react native实现可展开Text控件

原理：组件初始化时不设置Text控件的numberOfLines属性，测量一下组件高度（最大高度），然后在设置numberOfLines属性，再次测量一下组件高度（最小高度），若最大高度大与最小高度，表示需要显示“展开”。

/* eslint new-cap: ["error", { "capIsNew": false }] */

import React, {
  Component,
  PropTypes,
} from "react";

import {View, Image, StyleSheet, Animated, Text} from "react-native";
export default class CollapsibleText extends Component {
  static propTypes = {
    style: Text.propTypes.style,
    expandTextStyle:Text.propTypes.style,
    numberOfLines: PropTypes.number
  }
  constructor(props){
    super(props);
    this.state = {
      /** 文本是否展开 */
      expanded:true,
      numberOfLines:null,
      /** 展开收起文字是否处于显示状态 */
      showExpandText:false,
      expandText:"展开",
      /** 是否处于测量阶段 */
      measureFlag:true
    }
    this.numberOfLines = props.numberOfLines;
    /** 文本是否需要展开收起功能：（实际文字内容是否超出numberOfLines限制） */
    this.needExpand = true;
    this.measureFlag = true;
  }


  _onTextLayout(event){
    if(this.measureFlag){
      if(this.state.expanded){
        this.maxHeight = event.nativeEvent.layout.height;
        this.setState({expanded:false,numberOfLines:this.numberOfLines});
      }else{
        this.mixHeight = event.nativeEvent.layout.height;
        if(this.mixHeight == this.maxHeight){
          this.needExpand = false;
        }else{
          this.needExpand = true;
          this.setState({showExpandText:true})
        }
        this.measureFlag = false;
      }
    }

  }

  _onPressExpand(){
    if(!this.state.expanded){
      this.setState({numberOfLines:null,expandText:"收起",expanded:true})
    }else{
      this.setState({numberOfLines:this.numberOfLines,expandText:"展开",expanded:false})
    }
  }

  render() {
    const { numberOfLines, onLayout, expandTextStyle, ...rest } = this.props;
    let expandText = this.state.showExpandText?(
        <Text
          style={[this.props.style,styles.expandText,expandTextStyle]}
          onPress={this._onPressExpand.bind(this)}>
          {this.state.expandText}</Text>
      ) : null;
    return (
      <View>
        <Text
          numberOfLines={this.state.numberOfLines}
          onLayout={this._onTextLayout.bind(this)}
          {...rest}
          >
          {this.props.children}
        </Text>
        {expandText}
      </View>
    );
  }
}

const styles = StyleSheet.create({
  expandText: {
    color:"blue",
    marginTop:0
  }


});