我想从observable中获取Item,并通过foreach
对其进行转换,然后将结果保存到新变量中。
我不确定为什么这个代码不起作用:
policYears$: Observable<PolicyYear[]>;
policYearsSelector$: Observable<YearSelector.PolicyYear[]>;
this.policYearsSelector$ = this.policYears$.pipe(
map((year: YearSelector.PolicyYear[]) => year.forEach(y => y.isActive = this.params.policyYearIds.indexOf(y.id) !== -1))
);
我有一个错误:Type 'Observable<void>' is not assignable to type 'Observable<PolicyYear[]>'.
Type 'void' is not assignable to type 'PolicyYear[]'.
为什么它会返回虚空?
array.forEach
不会返回值,因为它只是用于迭代。因此year.forEach
不向map
返回任何内容,而CCD_5则不返回任何内容。
您需要使用year.map
并返回一个值
您正在从policeYears$
映射数据,其类型为"PolicyYears[]">
所以你必须把你的代码改成
policYears$: Observable<PolicyYear[]>;
policYearsSelector$: Observable<YearSelector.PolicyYear[]>;
this.policYearsSelector$ = this.policYears$.pipe(
map(
(year: PolicyYear[]): YearSelector.PolicyYear[] =>
year.forEach(
y => y.isActive = this.params.policyYearIds.indexOf(y.id) !== -1
)
)
);
year的类型为PolicyYear[],映射返回一个YearSelector。保单年度[]
热烈问候
问题是Array.forEach
返回void
(因此是您收到的错误消息,因为现在您正试图使用map
将PolicyYear[]
映射到void
(。
现在,根据你想做什么,你可以继续使用forEach
,只返回更新后的数组:
map((year: YearSelector.PolicyYear[]) => {
year.forEach(y => y.isActive = this.params.policyYearIds.indexOf(y.id) !== -1);
return year;
})
或者您可以使用Array.map
并返回一个新数组:
map((year: YearSelector.PolicyYear[]) => year.map(y => {
y.isActive = this.params.policyYearIds.indexOf(y.id) !== -1;
return y;
}))