Chapter 3: Develop A Multi-Page Web Application Liu, Jie Professor Department of Computer Science Western Oregon University

The Store Application  A Halloween Store – online retail One page for viewing the products  Accessing a database  Switch to a different page One page to view the shopping cart  Share information from the previous page  The Code

Some Skills  Add a class (OOP) Add an existing class  Right click on Solution Explorer  Add Existing Item Add a New class  Right click on Solution Explorer  Add Existing Item Refer a class in the class library  Add another page Right click on Solution Explorer  Add New Item, select Web Form, can provide the name of your new page  Change the name of a page Need to change the class name and “Inherits” directive manually  Set the start page Single form app, the form is displayed Or multi-form app, the selected/set one is displayed Or the default.aspx Or the directory listing -- need to set a start page  Redirect/Transfer to a different page Transfer (URL) -- ASPX only, fast because the shift happens at server, address not reflect the actual page Redirect (URL) – any page, less efficient because the shift happens at the client

Some Skills – Cross Page Posting  This is a different approach to move to a different page The new page’s URL is set in the PostBackUrl property of a button control Clicking the button results in the loading of a different page specified in the PostBackUrl property You may have access of the “Previous” Page and controls in the previous page This tool is used when no user input needs to be processed

Some Skills – Cross Page Posting Cross-page posting PageA Button PageB Previous Page  Code for the button PostBackUrl = “~/PageB.aspx”  Code to refer a control in the previous page Protected void Page_Load(object sender, EventArgs e) { if (PreviousPage != null) { TextBox txtQTY = (TextBox) PreviousPage.FindControl(“txtQTY”); lblQTY.Text = txtQTY.Text; }

Absolute and Relative URLs URLComment URL Checkout.aspxRelative URL to a file in the current directory /GoldMember/Checkout.aspxRelative URL to a file in a sub-directory../Register.aspxRelative URL at one level up../../Register.aspxRelative URL at two levels up /Register.aspxRelative URL at the root PostBackURL = “~/Intro.aspx”Relative URL at the root on controls  Absolute URLs – include domain name  Relative URLs – specify the page relative to the current page

About Data Sources  Assume you have a MS SQL Server DB  Having the data to show in a form is very easy – using the smart tag  Work on the smart tag menu to configure Select database Select retrieved data/columns

About Data Sources 

Using Data  More on later sections  Make sure the control allows postback  Make sure to bind the control with the data source  Use a Dataview to get the row and column names to get the values in the row

The Code protected void Page_Load(object sender, EventArgs e) { if (!IsPostBack) DropDownList1.DataBind(); } protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e) { Product selectedProduct; // show how to use an object to store a row if (DropDownList1.SelectedValue != "") { DataView dvProduct = (DataView) dtsProduct.Select(DataSourceSelectArguments.Empty); dvProduct.RowFilter = "ProductID = '" + DropDownList1.SelectedValue + "'"; DataRowView row = (DataRowView)dvProduct[0]; selectedProduct = new Product(); // initial the obj selectedProduct.UnitPrice = (decimal)row["UnitPrice"]; selectedProduct.LongDescription = row["LongDescription"].ToString(); selectedProduct.ImageFile = row["ImageFile"].ToString(); lblDescription.Text = selectedProduct.LongDescription; lblPrice.Text = selectedProduct.UnitPrice.ToString("c"); imgProduct.ImageUrl = "Images/Products/" + selectedProduct.ImageFile; }

Using Session State  The difference between an Application and a Session  SessionID – unique for each session and kept when a session state is added  It is stored as key/value pair with value being an object Session[“Cart”] = cart; // cart can be anything, a SortedList here Session.Add (“Cart”, cart); SortedList cart = (SortedList) Session[“Cart”]; SortedList cart = (SortedList) HttpContext.Current.Session[“Cart”];  Major Property: SessionID, Count, Timeout  Methods: Abandon, Clear, Remove