Microsoft Visual Basic .NET: Reloaded

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 Microsoft Visual Basic .NET: Reloaded

Objectives (continued) • Include a check box in an interface • Include a list box in an interface • Code a text box’s KeyPress event • Code a text box’s Enter event • Associate a procedure with different events Microsoft Visual Basic .NET: Reloaded

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 Microsoft Visual Basic .NET: Reloaded

HOW TO… Microsoft Visual Basic .NET: Reloaded

Using a Structure to Declare a Variable • Variables declared using a structure are often referred to as “structure variables” Microsoft Visual Basic .NET: Reloaded

Passing a Structure Variable to a Procedure • The personnel manager at Johnsons Lumber wants an application that he can use to save each manager’s 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 Microsoft Visual Basic .NET: Reloaded

Passing a Structure Variable to a Procedure (continued) Microsoft Visual Basic .NET: Reloaded

Passing a Structure Variable to a Procedure(continued) Microsoft Visual Basic .NET: Reloaded

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 Microsoft Visual Basic .NET: Reloaded

Creating an Array of Structure Variables(continued) Microsoft Visual Basic .NET: Reloaded

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 Microsoft Visual Basic .NET: Reloaded

Adding a Radio Button to the Form(continued) Microsoft Visual Basic .NET: Reloaded

Adding a Radio Button to the Form (continued) Microsoft Visual Basic .NET: Reloaded

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 Microsoft Visual Basic .NET: Reloaded

Adding a Check Box Control to the Form (continued) Microsoft Visual Basic .NET: Reloaded

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 Microsoft Visual Basic .NET: Reloaded

Adding a List Box to an Interface (continued) Microsoft Visual Basic .NET: Reloaded

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 item’s 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” Microsoft Visual Basic .NET: Reloaded

The SelectedItem and SelectedIndex Properties Microsoft Visual Basic .NET: Reloaded

The SelectedItem and SelectedIndex Properties (continued) Microsoft Visual Basic .NET: Reloaded

The SelectedItem and SelectedIndex Properties(continued) Microsoft Visual Basic .NET: Reloaded

Using the KeyPress Event • A control’s 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 Microsoft Visual Basic .NET: Reloaded

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 Microsoft Visual Basic .NET: Reloaded

Associating a Procedure with Different Events • List each event, separated by commas, in the Handles section of the procedure header Microsoft Visual Basic .NET: Reloaded

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 company’s sales manager, wants an application that allows her to enter an item number and then display either the wholesale price or the retail price Microsoft Visual Basic .NET: Reloaded

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 Microsoft Visual Basic .NET: Reloaded

TOE Chart Microsoft Visual Basic .NET: Reloaded

User Interface Microsoft Visual Basic .NET: Reloaded

Objects, Properties, and Settings Microsoft Visual Basic .NET: Reloaded

Tab Order Microsoft Visual Basic .NET: Reloaded

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 Microsoft Visual Basic .NET: Reloaded

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 Microsoft Visual Basic .NET: Reloaded

Code Microsoft Visual Basic .NET: Reloaded

Code (continued) Microsoft Visual Basic .NET: Reloaded

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 form’s Declarations section • A structure variable contains one or more member variables • You access a member variable using the structure variable’s name, followed by the dot member access operator and the member variable’s name Microsoft Visual Basic .NET: Reloaded

Microsoft Visual Basic .NET: Reloaded

Microsoft Visual Basic .NET: Reloaded

Presentation Transcript

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