Question

我在有角组件中有一个JSON数组，我想将其移动到另一个数组。

类型声明：

MeasurementDetails：

export interface MeasurementDetails {
  _id: string;
  measureTitle: string;
  measureDescription: string;
  measureSymbol: string;
}

和MeasureTypeElemetns：

export interface MeasureTypeElemetns {
  title: string;
  position: number;
  description: string;
  symbol: string;
}

我用这样的初始化声明了两个数组：

mp: MeasurementDetails[] = [];
ELEMENT_DATA: MeasureTypeElemetns[] = [];

我请求了HTTP请求，并且它响应了我。我在组件类的构造函数中这样称呼它：

  this.mpserv.getall().subscribe(
    x => {
      x.forEach(elementj => {
        this.mp.push(elementj);
      });
      this.filltoelements(this.mp);
    },
    err => console.error('Observer got an error: ' + err),
    () => console.log('Observer got a complete notification')
  );

“ filltoelements”函数声明如下：

filltoelements(mdata: MeasurementDetails[]) {
  if (!mdata) {
    console.log('data is undefined!!!!');
  } else {
    let i = -1;
    mdata.forEach(elementi => {
      i++;
      this.ELEMENT_DATA[i].position = (i + 1);
      this.ELEMENT_DATA[i].title = elementi.measureTitle;
      this.ELEMENT_DATA[i].description = elementi.measureDescription;
      this.ELEMENT_DATA[i].symbol = elementi.measureSymbol;
    });
  }
}

但是当我跑步时，它会显示一条消息：

"ERROR TypeError: Cannot set property 'position' of undefined
     at measure-type.component.ts:74
     at Array.forEach (<anonymous>)
     at MeasureTypeComponent.push../src/app/cc/measurement/measure- 
 type/measure-type.component.ts.MeasureTypeComponent.filltoelements"

我认为这与我的“ ELEMENT_DATA”数组的初始化有关。但我不知道如何解决。

Answer 1

ELEMENT_DATA是空数组，因此它返回undefined元素。

在访问其属性之前，只需分配一个this.ELEMENT_DATA[i] = {}之类的空对象即可。

此代码将起作用。

filltoelements(mdata: MeasurementDetails[]) {
  if (!mdata) {
    console.log('data is undefined!!!!');
  } else {
    let i = -1;
    mdata.forEach(elementi => {
      i++;
      this.ELEMENT_DATA[i] = {} as MeasureTypeElemetns;
      this.ELEMENT_DATA[i].position = (i + 1);
      this.ELEMENT_DATA[i].title = elementi.measureTitle;
      this.ELEMENT_DATA[i].description = elementi.measureDescription;
      this.ELEMENT_DATA[i].symbol = elementi.measureSymbol;
    });
  }
}

我不知道为什么收到以下消息：ERROR TypeError：无法设置未定义的属性“ position”

1 个答案: