ptg 434 CHAPTER 9 Using the SqlDataSource Control LISTING 9.29 DynamicImage.ashx <%@ WebHandler Language=”C#” Class=”DynamicImage” %> using System.Data; using System.Web; using System.Web.Configuration; using System.Web.UI; using System.Web.UI.WebControls; /// <summary> /// Displays an image corresponding to the Id passed /// in a query string field /// </summary> public class DynamicImage : IHttpHandler { public void ProcessRequest (HttpContext context) { // Get the Id of the image to display string imageId = context.Request.QueryString[“Id”]; // Use SqlDataSource to grab image bytes SqlDataSource src = new SqlDataSource(); src.ConnectionString = WebConfigurationManager.ConnectionStrings[“Images”].ConnectionString; src.SelectCommand = “SELECT Image FROM Images WHERE Id=” + imageId; // Return a DataView DataView view = (DataView)src.Select(DataSourceSelectArguments.Empty); context.Response.BinaryWrite( (byte[])view[0][“Image”]); // Return a DataReader //src.DataSourceMode = SqlDataSourceMode.DataReader; //IDataReader reader = (IDataReader)src.Select(DataSourceSelectArguments.Empty); //reader.Read(); //context.Response.BinaryWrite((byte[])reader[“Image”]); //reader.Close(); } public bool IsReusable { From the Library of Wow! eBook ptg 435 Caching Database Data with the SqlDataSource Control 9 get { return false; } } } In the ProcessRequest() method, an instance of the SqlDataSource control is created. The SqlDataSource control’s ConnectionString and SelectCommand properties are initial- ized. Finally, the SqlDataSource control’s Select() command is executed, and the results are rendered with the Response.BinaryWrite() method. The return value from the Select() method is cast explicitly to a DataView object. You need to cast the return value to either a DataView or IDataReader for it to work with the results of the Select() method. In Listing 9.29, the image bytes are returned in a DataView. To illustrate how you can use the Select() method to return a DataReader, I also included the code for returning the image with a DataReader, but I added comments to the code so that it won’t execute. Caching Database Data with the SqlDataSource Control The easiest way to dramatically improve the performance of a database-driven website is through caching. Retrieving data from a database is one of the slowest operations that you can perform in a web page. Retrieving data from memory, on the other hand, is lightning fast. The SqlDataSource control makes it easy to cache data in your server’s memory. Caching is discussed in detail in Chapter 29, “Caching Application Pages and Data.” In that chapter, you learn about all the different caching options supported by the SqlDataSource control. However, because it is so easy to cache data with the SqlDataSource control and caching has such a dramatic impact on performance, I want to provide you with a quick sample of how you can use the SqlDataSource control to cache data. The page in Listing 9.30 displays a list of movies cached in memory. LISTING 9.30 CacheSqlDataSource.aspx <%@ Page Language=”C#” %> <!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.1//EN” “http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd”> <script runat=”server”> From the Library of Wow! eBook ptg 436 CHAPTER 9 Using the SqlDataSource Control protected void srcMovies_Selecting(object sender, ➥ SqlDataSourceSelectingEventArgs e) { lblMessage.Text = “Retrieving data from database”; } </script> <html xmlns=”http://www.w3.org/1999/xhtml” > <head id=”Head1” runat=”server”> <title>Cache SqlDataSource</title> </head> <body> <form id=”form1” runat=”server”> <div> <asp:Label id=”lblMessage” EnableViewState=”false” Runat=”server” /> <br /><br /> <asp:GridView id=”grdMovies” DataSourceID=”srcMovies” Runat=”server” /> <asp:SqlDataSource id=”srcMovies” EnableCaching=”True” CacheDuration=”3600” SelectCommand=”SELECT * FROM Movies” ConnectionString=”<%$ ConnectionStrings:Movies %>” Runat=”server” OnSelecting=”srcMovies_Selecting” /> </div> </form> </body> </html> In Listing 9.30, two properties of the SqlDataSource control related to caching are set. First, the EnableCaching property is set to the value True. Next, the CacheDuration prop- erty is set to a value that represents 3,600 seconds (1 hour). The movies are cached in memory for a maximum of 1 hour. If you don’t supply a value for the CacheDuration property, the default value is Infinite. From the Library of Wow! eBook ptg 437 Caching Database Data with the SqlDataSource Control 9 WARNING You need to understand that there is no guarantee that the SqlDataSource control will cache data for the amount of time specified by its CacheDuration property. Behind the scenes, the SqlDataSource control uses the Cache object for caching. This object sup- ports scavenging. When memory resources become low, the Cache object automatically removes items from the cache. The page in Listing 9.30 includes a srcMovies_Selecting() event handler. This handler is called only when the movies are retrieved from the database rather than from memory. In other words, you can use this event handler to detect when the movies are dropped from the cache (see Figure 9.15). The page in Listing 9.30 illustrates only one type of caching that you can use with the SqlDataSource control. In Chapter 29, you learn about all the advanced caching options supported by the SqlDataSource control. For example, by taking advantage of SQL cache dependencies, you can reload the cached data represented by a SqlDataSource control automatically when data in a database is changed. For more information, see the final section of Chapter 25, “Using the ASP.Net URL Routing Engine.” FIGURE 9.15 Caching the data represented by a SqlDataSource control. From the Library of Wow! eBook ptg 438 CHAPTER 9 Using the SqlDataSource Control Summary In this chapter, you learned how to use the SqlDataSource control to connect and execute commands against a SQL relational database. In the first section, you learned how to represent database connection strings with the SqlDataSource control. You learned how to store connection strings in the web configuration file and encrypt the connection strings. Next, you learned how to execute both inline SQL commands and stored procedures. You also learned how to cancel commands and handle errors gracefully. This chapter also discussed the different types of ASP.NET parameters that you can use with the SqlDataSource control. You learned how to use the Parameter, ControlParameter, CookieParameter, FormParameter, ProfileParameter, SessionParameter, and QueryStringParameter objects. Finally, you learned how to improve the performance of your database-driven applications through caching. You learned how you can cache the data represented by a SqlDataSource control in server memory and avoid accessing the database with each page request. From the Library of Wow! eBook ptg CHAPTER 10 Using List Controls IN THIS CHAPTER . Overview of the List Controls . Working with the DropDownList Control . Working with the RadioButtonList Control . Working with the ListBox Control . Working with the CheckBoxList Control . Working with the BulletedList Control . Creating a Custom List Control . Summary The List controls enable you to display simple lists of options. For example, you can use the RadioButtonList control to display a group of radio buttons or the BulletedList control to display a list of links. In this chapter, you learn how to use each of the List controls included in the ASP.NET Framework. In particular, we discusses the DropDownList, RadioButtonList, ListBox, CheckBoxList, and BulletedList controls. You learn how to bind the different types of List controls to a data source such as a database table. You also learn how to work directly with the list items contained by a List control. Finally, at the end of this chapter, you learn how to build a custom List control. We create a client-side multiselect List control that enables you to select multiple list items at a time. Overview of the List Controls The five List controls inherit from the base ListControl class. This means that all the List controls share a common set of properties and methods. This section provides you with an overview of the common features of the List controls. Declaring List Items The List controls render a list of options. Each option is represented by an instance of the ListItem class. For example, you can use the page in Listing 10.1 to render a set of options for selecting your favorite movie (see Figure 10.1). From the Library of Wow! eBook ptg 440 CHAPTER 10 Using List Controls LISTING 10.1 FavoriteMovie.aspx <%@ Page Language=”C#” %> <!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.1//EN” “http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd”> <html xmlns=”http://www.w3.org/1999/xhtml” > <head id=”Head1” runat=”server”> <title>Favorite Movie</title> </head> <body> <form id=”form1” runat=”server”> <div> <asp:Label id=”lblMovies” Text=”Favorite Movie:” AssociatedControlID=”rblMovies” Runat=”server” /> FIGURE 10.1 Displaying a list of movies. From the Library of Wow! eBook ptg 441 Overview of the List Controls 10 <asp:RadioButtonList id=”rblMovies” Runat=”server”> <asp:ListItem Text=”The Remains of the Day” Value=”movie1” /> <asp:ListItem Text=”Star Wars” Value=”movie2” /> <asp:ListItem Text=”Pulp Fiction” Value=”movie3” /> </asp:RadioButtonList> </div> </form> </body> </html> The page in Listing 10.1 contains a RadioButtonList control that contains three ListItem controls that correspond to the three radio buttons. All the List controls use the ListItem control to represent individual list items. The ListItem control supports the following five properties: . Attributes—Enables you to add HTML attributes to a list item. . Enabled—Enables you to disable a list item. . Selected—Enables you to mark a list item as selected. . Text—Enables you to specify the text displayed by the List Item. . Value—Enables you to specify a hidden value associated with the List Item. You use the Text property to indicate the text that you want the option to display, and the Value property to indicate a hidden value associated with the option. For example, the hidden value might represent the value of a primary key column in a database table. The Selected property enables you to show a list item as selected. Selected radio buttons and check boxes appear checked. The selected option in a DropDownList is the default option displayed. Selected options in a ListBox appear highlighted. And in the case of a BulletedList control, the selected property has no effect whatsoever. The Enabled property has different effects when used with different List controls. When you set a ListItem control’s Enabled property to the value False when using the DropDownList or ListBox controls, the list item is not rendered to the browser. When you use this property with a CheckBoxList, RadioButtonList,or BulletedList control, the list item is ghosted and nonfunctional. From the Library of Wow! eBook ptg 442 Binding to a Data Source You can bind any of the List controls to a data source. The List controls support both declarative databinding and programmatic databinding. For example, the page in Listing 10.2 contains a DropDownList control bound to the Movies database table with declarative databinding (see Figure 10.2). CHAPTER 10 Using List Controls FIGURE 10.2 Displaying list items with declarative databinding. LISTING 10.2 DeclarativeDataBinding.aspx <%@ Page Language=”C#” %> <!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.1//EN” “http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd”> <html xmlns=”http://www.w3.org/1999/xhtml” > <head id=”Head1” runat=”server”> <title>Declarative DataBinding</title> </head> <body> From the Library of Wow! eBook ptg 443 Overview of the List Controls 10 <form id=”form1” runat=”server”> <div> <asp:DropDownList id=”ddlMovies” DataSourceID=”srcMovies” DataTextField=”Title” DataValueField=”Id” Runat=”server” /> <asp:SqlDataSource id=”srcMovies” SelectCommand=”SELECT Id, Title FROM Movies” ConnectionString=”<%$ ConnectionStrings:Movies %>” Runat=”server” /> </div> </form> </body> </html> The DropDownList control’s DataSourceID property points to the ID of the SqlDataSource control. When you open the page in Listing 10.2, the SqlDataSource control retrieves the records from the Movies database table. The DropDownList control grabs these records from the SqlDataSource control and creates a ListItem control for each data item. The DropDownList control has both its DataTextField and DataValueField properties set. When the DropDownList control creates each of its list items, it uses the values of the DataTextField and DataValueField properties to set the Text and Value properties of each list item. As an alternative to declarative databinding, you can programmatically bind any of the List controls to a data source. For example, the page in Listing 10.3 binds a ListBox control to a collection that represents a shopping cart (see Figure 10.3). From the Library of Wow! eBook . different types of ASP. NET parameters that you can use with the SqlDataSource control. You learned how to use the Parameter, ControlParameter, CookieParameter, FormParameter, ProfileParameter,. of Wow! eBook ptg 44 0 CHAPTER 10 Using List Controls LISTING 10.1 FavoriteMovie.aspx <%@ Page Language=”C#” %> <!DOCTYPE html PUBLIC -/ /W3C//DTD XHTML 1.1//EN” “http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd”>. CacheSqlDataSource.aspx <%@ Page Language=”C#” %> <!DOCTYPE html PUBLIC -/ /W3C//DTD XHTML 1.1//EN” “http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd”> <script runat=”server”>