Click File on the menu bar to view the individual menu items and their associated icons on the File menu.

Transcription

1 User Interface Design 387 STEP 3 Click File on the menu bar to view the individual menu items and their associated icons on the File menu. The standard File menu items (New, Open, Save, Save As, Print, Print Preview, and Exit) are displayed with their associated icons and shortcut keys (Figure 6-16). The other menus also contain standard items. You can code an event handler for each menu item by double-clicking the item. standard File menu FIGURE 6-16 ONLINE REINFORCEMENT To view a video of the process in the previous steps, visit scsite.com/vb2010/ch6 and then select Figure InputBox Function To calculate the average vehicle speed, the Highway Radar Checkpoint application uses an InputBox object where users enter the speed for each vehicle. The InputBox object is a dialog box that prompts the user to enter a value. Similar to a MessageBox object, you code the InputBox function to specify when the InputBox object appears. The InputBox function displays a dialog box that consists of a message asking for input, an input area, a title, an OK button, and a Cancel button (see Figure 6-3 on page 379). When the user enters the text and clicks the OK button, the InputBox function returns this text as a string. If the user clicks the Cancel button, the function returns a null string (""). The code shown in Figure 6-17 demonstrates the syntax of the InputBox function: General Format: InputBox Function strvariablename = InputBox("Question to Prompt User", "Title Bar") FIGURE 6-17

2 388 Chapter 6 Loop Structures For example, the code in Figure 6-18 creates a dialog box that requests the user s age for a driver s license application. The string returned by the InputBox function is assigned to the strage variable. FIGURE 6-18 When the application is executed, the InputBox object in Figure 6-19 opens, requesting that the user enter her age. The InputBox function can be used to obtain input instead of a TextBox object. assigned to strage FIGURE 6-19 The InputBox object returns all entered data as a string, which then can be converted to the appropriate data type. InputBox Object Default Value The InputBox object can be assigned a default value. For example, if a college application for admission requests the student s home state and the college or university is located in Virginia, the most likely state, Virginia, can be the default value in the InputBox, as shown in Figure default value FIGURE 6-20 The code to produce this input box is shown in Figure FIGURE 6-21

3 User Interface Design 389 As you can see, the third argument for the InputBox function call is the default value that is placed in the input box. It must be a string value and follow the syntax shown in Figure 6-21 on the previous page. InputBox Object for Highway Radar Checkpoint Application The Highway Radar Checkpoint application uses an InputBox object that requests the speed of vehicles numbered 1 10, as shown in Figure FIGURE 6-22 The code for the Radar Speed InputBox is shown in Figure Notice that the prompt message for the user is assigned to the strinputboxmessage variable, and the title bar text (Radar Speed) is assigned to the strinputboxheading variable. FIGURE 6-23 The variable intnumberofentries identifies the vehicle number. It is included in the prompt message through the use of concatenation. The variable intnumberofentries is incremented later in the code so that it refers to the correct vehicle each time the InputBox function call is executed. In Figure 6-23, the default value is specified as a space (" "). When the input box is displayed, a space will be selected in the input area. This space is required so that if a user clicks the OK button without entering any data, the InputBox will not return a null character (""), which indicates the user clicked the Cancel button. This normally is a good programming practice. When the user clicks the Cancel button in an input box and the InputBox function returns a null character, the program can test for the null character to determine further processing. HEADS UP An InputBox object allows you to gather input without placing a TextBox for the requested value on the Windows Form object.

4 390 Chapter 6 Loop Structures Displaying Data Using the ListBox Object In the Highway Radar Checkpoint application, the user enters the speed of each vehicle into the InputBox object, and the program displays these speeds in a list box (see Figure 6-1 on page 378). To create such a list, you use the provided in the Visual Basic Toolbox. A ListBox displays a group of values, called items, with one item per line. To add a to a Windows Form object, you can complete the following steps: STEP 1 Drag the from the Toolbox to the Windows Form object where you want to place the. When the pointer is in the correct location, release the left mouse button. The is placed on the form (Figure 6-24). ListBox.NET component FIGURE 6-24 STEP 2 With the selected, scroll in the Properties window to the (Name) property. Name the lstradarspeed. The name you entered is displayed in the (Name) property in the Properties window (Figure 6-25). Notice a name begins with lst. ONLINE REINFORCEMENT To view a video of the process in the previous steps, visit scsite.com/vb2010/ch6 and then select Figure (Name) property FIGURE 6-25

5 User Interface Design 391 After placing a on the Windows Form object, you can adjust the size as needed by dragging the size handles (see Figure 6-24 on the previous page). Be sure to resize the ListBox so that it is large enough to hold the application data. The for the Highway Radar Checkpoint application is designed to be wide enough to hold three digits, and long enough to hold 10 numbers (Figure 6-26). three-digit number 10 numbers FIGURE 6-26 To display the speed of each vehicle in the list box, you must write code to add each item to the. After an item is added, it is displayed in the list box. The general format of the statement to add an item to a is shown in Figure General Format: Adding Items to a ListBox Object lstlistboxname.items.add(variable Name) FIGURE 6-27 In Figure 6-27, the Add procedure will add the item contained in the variable identified by the Variable Name entry. The syntax for the statement must be followed precisely. The code to add the vehicle speed to the lstradarspeed and then display the speed of each vehicle (decvehiclespeed) in the is shown in Figure FIGURE 6-28

6 392 Chapter 6 Loop Structures If the number of items exceeds the number that can be displayed in the designated space of the, a scroll bar automatically is added to the right side of the as shown in Figure scroll bar FIGURE 6-29 To clear the items in a, the Clear method works as it does for the TextBox object. The syntax of the statement to clear the ListBox is shown in Figure General Format: Clear the ListBox Object lstlistboxname.items.clear() FIGURE 6-30 In the Highway Radar Checkpoint application, the user can select the Clear menu item to clear the form. The code in Figure 6-31 removes the items from the lstradarspeed ListBox. FIGURE 6-31

7 User Interface Design 393 Add Items During Design The Highway Radar Checkpoint application allows the user to add items to the during program execution, but you also can add items to a while designing the form. Adding items to the during the design phase allows the user to select an item from the during execution. For example, in an application to select a favorite clothing store, you can add items to a named lststores during the form design by completing the following steps: STEP 1 Assume the lststores already has been placed and named on the Windows Form object. Select the on the Windows Form object and then click the Items property in the Properties window. The Items property in the Properties window is selected. An ellipsis button appears to the right of the (Collection) entry (Figure 6-32). selected Items property ellipsis button FIGURE 6-32

8 394 Chapter 6 Loop Structures STEP 2 Click the ellipsis button in the right column of the Items property. The String Collection Editor window opens, allowing you to enter items that will be displayed in the named lststores (Figure 6-33). String Collection Editor window enter items to be placed in the FIGURE 6-33 STEP 3 Click in the String Collection Editor window. Type the following items to represent popular retail stores, pressing ENTER at the end of each line: Abercrombie & Fitch Aeropostale American Eagle Express Hollister The items representing favorite retail stores appear in the String Collection Editor window on separate lines (Figure 6-34). items entered for OK button FIGURE 6-34

9 User Interface Design 395 STEP 4 Click the OK button. The Windows Form object displays the stores in the lststores (Figure 6-35). The user can select one of the items in the during execution. items in FIGURE 6-35 ONLINE REINFORCEMENT To view a video of the process in the previous steps, visit scsite.com/vb2010/ch6 and then select Figure Selected Item Property The SelectedItem property identifies which item in the ListBox is selected. An assignment statement is used to assign that property to a variable, as shown in Figure General Format: Assign the Selected Item in a ListBox Object strvariablename = lstlistboxname.selecteditem FIGURE 6-36 The actual code to show the user s selection of their favorite store from the List- Box object named lststores in a message box is shown in Figure FIGURE 6-37