Javascript 角度ngrx示例理解重选

我看了一遍回购协议，不明白“重新选择”的用法

据我所知，

createSelector

函数接受两个接受相同参数的函数

例如：

const shopItemsSelector = state => state.shop.items
const taxPercentSelector = state => state.shop.taxPercent

const taxSelector = createSelector(
  subtotalSelector,
  taxPercentSelector,
  (subtotal, taxPercent) => subtotal * (taxPercent / 100)
)

这两个函数都将整个状态作为参数

但在ngrx示例中-

export const getLayoutState = (state: State) => state.layout;
export const getShowSidenav = (state: State) => state.showSidenav;
export const getShowSidenav = createSelector(getLayoutState, fromLayout.getShowSidenav);

store.select(fromRoot.getShowSidenav)

在上面的示例中，它们似乎采用了不同的参数，第一个参数采用整个状态，第二个参数采用布局状态

---

工作情况如何

这很混乱，因为它分布在多个文件中

在layout.ts的内部，我们有：

export const getShowSidenav = (state: State) => state.showSidenav;

export const getLayoutState = (state: State) => state.layout;
export const getShowSidenav = createSelector(getLayoutState, 
   fromLayout.getShowSidenav);

在index.ts中，我们有：

export const getShowSidenav = (state: State) => state.showSidenav;

export const getLayoutState = (state: State) => state.layout;
export const getShowSidenav = createSelector(getLayoutState, 
   fromLayout.getShowSidenav);

因此，如果我们在一个文件中完成所有操作，它将如下所示：

// getLayoutState works at the AppState level
export const getLayoutState = (state: State) => state.layout;

export const getShowSidenav = createSelector(getLayoutState, 
   // This fat arrow function operates only on what getLayoutState gives us
   (layoutState: LayoutState) => layoutState.showSidenav);

在本例中，当您使用createSelector时，第一个参数采用getLayoutState，它从整个AppState返回布局切片。然后将该值发送到createSelector的最终参数

下面是我所说的最终参数的进一步细分：

// getA values are passed to the final function as a
export const getSomething = createSelector(getA, 
   (a) => a);

// getA, getB values are passed to the final function as a, b
export const getSomething = createSelector(getA, getB, 
   (a, b) => a + b);

// getA, getB, getC values are passed to the final function as a, b, c
export const getSomething = createSelector(getA, getB, getC 
   (a, b, c) => a + b + c);

---

在所有这些情况下，最后一个参数始终是一个函数，它将以前的所有选择器都作为参数。

但重新选择的示例并非如此。在本例中，第二个参数没有得到第一个参数的结果。从它们的文档（）中，它表示：createSelector（…inputSelectors |[inputSelectors]，resultFunc）接受一个或多个选择器或一组选择器，计算它们的值并将它们作为参数传递给resultFunc。换句话说，第一组选择器将其值传递给最后一个参数resultFunc。在本例中，getLayoutState是一个inputSelector，最后一个fat arrow函数是resultFunc