I would like to create a carousel that scrolls automatically until the user scrolls / touches the ScrollView itself.
The auto-scrolling itself works fine with using scrollView.scrollTo but how could I detect if the user is interacting with the ScrollView? I took a look at the onScroll event but this does not seem to distinct between a user generated event and an event that was generated by calling scrollTo.
Also I'd like to know if it is possible to get the current scroll position from the ScrollView directly instead of reading it everytime from the onScroll event.
I'm very thankful for any tips and suggestions.
By digging into ScrollView's source code you can notice a few undocumented callbacks that will help you achieve what you're after, namely onTouchStart and onTouchEnd. These two callbacks are triggered only when user interacts with the ScrollView and not when you scroll programmatically.
You will probably want to clear your auto-scroll interval on onTouchStart and restart it after a delay on onTouchEnd.
Regarding your next question, the answer is no. As far as I know, no getter is currently exposed to retrieve the current scroll position. Therefore, you need to rely on the event passed to onScroll, retrieve event.nativeEvent.contentOffset['x' or 'y'], and store it in your component's state.
Note that if you're doing some heavy animations that need to follow scroll position closely (e.g. animated header or parallax image), it would be a good idea to use the native driver for Animated.event. You can learn more about it on React Native's blog.
Related
I am using React Native's FlatList component with pagination. I want to execute a callback with the destination page as a parameter whenever the user releases on scroll.
onScroll fires pre-maturely and switches pages before the users releases the screen.
onScrollDragEnd doesn't correctly give you the destination page unless you drag your finger at least half way across the screen (eg doesn't work if you do a quick swipe).
onMomentScrollEnd doesn't get fired until the display stops moving, which may not get fired if the user is constantly swiping.
Is there some sort of middle ground to achieve this functionality?
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!
I was researching this since last year from time to time. I always wonder how Instagram handles the feeds screen?
What kind a component they using for it?
I'm sure it's not a ScrollView becouse it's much more performant than a ScrollView.
It is not also a FlatList becouse I know the basics of the FlatList how it renders the rows etc... and I am sure that they don't use it. For example a FlatList renders the items on top of each other like a card stack. In this behavior you cannot achieve the current Pinch Zoom feature that they have.
I thought maybe they use flipkart's RecyclerListView which is based on Java and much more performant than ScrollView and FlatList, but I am not quite sure about that too.
Any ideas about what they using to achieve current functionality on the feeds screen?
I mean, is there a method or specific listing component to achieve same behavior with all the functions like Double Tap to Like, like Pinch Zoom with overlaying everything.
#Quick note about pinch zooming, it's nearly impossible to build a component with current states of ScrollView and FlatList which will be performant and has same functionality.
You can check out my other topic about that here
Long story short, I have tried a lot of methods and 3rd party components to achieve same thing, but still could not do it.
Thanks for your thoughts!
I have a ScrollView (actually Animated.ScrollView) that I'd like to decide whether to allow vertically scroll or not on scroll start, based on some states of inner components. I know there is a scrollEnabled property which works but the scroll view contains some components that that a few frames to render and changing scrollEnabled property based on inner views' interactions cause a re-render, which drops a few frames and because of the nature of my app needing to change this property based on some animation/smooth scrolling of the inner views, those dropped frames cause a negative user experience.
I've also tried preventDefault of the scroll begin drag event but nothing changed (it allows scrolling regardless of I call it or not).
How can I decide whether or not to allow scrolling of scroll view dynamically on scroll start without a state/props update (which causes a re-render of an expensive view tree, dropping frames)? Something like pan responder's onMoveShouldSetPanResponder[Capture] events might be of great help but returning false from them just don't work (it captures and scrolls regardlessly even though they are called). (I'm on React Native 0.64)
After reading the post in https://codedaily.io/courses/Master-React-Native-Animations/Using-and-Understanding-setNativeProps I solved it by setting native props on scroll view (that I reference directly using a ref) instead of updating state, preventing a re-render:
this.state.scrollView.current?.setNativeProps({
scrollEnabled: false
});
I would like to have a small menu that closes if the user interacts with any other component. For example if the user tries to scroll or interact with any of the content in a scrollview behind the menu (see the image below for reference).
I have two ideas for how this might be achieved:
A transparent layer behind the menu with an absolute position and dimensions matching the device. If this layer registers a touch event the menu can be dismissed. The problem with this is that from the users perspective the touch event was totally ignored. So for this to work well I would need to be able to still pass the touch event through the absolute layer to the content behind it.
Add callbacks to every component that could be interacted with to notify the menu that it should close. This option seems like it would be very messy and because of the large number of components in my use case it is not practical to implement and maintain.
Is there an other proper way to solve this problem? Can any of the issues I raised with the ideas above be resolved or mitigated?
Wrap your view with a TouchableWithoutFeedback component and provide it a onPress callback that hides the menu if it's open. Depending on how top-level the 'expand' icon is, you may want to track the menu's visibility in redux and dispatch an action onPress to track globally.