以新形式反应更新状态

Question

How can I update the state in a new form? I want to convert an image into base64 when uploaded and push it to the firebase.

However, I got an TypeError: this.setState is not a function error.

I also tried to update the value of input, but didn't work. document.getelementbyid("image").value = reader.result

Thank you!

import React from 'react'
import PropTypes from 'prop-types'
import { Formik, Field, Form } from 'formik'
import { TextField } from 'formik-material-ui'
import { makeStyles } from '@material-ui/core/styles'
import Button from '@material-ui/core/Button'
import Dialog from '@material-ui/core/Dialog'
import DialogTitle from '@material-ui/core/DialogTitle'
import DialogActions from '@material-ui/core/DialogActions'
import DialogContent from '@material-ui/core/DialogContent'
import styles from './NewProjectDialog.styles'

const useStyles = makeStyles(styles)

function NewProjectDialog({ onSubmit, open, onRequestClose }) {
  const classes = useStyles()

  function handleSubmit(values, { setSubmitting }) {
    return onSubmit(values).then(() => {
      setSubmitting(false)
    })
  }

  function previewFile() {
    const preview = document.querySelector('img');
    const file = document.querySelector('input[type=file]').files[0];
    const reader = new FileReader();

    reader.addEventListener("load", function () {
      // convert image file to base64 string
      preview.src = reader.result;
      this.setState({image: reader.result})
    }, false);

    if (file) {
      reader.readAsDataURL(file);
    }

    this.previewFile = this.preview.bind(this)
  }

  return (
    <Dialog open={open} onClose={onRequestClose}>
      <DialogTitle id="new-project-dialog-title">New Project</DialogTitle>
      <Formik initialValues={{ name: '' }} onSubmit={handleSubmit}>
        {({ errors, isSubmitting }) => (
          <Form className={classes.root}>
            <DialogContent>
              <Field
                name="isbn"
                label="ISBN"
                component={TextField}
                margin="normal"
                fullWidth
              />
              <Field
                name="title"
                label="Title"
                component={TextField}
                margin="normal"
                fullWidth
              />
              <Field
                name="status"
                label="Status"
                component={TextField}
                margin="normal"
                fullWidth
              />
              <Field
                name="price"
                label="Price"
                component={TextField}
                margin="normal"
                fullWidth
              />
              <Field
                id="image"
                name="image"
                component={TextField}
                style={{display:"none"}}
              />
              <input type="file" onChange={previewFile}/>
              <img src="" height="200" alt="Image preview..."></img>
            </DialogContent>
            <DialogActions>
              <Button onClick={onRequestClose} color="secondary">
                Cancel
              </Button>
              <Button type="submit" color="primary" disabled={isSubmitting}>
                {isSubmitting ? 'Creating...' : 'Create'}
              </Button>
            </DialogActions>
          </Form>
        )}
      </Formik>
    </Dialog>
  )
}

NewProjectDialog.propTypes = {
  onSubmit: PropTypes.func.isRequired,
  open: PropTypes.bool.isRequired,
  onRequestClose: PropTypes.func.isRequired
}

export default NewProjectDialog

---

I modified the code but the image was not stored in the firebase...

 function NewProjectDialog({ onSubmit, open, onRequestClose }) { const classes = useStyles() const [image, setImage] = useState({image: null}); (Omitted) function previewFile() { const preview = document.querySelector('img'); const file = document.querySelector('input[type=file]').files[0]; const reader = new FileReader(); reader.addEventListener("load", function () { // convert image file to base64 string preview.src = reader.result; setImage({image: reader.result}); }, false); if (file) { reader.readAsDataURL(file); } }

 -M0EVfPfzF1vjQ4wLXLU createdAt: 1581881931504 createdBy: "YcGWgfdbk2hs8CcWSdtsicYncyB3" isbn: "asdfa" name: "" price: "asdfasd" status: "asfdasfd" title: "asfdasfd"

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Answer 1

I guess this issue is coming from that this.setState can be used only in class based component. In function components like what you have - NewProjectDialog - you can use useState hook where you can create your state and the updater function.

What does useState return? It returns a pair of values: the current state and a function that updates it.

So you could have the defined state as:

const [image, setImage] = useState({image: null});

And instead of this.setState({image: reader.result}) you would modify as the following:

// updating value
setImage({image: reader.result});

Read further here: Using the State Hook

I hope that helps!