[英]Why is my *ngFor reacting to ngrx state changes but my subscribe method does only once
在我的应用程序中,我有一个 ngrx 存储,其中包含一组对象。 在我的构造函数中,我选择了数组并调用了一个方法 (onProductEntriesLoaded),该方法为该数组设置了一个变量。 在 html 代码中有一个 *ngFor 循环,它遍历这个变量并显示它们。 设置变量的方法也会调用另一个计算总和的方法。 但是,每次在状态中向此数组添加元素时,内容都会在 *ngFor 循环中正确显示。 但是没有调用将变量设置为数组的方法。 它仅在初始化时调用。 我认为订阅状态的应用程序的每个部分都会在状态发生变化时再次加载。 即使它是一个构造函数。 然而,它似乎并非如此。 有人可以向我解释这种行为。
这是我的 cart.component.html 的一部分
<div id="middle">
<div class="entries">
<div *ngFor="let entry of productEntries">
<img
*ngIf="!entry.product.image"
src="../../../assets/img/esansBottles Kopie.png"
/>
<img
*ngIf="entry.product.image"
src="../../../assets/img/{{ entry.product.image }}"
/>
{{ entry.product.title }}
{{ entry.variation.option }}
{{ entry.variation.price }}
{{ entry.amount }}
</div>
</div>
</div>
<div id="bottom">
<div>Summe {{ sumOfCart }} €</div>
<button>Zur Kasse</button>
</div>
这基本上就是cart.component.ts文件
export class CartComponent implements OnInit {
productEntries: ShoppingCartEntry[];
sumOfCart: number;
constructor(private store: Store<State>) {
this.store
.select(state => state.shoppingCartReducer.Entries)
.subscribe(data => this.onProductEntriesLoaded(data));
}
ngOnInit() {}
onProductEntriesLoaded(productEntries: ShoppingCartEntry[]) {
console.log("onProductEntreisLoaded called");
this.productEntries = productEntries;
console.log(productEntries);
console.log("next calculate sum");
this.calculateSum(productEntries);
console.log("after calculate sum");
}
calculateSum(shoppingCartEntries: ShoppingCartEntry[]) {
console.log("calculate sum called");
/*let sum = 0.0;
console.log(shoppingCartEntries);
if (shoppingCartEntries) {
shoppingCartEntries.forEach(element => {
sum = element.amount * element.variation.price + sum;
});
}
this.sumOfCart = sum;*/
}
这是我的 reducer.ts 文件的一部分
export function shoppingCartReducer(
state: ShoppinCartState = { CartIsOpen: false, Entries: [] },
action: ShoppingCartAction
) {
switch (action.type) {
case "CART_TOGGLE":
return {
...state,
CartIsOpen: !state.CartIsOpen
};
case "CART_CLOSE":
return {
...state,
CartIsOpen: false
};
case "CART_ADD_ENTRY":
return {
...state,
Entries: addEntryToCart(state.Entries, action.payload)
};
default:
return state;
}
}
function addEntryToCart(
currentEntries: ShoppingCartEntry[],
entry: ShoppingCartEntry
): ShoppingCartEntry[] {
//if currentEntries is null return empty array
if (currentEntries) {
// if entry is null return currentEntries
if (entry) {
// check if currentEntries contains entry
let index = currentEntries.findIndex(
x => x.product === entry.product && x.variation === entry.variation
);
if (index === -1) {
let newEntries = currentEntries;
newEntries.push(entry);
return newEntries;
} else {
currentEntries[index].amount += entry.amount;
return currentEntries;
}
} else {
return currentEntries;
}
} else {
return [];
}
}
问题是由我的减速器功能引起的。 在我的减速器中删除对 addEntryToCart 的函数调用并在减速器中实现功能后,问题就解决了。 我仍然不明白为什么调用函数会导致问题。
我就是这样解决的:
export function shoppingCartReducer(
state: ShoppinCartState = { CartIsOpen: false, Entries: [] },
action: ShoppingCartAction
) {
switch (action.type) {
case "CART_TOGGLE":
return {
...state,
CartIsOpen: !state.CartIsOpen
};
case "CART_CLOSE":
return {
...state,
CartIsOpen: false
};
case "CART_ADD_ENTRY":
let contains = state.Entries.findIndex(
entry =>
entry.product === action.payload.product &&
entry.variation === action.payload.variation
);
if (contains === -1) {
return {
...state,
Entries: [...state.Entries.concat(action.payload)]
};
} else {
return {
...state,
Entries: [
...state.Entries.map(entry =>
entry.product === action.payload.product &&
entry.variation === action.payload.variation
? {
product: entry.product,
variation: entry.variation,
amount: entry.amount + action.payload.amount
}
: entry
)
]
};
}
default:
return state;
}
}
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