itemTpl using an XTemplate did not work.

[stqp]

Hi
I am using XTemplate to create list-items ,but it did not work.
When I set string to the itemTpl, it works well.
Example

list.itemTpl = "{id}" 

But When I set XTemplate to the itemTpl, it did not.

Example

list.itemTpl = new XTemplate(
 '{id}'
)