TLegend is hided

Hello, everyone.I meet one problem during my drawing.
Firstly, I draw a canvas with TCanvas method,
then,build a pad with TPad() order,
Finally, when I want to draw out some characters with TLegend.I find the content of TLegend is hided by the drawed histogram in the pad.(I have checked it)
Please telling me how to put the content of legend appear? What orders I should take.
Thank you.

Can you send a small running macro showing the problem ?