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Chapter 12 – Web Applications
12.1 Programming for the Web, Part I
12.2 Programming for the Web, Part II
12.3 Using Databases in Web Programs
Web Programs
• The programs in this chapter require the use of either Visual Web Developer 2010 (packaged with this textbook) or the complete version of Visual Studio 2010.
• We assume that you are using one of these two software products.
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12.1 Programming for the Web, Part I
• Creating a Web Program with Visual Web Developer
• Using a Table to Lay Out a Web Page’s Content
• Accessing a Text File in a Web Program• Binding a Control to a LINQ Query• Opening an Existing Web Program• Building on an Existing Web Program
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Preliminary Settings
• The following setting need only be carried out once.
• Click on Options in the Tools menu, select General, click on Design View, and click on the OK button. (See next slide.)
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Options Settings
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click on OK button
Creating a Web Program
• Click on New Web Site in the File menu.
• Select Visual Basic in the left pane.
• Select ASP.NET Web Site in the middle pane.
• Select File System as the Web location.
• Give a name and path for the program.
• Click on the OK button.
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Creating a Web Program (continued)
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enter name
click on OK
Web Page (VWD Equivalent of the Form Designer)
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Main Content region
Web page tab
Web Page Tab
The Web page tab is titled “Default.aspx” instead of “Form1. vb [Design]”. The Web page is referred to as Default.aspx in the Solution Explorer window.
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Toolbox
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The common controls, such as button, text box, and list box are contained in the Standard group of the Toolbox.
Designing the Web Page
• Begin by clearing the Main Content region.
• Permanent text (called static text) can be typed into the page and formatted directly without the use of labels.
• Text boxes and buttons can be placed at the cursor position (called the insertion point) by double-clicking on them in the Toolbox.
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Sample Web Page
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Properties Window
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The name of a control is specified by the ID property instead of the Name property.
Code Editor
• The Code Editor tab reads “Default.aspc.vb” instead of “Form1.vb”.
• The code in the editor is referred to as the code behind.
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Sample CodeProtected Sub btnCalculate_Click(...) Handles _ btnCalculate.Click
Dim cost As Double = CDbl(txtCost.Text)
Dim percent As Double = CDbl(txtPercent.Text) / 100
txtTip.Text = FormatCurrency(percent * cost)
End Sub
Notice that “Sub” is proceeded by “Protected” instead of “Private”.
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Running a Program
• Press Ctrl+F5 to run program without debugging.
• Program runs in the computer’s Web browser.
• To terminate the program, close the browser by clicking on , the Close button.
• Close program by clicking on Close Project in the File menu.
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A Run of the Sample Program
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Tables
• A table control can be used to improve the layout of a Web page.
• Tables are created with the Insert Table command from the Table menu in the Toolbar.
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Sample Table
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This table has 5 rows and 2 columns. Each subdivision is called a cell.
cell
Cells
• Text and controls can be placed into cells.
• The alignment (such as right, left, or center) of the contents of a cell can be specified with the Align property from the Properties window.
• Commands from the Table menu allow you to insert and delete rows and columns, and to merge cells.
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Managing Tables
• Assorted arrows; such as , , , , , and , can be used to highlight groups of cells
and resize tables. • Dragging of the cursor also can be used to
highlight groups of cells.
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Text Files
• Normally placed in the Solution Explorer’s App_Data folder.
• A text file can be read into an array with a statement of the form
Dim strArrayName() As String = IO.File.ReadAllLines(MapPath("App_Data\" & filename))
• LINQ can then be used to obtain specific information.
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How to Display the Output of a LINQ Query in a List Box
lstBox.DataSource = query
lstBox.DataBind()
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How to Display the Output of a LINQ Query in a GridView
Note: The GridView is the VWD equivalent of the VB DataGridView.
grvGrid.DataSource = query
grvGrid.DataBind()
grvGrid.HeaderRow.Cells(0).Text = header for first column
grvGrid.HeaderRow.Cells(1).Text = header for second column etc.
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How to Open an Existing Web Program
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first click here
Then navigate to the program’s folder and click on the Open button.
12.2 Programming for the Web, Part II
• Multiple Web Pages
• Validation Controls
• Postback
• The Page Load Event
• Class-Level Variables
• The RadioButtonList Control
• The CheckBox Control
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How to Add an Additional Web Page to a Program
• Click on an existing Web page to make sure it has the focus.
• Click on Add New Item in the Website menu. (An Add New Item dialog box will appear.)
• Select Web Form in the center pane, type a name into the Name box, and click on the Add button.
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How to Add an Additional Web Page to a Program (cont.)
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select
click on Add button
change name
Hyperlink Control
• Found in the General group of the Toolbox.
• Appears on a page as underlined text.
• Used to navigate to another page.
• NavigateUrl property specifies the page to navigate to.
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Sample Web Page
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hyperlink control
Validation Controls
• Used to validate user input.
• The RequiredFieldValidator control checks that data has been entered into a text box or that an item of a list box has been selected.
• The RangeValidator control checks that the entry in a text box falls within a specified range of values.
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Sample Web Page
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RequiredFieldValidator
RangeValidator
Validation controls are not visible at run time. Only appear when input is missing or invalid.
RequiredFieldValidator Control
• The key properties are ControlToVerify and ErrorMessage.
• The ErrorMessage setting is the text that appears when input into the specified control does not meet the given criteria.
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RangeValidator Control
• The key properties are ControlToVerify, ErrorMessage, Type, MinimumValue, and MaximumValue.
• Possible settings for Type are String, Integer, Double, Date, and Currency.
• The entry in the text box must lie between the MinimumValue and the MaximumValue.
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Postback
• A postback occurs when the contents of a Web page are sent to the server for processing. Afterwards, the server sends a new page back to the browser.
• When a validation control is triggered, the matter is handled entirely by the browser—no postback occurs.
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The Page Load Event
• Raised when a Web page is first loaded and every time it is reloaded after a postback.
• The IsPostBack property can be used to guarantee that the page load event is raised only once.
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Class-Level Variables
• In VWD, class-level variables are of limited value since they do not retain their values after postbacks.
• Devises known as cookies or session variables can be used to retain values.
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RadioButtonList Control
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rblAgesrfvAge
VWD does not have a group box control. The radio-button list control is the counterpart of the VB group box containing a set of radio buttons.
RadioButtonList Control (continued)
• The radio-button list control is populated via a ListItem Collection Editor that is invoked from the Tasks button.
• In the previous slide, the control rfvAge, a RequiredFieldValidator, guarantees that a radio button has been selected before the button is clicked on.
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Check Box Control
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Example 5 of Section 4.4.
To convert this VB program to a VWD program, the AutoPostBack property of each check box must be set to True.
12.3 Using Databases in Web Programs
• Creating a Bar Chart from a Database
• Displaying Database Information in a Grid
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The Goal of Section 12.3 is to Generate the Bar Chart Below
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Note: The data will be extracted from a database.
Four Stages to Create Program
1. Design the Web page
2. Add a database connection
3. Create an object model for the database. (The object model is needed to enable LINQ queries to the database.)
4. Use a LinqDataSource control to display the bar chart.
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Stage 1: Design Web Page
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Chart control showing its default bar chart.
The Chart control is found in the Data group of the Toolbox.
Stage 2: Add a Database Connection
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click here
Stage 2: Add a Database Connection (continued)
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Make SQL Server Database File the data source. If necessary, use the Change button to alter the data source.
Stage 2: Add a Database Connection (continued)
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Click on the Browse button, navigate, and double-click on Megacities.mdf database. Then click on the OK button at bottom of window.
Stage 3: Create an Object Model for the Database
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select
Stage 3: Create an Object Model for the Database (cont.)
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select
click on Add buttonchange name
Stage 3: Create an Object Model for the Database (cont.)
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click on the Yes button
An Object Relational Designer will appear.
Stage 3: Create an Object Model for the Database (cont.)
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click on tables
Stage 3: Create an Object Model for the Database (cont.)
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drag to left pane of Object Relational Designer
Stage 3: Create an Object Model for the Database (cont.)
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The window below appears after the first table is dragged into the Object Relational Designer.
click on the Yes button
Stage 3: Create an Object Model for the Database (cont.)
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Stage 3: Create an Object Model for the Database (cont.)
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click on the Save All button
Stage 4: Add a LinqDataSource Control
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Place a LinqDataSource control (in the Data group of the Toolbox) at the bottom of the Web page.
click here
Stage 4: Add a LinqDataSource Control (continued)
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select MegacitiesDataContext
click on Next button
Stage 4: Add a LinqDataSource Control (continued)
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click on Finish button
Stage 4: Add a LinqDataSource Control (continued)
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double-click on the Display button to bring up the Code- Behind window
Code for btnDisplay_ClickDim mcDC As New MegacitiesDataContext
Dim query = From city In mcDC.Cities
Order By city.pop2010 Descending
Select city.name, city.pop2010
chtMegacities.DataBindTable(query, "name")
chtMegacities.ChartAreas(0).AxisX.Interval = 1
chtMegacities.ChartAreas(0).AxisX.Title = "City"
chtMegacities.ChartAreas(0).AxisY.Title = "2010 Population in Millions"
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Output of PopBarChart Program
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Displaying Database Information in a Grid
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use a GridView control, call it grvMegacities, instead of a Chart control
Code for btnDisplay_ClickDim mcDC As New MegacitiesDataContext
Dim query = From city In mcDC.Cities
Order By city.pop2010 Descending
Select city.name, city.pop2010
grvMegacities.DataSource = query
grvMegacities.DataBind()
grvMegacities.HeaderRow.Cells(0).Text = "City"
grvMegacities.HeaderRow.Cells(1) = "2010 Population in Millions"
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Output of PopGrid Program
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