Animating width of <Rect /> in react-native-svg

Question

I have simple animation interpolation going on for <Rect /> element, however I see no changes on my ui, as if width is staying 0.

I manually added my end value to the component as width={149.12} and it displayed it correctly, hence I am a bit confused now to why it is not picking up same value from animation?

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Targeting iOS 12

Here is full implementation, in essence a mana and health bar that take in current value and total value i.e. 50 and 100 should display half width for the rect. (Example uses typescript, but answer can be in plain js if needed)

import * as React from 'react'
import { Animated } from 'react-native'
import Svg, { Defs, LinearGradient, Rect, Stop } from 'react-native-svg'
import { deviceWidth } from '../services/Device'

const barWidth = deviceWidth * 0.3454
const barHeight = barWidth * 0.093
const AnimatedRect = Animated.createAnimatedComponent(Rect)

/**
 * Types
 */
export interface IProps {
  variant: 'MANA' | 'HEALTH'
  currentValue: number
  totalValue: number
}

export interface IState {
  width: Animated.Value
}

/**
 * Component
 */
class HealthManaBar extends React.Component<IProps, IState> {
  state = {
    width: new Animated.Value(0)
  }

  componentDidMount() {
    const { currentValue, totalValue } = this.props
    this.animate(currentValue, totalValue)
  }

  componentDidUpdate({ currentValue, totalValue }: IProps) {
    this.animate(currentValue, totalValue)
  }

  animate = (current: number, total: number) =>
    Animated.timing(this.state.width, {
      toValue: current !== 0 ? current / total : 0,
      duration: 400
    }).start()

  render() {
    const { variant } = this.props
    const { width } = this.state

    return (
      <Svg width={barWidth} height={barHeight}>
        <Defs>
          <LinearGradient
            id={`HeathManaBar-gradient-${variant}`}
            x1="0"
            y1="0"
            x2="0"
            y2={barHeight}
          >
            <Stop
              offset="0"
              stopColor={variant === 'HEALTH' ? '#EC561B' : '#00ACE1'}
              stopOpacity="1"
            />
            <Stop
              offset="0.5"
              stopColor={variant === 'HEALTH' ? '#8D1B00' : '#003FAA'}
              stopOpacity="1"
            />
            <Stop
              offset="1"
              stopColor={variant === 'HEALTH' ? '#9F3606' : '#007C97'}
              stopOpacity="1"
            />
          </LinearGradient>
        </Defs>
        <AnimatedRect
          x="0"
          y="0"
          rx="3"
          ry="3"
          width={width.interpolate({
            inputRange: [0, 1],
            outputRange: [0, barWidth]
          })}
          height={barHeight}
          fill={`url(#HeathManaBar-gradient-${variant})`}
        />
      </Svg>
    )
  }
}

export default HealthManaBar

Related library: https://github.com/react-native-community/react-native-svg

Answer 1

This was not initially possible with react-native-svg, but solution is currently being worked on and you can follow progress here

https://github.com/react-native-community/react-native-svg/issues/803