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.
Related
In my application I want to create a couple animations on my FlatList.
For example, after fetching the data and feeding it to the list I want the items that should be visible to slide from the left. When I'm scrolling each item (at the top) that supposed to disappear will slide out to the right and each item that should appear (at the bottom) should slide from the left. Is it possible in React Native?
I only managed to create one type of animation - items sliding right when they are about to disappear, but I don't have any idea how to make the items to appear from the left.
My Animated.View can receive only one type of transform. So how can create different types of input/output ranges for the top and the bottom of the list?
I tried to find some examples on the internet but couldn't find any for multiple animations, only for one type.
I think you will find React Native Reanimated's Entering and Exiting Animations API
useful for this task. It greatly simplifies animations like this in my experience.
In case you want to get more control. Using a FlatList, you can also use its onScroll prop to get the current value for YOffset (contentOffset.y) via the Reanimated useAnimatedScrollHandler. Thus you can figure out how much has been scrolled.
Which you could then use to manually apply any translateX's required to the Animated.View of whatever items the flatlist is rendering. The logic you'll of course have to figure out though. But it's a start.
Be sure to do any animation interpolates using UI thread worklets on Reanimated only. Good luck!
Hello I am building an app and was wondering what the best option would be for optimizing a very large flatlist. It will take some time to load each element inside a flatlist since it contains images, a lot of text, etc. Would it be better to use just a plane flatlist or something like react-native-snap-carousel, react-native-reanimated-carousel?
Use pagination technique to show large data from flatlist. Avoid third party libraries like react-native-snap-carousel. It may cause the issues as time passes and can also be the reason for large apk or ipa size.
If your flatlist will have large data, it is adviced to use pagination. You may use in-built Flatlist or packages like react-native-snap-carousel or react-native-reanimated-carousel. But since your data will have many images that will make the app UX slow if you load them all at once.
Better to use Pagination and use react-native-fast-image for faster loading of images via caching.
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 want to display several components (maybe up to 6) in my React Native app that continuously change their position, i.e. slowly but fluently float on the screen and change their moving direction randomly or based on an angle at which they approach the edge of their parent, if they do. What I don't know is how to change their position dynamically in a performance friendly way. Because I also want to let the user interact with them by tapping on them, it cannot be a video in a background or something similar.
If I were dealing with a standard React app running in a browser, I think I would simply manipulate the element's style attributes top and left. Since I want to implement this in React Native, I think there must be a solution that is way more performant and elegant, involving manipulation of the native elements that back the React Native views or using some animation mechanism, because re-rendering a view with like 6 components at least 30 times per second doesn't seem like an appropriate solution and an overhead in general.
Googling things like "react native dynamically move element" or "react native dynamically change element position" did not bring any obviously appropriate results. I came across a native element method setNativeProps, though, but couldn't find any information on what props I could set to change the element's position on the screen and how performant that would be. I also looked into React Native's Animated API, but could not quite relate my problem to the solutions that this API offers from a first glance.
Does anyone know a mechanism or maybe a library that would be appropriate to use in the situation that I described?
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