如何在react中加载图像并转换为blob

问题描述

我有一个关于React的问题.我有一种方法，单击后即开始导入图像.实际上，我在文件输入中有使用此方法的onChangeevent:

Hi I have an issue with react. I have a method which after click is starting to import image. Actualy I have onChangeevent with this method on my file input:

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

现在，我必须将此上传的文件转换为Blob.我该怎么办?

Now I have to convert this uploaded file to blob. How can I do this please?

我的其他代码如下:

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>
        );
    }

}

推荐答案

下面是一个示例，您如何使用 FileReader.readAsDataURL

Here's an example how can you use 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>

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