What is structure different between FlatList and ScrollView in react native?
It seems to they equal to each other for scrolling view in the application, but ScrollView is very simple rather than FlatList, so when we must use FlatList in code?
There's a big difference between FlatList and ScrollView
ScrollView will load the items (data for scrolling) immediately after the component has been loaded. As a result, all data will be stored in RAM, and you will be unable to use hundreds or thousands of items in it (due to low performance).
FlatList, on the other hand, has a better solution for this problem; it will mount 10 items (by default) to the screen, and as the user scrolls the view, other items will mount.
It's a significant advantage to use FlatList instead of ScrollView.
You can use ScrollView for a small number of items and FlatList for even 10000 items.
A really big difference that no one seems to be pointing out here is that component state is not maintained with the FlatList component but is maintained with ScrollView. This is due to the fact that ScrollView renders all the children in one go and maintains them. Meanwhile, FlatList unmounts components once they are way off the screen and recreates them from scratch once the item comes back from screen (thus state is lost).
They have different usages.
FlatList is built to render a large list of items. If you check the documentation, you need to pass an array of data and then render each item in the array with the renderItem callback. It is optimized to have very good performances with very large arrays because it actually only renders the items that need to be displayed at the moment.
ScrollView is built to render a generic content in a way that it scrolls when the content is bigger than the ScrollView itself. You don't pass an array of data, but you put elements inside the ScrollView in the same way you would use a normal View. Be careful however, it does not provide the same optimization of the flat list for very long content.
As a rule of thumb:
Do you need to render a list of similar items from an array? Use FlatList
Do you need to render generic content in a scrollable container? Use ScrollView
Related
I try to render a dropdown-picker (react-native-dropdownpicker) in a sectionlist but it's impossable to scroll the content of the dropdown. It only shows the first results.
I tried many things with zIndex, view with flex: 1 as parent but im unable to find the solution.
Is it possible to render in a sectionlist or should i be looking for another solution?
sectionlist with dropdown-picker
I think this is what you want.
List Modes
You have 3 options when choosing the list mode.
DEFAULT
FLATLIST
SCROLLVIEW
MODAL
listMode="FLATLIST"
Notes
The FlatList component shouldn't be nested inside ScrollView or you'll come across the VirtualizedLists should never be nested inside plain ScrollViews warning.
If this happens to you and you only have a few items, consider using the SCROLLVIEW mode. Otherwise, you have to use the MODAL mode.
Take a look at this snack:
https://snack.expo.dev/#devsaeedhabibi/dropdown-picker
My screen layout is SectionList inside a View and on onEndReached I am calling an API to get paginated data successfully (LoadMore behaviour).
As, SectionList is covering only 40% part of screen, I tried adding ScrollView so that complete screen becomes scrollable.
Problem: When the screen loads it fetches the initial paginated data. After rendering the UI, onEndReached event gets fired which in-turn calls api to get load more data again. This runs in loop until the complete data is fetched.
Has anyone faced the same issue. Any solution how to stop that.
Instead of adding a SectionList inside ScrollView, What you can do is by adding your above view (i.e. your other 60% area) as header of the SectionList. This way your entire screen will be treated as SectionList, and onEndReached will only gets called when user performs scroll.
Before I begin trying to build something I want to check my strategy.
I think the best way to define what I would like to achieve is to build a component using a FlatList that adjusts fontSize dynamically based on the size of the View (or other more appropriately defined size limiting area) in which it is being displayed.
For example, let's say I want a FlatList of items (of data returned from an API call) that displays full-screen on Screen 1 of my app, but in a small corner of Screen 2 of my app. Here's a quick mock of the behavior I would want:
It seems like the alignment of items, flex, other styles could be written so that the proportions/positions stay the same regardless of parent view in which the FlatList is displayed, so I might only have to adjust fontSize.
Can this behavior be achieved using a FlatList and a reference to a dynamic fontSize? If so, where should the "awareness" of the parent View be stored/passed?
I'm looking for general input as to how to achieve this simply, with or without FlatList. I like using FlatList because of how well it works off the shelf for my simple tasks. Hopefully I'm not trying to make it do something it cant.
Thanks!
I'd like to load images from items in a Flatlist, but only when they are visible.
I have a long list (well, technically a Sectionlist in the video I provide, but I'm currently experimenting with FlatList for my react native first app). There are 300+ items in my list and it seems everything is loaded when the FlatList appears. How can I approach that result
You can use removeClippedSubviews={true} in your flatlist.
I'm working on a chat like application and I have seen examples using ListView and ScrollView. What are the advantages of either? I need to render different looking items through out the chat (inputs vs. responses OR text vs. images). Does one handle this case better?
I think your question is "ScrollView vs FlatList - which one to use"?
According to React-Native docs:
ScrollView vs FlatList - which one to use?
ScrollView simply renders all its react child components at once. That makes it very easy to understand and use.
On the other hand, this has a performance downside. Imagine you have a very long list of items you want to display, maybe several screens worth of content. Creating JS components and native views for everythign all at once, much of which may not even be shown, will contribute to slow rendering and increased memory usage.
This is where FlatList comes into play. FlatList renders items lazily, just when they are about to appear, and removes items that scroll way off screen to save memory and processing time.
FlatList is also handy if you want to render separators between your items, multiple columns, infinite scroll loading, or any number of other features it supports out of the box.
I would use FlatList. This is what u need. It's more effective & lazy loads your data only when needed.