Data Template in Resource Dictionary [WPF]

Hi all....

I want to add a data template in resource dictionary...

Code:

---

<DataTemplate x:Key="SizeTextTemplate"  x:Name="SizeTextTemplate">
        <TextBlock Text="{Binding Path=FileInfo.Length}" TextAlignment="Right" Width="200"></TextBlock>
</DataTemplate>

---

But when I try to access that data Template from my class I can't use the key to find the data template. And when I want use the FindName method it is said that function is not supported in this kind of dictionary...

So how I can find my Data Template???