Question

尝试按角度过滤数组，出现以下控制台错误：

TypeError：无法读取未定义的属性“ filter”

我的课程代码在下面

export class FetchDataComponent {
  public forecasts: WeatherForecast[];
  public cacheForecasts: WeatherForecast[];
  public summaries: any[];

  constructor(http: HttpClient) {
    http.get<WeatherForecast[]>(BaseUrl + 'api/SampleData/WeatherForecasts').subscribe(result => {
      this.forecasts = result;
    }, error => console.error(error));

    http.get<any[]>(BaseUrl + 'api/SampleData/GetSummaries').subscribe(result => {
      this.summaries = result;
    }, error => console.error(error));
}

  filterForeCasts(filterVal: any) {
    if (filterVal === '0') {
      this.forecasts = this.cacheForecasts;
    } else {
      this.forecasts = this.cacheForecasts.filter((item) => item.summary === filterVal); // <--- error here
    }
  }
}

我在这里做什么错了？

Answer 1

尝试将cacheForecasts：WeatherForecast []初始化为一个空数组。如果构造函数调用的getWeather请求失败，则cacheForecasts将是未定义的

Answer 2

我意识到构造函数缺少过滤数组的初始化，因此以下代码可以正常工作：

  constructor(http: HttpClient) {
    http.get<WeatherForecast[]>(BaseUrl + 'api/SampleData/WeatherForecasts').subscribe(result => {
      this.forecasts = result;
      this.cacheForecasts = result;
    }, error => console.error(error));

    http.get<any[]>(BaseUrl + 'api/SampleData/GetSummaries').subscribe(result => {
      this.summaries = result;
    }, error => console.error(error));
}

Angular 7-TypeError：无法读取未定义的属性“ filter”

2 个答案: