javascript - FileReader onload 不在 Controller 范围内 Angular 2

Question

我正在尝试以 block 的形式发送文件以保存在数据库中，并且我正在使用 FileReader.readAsArrayBuffer() 来触发 onload 事件。一旦我进入 onload 事件，我的问题就会出现，“this”的范围仅包含 FileReader 属性，而我的类中没有任何内容。即使是在 onload 事件之前定义的变量也不可访问。我在想我可以尝试将“this”的值作为参数传递，这样我就可以访问我的函数、服务和变量，但到目前为止我还没有取得任何成功。有没有人尝试过类似的东西或者知道我是否已经达到某种限制？

谢谢你的帮助

这是我的组件类

export class UploadComponent {
title = 'Upload File';
fileData = null;
files = null;
fs;
@Input()
showUpload: boolean;

constructor(fileService: FileService) {
    this.fs = fileService;
}

uploadFile() {
    let temp = document.getElementById("fileToUpload");
    let fr = new FileReader();
    let file = temp.files[0];
    let fb = fr.readAsArrayBuffer(file);

    fr.onload = function(data) {
        this.fs.beginFileUpload(file.name, function(data) {
            let chunkSize = 200000;
            let startIndex = 0;
            let stopIndex = chunkSize;
            let file = data.target.result;
            let fileChunk = null;

            while (startIndex < file.length) {
                if (stopIndex < length) {
                    fileChunk = file.subArray(startIndex, stopIndex);
                    startIndex = stopIndex;
                    stopIndex += chunkSize;
                }
                else {
                    fileChunk = file.subArray(startIndex);
                    startIndex = stopIndex;
                }
                //fs.uploadChunk(fileChunk);
            }
        });

    }

}

我的组件模板

<input type="file" [(value)]="fileData" [(files)]="files" id="fileToUpload" />
<input type="button" (click)="uploadFile()" value="Upload File" />

Answer 1

使用 () => 而不是 function() 来保留 this

的范围

uploadFile() {
    let temp = document.getElementById("fileToUpload");
    let fr = new FileReader();
    let file = temp.files[0];
    let fb = fr.readAsArrayBuffer(file);

    fr.onload = (data) => {
        this.fs.beginFileUpload(file.name, (data) => {
            let chunkSize = 200000;
            let startIndex = 0;
            let stopIndex = chunkSize;
            let file = data.target.result;
            let fileChunk = null;

            while (startIndex < file.length) {
                if (stopIndex < length) {
                    fileChunk = file.subArray(startIndex, stopIndex);
                    startIndex = stopIndex;
                    stopIndex += chunkSize;
                }
                else {
                    fileChunk = file.subArray(startIndex);
                    startIndex = stopIndex;
                }
                //fs.uploadChunk(fileChunk);
            }
        });

    }
}

另见 https://developer.mozilla.org/de/docs/Web/JavaScript/Reference/Functions/Arrow_functions