio .NET IDE operates in two modes
• Tabbed documents mode is new to .NET and is used
  in this book
• MDI mode resembles previous versions
• Types of windows
• Document windows appear on tab groups
• Edit a form's visual interface with the Win Forms
  Designer
• Edit a form's corresponding code with the Code
  Editor
• Only one document window on a tab group is active
  at a time
• Tool windows can be docked, auto hidden, or float
  on the desktop

13
Document Windows
Document windows appear on a tab group
Solution Explorer appears as a tool window
14
Tool Windows

• The Solution Explorer manages the solution, its
  projects, and the files in those projects
• The Properties window is used to set design-time
  properties for the form and selected control
  instances
• The Toolbox contains controls
• Controls appear on different tabs based on their
  purpose
• Possible to create custom tabs

15
Tool Window Appearance

• Auto Hide - tool window is hidden along an edge
  of the desktop
• Auto hidden windows must be docked along an edge
  of the IDE
• Dockable windows can be docked along an edge of
  the IDE
• Floating windows can appear anywhere on the
  desktop
• Note some tool windows can appear as document
  windows

16
The Properties Window

• Properties window contains two columns
• Left column lists property names
• Edit property value in right column
• Object list box displays selected control
  instances
• Displays nothing when multiple control instances
  are selected
• Properties containing an object or structure can
  be expanded or collapsed
• Some properties are set using a dialog box called
  a property editor
• Different property editors exists for properties
  storing specific data types such as Color
• Properties can be set for multiple control
  instances simultaneously

17
The Properties Window (Color property editor)
Object list box
Web tab active in Color property editor
18
The Properties Window (Alignment property editor)
Middle-right justification
19
The Win Forms Designer

• Always appears as a document window on a tab
  group
• Optional resizable tray appears for invisible
  control instances
• Create a control instance on a form by clicking a
  control in the Toolbox and positioning it on the
  form
• Move or resize control instances by clicking them
  to activate them and using sizing handles
• Visual Studio .NET writes statements in the
  corresponding module to create control instances

20
The Code Editor

• The text editor used specifically to edit VB .NET
  module files
• Features
• Automatic statement indentation
• Statement completion of If, Select Case, and
  looping statements
• Clipboard ring supports multiple clipboards
  similar to Office
• Collapse and expand procedures and regions as
  necessary
• Copy and paste rectangular code regions

21
The Code Editor (Example)
Class Name list box
Method Name list box
Expand or collapse region
Windows Form Designer generated code is collapsed
22
The Structure of a Win Forms Designer Generated
Class Module

• Win Forms Designer generates statements as
  control instances are created on a form
• Statements are hidden inside of a region block

Public Class frmSplash Inherits
System.Windows.Forms.Form Region " Windows
Form Designer generated code " ' Statements
End Region End Class
23
Constructors

• A constructor is a Sub procedure named New
• VB .NET calls a constructor (New procedure) when
  the CLR creates an instance of a class
• Example
• Public Sub New(ByVal AircraftType As String
• ByVal pstrOrigin As String, _
• ByVal pstrDestination As String
• ' Statements
• End Sub

24
Destructors

• A destructor is called when a class instance gets
  destroyed
• Method is named Dispose

25
Statements Generated by the Win Forms Designer

• Win Forms Designer declares variables to store
  all control instances
• Statements appear in a procedure named
  InitializeComponent
• Do not modify the contents of this procedure
• Declare a variable to store a Label control
  instance
• Friend WithEvents lblName As _
• System.Windows.Forms.Label
• Create the control instance
• Me.lblName New _
• System.Windows.Forms.Label()

26
Configuring Control Instances

• Win Forms Designer generates statements to
  configure control instances
• Configure the Label control instance named
  lblCompany
• Me.lblCompany.ForeColor _
• System.Drawing.Color.Azure
• Me.lblCompany.Location New _
• System.Drawing.Point(40, 64)
• Me.lblCompany.Name "lblCompany"

27
The Basics of Windows Forms

• Every Windows Application project contains one or
  more forms
• Each form is derived from the System.Windows.Forms
  .Form class

28
System.Windows.Forms.Form Class (1)

• Properties
• AcceptButton defines the button designated as the
  AcceptButton
• Click event handler fires when user presses Enter
• AutoScroll defines whether scroll bars will
  appear when control instances do not fit in
  form's visible region
• Click event handler fires for CancelButton when
  user presses Escape key
• FormBorderStyle defines border characteristics
• StartPosition defines initial position on desktop

29
System.Windows.Forms.Form Class (2)

• Events
• Enter event fires when form gets focus
• Leave event fires when form loses focus
• Methods
• Close method unloads form
• Hide method makes form invisible without
  unloading it
• Show method displays a modeless form
• ShowDialog method displays a modal form

30
Setting the Startup Object

• Set the Startup object using the Project
  Properties Pages dialog box

General tab selected
Startup object
31
Displaying a Form

• Create an instance of the Form class
• New keyword creates class instance
• Dim frmSplashNew As New frmSplash()
• Call the ShowDialog method to display a modal
  form
• frmSplashNew.ShowDialog()

32
Execution Flow of Displaying Modal Dialog Boxes
33
Adding a Module
Select Module to add a module
Specify module name
34
The Basics of Controls

• Controls appear in the Toolbox and are part of
  the .NET Framework class library
• Controls are derived from System.Windows.Forms.Con
  trol
• Control class supplies keyboard input and mouse
  functionality
• Control class updates display as necessary

35
Common Controls

• Button, CheckBox, and RadioButton form clickable
  buttons
• ComboBox and ListBox are list controls
• Display items in a columnar list
• Horizontal and vertical scroll bars are
  scrollable controls
• Use to select a value from a range of values
• TextBox and RichTextBox used to edit text
• Label class displays text
• Panel control contains other controls

36
Changes to Controls

• VB .NET no longer supports control arrays
• Controls no longer have a Caption property
• Text property replaces Caption
• ToolTips are implemented using ToolTip control
• Positional properties are implemented differently

37
Control Hierarchy
38
The Timer Control

• Tick event fires at regular intervals
• Tick event only fires when Enabled property is
  True
• Interval property stores 32 bit Integer
• Value is measured in milliseconds
• 1000 is equal to 1 second

39
Menus and Menu Items

• MainMenu control is used to create a menu
• Typically one menu per form
• Create menus and menu items in place on the Win
  Forms Designer
• character in text defines hot key
• Each menu and menu item is an instance of the
  MenuItem class

40
The MenuItem Class

• Properties
• Checked property designates a checked menu item
• Boolean Enabled property defines whether control
  instance is enabled or not
• Shortcut and ShowShortcut properties define
  menu's shortcut key
• Text property contains text appearing on menu
• Visible property defines whether menu item is
  visible or not
• If a menu is not visible, its children are not
  visible
• Events
• Click event fires when user clicks menu item

41
Creating a Menu
Menu titles and menu items are edited in place
MainMenu control instance appears in resizable
tray
42
Editing Menu Names
43
The CheckBox Control

• Contains a box the user checks and a textual
  description
• Operates as a two-state or three-state control
• Two-state control can be checked or unchecked
• Use Checked property and CheckedChanged event in
  two-state mode
• Three-state control can be checked, unchecked, or
  indeterminate
• Use CheckState property and CheckStateChanged
  event in three-state mode

44
The Label and TextBox Controls (1)

• The TextBox displays an editable text region
• Properties
• AcceptsReturn causes return character to be
  embedded in text if True. If False, pressing
  Enter fires Click event handler for default
  button
• AcceptsTab, if true, causes tab key to be
  embedded in text
• Lines contains an array of strings. Each string
  represents 1 line
• MaxLength defines maximum number of characters
  the user can enter
• ReadOnly property defines whether or not text can
  be changed

45
The Label and TextBox Controls (1)

• Methods
• Clear removes contents
• Cut, Copy, and Paste perform clipboard operations
• Focus method sets input focus
• Events
• Enter event fires when control instance gets
  focus
• Leave event fires when control instances loses
  focus
• Validating event fires before control instance
  loses focus
• Event may be cancelled

46
The Button Control

• The Button control supplies a clickable button
• Create a Click event handler to execute when user
  clicks the button
• FlatStyle property defines 3-D appearance of the
  button
• Image property contains optional image
• ImageAlign property defines alignment of the
  image
• PerformClick method fires a Click event

47
Scroll Bar Controls

• Vertical and horizontal scroll bars work the same
  way
• Value property stores current value
• Integer Minimum and Maximum properties define the
  valid range for the Value property
• Minimum must be less than Maximum
• SmallChange and LargeChange properties define
  amount of change to the Value property when the
  scroll arrows and scroll region are clicked
• ValueChanged event fires when Value property
  changes

48
Radio Buttons

• A group of radio buttons is called a button group
• If multiple button groups exists on a form,
  create each button group in a GroupBox or Panel
  control instance

49
List and Combo Boxes

• Properties
• Items property contains a reference to Items
  collection
• Each item represents one item appearing in the
  list
• Add items at design-time using the String
  Collection Editor
• SelectedIndex contains 0-based index of selected
  item
• Value is -1 if no item is selected
• SelectedItem contains a reference to the selected
  item
• Note data type is System.Object to a list box can
  store anything
• Methods
• ClearSelected deselects items
• Events
• SelectedIndexChanged event fires when the user
  selects a different item

50
Adding a List Item at Runtime

• Call the Add method of the Items
  collectionlstDestination.Items.Add("Atlanta")
• Call the AddRange method to add multiple items
• Assume that pstrCities is an array of strings
• lstDestination.Items.AddRange(pstrCities)

51
The ToolTip Control

• Considered a provider control as it works in
  conjunction with another control
• Properties
• AutoPopupDelay defines how long the ToolTip is
  displayed
• InitialDelay property defines delay interval
  before first displaying the ToolTip
• Other control instances support a ToolTip on xxx
  property
• Contains text appearing to the user

52
Understanding Tab Order

• Tab order representsorder in which control
  instances get focus
• Click View, Tab Order to set the tab order

53
Introduction to Event Handlers

• Characteristics
• Always accept two arguments
• The first argument named sender contains a
  reference to the object firing the event
• Second argument derives from System.EventArgs
  class
• Use second argument to get information about
  event
• Handles clause causes a procedure to handle an
  event

54
Event Classes

• KeyEventArgs class has properties to get keyboard
  character pressed
• KeyPressEventArgs gets ASCII character that was
  pressed
• MouseEventArgs used to determine which mouse
  button was pressed or released
• CancelEventArgs used with Validating event
• Allows developer to cancel event when invalid
  input is discovered

55
Multicast Event Handlers

• One event handler handles an event for multiple
  control instances
• Include Handles class followed by a comma
  separated list of control.event names
• Handles rad737.CheckedChanged, _
  rad777.CheckedChanged

56
Casts

• CType function converts an object from one type
  to another
• First argument contains object to convert
• Second argument contains type of destination
  object
• Example Convert to RadioButton
• radCurrent Ctype(sender, _
  System.Windows.Forms.RadioButton)

57
Dynamic Event Handlers

• AddHandler statement creates a new event handler
• RemoveHandler removes a dynamic event handler
• AddressOf keyword contains name of procedure
  registered as event handler
• AddHandler chkSeats.CheckedChanged,_
• AddressOf _ chkSeats_CheckedChanged

58
Collections of Controls

• Controls collection contains a reference to each
  control instance created directly on a form
• Container controls have their own Controls
  collection
• Enumerate Controls collection with a For Each
  loop
• ExampleDim ctlCurrent As Control
• For Each ctlCurrent In Me.Controls
• ' Statements
• Next