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Click to edit Master title

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Title: Click to edit Master title Author: Richard Chrisman Last modified by: Mirella Misiaszek Created Date: 10/23/2003 2:16:34 PM Document presentation format – PowerPoint PPT presentation

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Title: Click to edit Master title


1
1
2
Objectives
  • Create a structure
  • Declare and manipulate a structure variable
  • Differentiate between a structure variable and
    member variables
  • Create an array of structure variables
  • Include a radio button in an interface

3
Objectives (continued)
  • Include a check box in an interface
  • Include a list box in an interface
  • Code a text boxs KeyPress event
  • Code a text boxs Enter event
  • Associate a procedure with different events

4
Structures
  • You can create your own data types using the
    Structure statement
  • Referred to as user-defined data types or
    structures
  • Structures contain member variables between
    Structure clause and End Structure clause
  • Member variables are declared using Public
    keyword followed by the variable name and then
    the desired data type

5
HOW TO
6
Using a Structure to Declare a Variable
  • Variables declared using a structure are often
    referred to as structure variables

7
HOW TO
8
Passing a Structure Variable to a Procedure
  • The personnel manager at Johnsons Lumber wants an
    application that he can use to save each
    managers employee number, name, and salary in a
    sequential access file
  • Figure 10.4 shows a sample run of the Johnsons
    Lumber application
  • Figure 10.5 shows how you can code the
    application without using a structure
  • Figure 10.6 shows coding the application using an
    Employee structure to group together the employee
    data

9
Passing a Structure Variable to a Procedure
(continued)
10
Passing a Structure Variable to a Procedure
(continued)
11
Passing a Structure Variable to a Procedure
(continued)
12
Passing a Structure Variable to a Procedure
(continued)
13
Passing a Structure Variable to a Procedure
(continued)
14
Passing a Structure Variable to a Procedure
(continued)
15
Creating an Array of Structure Variables
  • An array of structures can be used in place of
    two or more parallel arrays
  • Figures 10.7 and 10.8 demonstrate using an array
    of structure variables for the Takoda Tapahe
    application first introduced in chapter 9

16
Creating an Array of Structure Variables
(continued)
17
Creating an Array of Structure Variables
(continued)
18
Adding a Radio Button to the Form
  • Use Radio Button Tool in the toolbox
  • Radio Button allows you to limit user to only one
    choice in a group of two or more related and
    mutually exclusive choices.
  • Radio buttons are placed in a group box control
    or panel control to be mutually exclusive
  • Group box or panel control must be added to form
    before adding radio button
  • Set default button within group by setting
    Checked property to True

19
HOW TO
20
Adding a Radio Button to the Form (continued)
21
Adding a Radio Button to the Form (continued)
22
Adding a Radio Button to the Form (continued)
23
Adding a Check Box Control to the Form
  • Check boxes allow user to select any number of
    choices from a group of one or more independent
    and nonexclusive choices

24
Adding a Check Box Control to the Form (continued)
25
Adding a Check Box Control to the Form (continued)
26
Adding a Check Box Control to the Form (continued)
27
Adding a List Box to an Interface
  • Use a list box to display a list of choices from
    which the user can select zero, one, or more
    choices

28
Adding a List Box to an Interface (continued)
29
Adding Items to a List Box
  • Items in a list box belong to Items Collection
  • Collection is group of one or more individual
    objects treated as one unit
  • Items in the collection identified by an index
  • An index is a unique number determined by the
    items order of placement in the collection
    starting with zero
  • Add method adds items to the list box
  • The item selected when interface first appears is
    referred to as the default list box item

30
HOW TO
31
The SelectedItem and SelectedIndex Properties
32
The SelectedItem and SelectedIndex Properties
(continued)
33
The SelectedItem and SelectedIndex Properties
(continued)
34
The SelectedItem and SelectedIndex Properties
(continued)
35
Using the KeyPress Event
  • A controls KeyPress event occurs when the user
    presses a key while the control has focus
  • KeyPress event has two parameters sender and e
  • Use e.KeyChar property to determine which key was
    pressed
  • Use e.Handled property to cancel if key was
    inappropriate for desired action

36
HOW TO
37
Selecting the Existing Text in a Text Box
  • Use SelectAll method in appropriate Sub such as
    the Enter event for text box
  • Enter event occurs when user tabs to control and
    focus is received

38
Associating a Procedure with Different Events
  • List each event, separated by commas, in the
    Handles section of the procedure header

39
Programming Example Glovers Application
  • Glovers Industries stores the item numbers,
    wholesale prices, and retail prices of the items
    it sells in a sequential access file named
    items.txt.
  • Opal Jacoby, the companys sales manager, wants
    an application that allows her to enter an item
    number and then display either the wholesale
    price or the retail price

40
Programming Example Glovers Application
(continued)
  • Data is stored in items.txt, one item per line
  • Item number is first,
  • then wholesale price, and
  • then retail price

41
TOE Chart
42
User Interface
43
Objects, Properties, and Settings
44
Tab Order
45
Pseudocode
  • frmGlovers Load event procedure
  • Try
  • open items.txt for input
  • repeat until no more characters to read or end
    of array
  • read an item number, wholesale price, and
    retail price and
  • assign it to the mitmItems array
  • add the item number to the lstNumber control
  • add 1 to the variable that keeps track of the
    array subscripts
  • end repeat
  • close the items.txt file
  • select the first item in lstNumbers control
  • Catch (use general catch statement to handle
    any errors)
  • if error occurs, display exception description
    in a messagebox

46
Pseudocode (continued)
  • btnExit Click event procedure
  • close application
  • btnDisplay click Event procedure
  • assign item number selected in lstNumbers to
    strSearchFornumber variable
  • repeat until item number is located in mitmItems
    array
  • add 1 to the variable that keeps track of array
    subscripts
  • if radWholesale control is select
  • display in lblPrice wholesale price stored in
    mitmItems array
  • else
  • display in lblPrice retail price stored in
    mitmItems array
  • radRetail_Click, radWholesale_Click event
    procedures and
  • lstNumbers.SelectedIndex Changed procedure
  • clear the contents of the lblPrice control

47
Code
48
Code (continued)
49
Code (continued)
50
Summary
  • You can use the Structure statement to define a
    user-defined data type (or structure) in Visual
    Basic .NET
  • Typically enter the Structure statement in the
    forms Declarations section
  • A structure variable contains one or more member
    variables
  • You access a member variable using the structure
    variables name, followed by the dot member
    access operator and the member variables name

51
Summary (continued)
  • Use an assignment statement to assign a value to
    a member variable
  • Data type of value must match data type of member
    variable
  • Structure variable can be passed to procedures
  • You access a member variable in an array element
    using the arrays name, followed by the elements
    subscript enclosed in parentheses, the dot member
    access operator, and the member variables name

52
Summary (continued)
  • Use radio buttons when you want to limit the user
    to one of two or more related and mutually
    exclusive choices
  • Two is the minimum number of radio buttons in a
    group? recommended maximum is seven
  • The label in the radio buttons Text property
    should be entered using sentence capitalization
  • Assign a unique access key to each radio button
    in an interface

53
Summary (continued)
  • Use a group box control (or a panel control) to
    create separate groups of radio buttons
  • Only one button in each group can be selected at
    any one time
  • Designate a default radio button in each group of
    radio buttons
  • Use check boxes when you want to allow the user
    to select any number of choices from a group of
    one or more independent and nonexclusive choices

54
Summary (continued)
  • A list box should display minimum of three
    selections and maximum of eight selections at a
    time
  • Default item in list box should be either the
    most used selection or the first selection in the
    list
  • You can use the e parameters KeyChar and Handled
    properties to prevent a text box from accepting
    inappropriate characters
  • You can enter more than one event after the
    Handles keyword in a procedure
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