index.js

/**
 * Created by JetBrains WebStorm.
 * Author: yoon
 * Date: 18-7-30
 * Time: 上午9:31
 * Desc: 固定字体大小　不随系统字体大小而变化
 * @use import in root file (index.js)
 */
import React from 'react'
import {
  Text,
  TextInput,
  PixelRatio,
  Platform,
} from 'react-native'

const ReactNativePropRegistry = require('ReactNativePropRegistry');

const fontSizeScale = PixelRatio.getFontScale()

const originTextRender = Text.prototype.render
const originTextInputRender = TextInput.prototype.render

function defaultFontSize() {
  return Platform.OS === 'ios' ? 15 : 14
}

function fixedFontSize(target) {
  return function () {
    const originComponent = target.apply(this, arguments);
    return React.cloneElement(originComponent, {
      allowFontScaling: false
    })
  }
}

Text.prototype.render = fixedFontSize(originTextRender)
if (Platform.OS === 'ios') {
  TextInput.prototype.render = fixedFontSize(originTextInputRender)
} else {
  TextInput.prototype.render = function () {
    const originComponent = originTextInputRender.apply(this, arguments);
    try {

      const originText = originComponent.props.children
      let originStyle = originText.props.style
      let newStyle = {
        fontSize: defaultFontSize()
      }
      let textStyle = originStyle[0]

      if (Number.isInteger(textStyle)) {
        textStyle = ReactNativePropRegistry.getByID(textStyle)
      }

      if (Array.isArray(textStyle)) {
        newStyle = textStyle.reduce((pre, curr) => {
          let styleItem = curr || {}
          if (Number.isInteger(styleItem)) {
          styleItem = ReactNativePropRegistry.getByID(styleItem)
        }
        return {...pre, ...styleItem}
      }, newStyle)
      } else {
        newStyle = {...newStyle, ...(textStyle || {})}
      }
      newStyle.fontSize = newStyle.fontSize / fontSizeScale

      return React.cloneElement(originComponent, {
        children: {
          ...originText,
        props: {
          ...originText.props,
        style: newStyle
      }
    }
    })
    } catch (e) {
      return originComponent
    }
  }
}