Flutter ListView优化

Question

Displaying large/infinitive list with scrolling offset in Flutter framework can be unacceptably slow (depending on the offset size).

This can be solved by specifying itemExtend when all items have the same size.

But it is not usually possible to know itemExtend in advance even when all list items have the same size because the height might depend on font size which depends on user phone accessibility settings.

Is there any way to indicate to Flutter ListView that all list items have the same size without knowing what exactly the size is?

If not is there any way to calculate list item widget size first (and then use it to set itemExtend )?

Answer 1

I don't believe there is a way to automatically calculate the widget size first, however you can do manual calculations as much as you want. You can use DefaultTextStyle.of(context) to get the font size of the enclosing context and use a LayoutBuilder to get the maximum width of the list if that matters. You can then use those pieces of information to set the itemExtent .

However, you can get exactly what you want if you use a CustomScrollView and a SliverPrototypeExtentList . You simply provide your prototype along with a SliverChildDelegate (probably SliverChildBuilderDelegate ) and it should figure out the rest.

And finally... I'm a little bit curious whether you'd share the part of your code where you actually instantiate the list (and what's shown within it). In my experience, when you're in release mode you can throw an awful lot of stuff at a ListView and still have it be smooth, so it's possible there's something else you're doing that's causing the slowdown. In debug mode it's very different of course.