The ModeChanged event is raised when a FormView control attempts to switch between edit, insert, and read-only mode, but after the mode actually changes. This allows you to provide an event-handling method that performs a custom routine, such as synchronizing the FormView control with another control, whenever this event occurs.

For Example:

Say in your html you have a FormView declared like:

<asp:formview id="FormView1"
        datasourceid="FormViewSource"
        allowpaging="true"
        datakeynames="ItemID"
        headertext="Read-Only Mode"
        headerstyle-backcolor="Green"
        emptydatatext="No records found."
        onmodechanged="FormView1_ModeChanged" 
        runat="server">

Then in your codebehind you have your ModeChanged subroutine.

Sub FormView1_ModeChanged(ByVal sender As Object, ByVal e As EventArgs)
   'Display the current mode in the header row.
   Select Case FormView1.CurrentMode

     Case FormViewMode.Edit
       FormView1.HeaderText = "Edit Mode"
       FormView1.HeaderStyle.BackColor = System.Drawing.Color.Red

     Case FormViewMode.ReadOnly
       FormView1.HeaderText = "Read-Only Mode"
       FormView1.HeaderStyle.BackColor = System.Drawing.Color.Green

     Case Else
       FormView1.HeaderText = "Unsupported mode."
       FormView1.HeaderStyle.BackColor = System.Drawing.Color.Yellow

   End Select
End Sub

If you post some code or give a more detailed explaination of what you are trying to accomplish, we may be able to help more.