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Lecture Summary for IT 236 on 6/15/06

Review Questions

1. What do the following symbols mean in VB.NET?
   &     _     .     ( )     { }     "     '
   Ans: They mean concatenation ( & ), line continuation ( _ ), member selection operator ( . ), method call ( ( ) ), nothing in VB ( { } ), string delimiters ( " ), start of comment ( ' ).

2. List four ways to start a VB.NET application.
   Ans: Start button (triangular), Main Menu Debug >> Start, F5, double click on .exe file using the Windows Explorer.

3. List as many ways as you can to to stop a VB.NET application.
   Ans: Stop button (square), Alt F4, Close Button in the application control panel, click on image icon on left of title bar >> Close, right click on application in Taskbar >> Close, Use Control-Alt-Delete to invoke Task Manager and close application with it, use Me.Close( ) in the code.

4. What do Option Explicit On and Option Strict On mean?
   Ans: It means that automatic type conversions will NOT be performed.

5. What is the difference between a console application and a Windows application?
   Ans: A console application is prescriptive in the sense that its code tells the application what to input, what computations to perform, and what to output. A Windows application is reactive in the sense that it waits for the user to generate events (like Click or TextChanged) and then executes event handlers in response to those events.

6. What two properties should you immediately set after you place a new control on a form?
   Ans: Change the name to something more meaningful and set the Text property to make the application clear on the application user interface.

7. What is the difference between a method and an event?
   Ans: A method is something that the object does. An event is something that happens to the object that the object can detect.

8. What is an event handler?
   Ans: A method that executes when the corresponding event occurs.

9. How do you create an event handler for a control using the .NET IDE?
   Ans: Double click on the control to get the default event for the control. Use the drop down boxes above the Code Window to pick the control and event for an event handler more precisely.

10. What is the default event for a control?
    Ans: Every control has an event designated as its default event. When the user double clicks on that control in the Form Designer Window, an event handler for the default event is created.

11. Write a line of code that will display the image "c:\roses.gif" in the picture box picFlower. Ans:
    picFlower.Image = Image.FromFile("c:\roses.gif")

12. Give two ways of changing the Text property of the textbox txtA to "abc".
    Ans: Set the Text property of txtA in the Properties Window, Use the code txtA.Text = "abc".

13. Explain the difference between
    System.Console.WriteLine("Hello")
    and
    System.Console.Write("Hello")
    Ans: After writing its output to the console, WriteLine goes to a new line, whereas Write holds the line for the next output.

14. Use
    System.Console.WriteLine
    to output the greeting Hello, contatenated with the current value of the string variable name. Ans:
    System.Console.WriteLine("Hello, " & name & ".")

Intellisense

• Use Intellisense for help in writing .NET code.

• Intellisense provides dropdown boxes with three kinds of help:
  Quick Info:   Supplies a list of declarations that are possible after typing
  Dim variableName As
  and a space.

  List Members:   Lists the data members and methods after the object name and dot (member selection operator) are typed.

  Parameter Info:   Shows the type and meaning of each parameter for a method after typing the method name and left parenthesis. If the method is overloaded, any signature of the overloaded methods can be chosen.

Namespaces

• A namespace is a naming convention that organizes .NET items into related categories.

• A namespace can contain (among other things) classes, modules, enumerations, and additional namespaces.

• The most important namespace is System.

• Other examples of namespaces: System.IO, System.Data, System.Drawing, System.Drawing.Drawing2D, System.Drawing.Printing, System.Windows.Forms, System.Collections, Microsoft.VisualBasic.

• Every project has a root namespace that is specified in the project properties. The default root namespace is the same as the name of the project.

The Imports Statement

• Use the Imports Statement to allow members of namespaces, classes, or enumerations to be used without qualification.

• For example, if the statement
  Imports System.Console
  is used, the line
  WriteLine("Hello, World.")
  can be used instead of
  System.Console.WriteLine("Hello, World.")

• The statement
  Imports System
  is assumed, so it need not be included.

Practice Problems

• Work these problems from the textbook on page 70 of the text:
  17. Display "E. T. phone home." in lblTwo.
  lblTwo.Text = "E. T. phone home."

  19. Display "The stuff that dreams are made of." in red letters in txtBox.
  txtBox.ForeColor = Color.Red
  txtBox.Text = "The stuff that dreams are made of."

  21. Disable txtBox.
  txtBox.Enabled = False

  22. Change the words in the form's title bar to "Hello World".
  Me.Text = "Hello World"

  23. Make lblTwo disappear.
  lblTwo.Visible = False
  or lblTwo.Hide( )

  25. Enable the disabled button btnOutcome.
  btnOutcome.Enabled = True

  28. Give the focus to txtBoxTwo.
  txtBoxTwo.Focus( )

• Create a Windows application with a PictureBox control that displays happy.jpg when the cursor enters the picture box (MouseEnter event), then displays sad.jpg when the cursor leaves (MouseLeave event) the picture box.

  Ans: Here is the source code for the two event handlers:
  

  Public Sub picFace_MouseEnter(sender As Object, _
      e As MouseEventArgs)
  
      picFace.Image = Image.FromFile("happy.jpg")
  End Sub
  
  Public Sub picFace_MouseLeave(sender As Object, _
      e As MouseEventArgs)
  
      picFace.Image = Image.FromFile("sad.jpg")
  End Sub
  

Constants, Variables, and Datatypes

• For this course, you need only be familiar with the Integer, Double, String and Boolean datatypes.

Operators

• The following operators are available in VB.NET:
  Arithmetic
  Addition   +

  Subtraction   -

  Multiplication   *

  Division   /

  Integer Division   \

  Exponentiation   ^

  String
  Concatenation   &

  Relational
  Equal To   =

  Greater Than   >

  Greater Than Or Equal To   >=

  Less Than   <

  Less Than Or Equal To   <=

  Not Equal To   <>

  Reference Equality   Is

  Logical
  Boolean And   And

  Boolean Or   Or

  Assignment
  =     +=     -=     *=     /=     \=     ^=

• VB.NET Operator Precedence Table

Practice Problem

• Temperature1   Mortgage1   Temperature2

Changing the Name of a Form

1. Change the name of the Form in the properties window from Form1 to frmMain. This will have the effect of changing the name of the class in the code also.

2. Change the name of the source code file in the Solution Explorer from Form1.vb to frmMain.vb.

3. Right click on the name of the Project in the Solution Explorer, then choose Properties.
   Change the name of the Startup object from Form1 to frmMain.

Some Controls

• Label
  Properties:
  BorderStyle:   None, FixedSingle, Fixed3D

  Text:   String

  TextAlign:   TopLeft, TopCenter, TopRight, MiddleLeft, MiddleCenter, MiddleRight, BottomLeft, BottomCenter, BottomRight

• Button
  Properties:
  FlatStyle:   Flat, Popup, Standard, System

  Text:   String

  TextAlign:   Same Values as label control.

  Methods:
  PerformClick: Causes Click event handler to fire.

  Events:
  Click:   User clicks on the button.

  DoubleClick:   User clicks twice on the button in a short amount of time.

• TextBox
  Properties:
  BorderStyle:   Same values as Label control.

  CharacterCasing:   Lower, Normal, Upper

  MaxLength:   Integer

  Multiline:   False, True

  PasswordChar:   String (should be of length 1)

  ReadOnly:   False, True

  ScrollBars:   None, Horizontal, Vertical, Both

  Text:   String

  TextAlign:   Center, Left, Right

  WordWrap:   False, True

  Methods
  AppendText:   Append text to Text property.

  Clear:   Set Text to "".

  Events:
  Click:   Double click is preferred for textboxes. Click is used to set focus.

  DoubleClick:   Same as button DoubleClick event.

  TextChanged:   Fires when the Text property is changed by the user or application code.

The Control Class

• The Control class is the parent class for all .NET controls

• Properties common to all controls are defined in the Control class and inherited by individual controls.
  BackColor, Location, BackgroundImage, Cursor, Enabled, Focused, Font, ForeColor, Location, Name, TabIndex, TabStop, Tag, Text, Visible.

• Some Control Methods
  Focus, GetNextControl, Hide, Show, SetBounds

• Some Control Events
  Enter (control gains focus), Leave (control loses focus)

• Example: Mortgage2

Some Properties of the Form Class

• BackColor, Cursor, ForeColor, Text, WindowState (Maximized, Minimized, Normal), Opacity, AcceptButton, CancelButton.

The Form_Load Event Handler

• The Form_Load event occurs when the form is loaded into memory as the application first starts to run.

• Put code in the form load method that must execute before any events are generated by the user, such as Click, MouseEnter, MouseLeave.

• The following Handles clause is used for the Form_Load event:
  Handles MyBase.Load

Practice Problems

1. Work Problem 38 on Page 71 in the textbook.
   

The CurrencyConverter Project

Running a Windows Example using Visual Studio 2005

• Create a new Windows Example using Visual Studio 2005.

• Go to the Solution Explorer.

• Click the Show All Files button. You will see two source code files: Form1.vb, which contains the code that you add, and Form1.Designer.vb, which contains code that the Windows Forms Designer writes based on the controls that you add to the form.

• Open Form1.Designer.vb, press Control-A to select all the code, then press Delete. Since all of the examples on the course website are written with Visual Studio 2003, the code in Form1.Designer.vb is not needed.

• Copy and paste the code from the example on the class website into the file Form1.vb.

• Run the project as usual.