The DataBind approach is an important concept in asp.net, where almost all controls require it to control the operation of the data, which is performed when the data source is specified for the control. We've used it in the DataSet object instance in the previous chapter, using this method to bind data to the DataGrid control, that is, Datagrid.databind ().
Asp. NET controls that use the DataBind method to bind data are Web controls that have data collection properties in addition to the three dedicated data-bound controls, including Dropdownlist,listbox, The data sources that are used to specify are generally arrays (ArrayList), the HA Dilute table (HashTable), data Tables (DataTable), Data Views (DataView), and DataReader.
Here we use this method to bind the data source for the ListBox control.
First, establish an instance running environment. Open Visual Studio.NET 2003, create a new Web project, name Datacon, create a new form, and name lbdatabind.aspx. Add a ListBox control to the Lbdatabind.aspx form, as shown in Figure 9.1.
Figure 9.1 Adding a ListBox control to lbdatabind.aspx
Figure 9.2 Lbdatabind.aspx Run Results
In the example above, we used a ListBox control, but we didn't set the <asp:ListItem> property to add an item to it. In Lbdatabind.aspx's logical code, we use random numbers to generate an array of 20 items (arrylist), we specify this array as the data source for ListBox1, and use the DataBind method to perform data binding for it, thus implementing the ListBox control in a programmatic way Data-binding operations.
In the previous section, we learned the <%#%> syntax, where we demonstrated the use of the Page.DataBind method of ASPX files to implement data binding to the entire page. Once the entire page of ASPX is bound, the data within the page is monitored.
Create a new form in the Datacon Web project named Pagedatabind.aspx. Add a DropDownList control to the Pagedatabind.aspx, with the main HTML code as follows:
<body ms_positioning= "GridLayout" >
<form id= "Form1" method= "POST" runat= "Server" >
<font face= "Song Body" >
<span style= "Background-color: #cccccc" >
Please choose your favorite sports:</span>
<p>
<asp:dropdownlist
Id= "DropDownList1"
runat= "Server"
Width= "104px"
height= "32px"
autopostback= "True" >
<asp:listitem value= "Running" > Running </asp:ListItem>
<asp:listitem value= "Horseback riding" > Horseback riding </asp:ListItem>
<asp:listitem value= "shooting" > Shooting </asp:ListItem>
<asp:listitem value= "swimming" > Swimming </asp:ListItem>
<asp:listitem value= "playing football" > playing football </asp:ListItem>
<asp:listitem value= "playing basketball" > playing basketball </asp:ListItem>
<asp:listitem value= "Play tennis" > Play tennis </asp:ListItem>
<asp:listitem value= "Play table tennis" > Play table Tennis </asp:ListItem>
<asp:listitem value= "Play Badminton" > Play Badminton </asp:ListItem>
</asp:DropDownList>
<p>
<span style= "Background-color: #cccccc" > You chose:<br>.
<%# Dropdownlist1.selectedvalue%>
</span>
</FONT>
</form>
</body>
The AutoPostBack property of our set DropDownList1 is "True", that is, the control has the ability to respond automatically to events, and when the selected item in the list box changes, it is automatically returned to the server and executed. NET Framework delegate event procedure SelectedIndexChanged. The code we wrote for the DropDownList1_SelectedIndexChanged event procedure is as follows:
Private Sub dropdownlist1_selectedindexchanged (ByVal sender as System.Object, ByVal e as System.EventArgs) Handles Dropdo Wnlist1.selectedindexchanged
' The entire event procedure is a statement, and after the statement is executed, the ASPX page is data-bound
' When the page data changes, you can use the <%#%> method to display
Page.DataBind ()
End Sub
Save the compilation, pagedatabind.aspx run the results as shown in Figure 9.3.
Figure 9.3 Pagedatabind.aspx Run Results
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