Evjen c03.tex V2 - 01/28/2008 12:33pm Page 114 Chapter 3: ASP.NET Web Server Controls { Response.Write("OnTextChanged event triggered"); } protected void Button1_Click(object sender, EventArgs e) { Response.Write("OnClick event triggered"); } < /script > As you build and run this page, notice that you can type something in the text box, but once you tab out of it, the OnTextChanged event is triggered and the code contained in the TextBox1_TextChanged event runs.Tomakethiswork,youmustaddthe AutoPostBack attribute to the TextBox control and set it to True . This causes the Web page to look for any text changes prior to an actual page postback. For the AutoPostBack feature to work, the browser viewing the page must support ECMAScript. Using AutoCompleteType You want the forms you build for your Web applications to be as simple to use as possible. You want to make them easy and quick for the end user to fill out the information and proceed. If you make a form too onerous, the people who come to your site may leave without completing it. One of the great capabilities for any W eb form is smart auto-completion. You may have seen this yourself when you visited a site for the first time. As you start to fill out information in a form, a drop-down list appears below the text box as you type, showing you a value that you have typed in a previous form. The plain text box you were working with has become a smart text box. Figure 3-5 shows an example of this feature. Figure 3-5 A great new aspect of the TextBox control is the AutoCompleteType attribute, which enables you to apply the auto-completion feature to your own forms. You have to help the text boxes on your form to recognize the type of information that they should be looking for. What does that mean? Well, first look at the possible values of the AutoCompleteType attribute: BusinessCity Disabled HomeStreetAddress BusinessCountryRegion DisplayName HomeZipCode BusinessFax Email JobTitle BusinessPhone FirstName LastName BusinessState Gender MiddleName BusinessStateAddress HomeCity None BusinessUrl HomeCountryRegion Notes BusinessZipCode HomeFax Office Cellular Homepage Pager Company HomePhone Search Department HomeState 114 Evjen c03.tex V2 - 01/28/2008 12:33pm Page 115 Chapter 3: ASP.NET Web Server Controls From this list, you can see that if your text box is asking for the end user’s home street address, you want to use the following in your TextBox control: < asp:TextBox ID="TextBox1" runat="server" AutoCompleteType="HomeStreetAddress" >< /asp:TextBox > As you view the source of the text box you created, you can see that the following construction has occurred: < input name="TextBox1" type="text" vcard_name="vCard.Home.StreetAddress" id="TextBox1" / > This feature makes your forms easier to work with. Yes, it is a simple thing, but sometimes it is the little things that keep the viewers coming back again and again to your Web site. The Button Ser ver Control Another common control for your Web forms is a button that can be constructed using the Button server control. Buttons are the usual element used to submit forms. Most of the time you are simply dealing with items contained in your forms through the Button control’s OnClick event, as illustrated in Listing 3-5. Listing 3-5: The Button control’s OnClick event VB Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) ’ Code here End Sub C# protected void Button1_Click(object sender, EventArgs e) { // Code here } The Button control is one of the easier controls to use, but there are a couple of properties of which you must be aware: CausesValidation and CommandName . They are discussed in the following sections. The CausesValidation Property If you have more than one button on your Web page and you are working with the validation server con- trols, you may not want to fire the validation for each button on the form. Setting the CausesValidation property to False is a w ay to use a button that will not fire the validation process. This is explained in more detail in Chapter 4. The CommandName Property You can have multiple buttons on your form all working from a single event. The nice thing is that you can also tag the buttons so that the code can make logical decisions based on which button on the form 115 Evjen c03.tex V2 - 01/28/2008 12:33pm Page 116 Chapter 3: ASP.NET Web Server Controls was clicked. You must construct your Button controls in the manner illustrated in Listing 3-6 to take advantage of this behavior. Listing 3-6: Constructing multiple Button controls to work from a single function < asp:Button ID="Button1" runat="server" Text="Button 1" OnCommand="Button_Command" CommandName="DoSomething1" / > < asp:Button ID="Button2" runat="server" Text="Button 2" OnCommand="Button_Command" CommandName="DoSomething2" / > Looking at these two instances of the Button control, you should pay attention to several things. The first thing to notice is what is not present — any attribute mention of an OnClick event. Instead, you use the OnCommand event, which points to an event called Button_Command . You can see that both Button controls are working from the same event. How does the event differentiate between the two buttons being clicked? Through the value placed in the CommandName property. In this case, they are indeed separate values — DoSomething1 and DoSomething2 . The next step is to create the Button_Command event to deal with both these buttons by simply typing one out or by selecting the Command event from the drop-down list of available events for the Button control from the code view of Visual Studio. In either case, you should end up with an event like the one shown in Listing 3-7. Listing 3-7: The Button_Command event VB Protected Sub Button_Command(ByVal sender As Object, _ ByVal e As System.Web.UI.WebControls.CommandEventArgs) Select Case e.CommandName Case "DoSomething1" Response.Write("Button 1 was selected") Case "DoSomething2" Response.Write("Button 2 was selected") End Select End Sub C# protected void Button_Command(Object sender, System.Web.UI.WebControls.CommandEventArgs e) { switch (e.CommandName) { case("DoSomething1"): Response.Write("Button 1 was selected"); break; case("DoSomething2"): Response.Write("Button 2 was selected"); break; } } 116 Evjen c03.tex V2 - 01/28/2008 12:33pm Page 117 Chapter 3: ASP.NET Web Server Controls Notice that this method uses System.Web.UI.WebControls.CommandEventArgs instead of the typical System.EventArgs . This gives you access to the member CommandName used in the Select Case ( switch ) statement as e.CommandName . Using this object, you can check for the value of the CommandName property used by the button that was clicked on the form and take a specific action based upon the value passed. You can add some parameters to be passed in to the Command event beyond what is defined in the Com- mandName property. You do this by using the Button control’s CommandArgument property. Adding values to the property enables you to define items a bit more granularly if you want. You can get at this value via server-side code using e.CommandArgument from the CommandEventArgs object. Buttons That Work with Client-Side JavaScript Buttons are frequently used f or submitting information and causing actions to occur on a Web page. Before ASP.NET 1.0/1.1, people intermingled quite a bit of JavaScript in their pages to fire JavaScript events when a button was clicked. The process became more cumbersome in ASP.NET 1.0/1.1, but ever since ASP.NET 2.0, it is much easier. You can create a page that has a JavaScript event, as well as a server-side event, triggered when the button is clicked, as illustrated in Listing 3-8. Listing 3-8: Two types of events for the button VB < %@ Page Language="VB" % > < script runat="server" > Protected Sub Button1_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) Response.Write("Postback!") End Sub < /script > < script language="javascript" > function AlertHello() { alert(’Hello ASP.NET’); } < /script > < html xmlns="http://www.w3.org/1999/xhtml" > < head runat="server" > < title > Button Server Control < /title > < /head > < body > < form id="form1" runat="server" > < asp:Button ID="Button1" runat="server" Text="Button" OnClientClick="AlertHello()" OnClick="Button1_Click" / > < /form > Continued 117 Evjen c03.tex V2 - 01/28/2008 12:33pm Page 118 Chapter 3: ASP.NET Web Server Controls < /body > < /html > C# < %@ Page Language="C#" % > < script runat="server" > protected void Button1_Click(object sender, EventArgs e) { Response.Write("Postback!"); } < /script > The first thing to notice is the new attribute for the Button server control: OnClientClick . It points to the client-side function, unlike the OnClick attribute that points to the server-side event. T his example uses a JavaScript function called AlertHello() . One cool thing a bout Visual Studio 2008 is that it can work with server-side script tags that are right alongside client-side script tags. It all works together seamlessly. In the example, after the JavaScript alert dialog is issued (see Figure 3-6) and the end user clicks OK, the page posts back as the server-side event is triggered. Figure 3-6 Another interesting attribute for the button controls is PostBackUrl . It enables you to perform cross-page posting, instead of simply posting your ASP.NET pages back to the same page, as shown in the following example: < asp:Button ID="Button2" runat="server" Text="Submit page to Page2.aspx" PostBackUrl="Page2.aspx" / > Cross-page posting is covered in greater detail in Chapter 1. 118 Evjen c03.tex V2 - 01/28/2008 12:33pm Page 119 Chapter 3: ASP.NET Web Server Controls The LinkButton Server Control The LinkButton server control is a variation of the Button control. It is the same except that the LinkButton control takes the form of a hyperlink. Nevertheless, it is not a typical hyperlink. When the end user clicks the link, it behaves like a button. This is an ideal control to use if you have a large number of buttons on your Web form. A LinkButton server control is constructed as follows: < asp:LinkButton ID="LinkButton1" Runat="server" OnClick="LinkButton1_Click" > Submit your name to our database < /asp:LinkButton > Using the LinkButton control gives you the results shown in Figure 3-7. Figure 3-7 The ImageButton Ser ver Control The ImageButton control is also a variation of the Button control. It is almost exactly the same as the Button control except that it enables you to use a custom image as the form’s button instead of the typical buttons used on most forms. This means that you can create your own buttons as images and the end users can click the images to submit form data. A typical construction of the ImageButton is as follows: < asp:ImageButton ID="ImageButton1" runat="server" OnClick="ImageButton1_Click" ImageUrl="MyButton.jpg" / > The ImageButton control specifies the location of the image used by using the ImageUrl property. From this example, you can see that the ImageUrl points to MyButton.jpg . The big difference between the ImageButton control and the LinkButton or Button controls is that ImageButton takes a different con- struction for the OnClick event. It is shown in Listing 3-9. Listing 3-9: The Click event for the ImageButton control VB Protected Sub ImageButton1_Click(ByVal sender As Object, _ ByVal e As System.Web.UI.WebControls.ImageClickEventArgs) Continued 119 Evjen c03.tex V2 - 01/28/2008 12:33pm Page 120 Chapter 3: ASP.NET Web Server Controls ’ Code here End Sub C# protected void ImageButton1_Click(object sender, System.Web.UI.WebControls.ImageClickEventArgs e) { // Code here } The construction uses the ImageClickEventArgs object instead o f the System.EventArgs object usually used with the LinkButton and Button controls. You can use this object to determine where in the image the end user clicked by using both e.X and e.Y coordinates. The Search and Play Video buttons on the page shown in Figure 3-8 are image buttons. Figure 3-8 The HyperLink Ser ver Control The HyperLink server control enables you to programmatically work with any hyperlinks on your Web pages. Hyperlinks are links that allow end users to transfer from one page to another. You can set the text of a hyperlink using the control’s Text attribute: 120 Evjen c03.tex V2 - 01/28/2008 12:33pm Page 121 Chapter 3: ASP.NET Web Server Controls < asp:HyperLink ID="HyperLink1" runat="server" Text="Go to this page here" NavigateUrl="~/Default2.aspx" >< /asp:HyperLink > This server control creates a hyperlink on your page with the text Go to this page here . When the link is clicked, the user is redirected to the value that is placed in the NavigateUrl property (in this case, the Default2.aspx page). The interesting thing about the HyperLink server control is that it can be used for images as well as text. Instead of using the Text attribute, it uses the ImageUrl property: < asp:HyperLink ID="HyperLink1" runat="server" ImageUrl="~/MyLinkImage.gif" NavigateUrl="~/Default2.aspx" >< /asp:HyperLink > The HyperLink control is a great way to dynamically place hyperlinks on a Web page based either upon user input in a form or on database values that are retrieved when the page is loaded. The DropDownList Ser ver Control The DropDownList server control enables you to place an HTML select box on your Web page and program against it. It is ideal when you have a large collection of items from which you want the end user to select a single item. It is usually used for a medium- to large-sized collection. If the collection size is relatively small, consider using the RadioButtonList server control (described later in this chapter). The select box generated by the DropDownList control displays a single item and allows the end user to make a selection from a larger list of items. Depending on the number of choices available in the select box, the end user may have to scroll through a list of items. Note that the appearance of the scroll bar in the drop-down list is automatically created by the browser depending on the browser version and the number of items contained in the list. Here is the code for DropDownList control: < asp:DropDownList ID="DropDownList1" runat="server" > < asp:ListItem > Car < /asp:ListItem > < asp:ListItem > Airplane < /asp:ListItem > < asp:ListItem > Train < /asp:ListItem > < /asp:DropDownList > This code generates a drop-down list in the browser, as shown in Figure 3-9. Figure 3-9 The DropDownList control comes in handy when you start binding it to various data stores. The data stores can either be arrays, database values, XML file values, or values found elsewhere. For an example 121 Evjen c03.tex V2 - 01/28/2008 12:33pm Page 122 Chapter 3: ASP.NET Web Server Controls of binding the DropDownList control, this next example looks at dynamically generating a DropDown- List control from one of three available arrays, as shown in Listing 3-10. Listing 3-10: Dynamically generating a DropDownList control from an array VB < %@ Page Language="VB" % > < script runat="server" > Protected Sub DropDownList1_SelectedIndexChanged(ByVal sender As Object, _ ByVal e As System.EventArgs) Dim CarArray() As String = {"Ford", "Honda", "BMW", "Dodge"} Dim AirplaneArray() As String = {"Boeing 777", "Boeing 747", "Boeing 737"} Dim TrainArray() As String = {"Bullet Train", "Amtrack", "Tram"} If DropDownList1.SelectedValue = "Car" Then DropDownList2.DataSource = CarArray ElseIf DropDownList1.SelectedValue = "Airplane" Then DropDownList2.DataSource = AirplaneArray Else DropDownList2.DataSource = TrainArray End If DropDownList2.DataBind() DropDownList2.Visible = True End Sub Protected Sub Button1_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) Response.Write("You selected < b > "&_ DropDownList1.SelectedValue.ToString() & ": " & _ DropDownList2.SelectedValue.ToString() & " < /b > ") End Sub < /script > < html xmlns="http://www.w3.org/1999/xhtml" > < head runat="server" > < title > DropDownList Page < /title > < /head > < body > < form id="form1" runat="server" > < div > Select transportation type: < br / > < asp:DropDownList ID="DropDownList1" runat="server" OnSelectedIndexChanged="DropDownList1_SelectedIndexChanged" AutoPostBack="true" > < asp:ListItem > Select an Item < /asp:ListItem > < asp:ListItem > Car < /asp:ListItem > < asp:ListItem > Airplane < /asp:ListItem > < asp:ListItem > Train < /asp:ListItem > < /asp:DropDownList > &nbsp; < asp:DropDownList ID="DropDownList2" runat="server" Visible="false" > 122 Evjen c03.tex V2 - 01/28/2008 12:33pm Page 123 Chapter 3: ASP.NET Web Server Controls < /asp:DropDownList > < asp:Button ID="Button1" runat="server" Text="Select Options" OnClick="Button1_Click" / > < /div > < /form > < /body > < /html > C# < %@ Page Language="C#" % > < script runat="server" > protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e) { string[] CarArray = new string[4] {"Ford", "Honda", "BMW", "Dodge"}; string[] AirplaneArray = new string[3] {"Boeing 777", "Boeing 747", "Boeing 737"}; string[] TrainArray = new string[3] {"Bullet Train", "Amtrack", "Tram"}; if (DropDownList1.SelectedValue == "Car") { DropDownList2.DataSource = CarArray; } else if (DropDownList1.SelectedValue == "Airplane") { DropDownList2.DataSource = AirplaneArray; } else { DropDownList2.DataSource = TrainArray; } DropDownList2.DataBind(); DropDownList2.Visible = true; } protected void Button1_Click(object sender, EventArgs e) { Response.Write("You selected < b > "+ DropDownList1.SelectedValue.ToString() + ": " + DropDownList2.SelectedValue.ToString() + " < /b > "); } < /script > In this example, the second drop-down list is dynamically generated based upon the value selected from the first drop-down list. For instance, selecting Car from the first drop-down list dynamically creates a second drop-down list on the form that includes a list of available car selections. This is possible because of the use of the AutoPostBack feature of the DropDownList control. When the AutoPostBack property is set to True , the method provided through the OnSelectedIndexChanged event is fired when a selection is made. In the example, the DropDownList1_SelectedIndexChanged event is fired, dynamically creating the second drop-down list. In this method, the content of the second drop-down list is created in a string array and then bound to the second DropDownList control through the use of the DataSource property and the DataBind() method. When built and run, this page looks like the one shown in Figure 3-10. 123 . Page2.aspx" PostBackUrl="Page2.aspx" / > Cross-page posting is covered in greater detail in Chapter 1. 118 Evjen c 03. tex V2 - 01/28/2008 12 :33 pm Page 119 Chapter 3: ASP. NET Web. 12 :33 pm Page 116 Chapter 3: ASP. NET Web Server Controls was clicked. You must construct your Button controls in the manner illustrated in Listing 3- 6 to take advantage of this behavior. Listing. buttons being clicked? Through the value placed in the CommandName property. In this case, they are indeed separate values — DoSomething1 and DoSomething2 . The next step is to create the Button_Command event