The <asp:LinkButton> control displays a clickable text link that calls a subprogram. It is the text equivalent of the <asp:Button> control and should not be confused with an <asp:HyperLink> control that issues a URL request. The general format for a LinkButton control is shown below.

<asp:LinkButton id="id" Runat="Server"
  Text="label"
  OnClick="subprogram"
  OnCommand="subprogram"
  CommandName="command"
  CommandArgument="argument"
  PostBackUrl="url"
    property="value"...
/>

An id is not required unless the LinkButton itself is referenced in a script. The Text attribute provides the text label for the link. The OnClick event handler identifies a subprogram to run when the link is clicked. OnCommand, CommandName, and CommandArgument properties call a subprogram that is shared by other links to pass along information about processing to perform. PostBackUrl posts to a different page from the current page.

Calling a Subprogram

A single LinkButton calls a subprogram by coding an OnClick event handler. The following button operates in this way. The called subprogram simply assigns a text string to the accompanying Label control. Notice that the signature for a subprogram called by a LinkButton contains the same EventArgs argument as a subprogram called by a Button control.

<SCRIPT Runat="Server">

Sub Link_Click (Src As Object, Args As EventArgs)
  Message.Text = "The Link_Click subprogram was run."
End Sub

</SCRIPT>

<form Runat="Server">

<asp:LinkButton Text="Call Link_Click" OnClick="Link_Click" Runat="Server"/>
<asp:Label id="Message" Runat="Server"/>

</form>

Scripting Command Links

The LinkButton also can be configured as a command link so that a single subprogram that services multiple LinkButtons can determine which link was clicked and take appropriate action for the chosen link. As in the case of a command button, a command link has a CommandName property to pass processing control information. If additional information is needed for script processing, the LinkButton can pass a CommandArgument to the subprogram.

In the following example, two LinkButtons call a single subprogram, passing CommandName and CommandArgument arguments. The subprogram reports on values that are passed. You should recognize this application as identical to the previous example using command Buttons. The only difference is in the use of LinkButtons to call the subprogram.

<SCRIPT Runat="Server">

Sub Report_Arguments (Src As Object, Args As CommandEventArgs)

  PassedValues.Text  = "<b>Src.id</b> = " & Src.id & "<br/>"
  PassedValues.Text &= "<b>Args.CommandName</b>= " & _
                        Args.CommandName & "<br/>"
  PassedValues.Text &= "<b>Args.CommandArgument</b>= " & _
                        Args.CommandArgument & "<br/>"
	
End Sub

</SCRIPT>

<form Runat="Server">

<asp:LinkButton id="FirstButton" Runat="Server"
  Text="Report Arguments" 
  OnCommand="Report_Arguments" 
  CommandName="Do This"
  CommandArgument="With This Value"/>

<asp:LinkButton id="SecondButton" Runat="Server"
  Text="Report Arguments" 
  OnCommand="Report_Arguments" 
  CommandName="Do That"
  CommandArgument="With That Value"/>

<p><asp:Label id="PassedValues" Runat="Server"/></p>

</form>

Using LinkButtons for Database Display

The following example is a minor rewrite of the previous application of command Buttons to display different sets of book types from the BooksDB.mdb database. These LinkButtons are configured as command buttons to call a subprogram to issue different SQL statements to create display tables through a GridView control.

Script and control coding for this output is shown below. All LinkButtons have CommandName values indicating the BookType field from the database to be used for selecting subsets of records. These BookType values, passed as Args.CommandName through the subprogram argument list, are concatenated within an SQL statement to issue an appropriate command to retrieve records with the matching value.

<SCRIPT Runat="Server">

Sub Show_Books (Src As Object, Args As CommandEventArgs)
  
  Dim SQLString As String
  SQLString = "SELECT BookID, BookTitle, BookPrice FROM Books " & _
              "WHERE BookType = '" & Args.CommandName & "'"
  BookSource.SelectCommand = SQLString

End Sub

</SCRIPT>

<form Runat="Server">

<h3>View Book Types</h3>

<asp:LinkButton Runat="Server"
  Text="Database"
  OnCommand="Show_Books"
  CommandName="Database"
  Width="80"/>

<asp:LinkButton Runat="Server"
  Text="Graphics"
  OnCommand="Show_Books"
  CommandName="Graphics"
  Width="80"/>

<asp:LinkButton Runat="Server"
  Text="Hardware"
  OnCommand="Show_Books"
  CommandName="Hardware"
  Width="80"/><br/>

<asp:LinkButton Runat="Server"
  Text="Software"
  OnCommand="Show_Books"
  CommandName="Software"
  Width="80"/>

<asp:LinkButton Runat="Server"
  Text="Systems"
  OnCommand="Show_Books"
  CommandName="Systems"
  Width="80"/>

<asp:LinkButton Runat="Server"
  Text="Web"
  OnCommand="Show_Books"
  CommandName="Web"
  Width="80"/>

<asp:AccessDataSource id="BookSource" Runat="Server"
  DataFile="../Databases/BooksDB.mdb"
  SelectCommand="SELECT BookID, BookTitle, BookPrice FROM Books
                 WHERE BookType = 'Database'"/>

<p><asp:GridView DataSourceID="BookSource" Runat="Server"/></p>

</form>

Both Button and LinkButton controls provide the same functionality. Their choice is a matter of visual preference about whether you wish to display buttons or text links to activate scripts.