T U T O R I A L 2009 Pearson Education, Inc. All rights reserved. 1 20 Shipping Hub Application Introducing Generic Collections, LINQ, For Each...Next

T U T O R I A L

2009 Pearson Education, Inc. All rights reserved.

1

20Shipping Hub

ApplicationIntroducing Generic Collections, LINQ, For Each...Next and

Access Keys


2

Outline

20.1 Test-Driving the Shipping Hub Application

20.2 Package Class

20.3 Using Properties TabIndex and TabStop20.4 Using Access Keys

20.5 Collections


3

Outline

20.6 Shipping Hub Application: Using Class List(Of T)

20.7 For Each...Next Repetition Statement

20.8 Language-Integrated Query (LINQ)


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In this tutorial you will learn: ■ Use generic collections.■ Create and manipulate a List(Of T) object.■ Use Language Integrated Query (LINQ) to select

elements from a collection.■ Set the MaxLength property of a TextBox.

Objectives


5

In this tutorial you will learn: ■ Specify the tab order in a GUI using the TabStop

and TabIndex properties of the controls.■ Create an access key for a control.■ Use a For Each...Next loop to iterate through

a collection.■ Obtain a String representation of an object.

Objectives

Application Requirements


6

20.1 Test-Driving the Shipping Hub Application

A shipping company receives packages at its headquarters, which functions as its shipping hub. After receiving the packages, the company ships them to one of the following states: Alabama, Florida, Georgia, Kentucky, Mississippi, North Carolina, South Carolina, Tennessee, West Virginia or Virginia. The company needs an application to track the packages that pass through its shipping hub. For each package that arrives at the hub, the user clicks the application’s Scan New Button, to generate a package ID number. Once a package has been scanned, the user should be able to enter the shipping address for it. The user should be able to navigate through the list of scanned packages by using < BACK or NEXT > Buttons and by viewing a list of all packages destined for a particular state.


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Test-Driving the Shipping Hub Application

■ Run the completed application (Fig. 20.1).

Figure 20.1 | Shipping Hub application when first run.


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Test-Driving the Shipping Hub Application (Cont.)

■ Click the Scan New Button.

■ The application displays a package ID number and the arrival time, enables the TextBoxes and allows the user to enter the package information (Fig. 20.2).

Figure 20.2 | Scanning a new package.


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■ Type 318 Some Street in the Address: TextBox, then press the Tab key. Note that the cursor moves to the City: TextBox (Fig. 20.3).

■ Fill in other input values, then click the Add Button to add the package to the application’s List.


Figure 20.3 | Pressing the Tab key moves the cursor to the next TextBox.

Cursor now appearsin the City: TextBox


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GUI Design Tip

Using the Tab key is an efficient way for users to navigate through the controls in a GUI.


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■ The application’s NEXT > and < BACK Buttons allow the user to navigate the list of packages.

■ The user can click on the Remove Button to delete packages and on the Edit Button to update a particular package’s information.

■ The ComboBox on the right side of the application allows the user to select a state.

– When a state is selected, all of the package ID numbersof packages destined for that state are displayed in the ListBox (Fig. 20.4).



12

Figure 20.4 | Viewing all packages going to South Carolina.



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■ The table in Fig. 20.5 describes the properties for class Package.

Figure 20.5 | Properties of class Package.

20.2 Package Class

Property Description

Address Provides access to instance variable addressValue, which represents the package’s address as a String.

City Provides access to instance variable cityValue, which represents the package’s city as a String.

State Provides access to instance variable stateValue, which stores the package’s state as a String. It uses the standard two-letter state abbreviations. For example, NC is used for North Carolina.

Zip Provides access to instance variable zipValue. Represents the zip code as a String.

PackageNumber Provides access to instance variable packageNumberValue, which stores the package’s identification number as an Integer.

ArrivalTime Provides access to instance variable timeValue, which stores the package’s arrival time as a Date.


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■ Open the template application.

■ In the Solution Explorer, right click the ShippingHub project.

– Select Add > Existing Item....

– When the Add Existing Item dialog appears, select the Package.vb file and click Add (Fig 20.6).

Adding a Class to an Application

Figure 20.6 | Solution Explorer with Package.vb added.

Package class added to the ShippingHub project


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■ It is awkward for users to have to select each TextBox.

■ Most applications allow the user to press the Tab key to navigate between the controls on the Form.

■ The TabIndex property allows you to specify the order in which focus transfers between controls.

– Some controls, such as a read-only TextBox, should not be selected using the Tab key.

– The TabStop property specifies whether the user can select the control using the Tab key.

20.3 Using Properties TabIndex and TabStop


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■ The TabStop property defaults to True for controls that receive user input.

■ The IDE provides a view called Tab Order. – Select the Form, then select View > Tab Order

(Fig. 20.7).

Setting Properties TabIndex and TabStop

Figure 20.7 | Setting the TabIndex properties using the Tab Orderview of the Shipping Hub application.

TabIndex box set to zero

TabIndex boxes (not modified)


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■ Click the Package Information GroupBox, and note that its value becomes 0. Then click the Address: TextBox.

– Now the value changes to 0.0. The first zero refers to the TabIndex of the container, and the second zero refers to the TabIndex for that control within the container.

Setting Properties TabIndex and TabStop (Cont.)


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GUI Design Tip

Use the TabIndex property to define the logical order in which the user should enter data. Usually the order transfers the focus of the application from top to bottom and left to right.


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■ Continue setting the TabIndex properties by clicking the Scan New Button. Then click the remaining unchanged controls in the order indicated in Fig. 20.8.

■ Exit the Tab Order view by selecting View > Tab Order or by pressing the Esc key.

Figure 20.8 | Tab Order view of the Shipping Hub application.

Setting Properties TabIndex and TabStop (Cont.)


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■ Access keys (or keyboard shortcuts) allow the user to perform an action on a control using the keyboard.

– Insert an & symbol in the control’s Text property before the letter you wish to use as an access key.

■ To display an ampersand character on a control, type &&.

20.4 Using Access Keys


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■ Insert an & symbol before the letter S in the Text property of the Scan New Button (Fig. 20.9).

■ If the user presses Alt, then S, this has the same effect as “clicking” the Scan New Button.

■ Create access keys for the remaining Buttons.■ The access key does not have to be the first letter.

Figure 20.9 | Creating an access key.

Creating Access Keys

Using the & symbol to create

an access key (there is nospace between & and S)

Access key letters underlined (may need to

press the Alt key first)


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GUI Design Tip

Use access keys to allow users to “click” a control using the keyboard.


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■ The .NET Framework Class Library provides several collections.

– These classes provide methods that facilitate the storage and organization of your data.

– Collections simplify the details of how the objects are being stored.

■ List(Of T) provides a convenient alternative to arrays.

– The identifier T is a placeholder which you replace with an actual type.

Dim list As List(Of Integer)

Dim list2 As List(Of Package)

– Dynamic resizing enables the List object to change its size.

20.5 Collections


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Software Design Tip

Use a List to store a group of values when the number of elements in the group varies during the running of an application.


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When the Form loads:Generate a random initial package ID number and

arrival timeSet the SelectedIndex of the State ComboBox to 0Create an empty List of Packages

When the user clicks the Scan New Button:Generate the next package ID number Create a new Package objectDisplay the new Package’s package number and

arrival timeEnable the TextBoxes, the ComboBox and the Add

Button

20.6 Shipping Hub Application: UsingClass List(Of T)


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When the user clicks the Add Button:Retrieve address, city, state and zip code values;

and disable input controlsAdd the package to the ListEnable the Package Information GroupBox and the

appropriate ButtonsDisable the Add ButtonAdd the package number to the ListBox Change the Packages by Destination ComboBox

value to the package’s destination stateEnable the New Button

20.6 Shipping Hub Application: UsingClass List(Of T) (Cont.)


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When the user clicks the < BACK Button:Display the previous package in the List

When the user clicks the NEXT > Button:Display the next package in the List

When the user clicks the Remove Button:Remove the package from the Packages by Destination

ListBoxRemove the package from the List



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When the user clicks the Edit Button:Change the Button to read UpdateAllow the user to modify package address

information

When the user clicks the Update Button:Update the package’s information in the ListDisable controls that allow user input, and change

the Update Button to read Edit

When the user chooses a different state in the Packages by Destination ComboBox:

Display the package number for each package destined for that state in the ListBox



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Action Control/Object Event

Label the application’s controls informationGroupBox, listByGroupBox, arrivedLabel, packageIDLabel, addressLabel, cityLabel, stateLabel, zipLabel

Application is run

ShippingHubForm Load

Generate a random initial package ID

number and arrival time

randomObject

Set the SelectedIndex of the State

ComboBox to 0

stateComboBox

Create an empty List of Packages list

■ Use an ACE table to convert the pseudocodeto Visual Basic (Fig. 20.10).

Figure 20.10 | ACE table for the Shipping Hub application. (Part 1 of 5.)

Action/Control/Event (ACE) Table forthe Shipping Hub Application


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newButton Click

Generate the next package ID number

Create a new Package object packageObject

Display the new Package’s package number

and arrival time

packageNumberLabel, arrivalTimeLabel

Enable the TextBoxes, the CboBox and the

Add Button

addButton, addressTextBox, cityTextBox, stateComboBox, zipTextBox

addButton Click

Enable the Package Information GroupBox

and the approptiate Buttons

informationGroupBox, (call SetButtons with True as an argument for the Buttons)

Disable the Add Button addButton


Action/Control/Event (ACE) Table forthe Shipping Hub Application (Cont.)


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Add the package to the List list Click

Add the package number to the ListBox packagesListBox

Change the Packages by Destination

ComboBox value to the package’s

destination state

stateComboBox

Enable the New Button newButton

backButton Click

Display the previous package in the List list, packageNumberLabel, arrivalTimeLabel addressTextBox, cityTextBox, stateComboBox, zipTextBox




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nextButton Click

Display the next package in the List list, packageNumberLabel, arrivalTimeLabel addressTextBox, cityTextBox, stateComboBox, zipTextBox

removeButton Click

Remove the package from the Packages by

Destination ListBox

packagesListBox

Remove the package from the List list

editUpdateButton Click

Change the Button to read Update editUpdateButton

Allow the user to modify package address

information

addressTextBox, cityTextBox, stateComboBox, zipTextBox




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editUpdateButton Click

Update the package’s information in the

List

list

Disable controls that allow user input, and

change the Update Button to read Edit

addressTextBox, cityTextBox, stateComboBox, zipTextBox, editUpdateButton

viewPackagesComboBox SelectedIndex Changed

Display the package number for each

package destined for that state in the

ListBox

packagesListBox




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■ Declare a List(Of Package) list (Fig. 20.11).

Figure 20.11 | Declaring the List(Of Package) reference.

Creating a List of Packages

Declaring a List(Of Package)

reference


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■ Assign the reference of a new List(Of Package) to the instance variable list (Fig. 20.12).

Figure 20.12 | Creating a List(Of Package) object.

Creating a List of Packages (Cont.)

Initializing theList(Of Package)

reference


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■ The user clicks the Scan New Button when a new package arrives at the shipping hub.

■ Line 28 (Fig. 20.13) increments packageID to ensure that all packages have a unique identification number.

Figure 20.13 | Creating a Package object.

Adding and Removing Packages

Create a new Package object with a unique ID


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■ The application should display a scanned package’s arrival time and package number (Fig. 20.14).

■ The ToString method returns a String representation of an object.

– Date’s ToString method returns the date as a String.

– For some .NET classes, ToString merely returns the class name.

Adding and Removing Packages (Cont.)

Displaying arrival time and package ID number in Labels

Figure 20.14 | Displaying the package’s number and arrival time.


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■ This code (Fig. 20.15) stores the package information by adding the Package object to list using the List’s Add method.

■ New Packages are added to the end of the List.

Figure 20.15 | Adding a package to the List.

Adding a Packageobject to a List



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■ An element’s location in the List is the element’s index.

■ The List class provides a simple way to remove elements from the List.

– The RemoveAt method removes a package from the List (Fig. 20.16).

– The argument passed to the method RemoveAt is the index of the Package in the List.


Removing the current Package from the List

Figure 20.16 | Removing a Package from the List.


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■ If a Package at index 3 is removed from the List, the Package that was previously at index 4 will then be located at index 3.

■ The Count property returns the number of elements currently stored in the List.



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■ When the Edit Button is clicked, line 135 (Fig. 20.17) changes the text on the Edit Button to &Update.

■ This indicates that the user should click the same Button to submit changes to the package information.

Figure 20.17 | Changing the Edit Button to display Update.

Using code to change thetext displayed on a Button

Updating Package Information


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■ When the user chooses to alter the package information, the Package is removed from the List and a new one with the updated address information is added (Fig. 20.18).

Figure 20.18 | Removing and inserting a Package to update data.

Updating the List with new package information

Updating Package Information (Cont.)

■ The Insert method allows you to specify the index in the List at which to insert the Package.


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■ After the user clicks the Update Button, the TextBoxes are disabled, and the text on the Update Button is reset to Edit (Fig. 20.19).

Figure 20.19 | Setting the Button’s Text property back to Edit.

Using code to display the text on the Button

Updating Package Information (Cont.)


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■ Retrieve the data from the List using the elements index enclosed in parentheses (Fig. 20.20).

Figure 20.20 | Retrieving a Package from the List.

Retrieving a Package object from a List

Displaying a Package


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■ These lines retrieve the package information from packageObject and display the data in the corresponding controls on the Form (Fig. 20.21).

Figure 20.21 | Displaying the package data in the Form’s controls.

Displaying data stored

in the Package object

Displaying a Package (Cont.)


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■ The For Each...Next repetition statement iterates through all the elements in an array or a collection.

■ The statement uses a control variable that can be assigned each element in the collection:

For Each packageObject As Package In list

packagesListBox.Items.Add(packageObject. PackageNumber)

Next

20.7 For Each...Next Repetition Statement


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■ The statement requires both a group and an element. – The group specifies the collection through which you wish

to iterate.

– The element is used to store a reference to an object in the group.

– The statement assigns the current element in the collection to the element variable.

20.7 For Each...Next Repetition Statement (Cont.)


48

Good Programming Practice

Use a For Each...Next repetition statement to iterate through values in an array or collection without using a counter variable.


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Common Programming Error

If the element in a For Each...Next statement cannot be converted to the same type as the groups’s objects, a compilation error occurs. For example, if a List contained Date values, declaring a reference to a Package object as the element would cause a compilation error.


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■ Figure 20.22 shows the UML activity diagram for the For Each...Next statement.

Figure 20.22 | UML activity diagram for For Each...Next repetition statement.

20.7 For Each...Next Repetition Statement (Cont.)


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■ This loop (Fig. 20.23) iterates through list.

■ This code is added to a ComboBox’s SelectedIndexChanged event handler.

– The SelectedIndexChanged event occurs when the value selected in the ComboBox changes.

Inserting a For Each...Next Statement

For Each...Next header

Figure 20.23 | Writing a For Each...Next statement.


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■ These lines contain an If...Then statement (Fig. 20.24) that tests each package’s destination state against the state name displayed in the Packages by Destination ComboBox.

Figure 20.24 | Displaying all packages going to selected state.

Inserting a For Each...Next Statement (Cont.)

Displaying package IDnumbers only for packages

destined for the specified state


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■ Visual Basic 2008 and the .NET 3.5 framework introduce Language-Integrated Query (LINQ).

– A query retrieves specific information from a data source, such as a collection.

■ A typical LINQ query contains three clauses:– The From clause specifies a range variable and the data

source to query.

– The Where clause specifies the conditions that must be met for the item to be included in the results.

– The Select clause specifies the value(s) placed in the results.

20.8 Language-Integrated Query (LINQ)


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■ The following LINQ to Objects query selects all the Packages in list that are destined for Boston:

Dim cityQuery = From p In list _ Where p.City = "Boston" _ Select p

■ If the expression in the Where clause evaluates to True, the Select clause includes the corresponding Package in the result.

■ LINQ uses deferred execution—the query does not execute until you attempt to iterate through the query results.

20.8 Language-Integrated Query (LINQ) (Cont.)


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■ Lines 222–225 of Figure 20.25 declare a LINQ query that selects from list all the Packages destined for the specified state.

Figure 20.25 | Declaring a LINQ query.

Using LINQ to Select Packages from a List

Declaring a LINQ query toselect Packages destined

for specified state


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■ The query results are contained in an IEnumerable(Of Package) object.

– IEnumerable is an interface—a set of methods that can be called on an object to tell the object to perform some task or return some piece of information.

– You can call any IEnumerable method on an array or collection object to iterate through its elements.

Using LINQ to Select Packages from a List (Cont.)


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Figure 20.26 | Iterating through query results using a For Each...Next statement.

Use a For Each...Next statement to display the results

of the query

Using LINQ to Select Packages from a List (Cont.)

■ Replace the previous Package-selection code with lines 227-231 of Fig. 20.26.


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1 Public Class ShippingHubForm

2

3 Private list As List(Of Package)

4 Private packageObject As Package ' current package

5 Private position As Integer ' position of current package

6 Private randomObject As Random ' random number for package ID

7 Private packageID As Integer ' individual package number

8

9 ' Form Load event

10 Private Sub ShippingHubForm_Load(ByVal sender As _

11 System.Object, ByVal e As System.EventArgs) _

12 Handles MyBase.Load

13

14 position = 0 ' set initial position to zero

15 randomObject = New Random() ' create new Random object

16 packageID = randomObject.Next(1, 100000) ' new package ID

17

18 ' show first state in ComboBox

19 stateComboBox.SelectedIndex = 0

20

21 list = New List(Of Package)() ' create the List

22 End Sub ' ShippingHubForm_Load

■ Figure 20.27 presents the source codefor the Shipping Hub application.

Outline

(1 of 12 )

Declares a List to be usedto store packages

Initially, there are no objects in the List, so set the position to zero

Use a Random object to generate a random number for package IDs

Create a List object


59

23

24 ' Scan New Button Click event

25 Private Sub newButton_Click(ByVal sender As System.Object, _

26 ByVal e As System.EventArgs) Handles newButton.Click

27

28 packageID += 1 ' increment package ID

29 packageObject = New Package(packageID) ' create package

30

31 ClearControls() ' clear fields

32 packageNumberLabel.Text = _

33 packageObject.PackageNumber.ToString() ' package number

34 arrivalTimeLabel.Text = _

35 packageObject.ArrivalTime.ToString() ' display arrival time

36

37 ' only allow user to add package

38 informationGroupBox.Enabled = True ' enable GroupBox

39 SetButtons(False) ' enable/disable Buttons

40 addButton.Enabled = True ' enable Add Button

41 newButton.Enabled = False ' disable Scan New Button

42 addressTextBox.Focus() ' transfer the focus to addressTextBox

43 End Sub ' newButton_Click

Outline

(2 of 12 )

Use ToString to convert values


60

44

45 ' Add Button Click event

46 Private Sub addButton_Click(ByVal sender As System.Object, _

47 ByVal e As System.EventArgs) Handles addButton.Click

48

49 SetPackage() ' set Package properties from TextBoxes

50 list.Add(packageObject) ' add package to the List

51

52 informationGroupBox.Enabled = False ' disable GroupBox

53 SetButtons(True) ' enable appropriate Buttons

54

55 ' package cannot be added until Scan New is clicked

56 addButton.Enabled = False ' disable Add Button

57

58 if package’s state displayed, add ID to ListBox

59 If stateComboBox.Text = viewPackagesComboBox.Text Then

60 packagesListBox.Items.Add(packageObject.PackageNumber)

61 End If

62

63 viewPackagesComboBox.Text = packageObject.State ' list package

64 newButton.Enabled = True ' enable Scan New Button

65 End Sub ' addButton_Click

Outline

(3 of 12 )


61

66

67 ' Back Button Click event

68 Private Sub backButton_Click(ByVal sender As System.Object, _

69 ByVal e As System.EventArgs) Handles backButton.Click

70

71 ' move backward one package in the list

72 If position > 0 Then

73 position -= 1

74 Else ' wrap to end of list

75 position = list.Count - 1

76 End If

77

78 LoadPackage() ' load package data from item in list

79 End Sub ' backButton_Click

80

81 ' Next Button Click event

82 Private Sub nextButton_Click(ByVal sender As System.Object, _

83 ByVal e As System.EventArgs) Handles nextButton.Click

84

Outline

(4 of 12 )

When the user clicks the < BACK Button, decrement the position. If the position was zero, set the position to the last object in the List


62

85 ' move forward one package in the list

86 If position < list.Count - 1 Then

87 position += 1

88 Else

89 position = 0 ' wrap to beginning of list

90 End If

91


93 End Sub ' nextButton_Click

94

95 ' Remove Button click event

96 Private Sub removeButton_Click(ByVal sender As _


98 Handles removeButton.Click

99

100 ' remove ID from ListBox if state displayed

101 If stateComboBox.Text = viewPackagesComboBox.Text Then

102 packagesListBox.Items.Remove(packageObject.PackageNumber)

103 End If

104

Outline

(5 of 12 )

When the user clicks the NEXT > Button, increment the position.If the position was the last object in the array, set the position to zero


63

105 list.RemoveAt(position) ' remove package from list

106

107 ' load next package in list if there is one

108 If list.Count > 0 Then

109 ' if not at first position, go to previous one

110 If position > 0 Then

111 position -= 1

112 End If

113


115 Else

116 ClearControls() ' clear fields

117 End If

118


120 End Sub ' removeButton_Click

121

Outline

(6 of 12 )

Set the position to the next package in the List


64

122 ' Edit/Update Button Click event

123 Private Sub editUpdateButton_Click(ByVal sender As _


125 Handles editUpdateButton.Click

126

127 ' when Button reads "Edit", allow user to

128 ' edit package information only

129 If editUpdateButton.Text = "&Edit" Then

130 informationGroupBox.Enabled = True ' enable GroupBox

131 SetButtons(False)

132 editUpdateButton.Enabled = True

133

134 ' change Button text from "Edit" to "Update"

135 editUpdateButton.Text = "&Update"

136 Else

137 ' when Button reads "Update" remove the old package

138 ' data and add new data from TextBoxes

139 SetPackage()

140 list.RemoveAt(position)

141 list.Insert(position, packageObject)

142

Outline

(7 of 12 )

Using & in the Text property of a Button to create an access key

Removing and inserting items from/into a List


65

143 ' display state in ComboBox

144 viewPackagesComboBox.Text = packageObject.State

145

146 ' when done, return to normal operating state

147 informationGroupBox.Enabled = False ' disable GroupBox


149

150 ' change Button text from "Update" to "Edit"

151 editUpdateButton.Text = “&Edit”

152 End If

153 End Sub ' editUpdateButton_Click

154

155 ' set package properties

156 Private Sub SetPackage()

157 packageObject.Address = addressTextBox.Text

158 packageObject.City = cityTextBox.Text

159 packageObject.State = _

160 stateComboBox.SelectedItem.ToString()

161 packageObject.Zip = zipTextBox.Text

162 End Sub ' SetPackage

163

Outline

(8 of 12 )

Using & in the Text property of a Button to create an access key

Retrieve data from user, and store it in the Package object


66

164 ' load package information into Form

165 Private Sub LoadPackage()

166

167 ' retrieve package from list

168 packageObject = list(position)

169

170 ' display package data

171 addressTextBox.Text = packageObject.Address

172 cityTextBox.Text = packageObject.City

173 stateComboBox.Text = packageObject.State

174 zipTextBox.Text = packageObject.Zip

175 arrivalTimeLabel.Text = _

176 packageObject.ArrivalTime.ToString()

177 packageNumberLabel.Text = _

178 packageObject.PackageNumber.ToString()

179 End Sub ' LoadPackage

180

Outline

(9 of 12 )

Using ToString to convert values


67

181 ' clear all the input controls on the Form

182 Private Sub ClearControls()

183 addressTextBox.Clear()

184 cityTextBox.Clear()

185 zipTextBox.Clear()

186 stateComboBox.SelectedText = ""

187 arrivalTimeLabel.Text = ""

188 packageNumberLabel.Text = ""

189 End Sub ' ClearControls

190

191 ' enable/disable Buttons

192 Private Sub SetButtons(ByVal state As Boolean)

193 removeButton.Enabled = state

194 editUpdateButton.Enabled = state

195 nextButton.Enabled = state

196 backButton.Enabled = state

197

198 ' disable navigation if not multiple packages

199 If list.Count < 2 Then

200 nextButton.Enabled = False

201 backButton.Enabled = False

202 End If

Outline

(10 of 12 )

Enable or disable Buttons depending on value of state


68

203

204 ' if no items, disable Remove and Edit/Update Buttons

205 If list.Count = 0 Then

206 editUpdateButton.Enabled = False

207 removeButton.Enabled = False

208 End If

209 End Sub ' SetButtons

210

211 ' event raised when user selects a new state in ComboBox

212 Private Sub viewPackagesComboBox_SelectedIndexChanged( _

213 ByVal sender As System.Object, ByVal e As System.EventArgs) _

214 Handles viewPackagesComboBox.SelectedIndexChanged

215

216 Dim state As String = _

217 viewPackagesComboBox.SelectedItem.ToString()

218

Outline

(11 of 12 )


69

219 packagesListBox.Items.Clear() ' clear ListBox

220

221 ' LINQ query to select packages destined for specified state

222 Dim stateQuery = From p In list _

223 Where p.State = state _

224 Select p

225

226 ' list all packages for current state in ListBox

227 For Each viewPackage As Package In stateQuery

228 ' display the Package’s id in the ListBox

229 packagesListBox.Items.Add(viewPackage.PackageNumber)

230 Next

231 End Sub ' viewPackagesComboBox_SelectedIndexChanged

232 End Class ' ShippingHubForm

Outline

(12 of 12 )

Declare a LINQ query to select Packages destined for specified state

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T U T O R I A L 2009 Pearson Education, Inc. All rights reserved. 1 20 Shipping Hub Application Introducing Generic Collections, LINQ, For Each...Next