C# – Control inside EditItemTemplate will be available in Page_Load() only if

On my page I’ve defined controls TextBox1, Label1 and GridView1. Inside GridView1 I’ve defined the following template:

           <asp:TemplateField>

              <ItemTemplate>
                <asp:LinkButton runat="server" Text="Edit" CommandName="Edit" ID="cmdEdit" />         
              </ItemTemplate>

              <EditItemTemplate>
                <asp:TextBox Text='<%# Bind("Notes") %>' runat="server" id="textBoxNotes" />
                <br /><br />
                <asp:LinkButton runat="server" Text="Update" 
                 CommandName="Update" ID="cmdUpdate" /> 
                <asp:LinkButton runat="server" Text="Cancel" 
                 CommandName="Cancel" ID="cmdCancel" />
              </EditItemTemplate>

            </asp:TemplateField>

If user enters a text into textBoxNotes and clicks cmdUpdate button, then on postback this text will already be available when Page_Load() is called.

Thus, if user, before clicking the update button cmdUpdate, also entered into TextBox1 a string “something”, then the following code will extract the text user entered into textBoxNotes

    protected void Page_Load(object sender, EventArgs e)
    {
        if(TextBox1.Text=="text from Notes")
        Label1.Text =((TextBox)gridEmployees.Rows[0].Cells[0].FindControl("textBoxNotes")).Text;
    }

A) The following code should also extract the text user entered into textBoxNotes, but the moment I click cmdEdit button, I get “Object reference not set to an instance of an object.” exception

    protected void Page_Load(object sender, EventArgs e)
    {
        if(IsPostBack)
        Label1.Text =((TextBox)gridEmployees.Rows[0].Cells[0].FindControl("textBoxNotes")).Text;
    }

Why do I get this exception? It appears as if textBoxNotes doesn’t exist. But why wouldn’t it exist?

thanx