I have a customscrollview which has some slivers inside it and it contains a sliverlist, the issue I'm facing is that when i scroll down or top the list's children get rebuilt, and that what i need to avoid, thanks in advance
I need a solution without relying on keep alive mixin
Related
Consider the case that I have 3 adjacent list view with each list view having a sized widget of some height. Each list view has around 24 child items. I'm trying to scale the widget using onScaleUpdate in GestureDetector.
onScaleUpdate I want to change the height of each child item of all the 3 listviews.
Is rebuilding all child better or should I rebuild the whole widget?
As #Yeasin Sheikh pointed out, using ListView.builder is good because it builds only the needed children (the ones inside the screen and just a few ones outside as precaution). And as to actually answering your question, I'm no Flutter expert, but using ListView.builder I don't think it makes that much difference, Flutter is intelligent enough to solve this by itself.
I have listview.builder widget which have several ListView.builder and GridView.count with scrollDirection:Axis.horizontal inside of it. All the data comes from the services and I am using FutureBuilder to fetch them. My problem is whenever I scroll the main ListView.builder,other listview items comes with animation(items comes from left, from right). Specially if I scroll fast. I didn't use any animation, and I don't have any idea about the problem, maybe its rebuilding everytime I scroll the lisview, but I am using AutomaticKeepAliveClientMixin for main ListView. Do you have any idea? Thanks for reading.
This question might be duplicate, I solved my problem using this answer: https://stackoverflow.com/a/57984979/10025471
The problem is everytime I scroll the listview, it's children rebuilding again and again. So I convert to stateful widget all of the children and I added AutomaticKeepAliveClientMixin to all of them. Now, there is no unwanted animation, and redundant rebuild
Like the topic I was wondering of there are any circumstances one should use the regular ListView instead of the ListView.builder in flutter, like if there are few items in a list could the ListView give better performance?
ListView has actually four different ways to use it , But let discuss ListView and ListView.builder
ListView : It has a children
property that takes a collection of static widgets. A ListView takes a small number of other widgets and makes it scrollable. Why a “small number”? Because this is designed to be a static list, one that you, the developer, simply types into the build() method
by hand.
ListView.builder : ListView’s alternative constructor, ListView.builder receives two
parameters, an itemCount and an ItemBuilder property that is a
function. This makes the ListView lazy-loaded. The itemBuilder function
dynamically creates children widgets on demand. As the user scrolls close
to the bottom of the list, itemBuilder creates new items to be scrolled into
view. And when we scroll something far enough off the screen, it is paged
out of memory and disposed of. Pretty cool.
Reference : taken from Rap Payne's Beginning App Development with Flutter (Great Book for beginners! , not an affiliate link).
official documentation for ListView .
ListView is the most commonly used scrolling widget. It displays its children one after another in the scroll direction. So if you just want to show some widgets below earch other and you need to scroll them you use ListView.
ListView.builder is a way of constructing the list where children’s (Widgets) are built on demand. However, instead of returning a static widget, it calls a function which can be called multiple times (based on itemCount ) and it’s possible to return different widget at each call.
I guess the simple answer you were looking for is:
Use ListView.builder whenever you iterate over an array of 'similar' elements.
Use ListView when items in your list are completely different from one another.
Think of ListView as scrollable Column
Is it possible to add new elements into the top of the ListVeiw or CustomScrollView and keep the scroll position as it's with Flutter
I've tried the following
extentAfter = _scrollController.position.extentAfter;
_scrollController.jumpTo(_scrollController.position.maxScrollExtent - extentAfter);
but this won't work well with SliverAppBar - floating and its actually not optimal solution.
Actually the cleanest way would be to add those items only when user scrolls back to the top of the ListView. You can cache them in memory for the moment user is far enough from the top (in your case) of the list.
What are the differences between SliverList and ListView in Flutter?
There's almost no difference.
ListView is a SliverList. Same with GridView, which is a SliverGrid.
They are doing exactly the same thing. The only difference between them is that SliverList is a sliver, not a widget. Which means it's used inside a ScrollView, usually CustomScrollView.
ListView is nothing else but a biding of SliverList to transform it into a Widget to make it usable alongside other widgets such as Row/Container.
Most of the time, use ListView.
But if you want advanced scroll behavior such as appbar animations with scroll ; you'll need to use a CustomScrollView. Which will force you to use SliverList instead of ListView.
According this article,
All of the scrollable views you use, like ListView and GridView,
are actually implemented using Slivers. You can kind of think of
Slivers as a lower-level interface, providing finer-grained control on
implementing scrollable area. Because slivers can lazily build each
item just as it scrolls into view, slivers are particularly useful for
efficiently scrolling through large numbers of children.