如何停止重置属性
如何停止重置属性
提问于 2019-04-23 08:30:55
在我的BaseViewModel上，我有一个名为OrderService的静态类，它有一个orders集合，每个Order都有一个IFoodItems集合。当我调用AddOrder方法并传递顺序时，它会正确地保存它，并且IFoodItems上的属性值也是正确的。当我在不同的ViewModel上调用我的GetOrders方法时，IFoodItems上的Quantity属性被重置为零，我不希望这种情况发生。如何保值？
我已经尝试使列表成为静态列表，在添加之前捕获食品列表，并使用MessageCenter类发送它。
ViewModel：
class TakeOrderViewModel : BaseViewModel
{
#region Properties
private double _orderPrice;
ObservableCollection<IFoodItems> _FoodList;
public ObservableCollection<IFoodItems> FoodList {
get { return _FoodList; }
set {
SetProperty<ObservableCollection<IFoodItems>>(ref _FoodList, value);
}
}
public ICommand SaveOrderCommand { get; private set;}
public double OrderPrice
{
get { return _orderPrice; }
set {
SetProperty<double>(ref _orderPrice, value);
}
}
#endregion
public TakeOrderViewModel()
{
FoodList = menuService.getMenu();
OrderPrice = 0;
SaveOrderCommand = new Command<string>(SaveOrder);
}
public void SaveOrder(string name)
{
Order CustomerOrder = new Order(name);
if(IsOrderEmpty())
{
App.Current.MainPage.DisplayAlert("Error", "The order has no quantity.", "OK");
}
else
{
foreach (IFoodItems item in FoodList)
{
if(item.Quantity > 0)
{
CustomerOrder.AddItem(item);
}
}
CustomerOrder.SetPrice(OrderPrice);
//MessagingCenter.Send<TakeOrderViewModel, Order>(this, "orderSender", CustomerOrder);
OrderService.AddOrder(CustomerOrder);
App.Current.MainPage.DisplayAlert("Message", "Order has been saved", "OK");
//ClearOrder();
}
}
public bool IsOrderEmpty()
{
double temp = 0;
foreach (IFoodItems item in FoodList)
{
temp += item.Quantity;
}
if (temp == 0)
return true;
else
return false;
}
public void ClearOrder()
{
foreach(IFoodItems item in FoodList)
{
item.Quantity = 0;
}
OrderPrice = 0;
}
}OrderService：
public class OrderService
{
ObservableCollection<Order> OrderList;
public OrderService()
{
OrderList = new ObservableCollection<Order>();
}
public void AddOrder(Order value)
{
//one of the ways i tried to preserve the values
ObservableCollection<IFoodItems> foods = value.foodItems;
OrderList.Add(new Order(foods,value));
//OrderList.Add(value);
}
public ObservableCollection<Order> GetOrders()
{
return OrderList;
}Order类：
public class Order
{
public string Name { get; set; }
public ObservableCollection<IFoodItems> foodItems;
public double Price { get; set; }
public string PriceString { get; set; }
public Order(string name)
{
Name = name;
foodItems = new ObservableCollection<IFoodItems>();
}
public Order(ObservableCollection<IFoodItems> order, Order val)
{
this.Name = val.Name;
this.foodItems = order;
this.Price = val.Price;
this.PriceString = val.PriceString;
}
public void SetPrice(double value)
{
Price = value;
PriceString = "Price: " + Price + " tickets";
}
public void AddItem(IFoodItems food)
{
foodItems.Add(food);
}
}IFoodItem：
public interface IFoodItems : INotifyPropertyChanged
{
int Quantity { get; set; }
double Weight_lbs { get; }
double TicketPrice { get; }
string Name{ get; set; }
double GetDollarsMade();
double GetTicketPrice();
double GetAmountUsed();
}BaseViewModel：
public class BaseViewModel : INotifyPropertyChanged
{
protected MenuService menuService;
protected static OrderService OrderService;
public BaseViewModel()
{
menuService = new MenuService();
OrderService = new OrderService();
}
#region INotifyPropertyChanged
protected bool SetProperty<T>(ref T backingStore, T value,
[CallerMemberName]string propertyName = "",
Action onChanged = null)
{
if (EqualityComparer<T>.Default.Equals(backingStore, value))
return false;
backingStore = value;
onChanged?.Invoke();
OnPropertyChanged(propertyName);
return true;
}
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged([CallerMemberName] string propertyName = "")
{
var changed = PropertyChanged;
if (changed == null)
return;
changed.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
#endregion
}回答 1
Stack Overflow用户
回答已采纳
发布于 2019-04-23 12:55:16
每次继承BaseViewModel并实例化一个子代时，都会调用基构造器并创建一个新的OrderService实例。
protected static OrderService OrderService = new OrderService();并将其从构造函数中移除。
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/55802723
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