Navigation Page don't work ?

I want when I click to image to navigate to other page , I have a code like this
'
<Image.GestureRecognizers>


</Image.GestureRecognizers>
'

c#
'private void TapGestureRecognizer_Tapped_7(object sender, EventArgs e)
{
Navigation.PushAsync(new AddFriendPage());
}'

It's not working why ??