You just have to set a number of lines in your TextView
like this:
android:maxLines = "10"
and you must also add:
android:minLines="1"
The rest of this not necessary if you are not using scrolling
and a property which says that this TextView should be scrollable vertically:
android:scrollbars = "vertical"
And in your Java-code:
yourTextView.setMovementMethod(new ScrollingMovementMethod())