角度：實例化對象錯誤，無法設置屬性

Question

所以我試圖填充我的數組，但是我首先沒有實例化它。

模型：

user: User = {
  firstName: "",
  lastName: "",
  adress: ""
}
order: Order = {
  OrderId: "",
  User: this.user,
  TotalPrice: 0,
  OrderItems: []

}

在這里，我試圖填充我的訂單：

    this.Identity.getMail().then(user => this.order.OrderId == user.email);
this.order.User = this.user;
this.order.TotalPrice = this.cartTotal;
this.cartItems.forEach((item, index) => {
  this.order.OrderItems[index].ProductName = item.productName,
  this.order.OrderItems[index].ProductPrice = item.price,
  this.order.OrderItems[index].ProductQuantity = item.quantity
})

我收到此錯誤：

CartFullComponent.html:21 ERROR TypeError: Cannot set property 'ProductName' of undefined

那么，如何實例化order.OrderItems以便它們接受某些值？

Answer 1

您可以使用this.order.OrderItems.push(item)而不是分配屬性。

this.Identity.getMail().then(user => this.order.OrderId == user.email);
this.order.User = this.user;
this.order.TotalPrice = this.cartTotal;
this.cartItems.forEach((item, index) => {
  this.order.OrderItems.push({ 
    ProductName : item.productName, 
    ProductPrice : item.price,
    ProductQuantity : item.quantity
  });
})