如何在角度4中为窗体组中的键添加值[复制]

我想提交一份包含文件的表格。 所以我用 ng2-file-upload

component.html 是-

<input type="file" ng2FileSelect [uploader]="uploader" (onFileSelected)="onFileSelected($event)">

我的组件是-

public uploader: FileUploader = new FileUploader({});

  uploadForm: FormGroup;

  constructor(
    private formBuilder: FormBuilder,
    private userService: UserServiceService
  ) {
  }

  ngOnInit() {

    this.uploadForm = this.formBuilder.group({
      branch         : ['cs', Validators.required],
      document       : [null, Validators.required],
      semester       : ['3', Validators.required],
    });


  }


  //////////// File Converted into base64/////////////////


  onFileSelected(event: EventEmitter<File[]>) {
    const file: File = event[0];

    readBase64(file)
      .then(function(data) {
         console.log(data);

        this.uploadForm.patchValue({  // Showing error -- Potentially invalid reference access to a class field via 'this.' 
          document: data
        });
      });

  }

我正在生成文件的base64 onFileSelected() document 输入我的 formGroup this.uploadForm.patchValue()

Potentially invalid reference access to a class field via 'this.'

我只是想补充一下 data 在我的 钥匙 uploadForm