组件中的 React / Gatsby 动态背景图像

Question

我有一个 React 组件，它主要处理相关内容，向用户显示站点内的下一个/上一个内容。

这个组件需要导入背景图片，所以我可以将它们用作组件内部的内联样式。但是，要知道我要导入 哪个 背景图像，我必须查看像这样定义的道具：

<LocationRelated 
  previousLocationName="Columbus, OH"
  previousLocationPath="columbus"
  nextLocationName="St. Pete Beach, FL"
  nextLocationPath="st-pete-beach"
/>

但是，据我所知，没有办法在组件进入 React 的 render 函数之前查看它的 props - 因此无法进行动态导入。

这是我在导入中使用 ES6 模板文字的失败尝试：

import React from "react"
import pfbRelatedPrevBGImagePath from '`../../images/grid/PFB_${this.props.previousLocationPath}.jpg`'
import pfbRelatedNextBGImagePath from '`../../images/grid/PFB_${this.props.nextLocationPath}.jpg`'

class LocationRelated extends React.Component {

  render() {

    const pfbRelatedPrevBG = { 
      backgroundImage: `linear-gradient( to bottom, rgba(1,1,1,0.2), rgba(2,2,2,0.2) ), url(${ pfbRelatedPrevBGImagePath })` 
    }
    const pfbRelatedNextBG = { 
      backgroundImage: `linear-gradient( to bottom, rgba(1,1,1,0.2), rgba(2,2,2,0.2) ), url(${ pfbRelatedNextBGImagePath })` 
    }

    return (
      <div>
        <aside className="pfb-longform-container">
          <section className="pfb-related-content">
            <h3 className="pfb-related-content-title">Additional Locations</h3>
            <section className="pfb-related-image-container">
              <div 
                className="pfb-related-1" 
                style= { pfbRelatedPrevBG }
              >
                <p className="pfb-related-text">{ this.props.previousLocationName }</p>
              </div>
              <div 
                className="pfb-related-2"
                style= { pfbRelatedNextBG }
              >
                <p className="pfb-related-text">{ this.props.nextLocationName }</p>
              </div>
            </section>
          </section>
        </aside>
      </div>
    )
  }
}

export default LocationRelated

我的 webpack builder 出错，说它基本​​上无法读取 this.props.whatever，因为它在尝试读取 import 时尚未定义。有没有办法做到这一点？

附加说明：我正在为该站点使用 Gatsby 静态站点生成器，但这不会真正影响正在发生的事情（至少我认为不会）。

Answer 1

据我所知，上述方法是不可能的，但正如我发现的那样，这是有充分理由的。你必须完全接受 React (Gatsby) 的做事方式，我上面的方法是尝试从 Drupal/WordPress-CMS-build 的角度来做到这一点。

查看我修改后的 LocationRelated 组件：

import React from "react"
import Link from 'gatsby-link'

class LocationRelated extends React.Component {

  render() {

    // Setup inline style objects using ES6 template literals which pull in the correct paths from the content pages themselves
    const pfbRelatedPrevBG = { 
      backgroundImage: `linear-gradient( to bottom, rgba(1,1,1,0.2), rgba(2,2,2,0.2) ), url(${ this.props.prevLocationImgPath.sizes.src })` 
    }
    const pfbRelatedNextBG = { 
      backgroundImage: `linear-gradient( to bottom, rgba(1,1,1,0.2), rgba(2,2,2,0.2) ), url(${ this.props.nextLocationImgPath.sizes.src })` 
    }

    return (
      <div className="pfb-related-bg-container">
        <aside className="pfb-related-container">
          <section className="pfb-related-content">
            <section className="pfb-related-image-container">
              <Link 
                to={ this.props.prevLocationPath }
                className="pfb-related-left-arrow"
              >
                <img src= { LeftArrow } alt="Navigate to the previous location in the PFB Annual Report" />
                <div className="pfb-related-left-arrow-text">Previous</div>
              </Link>
              <Link 
                to={ this.props.prevLocationPath }
                className="pfb-related-1" 
                style={ pfbRelatedPrevBG }
              >
                <p className="pfb-related-text">{ this.props.prevLocationName }</p>
              </Link>
              <Link 
                to={ this.props.nextLocationPath }
                className="pfb-related-2"
                style= { pfbRelatedNextBG }
              >
                <p className="pfb-related-text">{ this.props.nextLocationName }</p>
              </Link>
              <Link 
                to={ this.props.nextLocationPath }
                className="pfb-related-right-arrow"
              >
                <img src= { RightArrow } alt="Navigate to the next location in the PFB Annual Report" />
                <div className="pfb-related-right-arrow-text">Next</div>
              </Link>
            </section>
          </section>
        </aside>
      </div>
    )
  }
}

export default LocationRelated

您会注意到与上述尝试没有太大区别，但请注意 backgroundImage 对象文字中使用的 this.props.nextLocationImgPath.sizes.src 路径。您必须将backgroundImage 源路径作为道具传递。不要像我一样尝试在组件中执行此操作。 React 的关注点分离是从组件中获取数据，而不是通过 props 输入数据。

那么问题就变成了：如果你必须将路径作为道具传入，那么在页面级别调用组件时如何获取路径？

如果您使用Gatsby（并且应该），则需要使用 GraphQL 来获取优化的图像路径。在我的示例中，我们将在调用LocationRelated 组件的同一页面上调用background-image 路径。

我的页面的简化示例，专注于手头的问题：

import React from 'react'
import Img from "gatsby-image";

import LocationRelated from '../components/LocationRelated'

class CharlotteLocation extends React.Component {
  render() {
    return (
      <div>    
        <LocationRelated 
          prevLocationName="Detroit"
          prevLocationPath="detroit"
          prevLocationImgPath= { this.props.data.charlottePrevImage }
          nextLocationName="Montana"
          nextLocationPath="montana"
          nextLocationImgPath= { this.props.data.charlotteNextImage }
        />
      </div>
    )
  }
}

export default CharlotteLocation 

// GraphQL queries for each image
export const CharlotteImageQuery = graphql`
  query CharlotteImageQuery {
    charlottePrevImage: imageSharp(id: { regex: "/PFB_DETROIT/" }) {
      sizes(maxWidth: 600 ) {
        ...GatsbyImageSharpSizes_withWebp
      }
    },
    charlotteNextImage: imageSharp(id: { regex: "/PFB_MONTANA/" }) {
      sizes(maxWidth: 600 ) {
        ...GatsbyImageSharpSizes_withWebp
      }
    }
  }
`

这些 GraphQL 查询提供了我们需要的文件的优化路径，现在我们可以通过this.props.data 将它们发送到我们的LocationRelated 组件。

gatsby-image 和 GraphQL 一开始使用起来有点棘手，所以请查看this nice tutorial by Kyle Gill。它让我比 Gatsby 文档做得更好。

作为参考，这是我如何在项目中设置我的 gatsby-config.js 以使所有这些插件很好地协同工作（我从项目中的独立 images 目录而不是组件中提取图像，所以我需要gatsby-source-filesystem 和gatsby-image、gatsby-transformer-sharp、gatsby-plugin-sharp,) 一起完成所有这些工作：

module.exports = {
  siteMetadata: {
    title: 'PFB2017 Site',
  },
  //pathPrefix: "/pfb2017-site",
  plugins: [
    // Adds in React Helmet for metadata
    `gatsby-plugin-react-helmet`,

    // Gives us sass in the project
    `gatsby-plugin-sass`,

    // This plugin transforms JSON, which is how we are storing our location data
    `gatsby-transformer-json`,

    // Adds in Gatsby image handling
    `gatsby-image`,
    `gatsby-transformer-sharp`,
    `gatsby-plugin-sharp`,

    /** 
     * This is how you customize gatsby-source-filesystem
     * Check this page out for more background 
     * https://www.gatsbyjs.org/docs/building-with-components 
     * By default, the gatsby-default starter kit comes with the `pages` directory wired up
     * I'm adding it here for consistency but you don't need it
     * What I have added into the starter are `images` and `data`, subfolders we'll need for the PFB project
     * 
     */

    {
      resolve: `gatsby-source-filesystem`,
      options: {
        name: `pages`,
        path: `${__dirname}/src/pages`,
      },
    },    
    {
      resolve: `gatsby-source-filesystem`,
      options: {
        name: `data`,
        path: `${__dirname}/src/data`,
      },
    },
    {
      resolve: `gatsby-source-filesystem`,
      options: {
        name: `images`,
        path: `${__dirname}/src/images`
      }
    }
  ],
};