Activity.AddView(buttonadd, 0, 92%y, 250, 120%y)
This is strange ?
The Top property is 92%y and the Height property is 120%y bigger than the screen size.
This means with a screen height of 800 pixels.
Top = 735 pixels and the height is 960 pixels so the bottom is at 1695 pixels.
The biggest part of the Button is out of the screen and of cours you won't see any text !!!
Best regards.