循环中的所有异步调用完成后如何调用函数？

Question

reader.onloadend 调用异步函数 addData 并且 reader.onloadend 处于循环中。

const uploadFiles = () => {
    console.log(acceptedFiles)
    setLoading(true)
    console.log(loading)
    let i = 0
    let l = acceptedFiles.length

    for (i = 0; i < l; i++) {
      let file = acceptedFiles[i]
      const reader = new window.FileReader()
      reader.readAsArrayBuffer(file)
      reader.onloadend = () => {
        let buffer = Buffer(reader.result)
        console.log(buffer)
        addData(file.path, buffer)
      }
    }
  }

这是我的异步函数 addData

async function addData(name, buffer) {
    const file = await myfunction()
    
  }

我想在循环中的所有异步 addData 被调用后调用 setLoading(false) 。onClick 函数不起作用，当我在所有异步函数完成之前单击按钮时，加载设置为 false。

const [loading, setLoading] = useState(false)
<button onClick={() => {
                uploadFiles()
                 setLoading(false) 
             }}
            disabled={loading}
          >

Answer 1

使用承诺，您可以知道所有文件何时已被读取。基本思路如下

const uploadFiles = (evt) => {

  // set loading to true;

  const acceptedFiles = [...evt.target.files];

  // Create a map of promises that will resolve when file is read
  const readerPromises = acceptedFiles.map(file => {
    return new Promise(resolve => {
      const reader = new window.FileReader()
      reader.readAsArrayBuffer(file)
      reader.onloadend = () => {
        console.log(file);
        let buffer = reader; // Buffer(reader.result)
        resolve([file.name, buffer])
      }      
    });
  });

  // Detects when all of the promises are fully loaded
  Promise.all(readerPromises).then(results => {
    console.log(results);
    // set loading to false;
  });
  
};

<input type="file" multiple onchange="uploadFiles(event)" />