I found it a bit baffling when I entered in a number into the text-size field and the control just disappeared. At first I was annoyed, wandering why such a stupid feature wasn't tested properly.
Then when I looked it up, I realised it needed a little bit more information from me. The way that text resizing on the user interface was implemented in Android was intended to be flexible, and inherently a little more complicated.
The text-size attribute (much like margin and padding attributes) require values and units.
If you enter in "20px", it'd be a fixed 20 pixel size. Not quite helpful when you work with various pixel densities and screen sizes.
A much more suitable measurement unit would be "20sp", which is 20 density independant pixels (dips), but scaled to suit the user's font size settings.
There are other units such as:
- in (inches)
- mm (millimeters)
- pt (point - font size)
- dp (density independant pixels)
- sp (density independant pixels, scaled to user's font size preferences)
Alot of tutorials will focus mainly on px and dp, which aren't entirely the best way of going about creating a multi-device compatible code.