I am new to React Native animated, and I am trying to incorporate it into my app. I currently have an object that appears to fall from the middle to the bottom of the screen, using frequent state updates like this:
const [objHeight, setObjHeight] = useState((Dimensions.get("screen").height)/2)
useEffect(()=>{
if(objHeight > 0){
timerId = setInterval(()=>{
setObjHeight(objHeight => objHeight - 3)
}, 30) //30ms
return ()=>{
clearInterval(timerId)
}
},[objHeight])
//then the object looks like:
<View
style = {[{
position: "absolute",
backgroundColor: 'blue',
width: 50,
height: 60,
bottom: objHeight,
}]}>
</View>
I understand that this is an inefficient way to do animations on react, and that by using react animated we can make animate this on the UI thread instead. I have tried to replicate the above using react native animated.
const objHeight = new Animated.Value(screenHeight/2)
Animated.loop(
Animated.timing(objHeight, {
toValue: objHeight>0 ? objHeight - gravity : null,
duration: 3000,
useNativeDriver: true
}),
{iterations: 1000}
).start()
<Animated.View
style = {[{
backgroundColor: 'blue',
width: 50,
height: 60,
bottom: 200,
transform:[{translateY: objHeight}]
}]}>
</Animated.View>
However, the object does not move/animate. It just stays at the same height. What am I doing wrong? I find the documentation on react native animated is not particularly helpful.
Thank you
First create an Animated.Value with some initial value:
const bottomAnim = useRef(new Animated.Value(Dimensions.get('screen').height / 2)).current;
Then on component mount start the animation:
useEffect(() => {
Animated.timing(bottomAnim, {
toValue: 0,
duration: 3000,
useNativeDriver: true,
}).start();
}, []);
Finally, bind the animated value to the component:
return (
<Animated.View
style={[
{
position: 'absolute',
backgroundColor: 'blue',
width: 50,
height: 60,
bottom: bottomAnim,
},
]}/>
);