Sat 05 July 2014
Another Kivy question that I often see (particularly recently for some reason) is about using the Label widget - how to have text wrap automatically, or the opposite, how to have the label automatically grow to accommodate its text. I’ve covered this before in the 9th Kivy crash course video, but here’s a quick write up of the basics.
The first thing to realise is how the Label works by default, it takes the text and draws it to a texture - in practical terms that’s an image of the characters. Everything you might want to do with the Label revolves around what this texture is really doing. By default, it does not wrap the text (unless you put in linebreak characters manually), it just makes one long image on a single row. This image is is placed right in the middle of the label, centered in both directions, which is fine for short text snippets but will overhang the Label on both sides if the text is too long.
This also leads to some other annoying behaviour - as well as the text not wrapping, you might have observed that the halign and valign properties seem to do nothing by default. This is because they orient things not inside the widget, but inside the texture…which is the exact size it needs to contain the text so alignments change nothing.
To solve all these problems, you can manually set the size of the
text_size, a tuple of width and height, e.g.
Label: text_size: self.size
This reverses the default behaviour - instead of the texture growing
to fit the text, the text will be wrapped to fit the texture! If there
is space to spare, it is aligned within the texture according to the
The Label also has another useful property, the
which holds the actual size of the texture. You can use that do bind
behaviour to the size of the text. For instance, a common requirement
is to create a Label that grows as long as it needs to contain its
text, but which wraps it to a certain width. We can combine both of
the above ideas to accomplish this:
Label: size_hint_y: None text_size: self.width, None height: self.texture_size
If you (for instance) place this label in a ScrollView, it will be Scrollable over exactly the right distance to fit in all the text.