Should use "sp" instead of "dp" for text sizes

Question

When I use

android:textSizes="20dp" 

in my XML for a textView, I got a warning "Should use "sp" instead of "dp" for text sizes."

Why should "dp" not be used? What is the correct approach? How can I achieve same textsizes on different displays?

Answer 1

You should always use SP for fonts as it respects the user preferences. Here is an example Lets understand it with the help of an example -

Text with SP and DP

Change the device text setting (Settings -> Display -> Font Size)

Now reopen the app and relook at the texts, You will see that the text which was using SP has different height than DP.

Answer 2

You can use sp and dp. As you know in Android settings you can change text size (Settings -> My device -> Display -> Font size). All your textView in sp would change after changing font size in settings, dp - would not change

Answer 3

You may use both

sp for font sizes
dp for everything else.

dp
Density-independent Pixels - an abstract unit that is based on the physical density of the screen. These units are relative to a 160 dpi screen, so one dp is one pixel on a 160 dpi screen. The ratio of dp-to-pixel will change with the screen density, but not necessarily in direct proportion. Note: The compiler accepts both "dip" and "dp", though "dp" is more consistent with "sp".

sp
Scale-independent Pixels - this is like the dp unit, but it is also scaled by the user's font size preference. It is recommend you use this unit when specifying font sizes, so they will be adjusted for both the screen density and user's preference.

For more info see at Difference between px, dp, dip and sp in Android?