The TextArea may be set when I create the object by

myTextArea.setPrefRowCount(i);

with no problem, but if I use the "onKeyTyped" function and try to use

myTextArea.setPrefRowCount(i);

(so I can change its heigth in a way that it grows with the text it contains)

myTextArea.setPrefHeight( (i*fontheight) + additionalheight );

works well.

It feels like the setPrefRowCount(int); only is used to get the prefHeight once (checked every variable and only the prefheight is not "updated".)

If you got questions, feel free to ask.
thx