Angular 4如何在回调函数中更新类的值？ [复制]

Question

我有这个代码，其中我的“this.index”和“this.result”是未定义的，我如何制作它以便当我更新它们的值时它就像通过引用传递一样：

  submitQuiz(addsMemberPoints, pointsCallback) {
    this.getValues(this.answers, this.totalPoints, this.index, function(answers, totalPoints, ranks, index){
      pointsCallback(answers, ranks, addsMemberPoints, totalPoints, index, function(index, points){
        function getMember(obj) {
          return Object.keys(obj).reduce(function(a, b){ return obj[a] > obj[b] ? a : b });
        }
        // would like to change index and result of initial class with new values
        this.result = getMember(points);
        this.index = index;
      });
    });

  }

产生的错误被重现

Answer 1

通过使用“那个”技巧。

submitQuiz(addsMemberPoints, pointsCallback) {
    var that = this;

    this.getValues(this.answers, this.totalPoints, this.index, function(answers, totalPoints, ranks, index){
      pointsCallback(answers, ranks, addsMemberPoints, totalPoints, index, function(index, points){
        function getMember(obj) {
          return Object.keys(obj).reduce(function(a, b){ return obj[a] > obj[b] ? a : b });
        }
        // changed this to that
        that.result = getMember(points);
        that.index = index;
      });
    });

  }

Answer 2

为什么不使用arrow functions？

箭头函数不会丢失当前的this 上下文，允许您在不定义that 或self 变量的情况下访问它。

查看这个 ES6 示例并查看 getCommaSaperatedImages 函数 -

class Hotel {

  constructor(images) {
    if (images && images.length) {
      this.images = images;
    }
  }

  getCommaSaperatedImages() {
    this.imageString = "";
    if (this.images && this.images.length) {
      this.images.forEach((image, index, images) => {
        //notice here `this` is still pointing to `Hotel` class.
        this.imageString += image.url;
        if (index === images.length - 1) {
          return;
        }
        this.imageString += ", ";
      });
    }
    return this.imageString;
  }
}

let hotel = new Hotel([{
  id: 1,
  url: 'http://image1.png'
}, {
  id: 2,
  url: 'http://image2.png'
}]);

console.log(hotel.getCommaSaperatedImages());

Typescript 应该完全一样。

我希望这会有所帮助:)。