如何在 React 中加载图像并转换为 blob

Question

嗨，我对反应有疑问。我有一个点击后开始导入图像的方法。实际上，我的文件输入上有使用此方法的 onChangeevent：

 fileUploadInputChange(e) {
  console.log(e.target.value); // return url of image like C:\fakepath\pokemon-pikachu-wall-decal.jpg
};

现在我必须将这个上传的文件转换为 blob。请问我该怎么做？

我的其他代码如下所示：

 export class GeneralySettings extends Component {
    /**
     * PropTypes fot component
     * @return {object}
     */
    static get propTypes() {
        return {
            userData: PropTypes.object.isRequired,
        };
    };

    constructor(props) {
        super(props);
        this.state = {
            showAvatarChangeButton: false,
            uploadedImage : '',
        };
        this.inputReference = React.createRef();

    }

    fileUploadAction(){
        this.inputReference.current.click();
    };

    fileUploadInputChange(e){
            console.log(e.target.value);
        };

    /**
     * Render method for user profile
     * @return {*}
     */
    render() {
        return (

                        <div className={'d-flex flex-column mr-2'}>
                            <div className={'position-relative'}
                                 onMouseEnter={() => this.setState({showAvatarChangeButton: true})}
                                 onMouseLeave={() => this.setState({showAvatarChangeButton: false})}>
                                <Avatar name="Foo Bar" className={'position-relative button-cursor'}/>
                                <div
                                    className={`position-absolute ${(this.state.showAvatarChangeButton ? 'd-inlene-block' : 'd-none')}`}
                                    id={'changeAvatarButton'}>
                                    <Button variant={'dark'} size={'sm'} block
                                            onClick={this.fileUploadAction.bind(this)}> Zmeniť</Button>
                                    <input type="file" hidden ref={this.inputReference}
                                           onChange={(e) => this.fileUploadInputChange(e)}/>
                                </div>
            </div>
        );
    }

}

原文由 Young L. 发布，翻译遵循 CC BY-SA 4.0 许可协议

Answer 1

这是一个示例，您如何使用 FileReader.readAsDataURL

 const {useState} = React;

const fileToDataUri = (file) => new Promise((resolve, reject) => {
    const reader = new FileReader();
    reader.onload = (event) => {
      resolve(event.target.result)
    };
    reader.readAsDataURL(file);
    })

const App = () => {
  const [dataUri, setDataUri] = useState('')

  const onChange = (file) => {

    if(!file) {
      setDataUri('');
      return;
    }

    fileToDataUri(file)
      .then(dataUri => {
        setDataUri(dataUri)
      })

  }

  return <div>
  <img width="200" height="200" src={dataUri} alt="avatar"/>
  <input type="file" onChange={(event) => onChange(event.target.files[0] || null)} />
  </div>
}

ReactDOM.render(
    <App/>,
    document.getElementById('root')
  );

 <script src="https://unpkg.com/react/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom/umd/react-dom.development.js"></script>
<script src="https://unpkg.com/babel-standalone@6/babel.min.js"></script>
<div id="root"></div>

原文由 Józef Podlecki 发布，翻译遵循 CC BY-SA 4.0 许可协议

Answer 2

使用文件阅读器

fileUploadInputChange(e) {
    let reader = new FileReader();
    reader.onload = function(e) {
      this.setState({uploadedImage: e.target.result});
    };
    reader.readAsDataURL(event.target.files[0]);
}

显示/预览图像：

 <Avatar src={this.state.uploadedImage} name="Foo Bar" className={'position-relative button-cursor'}/>

// or .. for image , use below
<img src={this.state.uploadedImage} alt={""} />

原文由 gdh 发布，翻译遵循 CC BY-SA 4.0 许可协议