How to change displaytext while changing format

[Christin]

I've got some problems during change displaytext while changing format, would someone help?

<telerik:HeaderedContentControl Height="194" HorizontalAlignment="Left" Margin="316,241,0,0" Name="headeredContentControl1" VerticalAlignment="Top" Width="277">
    <StackPanel Orientation="Horizontal">
        <ComboBox Name="comboMode" Width="140" SelectionChanged="comboMode_SelectionChanged"></ComboBox>
        <telerik:RadDatePicker Width="120" Name="dtPicker"></telerik:RadDatePicker>
    </StackPanel>
</telerik:HeaderedContentControl>

 

public MainPage()

 {

     InitializeComponent();

     this.Loaded += new RoutedEventHandler(MainPage_Loaded);

 }

 

 void MainPage_Loaded(object sender, RoutedEventArgs e)

 {

     dtPicker.Culture = new System.Globalization.CultureInfo(Thread.CurrentThread.CurrentUICulture.Name);   // actually is "zh-cn"


    SetData();

 }

 private void SetData()

 {

     IDictionary<string,string> dic = new Dictionary<string,string>();

     dic.Add("Day","日");

     dic.Add("Month","月");

     dic.Add("Year","年");

 

     comboMode.ItemsSource = dic;

     comboMode.DisplayMemberPath = "Value";

     comboMode.SelectedValuePath = "Key";

 }

 

 private void comboMode_SelectionChanged(object sender, SelectionChangedEventArgs e)

 {

     string item = comboMode.SelectedValue.ToString();

 

     switch (item)

     {

         case "Day":

             dtPicker.DateSelectionMode = DateSelectionMode.Day;

             dtPicker.Culture.DateTimeFormat.ShortDatePattern = "yyyy年MM月dd日";   // sounds invalid?             

             break;

         case "Month":

             dtPicker.DateSelectionMode = DateSelectionMode.Month;

             //dtPicker.Culture.DateTimeFormat.ShortDatePattern = "yyyy年MM月";

             dtPicker.Culture.DateTimeFormat.ShortDatePattern = "yyyy-MM";

             break;

         case "Year":

             dtPicker.DateSelectionMode = DateSelectionMode.Year;

             dtPicker.Culture.DateTimeFormat.ShortDatePattern = "yyyy";             

             break;

     }

 }

questions are:
1. Error occurs when i choose combobox to "Day";
2. i want to change the display text while the combobox.selectionchanged fired, actually it's never happend.
    for example, when i changed to "day", it would display "2012-03-29", the display "2012" when changed to "year".
3.when i changed from "Day" to "Year", the current year become "2009" but not "2012" when the dropdown is open ,do i got sth wrong?

your help would be appreciated, thanks!