反应，gatsbyjs：循环通过 object - 组件没有被渲染

Question

I have the following component in a Gatsbyjs project:

styleItem.js

import React from 'react'
import styled from 'styled-components'
import BackgroundImage from 'gatsby-background-image'
import {StaticQuery, graphql } from "gatsby"
import {Col } from 'react-bootstrap'

import '../styles/styles.css'

const StyleItem = (props) => {
    return (
        <StaticQuery 
            query={graphql`
                query {
                    street: file(relativePath: { eq: "2.jpg" }) {
                        childImageSharp {
                        fluid(quality: 90, maxWidth: 1920) {
                            ...GatsbyImageSharpFluid_withWebp
                            }
                        }
                    }
                    casual: file(relativePath: { eq: "3.jpg" }) {
                        childImageSharp {
                        fluid(quality: 90, maxWidth: 1920) {
                            ...GatsbyImageSharpFluid_withWebp
                            }
                        }
                    }
                    athletic: file(relativePath: { eq: "3.jpg" }) {
                        childImageSharp {
                        fluid(quality: 90, maxWidth: 1920) {
                            ...GatsbyImageSharpFluid_withWebp
                            }
                        }
                    }
                }
            `}

            render={data => { Object.keys(data).map((image, i ) => {

                    console.log(props.stylesItem[image].name)
                    console.log(image)
                    return (
                        <Col md={4}>
                            <div class="style-box">
                                <StyledBackgroundImage
                                    Tag="div"
                                    className="style-box-img"
                                    fluid={data[image].childImageSharp.fluid}
                                >
                                </StyledBackgroundImage>
                                <div class="style-text-box">
                                    <h5 class="h5">{props.stylesItem[image].style}</h5>
                                    <h3 class="h3 style-description">{props.stylesItem[image].name}</h3>
                                    <div class="extra-style-details">
                                        <p class="style-short-desc">{props.stylesItem[image].tagline}</p>
                                        <p>{props.stylesItem[image].text}</p>
                                        <ul class="hashtag-list">
                                            <li class="style-attribut"></li>
                                        </ul>
                                    </div>
                                </div>
                            </div>
                        </Col>
                        )
                    })
                }
            }
        />
    )
}

export default StyleItem

const StyledBackgroundImage = styled(BackgroundImage)`
    background-size: cover;
    background-position: center;
    background-repeat: no-repeat;
`

I'm passing in the following props to this component (abc dummy strings for better readability):

    stylesItem: {
            street: {
                style: "// STREET",
                name: "THE CANVAS",
                tagline: "abc",
                text: "abc",
                hashtags: [
                    "abc", "abc", "abc", "abc"
                ]
            },
            casual: {
                style: "// CASUAL",
                name: "THE CLASSIC",
                tagline: "abc",
                text: "abc",
                hashtags: [
                    "abc", "abc", "abc", "abc", "abc", "abc"
                ]
            },
            athletic: {
                style: "// ATHLETIC",
                name: "THE PERFORMER",
                tagline: "abc",
                text: "abc",
                hashtags: [
                    "abc", "abc", "abc", "abc", "abc", "abc"
                ]
            }
        }

I'm using Gatsby's Staticquery to load in 3 images (street, casual, athletic) and want to render the part in the second return statement 3 times (1 for each image), each time with the background image loading in dynamically as well as the content.

The 2 console.log() statements print out as expected.

console.log(props.stylesItem[image].name)
console.log(image)

THE CANVAS
street
THE CLASSIC
casual
THE PERFORMER
athletic

However nothing gets rendered to the screen and I'm not seeing any errors. What am I doing wrong?

Thanks in advance for your help

Answer 1

Your render prop on StaticQuery doesn't return anything, and therefore doesn't render anything.

In the StaticQuery render prop you are mapping over the keys of the queried data, then generating a bunch of JSX successfully. But notice you are not actually doing anything with it because the resulting JSX doesn't get returned.

So the entire StyleItem component does a bunch of work and then doesn't render anything, because the only thing it renders is StaticQuery .

const StyleItem = ({ stylesItem }) => {
  return (
    <StaticQuery
      query={graphql`
        query {
          street: file(relativePath: { eq: "1.png" }) {
            childImageSharp {
              fluid(quality: 90, maxWidth: 1920) {
                ...GatsbyImageSharpFluid_withWebp
              }
            }
          }
          casual: file(relativePath: { eq: "2.png" }) {
            childImageSharp {
              fluid(quality: 90, maxWidth: 1920) {
                ...GatsbyImageSharpFluid_withWebp
              }
            }
          }
          athletic: file(relativePath: { eq: "3.png" }) {
            childImageSharp {
              fluid(quality: 90, maxWidth: 1920) {
                ...GatsbyImageSharpFluid_withWebp
              }
            }
          }
        }
      `}
      render={data => {
        // Make sure to return something here
        return Object.keys(data).map(imageTitle => {
          const fluidProp = data[imageTitle].childImageSharp.fluid
          const imageData = stylesItem[imageTitle]
          return (
            <>
              <StyledBackgroundImage
                Tag="div"
                className="style-box-img"
                fluid={fluidProp}
              ></StyledBackgroundImage>
              <div>
                <h5>{imageData.style}</h5>
                <h3>{imageData.name}</h3>
                <p>{imageData.tagline}</p>
                <p>{imageData.text}</p>
              </div>
            </>
          )
        })
      }}
    />
  )
}

---

Something worth nothing with Arrow functions is that

when the only statement in an arrow function is return , we can remove return and remove the surrounding curly brackets

(param1, param2, …, paramN) => expression  
// equivalent to: => { return expression; }

So the above render prop on StaticQuery could be further simplified as:

render={data =>
  Object.keys(data).map(imageTitle => {...})
}