Why LongListSelector ItemTemplate Doesn't Show Anything?

I need a pivot page that in every pivot page there is a longlistselector to list the data...

this is the code that i write when i create a simple pivot page

<phone:PivotItem Header="all">
            <phone:LongListSelector Name="AllNotes"
                                    Background="Black"
                                    Margin="0,0,0,0">
                <phone:LongListSelector.ItemTemplate>
                    <DataTemplate>
                        <StackPanel Background="White"
                                    Margin="0,17,0,0">
                            <TextBlock Text="aaaa">

                            </TextBlock>
                        </StackPanel>
                    </DataTemplate>
                </phone:LongListSelector.ItemTemplate>
            </phone:LongListSelector>
        </phone:PivotItem>

but there isn't anything in the pivot item

i mean by defining a data template and then a stackpanel, there is nothing shown in the pivot item

can you help me ti figure out whats happening exactly?

I finally solve this problem in the way that I don't believe it!

The answer is that we have to start writing the application in the base of Pivot Application !!!

That I don't believe this in the first place!

But Thank You Anyway :)