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11
2Objectives
- 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
3Objectives (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
4Structures
- 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
5HOW TO
6Using a Structure to Declare a Variable
- Variables declared using a structure are often
referred to as structure variables
7HOW TO
8Passing 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
9Passing a Structure Variable to a Procedure
(continued)
10Passing a Structure Variable to a Procedure
(continued)
11Passing a Structure Variable to a Procedure
(continued)
12Passing a Structure Variable to a Procedure
(continued)
13Passing a Structure Variable to a Procedure
(continued)
14Passing a Structure Variable to a Procedure
(continued)
15Creating 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
16Creating an Array of Structure Variables
(continued)
17Creating an Array of Structure Variables
(continued)
18Adding 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
19HOW TO
20Adding a Radio Button to the Form (continued)
21Adding a Radio Button to the Form (continued)
22Adding a Radio Button to the Form (continued)
23Adding 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
24Adding a Check Box Control to the Form (continued)
25Adding a Check Box Control to the Form (continued)
26Adding a Check Box Control to the Form (continued)
27Adding 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
28Adding a List Box to an Interface (continued)
29Adding 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
30HOW TO
31The SelectedItem and SelectedIndex Properties
32The SelectedItem and SelectedIndex Properties
(continued)
33The SelectedItem and SelectedIndex Properties
(continued)
34The SelectedItem and SelectedIndex Properties
(continued)
35Using 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
36HOW TO
37Selecting 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
38Associating a Procedure with Different Events
- List each event, separated by commas, in the
Handles section of the procedure header
39Programming 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
40Programming 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
41TOE Chart
42User Interface
43Objects, Properties, and Settings
44Tab Order
45Pseudocode
- 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
46Pseudocode (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
-
47Code
48Code (continued)
49Code (continued)
50Summary
- 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
51Summary (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
52Summary (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
53Summary (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
54Summary (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