c# - populating a text box with FindControl -

i have multiple textboxes , want programatically populate them same method.

<asp:content id="content2" contentplaceholderid="contentplaceholder1" runat="server">     <asp:scriptmanager id="scriptmanager1" runat="server">     </asp:scriptmanager>         <asp:updateprogress id="updateprogress1" runat="server" displayafter="500">         <progresstemplate>             <div id="freezeupdate" class="freezepaneon">                <div id="innerfreezepane" class="innerfreezepane gradient"><asp:literal id="litprogress" runat="server" text="<%$ resources:localizedtext, freezemsg_processingpleasewait %>"></asp:literal></style></div>             </div>         </progresstemplate>     </asp:updateprogress>     <asp:updatepanel id="updatepanel1" runat="server">         <asp:textbox id="tbxcollectionaddress" runat="server" textmode="multiline" readonly="true" cssclass="address"></asp:textbox>         <asp:textbox id="tbxreturnaddress" runat="server" textmode="multiline" readonly="true" cssclass="address"></asp:textbox>     </asp:updatepanel> </asp:content> 

then method...

protected void populateaddress(string txttextbox, address adraddress)     {         textbox txtaddress = (textbox)findcontrol(txttextbox);          txtaddress.text = "hello world";      } 

when call method below...

populateaddress("tbxreturnaddress", collectionaddress); 

...i exception...

system.nullreferenceexception: object reference not set instance of object.

...and highlights txtaddress.text = "hello world"; line.

i'd like method because there 3 separate addresses need populate on form i'd try using re-usable code feeding in address object , textbox id, i'm falling on @ findcontrol stage.

what missing?

firstly , test function likes

  textbox txtaddress = (textbox)findcontrol("tbxreturnaddress"); 

or

you can try likes ,

  textbox txtaddress = (textbox)page.findcontrol("tbxreturnaddress"); 

edit

if text-box in updatepanel ,

  textbox txtaddress = (textbox)updatepanel1.findcontrol("tbxreturnaddress");