ASP .net material Part-4

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ASP.NET - Data Binding

We may use data binding to fill lists with selectable items from an imported data source, like a database, an XML file, or a script.

Data Binding

The following controls are list controls which support data binding:
  • asp:RadioButtonList
  • asp:CheckBoxList
  • asp:DropDownList
  • asp:Listbox
The selectable items in each of the above controls are usually defined by one or more asp:ListItem controls, like this:
<html>
<body>

<form runat="server">
<asp:RadioButtonList id="countrylist" runat="server">
<asp:ListItem value="N" text="Norway" />
<asp:ListItem value="S" text="Sweden" />
<asp:ListItem value="F" text="France" />
<asp:ListItem value="I" text="Italy" />
</asp:RadioButtonList>
</form>

</body>
</html>
However, with data binding we may use a separate source, like a database, an XML file, or a script to fill the list with selectable items.
By using an imported source, the data is separated from the HTML, and any changes to the items are made in the separate data source.
In the next three chapters, we will describe how to bind data from a scripted data source.

ASP.NET - The ArrayList Object

The ArrayList object is a collection of items containing a single data value.

Create an ArrayList

The ArrayList object is a collection of items containing a single data value.
Items are added to the ArrayList with the Add() method.
The following code creates a new ArrayList object named mycountries and four items are added:
<script runat="server">
Sub Page_Load
if Not Page.IsPostBack then
  dim mycountries=New ArrayList
  mycountries.Add("Norway")
  mycountries.Add("Sweden")
  mycountries.Add("France")
  mycountries.Add("Italy")
end if
end sub
</script>
By default, an ArrayList object contains 16 entries. An ArrayList can be sized to its final size with the TrimToSize() method:
<script runat="server">
Sub Page_Load
if Not Page.IsPostBack then
  dim mycountries=New ArrayList
  mycountries.Add("Norway")
  mycountries.Add("Sweden")
  mycountries.Add("France")
  mycountries.Add("Italy")
  mycountries.TrimToSize()
end if
end sub
</script>
An ArrayList can also be sorted alphabetically or numerically with the Sort() method:
<script runat="server">
Sub Page_Load
if Not Page.IsPostBack then
  dim mycountries=New ArrayList
  mycountries.Add("Norway")
  mycountries.Add("Sweden")
  mycountries.Add("France")
  mycountries.Add("Italy")
  mycountries.TrimToSize()
  mycountries.Sort()
end if
end sub
</script>
To sort in reverse order, apply the Reverse() method after the Sort() method:
<script runat="server">
Sub Page_Load
if Not Page.IsPostBack then
  dim mycountries=New ArrayList
  mycountries.Add("Norway")
  mycountries.Add("Sweden")
  mycountries.Add("France")
  mycountries.Add("Italy")
  mycountries.TrimToSize()
  mycountries.Sort()
  mycountries.Reverse()
end if
end sub
</script>

Data Binding to an ArrayList

An ArrayList object may automatically generate the text and values to the following controls:
  • asp:RadioButtonList
  • asp:CheckBoxList
  • asp:DropDownList
  • asp:Listbox
To bind data to a RadioButtonList control, first create a RadioButtonList control (without any asp:ListItem elements) in an .aspx page:
<html>
<body>

<form runat="server">
<asp:RadioButtonList id="rb" runat="server" />
</form>

</body>
</html>
Then add the script that builds the list and binds the values in the list to the RadioButtonList control:

Example

<script runat="server">
Sub Page_Load
if Not Page.IsPostBack then
  dim mycountries=New ArrayList
  mycountries.Add("Norway")
  mycountries.Add("Sweden")
  mycountries.Add("France")
  mycountries.Add("Italy")
  mycountries.TrimToSize()
  mycountries.Sort()
  rb.DataSource=mycountries
  rb.DataBind()
end if
end sub
</script>

<html>
<body>

<form runat="server">
<asp:RadioButtonList id="rb" runat="server" />
</form>

</body>
</html>

Show example »
The DataSource property of the RadioButtonList control is set to the ArrayList and it defines the data source of the RadioButtonList control. The DataBind() method of the RadioButtonList control binds the data source with the RadioButtonList control.
Note: The data values are used as both the Text and Value properties for the control. To add Values that are different from the Text, use either the Hashtable object or the SortedList object.

ASP.NET - The Hashtable Object

The Hashtable object contains items in key/value pairs.

Create a Hashtable

The Hashtable object contains items in key/value pairs. The keys are used as indexes, and very quick searches can be made for values by searching through their keys.
Items are added to the Hashtable with the Add() method.
The following code creates a Hashtable named mycountries and four elements are added:
<script runat="server">
Sub Page_Load
if Not Page.IsPostBack then
  dim mycountries=New Hashtable
  mycountries.Add("N","Norway")
  mycountries.Add("S","Sweden")
  mycountries.Add("F","France")
  mycountries.Add("I","Italy")
end if
end sub
</script>

Data Binding

A Hashtable object may automatically generate the text and values to the following controls:
  • asp:RadioButtonList
  • asp:CheckBoxList
  • asp:DropDownList
  • asp:Listbox
To bind data to a RadioButtonList control, first create a RadioButtonList control (without any asp:ListItem elements) in an .aspx page:
<html>
<body>

<form runat="server">
<asp:RadioButtonList id="rb" runat="server" AutoPostBack="True" />
</form>

</body>
</html>
Then add the script that builds the list:
<script runat="server">
sub Page_Load
if Not Page.IsPostBack then
  dim mycountries=New Hashtable
  mycountries.Add("N","Norway")
  mycountries.Add("S","Sweden")
  mycountries.Add("F","France")
  mycountries.Add("I","Italy")
  rb.DataSource=mycountries
  rb.DataValueField="Key"
  rb.DataTextField="Value"
  rb.DataBind()
end if
end sub
</script>

<html>
<body>

<form runat="server">
<asp:RadioButtonList id="rb" runat="server" AutoPostBack="True" />
</form>

</body>
</html>
Then we add a sub routine to be executed when the user clicks on an item in the RadioButtonList control. When a radio button is clicked, a text will appear in a label:

Example

<script runat="server">
sub Page_Load
if Not Page.IsPostBack then
  dim mycountries=New Hashtable
  mycountries.Add("N","Norway")
  mycountries.Add("S","Sweden")
  mycountries.Add("F","France")
  mycountries.Add("I","Italy")
  rb.DataSource=mycountries
  rb.DataValueField="Key"
  rb.DataTextField="Value"
  rb.DataBind()
end if
end sub

sub displayMessage(s as Object,e As EventArgs)
lbl1.text="Your favorite country is: " & rb.SelectedItem.Text
end sub
</script>

<html>
<body>

<form runat="server">
<asp:RadioButtonList id="rb" runat="server"
AutoPostBack="True" onSelectedIndexChanged="displayMessage" />
<p><asp:label id="lbl1" runat="server" /></p>
</form>

</body>
</html>

Show example »
Note: You cannot choose the sort order of the items added to the Hashtable. To sort items alphabetically or numerically, use the SortedList object.

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