Angular 等待订阅完成并为其他函数赋值

Question

我有以下功能

文件：subcategory.service.ts

getSubCategoriesById(inp_subCatid: String): Observable<any>{
  this.getSubCategoriesList().snapshotChanges().pipe(
    map(changes =>
     changes.map(c =>
      ({ key: c.payload.key, ...c.payload.val() })
     )
    )
  ).subscribe(subCategories => {
    subCategories.filter(function (subCat) {
     return subCat.id == inp_subCatid;
   });
});

我正在调用以下文件中的顶级函数

文件：subcategory.page.ts

this.SubCategoryService.getSubCategoriesById(subCatid).subscribe((subCategories: any) => {
  this.subCat = subCategories ;
})

我遇到的问题是我收到以下错误消息：错误类型错误："this.SubCategoryService.getSubCategorysById(...) is undefined"

我想在从文件加载数据时获取数据"subcategory.service.ts" 希望有人能帮助我。

Answer 1

你的方法应该是这样的：

getSubCategories(inp_subCatid: string): Observable<any> {
  return this.getSubCategoriesList().snapshotChanges().pipe(
    map(changes => changes.map(c => 
        ({ key: c.payload.key, ...c.payload.val() })
      ).filter((subCat) => subCat.id === inp_subCatid)
    ));
}

那么你就可以这样使用了：

this.subCategoryService.getSubCategories(subCatid)
  .subscribe(subCategories => this.subCat = subCategories);

如果我正确地解释了您的方法，在我看来您正在使用 firebase...如果是这样，在您第一次致电 this.yourService.getSubCategories(subCatid) 后，您的订阅将保持有效，以便您的子类别将针对数据库中的每个更改进行更新，即使您更改了 subCatid，之前的数据库查询仍然有效。为避免这种情况，我建议您只发射一次 snapshotChanges():

getSubCategories(inp_subCatid: string): Observable<any> {
  return this.getSubCategoriesList().snapshotChanges().pipe(
    // finish the subscription after receiving the first value
    take(1),
    map(changes => changes.map(c => 
        ({ key: c.payload.key, ...c.payload.val() })
      ).filter((subCat) => subCat.id === inp_subCatid)
    ));
}

Answer 2

非常感谢

如果我想过滤特定数据怎么办？？喜欢 "id"

getSubCategoriesbyId(inp_subCatid): Observable<any>{
  this.getSubCategoriesList().snapshotChanges().pipe(
    map(changes =>
      changes.map(c =>
        ({ key: c.payload.key, ...c.payload.val() })
      )
    )
  ).subscribe(subCategories => {
     subCategories.filter(function (subCat) {
    return subCat.id == inp_subCatid;
  });
  });
}

然后取回过滤后的数据

this.yourService.getSubCategoriesbyId(subCatid)
  .subscribe(subCategories => console.log(subCategories));

Angular 等待订阅完成并为其他函数赋值

Angular wait until subscribe is done and give values to other function

javascript

asynchronous

subscribe

angular