How to use Language Selector declaratively ?

Hi,

I want to use language selector in my user control.

I did this 

 <sf:LanguageSelector runat="server" ID="lngSelector"></sf:LanguageSelector>

and got this error :

Server Error in '/' Application.

Object reference not set to an instance of an object.Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error: 

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.
Stack Trace: 

[NullReferenceException: Object reference not set to an instance of an object.] Telerik.Sitefinity.Web.UI.ItemSelector.GetScriptDescriptors() +276 Telerik.Sitefinity.Web.UI.FlatSelector.GetScriptDescriptors() +22 System.Web.UI.ScriptControlManager.RegisterScriptDescriptors(IScriptControl scriptControl) +175 Telerik.Sitefinity.Web.UI.SimpleScriptView.Render(HtmlTextWriter writer) +145 System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +149 System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +245 System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +149 System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +245 System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +149 System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +245 System.Web.UI.WebControls.WebControl.RenderContents(HtmlTextWriter writer) +14 System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter writer) +51 System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +149 System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +245 System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +149 System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +245 System.Web.UI.HtmlControls.HtmlForm.RenderChildren(HtmlTextWriter writer) +393 System.Web.UI.HtmlControls.HtmlContainerControl.Render(HtmlTextWriter writer) +48 System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +149 System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +245​

Hi Majid,

You have to set its DataKeyNames to "DefinedFrontendLanguages" or "DefinedBackendLanguages" in the backend to make it work like so: