7-3. Feed Component

klaystagram-feed

1. Feed component's role

2. Read data from contract: getFeed method

3. Save data to store: setFeed action

4. Show data in component: Feed component

1) Feed component's role

In chapter 4. Write Klaystagram Smart Contract, we wrote PhotoData struct, and located it inside _photoList mapping. Feed component's role is as follows: 1. Read PhotoData via calling Klaystagram contract method (redux/actions/photos.js) 2. Show PhotoData(feed) with its owner information (components/Feed.js)

2) Read data from contract: getPhoto method

1. Call contract method: getTotalPhotoCount()

   If there are zero photos, call setFeed action with an empty array.

2. Call contract method:getPhoto(id)

   If there are photos, get each photo data as a promise and push it in the feed array. When all promises have resolved, return the feed array.

3. Call redux action: setFeed(feed)

   Get resolved feed array and save it to redux store.

// src/redux/actions/photos.js

const setFeed = (feed) => ({
  type: SET_FEED,
  payload: { feed },
})

export const getFeed = () => (dispatch) => {
  // 1. Call contract method(READ): `getTotalPhotoCount()`
  // If there is no photo data, call `setFeed` action with empty array
  KlaystagramContract.methods.getTotalPhotoCount().call()
    .then((totalPhotoCount) => {
      if (!totalPhotoCount) return []
      const feed = []
      for (let i = totalPhotoCount; i > 0; i--) {
        // 2. Call contract method(READ):`getPhoto(id)`
        // If there is photo data, call all of them
        const photo = KlaystagramContract.methods.getPhoto(i).call()
        feed.push(photo)
      }
      return Promise.all(feed)
    })
    .then((feed) => {
      // 3. Call actions: `setFeed(feed)`
      // Save photo data(feed) to store
      dispatch(setFeed(feedParser(feed))
    })
}

3) Save data to store: setFeed action

After we successfully fetch photo data (feed) from the Klaystagram contract, we call setFeed(feed) action. This action takes the photo data as a payload and saves it in a redux store.

4) Show data in component: Feed component

// src/components/Feed.js
import React, { Component } from 'react'
import { connect } from 'react-redux'
import moment from 'moment'
import Loading from 'components/Loading'
import PhotoHeader from 'components/PhotoHeader'
import PhotoInfo from 'components/PhotoInfo'
import CopyrightInfo from 'components/CopyrightInfo'
import TransferOwnershipButton from 'components/TransferOwnershipButton'
import { drawImageFromBytes} from 'utils/imageUtils'
import { last } from 'utils/misc'

import * as photoActions from 'redux/actions/photos'

import './Feed.scss'

class Feed extends Component {
  constructor(props) {
    super(props)
    this.state = {
      isLoading: !props.feed,
    }
  }

  static getDerivedStateFromProps = (nextProps, prevState) => {
    const isUpdatedFeed = (nextProps.feed !== prevState.feed) && (nextProps.feed !== null)
    if (isUpdatedFeed) {
      return { isLoading: false }
    }
    return null
  }

  componentDidMount() {
    const { feed, getFeed } = this.props
    if (!feed) getFeed()
  }

  render() {
    const { feed, userAddress } = this.props

    if (this.state.isLoading) return <Loading />

    return (
      <div className="Feed">
        {feed.length !== 0
          ? feed.map(({
            id,
            ownerHistory,
            data,
            name,
            location,
            caption,
            timestamp,
          }) => {
            const originalOwner = ownerHistory[0]
            const currentOwner = last(ownerHistory)
            const imageUrl = drawImageFromBytes(data)
            const issueDate = moment(timestamp * 1000).fromNow()
            return (
              <div className="FeedPhoto" key={id}>
                <PhotoHeader
                  currentOwner={currentOwner}
                  location={location}
                />
                <div className="FeedPhoto__image">
                  <img src={imageUrl} alt={name} />
                </div>
                <div className="FeedPhoto__info">
                  <PhotoInfo
                    name={name}
                    issueDate={issueDate}
                    caption={caption}
                  />
                  <CopyrightInfo
                    className="FeedPhoto__copyrightInfo"
                    id={id}
                    issueDate={issueDate}
                    originalOwner={originalOwner}
                    currentOwner={currentOwner}
                  />
                  {
                    userAddress === currentOwner && (
                      <TransferOwnershipButton
                        className="FeedPhoto__transferOwnership"
                        id={id}
                        issueDate={issueDate}
                        currentOwner={currentOwner}
                      />
                    )
                  }
                </div>
              </div>
            )
          })
          : <span className="Feed__empty">No Photo :D</span>
        }
      </div>
    )
  }
}

const mapStateToProps = (state) => ({
  feed: state.photos.feed,
  userAddress: state.auth.address,
})

const mapDispatchToProps = (dispatch) => ({
  getFeed: () => dispatch(photoActions.getFeed()),
})

export default connect(mapStateToProps, mapDispatchToProps)(Feed)

At the first time, you can only see the text "No photo :D" because there is no photo data in contract yet. Let's make a UploadPhoto component to send photo data to contract!