WPF：ObservableCollection项目中计算字段的刷新值 [英] WPF: refreshing value of a computed field in an item of an ObservableCollection

问题描述

我有一个与我的WPF ObservableCollection的问题。

我有一个ObservableCollection（_additionalCosts）绑定到一个ListView，其中包含一个只读的计算字段基于其他的值项目中的属性，最重要的是另一个下拉列表的值。

当我更改所选项目的下拉列表时，我想要计算的字段刷新，它是

我的视图类看起来像这样：

  [Serializable] 
 public class BookingView：ViewBase 
 {
 private ObservableCollection< AdditionalCostView> _additionalCosts = new ObservableCollection< AdditionalCostView>（）; 
 
 //..其他成员
 
 public ReferenceDataView SellPriceCurrency 
 {
 get {return _sellPriceCurrency; } 
 set 
 {
 this.OnPropertyChanged（SellPriceCurrency）; 
} 
} 
 
 //..其他成员
} 
  

AdditionalCostView的项目如下所示：

  [Serializable（）] 
 public class AdditionalCostView：ViewBase，IEquatable< AdditionalCostView> 
 {
 //..其他成员
私有十进制数？ _margin; 
 
 public decimal？ Margin 
 {
 get 
 {
 if（_charterSellPriceCurrency == null）
 return null; 
 
 if（_sellPrice.HasValue&& _buyPrice.HasValue）
 {
 return _exchangeRateConverter.ConvertUsingExchangeRate（1，_sellPriceCurrency.Name，_charterSellPriceCurrency.Name，_sellPrice.Value） 
 _exchangeRateConverter.ConvertUsingExchangeRate（1，_buyPriceCurrency.Name，_charterSellPriceCurrency.Name，_buyPrice.Value） 
} 
 
返回null; 
} 
} 
 
 //..其他成员
} 
  

如果您需要更多代码，请让我知道。

如何实现？

解决方案

我想你的ViewBase类实现了INotifyPropertyChanged。
从你的代码我明白，每次 _charterSellPriceCurrency 或 _sellPrice 或 _buyPrice 更改，保证金属性必须重新计算。

此代码仅考虑_ charterSellPriceCurrency 更改，但很容易将其扩展到其他字段。

  private YourType _charterSellPriceCurrency; 
 private Nullable< decimal> _margin; 
 
 public YourType CharterSellPriceCurrency 
 {
 get 
 {
 return _charterSellPriceCurrency; 
} 
 private set 
 {
 if（value！= _charterSellPriceCurrency）
 {
 _charterSellPriceCurrency = value; 
 OnPropertyChanged（CharterSellPriceCurrency）; 
计算金额（）; 
} 
} 
} 
 
 public Nullable< decimal> Margin 
 {
 get 
 {
 return _margin; 
} 
 private set 
 {
 if（value！= _margin）
 {
 _margin = value; 
 OnPropertyChanged（Margin）; 
} 
} 
} 
 
 private void CalculateMargin（）
 {
 if（_charterSellPriceCurrency == null）
 {
 Margin = null; 
 return; 
} 
 
 if（_sellPrice.HasValue&& _buyPrice.HasValue）
 {
 Margin = _exchangeRateConverter.ConvertUsingExchangeRate（1，_sellPriceCurrency.Name，_charterSellPriceCurrency.Name ，_sellPrice.Value） -  
 _exchangeRateConverter.ConvertUsingExchangeRate（1，_buyPriceCurrency.Name，_charterSellPriceCurrency.Name，_buyPrice.Value）; 
 return; 
} 
 
 Margin = null; 
} 
  

重点是您必须通知UI保证金属性已更改，无论是只读属性，如果更改，您必须提出事件。否则，用户界面无法察觉到它已被重新计算。

I have an issue with my WPF ObservableCollection.

I have an ObservableCollection (_additionalCosts) bound to a ListView which includes one readonly computed field based on the value of other properties in the item and, crucially, the value of another dropdown.

When I change the selected item of the dropdown I would like the computed field to refresh, which it is not doing at the moment.

My view class looks like this:

[Serializable]
public class BookingView : ViewBase
{
    private ObservableCollection<AdditionalCostView> _additionalCosts = new ObservableCollection<AdditionalCostView>();

    //..other members

    public ReferenceDataView SellPriceCurrency
    {
        get { return _sellPriceCurrency; }
        set
        {
            this.OnPropertyChanged("SellPriceCurrency");
        }
    }

    //..other members
}

The items of the AdditionalCostView looks like this:

[Serializable()]
public class AdditionalCostView : ViewBase, IEquatable<AdditionalCostView>
{
    //..other members
    private decimal? _margin;

    public decimal? Margin
    {
        get
        {
            if (_charterSellPriceCurrency == null)
                return null;

            if (_sellPrice.HasValue && _buyPrice.HasValue)
            {
                return _exchangeRateConverter.ConvertUsingExchangeRate(1, _sellPriceCurrency.Name, _charterSellPriceCurrency.Name, _sellPrice.Value) -
                       _exchangeRateConverter.ConvertUsingExchangeRate(1, _buyPriceCurrency.Name, _charterSellPriceCurrency.Name, _buyPrice.Value);
            }

            return null;
        }
    }

    //..other members
}

If you need any more code, please let me know.

How do I accomplish this?

解决方案

I suppose that your ViewBase class implements INotifyPropertyChanged. From your code I understand that everytime that _charterSellPriceCurrency or _sellPrice or _buyPrice changes, the Margin property has to be recalculated.

This code consider just the _charterSellPriceCurrency changings, but it is easy to extend it to the other fields.

private YourType _charterSellPriceCurrency;
private Nullable<decimal> _margin;

public YourType CharterSellPriceCurrency 
{
    get
    {
        return _charterSellPriceCurrency;
    }
    private set
    {
        if (value != _charterSellPriceCurrency)
        {
            _charterSellPriceCurrency = value;
            OnPropertyChanged("CharterSellPriceCurrency");
            CalculateMargin();
        }
    }
}

public Nullable<decimal> Margin
{
    get
    {
        return _margin;
    }
    private set
    {
        if (value != _margin)
        {
            _margin = value;
            OnPropertyChanged("Margin");
        }
    }
}

private void CalculateMargin()
{
    if (_charterSellPriceCurrency == null)
    {
        Margin = null;
        return;
    }

    if (_sellPrice.HasValue && _buyPrice.HasValue)
    {
        Margin = _exchangeRateConverter.ConvertUsingExchangeRate(1, _sellPriceCurrency.Name, _charterSellPriceCurrency.Name, _sellPrice.Value) -
                _exchangeRateConverter.ConvertUsingExchangeRate(1, _buyPriceCurrency.Name, _charterSellPriceCurrency.Name, _buyPrice.Value);
        return;
    }

    Margin = null;
}

The point is that you must notify to the UI that the Margin property changed, no matter if it is a read only property, if it changes you have to raise the event. Otherwise the UI can't be aware that it was recalculated.

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