JavaFX TextArea and autoscroll

Question

I am trying to get a TextArea to autoscroll to the bottom with new text which is put in via an event handler. Each new entry is just one long string of text with each entry separated by a line break. I have tried a change handler which sets setscrolltop to Double.MIN_VALUE but to no avail. Any ideas of how this could be done?

Answer 1

I don't have enough reputation to comment, but wanted to give some insight for future readers as to why setText doesn't appear to trigger the listener, but appendText does, as in Math's answer.

I Just found this answer while encountering similar issues myself, and looked into the code. This is currently the top result for 'javafx textarea settext scroll' in a google search.

setText does indeed trigger the listener. According to the javadoc on the doSet method in TextInputControl (TextArea's superclass):

     * doSet is called whenever the setText() method was called directly
     * on the TextInputControl, or when the text property was bound,
     * unbound, or reacted to a binding invalidation. It is *not* called
     * when modifications to the content happened indirectly, such as
     * through the replaceText / replaceSelection methods.

Inside the doSet method, a call is made to updateText(), which TextArea overrides:

  @Override final void textUpdated() {
        setScrollTop(0);
        setScrollLeft(0);
    }  

So, when you set the scroll amount in the listener as in Math's answer, the following happens:

1. The TextProperty is updated
2. Your listener is called, and the scroll is set
3. doSet is called
4. textUpdated is called
5. The scroll is set back to the top-left

When you then append "",

1. The TextProperty is updated
2. Your listener is called, and the scroll is set

The javadoc is above is clear why this is the case - doSet is only called when using setText. In fact, appendText calls insertText which calls replaceText - and the javadoc further states that replaceText does NOT trigger a call to doSet.

The behaviour is rather irritating, especially since these are all final methods, and not obvious at first glance - but is not a bug.