React-Dropzone图像预览不显示

Question

使用react-dropzone (https://www.npmjs.com/package/react-dropzone)并将文件记录到控制台，但无法在状态更改时获取图像预览。知道我做错了什么吗？

export default class JoinForm extends Component {
    constructor(props) {
    super(props)
        this.state = {
            imageFiles: []
    }
}

onDrop(imageFiles) {
    this.setState({
        imageFiles: imageFiles
    })
    console.log(imageFiles)  
}

render() {

    return(
        <form className='join-form' ref='joinForm' autoComplete='off'>
            <Dropzone
                onDrop={this.onDrop}
                className='dropzone'
                activeClassName='active-dropzone'
                multiple={false}>
      <div>Drag and drop or click to select a 550x550px file to upload.</div>
    </Dropzone>

            {this.state.imageFiles.length > 0 ? <div>
    <h2>Uploading {this.state.imageFiles.length} files...</h2>
    <div>{this.state.imageFiles.map((file) => <img src={file.preview} /> )}</div>
    </div> : null}
        </form>
    )
}

}；

Answer 1

正确的答案是:做一个傀儡，忘记绑定这个。

<Dropzone
  onDrop={this.onDrop.bind(this)} //<= Here
  className='dropzone'
  activeClassName='active-dropzone'
  multiple={false}
  style={imageUploadStyle}>
    <div>Drag and drop or click to select a 550x550px file to upload.</div>
</Dropzone>

https://toddmotto.com/react-create-class-versus-component/

Answer 2

您将文件存储在imageFiles中，但在render方法中，您将映射到this.state.files数组。

更改：

<div>{this.state.files.map((file) => <img src={file.preview} /> )}</div>

至：

<div>{this.state.imageFiles.map((file) => <img src={file.preview} /> )}</div>

或者，因为您有这个常量const files = this.state.imageFiles，所以可以将前面提到的语句更改为：

<div>{files.map((file) => <img src={file.preview} /> )}</div>

Answer 3

将渲染函数更改为imageFiles

render() {
    const files = this.state.imageFiles

    return(
        <form className='join-form' ref='joinForm' autoComplete='off'>
            <Dropzone
                onDrop={this.onDrop}
                className='dropzone'
                activeClassName='active-dropzone'
                multiple={false}>
      <div>Drag and drop or click to select a 550x550px file to upload.</div>
    </Dropzone>

            {this.state.imageFiles.length > 0 ? <div>
    <h2>Uploading {this.state.imageFiles.length} files...</h2>
    <div>{this.state.imageFiles.map((file) => <img src={file.preview} /> )}</div>
    </div> : null}
        </form>
    )