How to make a circular slider in react-native

问题

I want to add a like range component. But one that is actually circular and i have no idea how to do it. Can you point me to some help please.

Te example of what i want:

回答1:

I've been working with react-native-svg lately and I think it is fantastic - SVG and React are a match made in geek-heaven, just perfect for creating custom UI's with no need to drop down to native drawing code.

Here's a little CircularSlider component that implements what you described above:

import React,{Component} from 'react'
import {PanResponder,View} from 'react-native'
import Svg,{Path,Circle,G,Text} from 'react-native-svg'

class CircularSlider extends Component {
  constructor(props){
    super(props)
    this.handlePanResponderMove = this.handlePanResponderMove.bind(this)
    this.cartesianToPolar = this.cartesianToPolar.bind(this)
    this.polarToCartesian = this.polarToCartesian.bind(this)
    const {width,height} = props
    const smallestSide = (Math.min(width,height))
    this.state = {
      cx: width/2,
      cy: height/2,
      r: (smallestSide/2)*0.85
    }
  }
  componentWillMount = () => {
    this._panResponder = PanResponder.create({
      onStartShouldSetPanResponder: () => true,
      onMoveShouldSetPanResponder: () => true,
      onPanResponderMove: this.handlePanResponderMove
    })
  }
  polarToCartesian(angle){
    const {cx,cy,r} = this.state
        , a = (angle-270) * Math.PI / 180.0
        , x = cx + (r * Math.cos(a))
        , y = cy + (r * Math.sin(a))
    return {x,y}
  }
  cartesianToPolar(x,y){
    const {cx,cy} = this.state
    return Math.round((Math.atan((y-cy)/(x-cx)))/(Math.PI/180)+((x>cx) ? 270 : 90))
  }
  handlePanResponderMove({nativeEvent:{locationX,locationY}}){
    this.props.onValueChange(this.cartesianToPolar(locationX,locationY))
  }
  render(){
    const {width,height,value,meterColor,textColor,onValueChange} = this.props
        , {cx,cy,r} = this.state
        , startCoord = this.polarToCartesian(0)
        , endCoord = this.polarToCartesian(value)
    return (
      <Svg onLayout={this.onLayout} width={width} height={height}>
        <Circle cx={cx} cy={cy} r={r} stroke='#eee' strokeWidth={0.5} fill='none'/>
        <Path stroke={meterColor} strokeWidth={5} fill='none'
          d={`M${startCoord.x} ${startCoord.y} A ${r} ${r} 0 ${value>180?1:0} 1 ${endCoord.x} ${endCoord.y}`}/>
        <G x={endCoord.x-7.5} y={endCoord.y-7.5}>
          <Circle cx={7.5} cy={7.5} r={10} fill={meterColor} {...this._panResponder.panHandlers}/>
          <Text key={value+''} x={7.5} y={1} fontSize={10} fill={textColor} textAnchor="middle">{value+''}</Text>
        </G>
      </Svg>
    )
  }
}

export default CircularSlider

The full sample project code is in github here.

This is just a quick prototype to give you the idea, but here's how it looks (two instances of CircularSlider, absolutely positioned so they have the same centres):

回答2:

cool project. be sure to share what you create. I think others would really find this useful as well. Unfortunately, I haven't seen much like it yet. If I were doing this though, I'd start by looking at how the jQuery plugins do it. Something like https://github.com/magicismight/react-native-svg could help you draw the shapes. Wish I could be more helpful. Good luck!

来源：https://stackoverflow.com/questions/38253804/how-to-make-a-circular-slider-in-react-native

标签

javascript

reactjs

react-native

reactive-programming