Professional ASP.NET 3.5 in C# and Visual Basic Part 124 docx

Evjen c25.tex V2 - 01/28/2008 3:42pm Page 1190 Chapter 25: File I/O and Streams Listing 25-29: Sending mail from a Web page VB Dim message As _ New System.Net.Mail.MailMessage("webmaster@ineta.org", "webmaster@ineta.org") message.Subject = "Sending Mail with ASP.NET 3.5" message.Body = _ "This is a sample email which demonstrates sending email using ASP.NET 3.5" Dim smtp As New System.Net.Mail.SmtpClient("localhost") smtp.Send(message) C# System.Net.Mail.MailMessage message = new System.Net.Mail.MailMessage("webmaster@ineta.org","webmaster@ineta.org"); message.Subject = "Sending Mail with ASP.NET 3.5"; message.Body = "This is a sample email which demonstrates sending email using ASP.NET 3.5"; System.Net.Mail.SmtpClient smtp = new System.Net.Mail.SmtpClient("localhost"); smtp.Send(message); In this sample, you first create a MailMessage object, which is the class that contains the actual message you want to send. The MailMessage class requires the To and From address be provided to its construc- tor, and you can either provide the parameters as strings, or you can use the MailAddressCollection class to provide multiple recipients’ e-mail addresses. After you create the Message ,youusethe SmtpClient class to actually send the message to your local SMTP server. The SmtpClient class allows you to specify the SMTP Server from which you want to relay your e-mail. Summary In this chapter, you looked at some of the other classes in the .NET Framework. You looked at manag- ing the local file system by using classes in the System.IO namespace such as DirectoryInfo and the FileInfo , and you learned how to enumerate the local file system and manipulate both directory and file properties and directory and file Access Control Lists. Additionally, the chapter discussed the rich functionality .NET provides for working with paths. The chapter also covered how the .NET Framework enables you to read and write data to a multitude of data locations, including the local file system, network file system, and even system memory through a common Stream architecture. The Framework provides you with specialized classes to deal with each kind of data location. Additionally, the Framework makes working with streams even easier by provid- ing Reader and Writer classes. These classes hide much of the complexity of reading from and writing to underlying streams. Here, too, the Framework provides you with a number of different Reader and Writer classes that give you the power to control exactly how your data is read or written, be it character, binary, string, or XML. 1190 Evjen c25.tex V2 - 01/28/2008 3:42pm Page 1191 Chapter 25: File I/O and Streams You were also introduced to a new feature of the .NET 2.0 Framework that allows you to communicate with serial ports. Finally, you learned about the variety of network communication options the .NET Framework provides. From making and sending Web requests over HTTP, FTP, and File, to sending mail, the .NET Framework offers you a full plate of network communication services. 1191 Evjen c26.tex V2 - 01/28/2008 3:48pm Page 1193 User and Server Controls In an object-oriented environment like .NET, the encapsulation of code into small, single-purpose, reusable objects is one of the keys to developing a robust system. For instance, if your application deals with customers, you might want to consider creating a customer’s object that encapsulates all the functionality a customer might need. The advantage is that you create a single point with which other objects can interact, and you have only a single point of code to create, debug, deploy, and maintain. In this scenario, the customer object is typically known as a business object because it encapsulates all the business logic needed for a customer. Several other types of reusable objects are available in .NET. In this chapter, we concentrate on discussing and demonstrating how you can create reusable visual components for an ASP.NET application. The two types of reusable components in ASP.NET are user controls and server con- trols. A user control encapsulates existing ASP.NET controls into a single container control, which you can easily reuse throughout your Web project. A server control encapsulates the visual design, behavior, and logic for an element that the user interacts with on the Web page. Visual Studio ships with a large number of server controls that you are probably already familiar with, such as the Label, Button, and TextBox controls. This chapter talks about how you can create custom server controls and extend existing server controls. Because the topics of user controls and server controls are so large, and because discussing the intricacies of each could easily fill an entire book by itself, this chapter can’t possibly investigate every option available to you. Instead, it attempts to give you a brief overview of building and using user controls and server controls and demonstrates some common scenarios for each type of control. By the end of this chapter, you should have learned enough that you can get started building basic controls of each type and be able to continue to learn on your own. Evjen c26.tex V2 - 01/28/2008 3:48pm Page 1194 Chapter 26: User and Server Controls User Controls User controls represent the simplest form of ASP.NET control encapsulation. Because they are the sim- plest, they are also the easiest to create and use. Essentially a user control is the grouping of existing server controls into a single-container control. This enables you to create powerful objects that you can easily use throughout an entire Web project. Creating User Controls Creating user controls is very simple in Visual Studio 2008. To create a new user control, you first add a new User Control file to your Web site. From the Website menu, select the Add New Item option. After the Add New File dialog appears, select the Web User Control File template from the list and click OK. Notice that after the file is added to the project, the file has an .ascx extension. This extension signals to ASP.NET that this file is a user control. If you attempt to load the user control directly into your browser, ASP.NET returns an error telling you that this type of file cannot be served to the client. If you look at the HTML source (shown in Listing 26-1) for the user control, you see several interesting differences from a standard ASP.NET Web page. Listing 26-1: A Web user control file template <%@ Control Language="VB" ClassName="WebUserControl1" %> <script runat="server"> </script> First, notice that the source uses the @Control directive rather than the @Page directive, which a standard Web page would use. Second, notice that unlike a standard ASP.NET Web page, no other HTML tags besides the < script > tags exist in the control. The Web page containing the user control provides the basic HTML, such as the < body > and < form > tags. In fact, if you try to add a server-side form tag to the user control, ASP.NET returns an error when the page is served to the client. The error message tells you that only one server-side form tag is allowed in your Web page. To add controls to the form, simply drag them from the Toolbox onto your user control. Listing 26-2 shows the user control after a Label and a Button have been added. Listing 26-2: Adding controls to the Web user control <%@ Control Language="VB" ClassName="WebUserControl2" %> <script runat="server"> </script> <asp:Label ID="Label1" runat="server" Text="Label"></asp:Label> <asp:Button ID="Button1" runat="server" Text="Button" /> After you add the controls to the user control, you put the user control onto a standard ASP.NET Web page. To do this, drag the file from the Solution Explorer onto your Web page. 1194 Evjen c26.tex V2 - 01/28/2008 3:48pm Page 1195 Chapter 26: User and Server Controls If you are familiar with using user controls in prior versions of Visual Studio, you probably remember the gray control representation that appeared in the page designer when you dropped a user control onto a Web page. In Visual Studio 2005, this experience was improved and user controls are now fully rendered on the host Web page during design time. This allows you to see an accurate representation of what the entire page will look like after it is rendered to the client. Figure 26-1 shows the user control after it has been dropped onto a host Web page. Figure 26-1 After you have placed the user control onto a Web page, open the page in a browser to see the fully rendered Web page. User controls fully participate in the page-rendering lifecycle, and controls contained within a user control behave identically to controls placed onto a standard ASP.NET Web page. This means that the user control has its own page execute events (such as Init, Load, and Prerender) that execute as the page 1195 Evjen c26.tex V2 - 01/28/2008 3:48pm Page 1196 Chapter 26: User and Server Controls is processed. It also means that child control events, such as a button-click event, will behave identically. Listing 26-3 shows how to use the User Controls Page_Load event to populate the label and to handle the button-click event. Listing 26-3: Creating control events in a user control VB <%@ Control Language="VB" ClassName="WebUserControl1" %> <script runat="server"> Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Me.Label1.Text = "The quick brown fox jumped over the lazy dog" End Sub Protected Sub Button1_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) Me.Label1.Text = "The quick brown fox clicked the button on the page" End Sub </script> <asp:Label ID="Label1" runat="server" Text="Label"></asp:Label> <asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click" /> C# <%@ Control Language="C#" ClassName="WebUserControl1" %> <script runat="server"> protected void Page_Load(object sender, EventArgs e) { this.Label1.Text = "The quick brown fox jumped over the lazy dog"; } protected void Button1_Click(object sender, EventArgs e) { this.Label1.Text = "The quick brown fox clicked the button on the page"; } </script> <asp:Label ID="Label1" runat="server" Text="Label"></asp:Label> <asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click" /> Now when you render the Web page, you see that the text of the label changes as the user control loads, and again when you click the bottom of the page. In fact, if you put a breakpoint on either of these two events, you can see that ASP.NET does indeed break, even inside the user control code when the page is executed. Interacting with User Controls So far, you have learned how you can create user controls and add them to a Web page. You have also learned how user controls can execute their own code. Most user controls, however, are not islands on their parent page. Many scenarios require that the hostWebpagebeabletointeractwithusercontrols that have been placed on it. For instance, you may decide that the text you want to load in the label must be given to the user control by the host page. To do this, you simply add a public property to the user control, and then assign text using the property. Listing 26-4 shows the modified user control. 1196 Evjen c26.tex V2 - 01/28/2008 3:48pm Page 1197 Chapter 26: User and Server Controls Listing 26-4: Exposing user control properties VB <%@ Control Language="VB" ClassName="WebUserControl" %> <script runat="server"> Private _text As String Public Property Text() As String Get Return _text End Get Set(ByVal value As String) _text = value End Set End Property Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Me.Label1.Text = Me.Text End Sub Protected Sub Button1_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) Me.Label1.Text = "The quick brown fox clicked the button on the page" End Sub </script> <asp:Label ID="Label1" runat="server" Text="Label"></asp:Label> <asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click" /> C# <%@ Control Language="C#" ClassName="WebUserControl" %> <script runat="server"> private string _text; public string Text { get { return _text; } set { _text = value; } } protected void Page_Load(object sender, EventArgs e) { this.Label1.Text = this.Text; } Continued 1197 Evjen c26.tex V2 - 01/28/2008 3:48pm Page 1198 Chapter 26: User and Server Controls protected void Button1_Click(object sender, EventArgs e) { this.Label1.Text = "The quick brown fox clicked the button on the page"; } </script> <asp:Label ID="Label1" runat="server" Text="Label"></asp:Label> <asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click" /> After you modify the user control, you simply populate the property from the host Web page. Listing 26-5 shows how to set the Text property in code, but public properties exposed by user controls will also be exposed by the Property Browser. Listing 26-5: Populating user control properties from the host Web page VB Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Me.WebUserControl1.Text = "The quick brown fox jumped over the lazy dog" End Sub C# protected void Page_Load(object sender, EventArgs e) { this.WebUserControl1.Text = "The quick brown fox jumped over the lazy dog"; } User controls are simple ways of creating powerful, reusable components in ASP.NET. They are easy to create using the built-in templates. Because they participate fully in the page lifecycle, you can create controls that can interact with their host page and even other controls on the host page. Loading User Controls Dynamically User controls can also be created and added to the Web form dynamically at runtime. The ASP.NET Page object includes the LoadControl method, which allows you to load user controls at runtime by providing the method with a virtual path to the user control you want to load. The method returns a generic Control object that you can then add to the page’s Controls collection. Listing 26-6 demonstrates how you can use the LoadControl method to dynamically add a user control to a Web page. Listing 26-6: Dynamically adding a user control VB <%@ Page Language="VB" %> <script runat="server"> Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Dim myForm As Control = Page.FindControl("form1") Dim c1 As Control = LoadControl("~/WebUserControl.ascx") myForm.Controls.Add(c1) End Sub </script> 1198 Evjen c26.tex V2 - 01/28/2008 3:48pm Page 1199 Chapter 26: User and Server Controls <html xmlns="http://www.w3.org/1999/xhtml" > <head runat="server"> <title>Untitled Page</title> </head> <body> <form id="form1" runat="server"> <div> </div> </form> </body> </html> C# <script runat="server"> void Page_Load(object sender, EventArgs e) { Control myForm = Page.FindControl("Form1"); Control c1 = LoadControl("~/WebUserControl.ascx"); myForm.Controls.Add(c1); } </script> The first step in adding a user control to the page is to locate the page’s Form control using the FindControl method. Should the user control contain ASP.NET controls that render form elements such as a button or text box, this user control must be added to the Form element’s Controls collection. It is possible to add user controls containing certain ASP.NET elements such as a Label, HyperLink, or Image directly to the Page object’s Controls collection; however, it is generally safer to be consistent and add them to the Form. Adding a control that must be contained within the Form, such as a Button control, to the Pages Controls collection results in a runtime parser error. After the form has been found, the sample uses the Page’s LoadControl() method to load an instance of the user control. The method accepts a virtual path to the user control you want to load and returns the loaded user control as a generic Control object. Finally, the control is added to the Form object’s Controls collection. You can also add the user control to other container controls that may be present on the Web page, such as a Panel or Placeholder control. Remember that you need to re-add your control to the ASP.NET page each time the page performs a postback. After you have the user control loaded, you can also work with its object model, just as you can with any other control. To access properties and methods that the user control exposes, you cast the control from the generic Control type to its actual type. To do that, you also need to add the @Reference directive to the page. This tells ASP.NET to compile the user control and link it to the ASP.NET page so that the page knows where to find the user control type. Listing 26-7 demonstrates how you can access a custom property of your user control by casting the control after loading it. The sample loads a modified user control that hosts an ASP.NET TextBox control and exposes a public property that allows you to access the TextBox control’s Text property. 1199 Evjen c26.tex V2 - 01/28/2008 3:48pm Page 1200 Chapter 26: User and Server Controls Listing 26-7: Casting a user control to its native type VB <%@ Page Language="VB" %> <%@ Reference Control="~/WebUserControl.ascx" %> <script runat="server"> Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Dim myForm As Control = Page.FindControl("form1") Dim c1 As WebUserControl = _ CType(LoadControl("~/WebUserControl.ascx"), WebUserControl) myForm.Controls.Add(c1) c1.ID = "myWebUserControl1" c1.Text = "My users controls text" End Sub </script> C# <%@ Page Language="C#" %> <%@ Reference Control="~/WebUserControl.ascx" %> <script runat="server"> void Page_Load(object sender, EventArgs e) { Control myForm = Page.FindControl("Form1"); WebUserControl c1 = (WebUserControl)LoadControl("WebUserControl.ascx"); myForm.Controls.Add(c1); c1.ID = "myWebUserControl1"; c1.Text = "My users controls text"; } </script> Notice that the sample adds the control to the Form’s Controls collection and then sets the Text property. This ordering is actually quite important. After a page postback occurs the control’s ViewState is not calculated until the control is added to the Controls collection. If you set the Text value (or any other property of the user control) before the control’s ViewState, the value is not persisted in the ViewState. One twist to dynamically adding user controls occurs when you are also using Output Caching to cache the user controls. In this case, after the control has been cached, the LoadControl method does not return a new instance of the control. Instead, it returns the cached copy of the control. This presents problems when you try to cast the control to its native type because, after the control is cached, the LoadControl method returns it as a PartialCachingControl object rather than as its native type. Therefore, the cast in the previous sample results in an exception being thrown. To solve this problem, you simply test the object type before attempting the cast. This is shown in Listing 26-8. Listing 26-8: Detecting cached user controls VB <script runat="server"> Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Dim myForm As Control = Page.FindControl("form1") Dim c1 As Control = LoadControl("~/WebUserControl.ascx") myForm.Controls.Add(c1) 1200 . "webmaster@ineta.org") message.Subject = "Sending Mail with ASP. NET 3. 5& quot; message.Body = _ "This is a sample email which demonstrates sending email using ASP. NET 3. 5& quot; Dim. "Sending Mail with ASP. NET 3. 5& quot;; message.Body = "This is a sample email which demonstrates sending email using ASP. NET 3. 5& quot;; System .Net. Mail.SmtpClient smtp = new System .Net. Mail.SmtpClient("localhost"); smtp.Send(message); In. Evjen c 25. tex V2 - 01/28/2008 3: 42pm Page 1190 Chapter 25: File I/O and Streams Listing 25- 29: Sending mail from a Web page VB Dim message As _ New System .Net. Mail.MailMessage("webmaster@ineta.org",