如何设置空的iCollection c#

Question

我有三个系列:

private ICollection<FPTAssetClassAsset> wrassets;
private ICollection<FPTFundAsset> wrfunds;
private ICollection<FPTManagedStrategyAsset> wrstrats;

如果foreach循环返回0个对象,则集合不会被设置,因此为null.当我将这个icollection(Union)添加到另一个icollection时,它失败了:"Value不能为null"因为icollection为null,而不是Empty.我怎样才能将此集合设置为空？

环:

    public void GetWrapperAssets(FPT fpt)
    {
        foreach (var w in fpt.CouttsPositionSection.Wrappers
        .Union(fpt.StandAloneSection.Wrappers)
        .Union(fpt.BespokePropositionSection.Wrappers)
        .Union(fpt.NonCouttsPositionSection.Wrappers)
        )
        {
            foreach (var a in w.UnderlyingAssets.OfType<FPTManagedStrategyAsset>())
            {
                wrstrats.Add(a);
            }
            foreach (var a in w.UnderlyingAssets.OfType<FPTAssetClassAsset>())
            {
                wrassets.Add(a);
            }
            foreach (var a in w.UnderlyingAssets.OfType<FPTFundAsset>())
            {
                wrfunds.Add(a);
            }
        }
    }

Answer 1

如果您Array.Empty<T>只是在寻找不会在阅读时崩溃的东西，那么您可以使用它，直到您可以抽出时间用您认真使用的东西替换它：

private ICollection<FPTAssetClassAsset> wrassets      = Array.Empty<FPTAssetClassAsset>();
private ICollection<FPTFundAsset> wrfunds             = Array.Empty<FPTFundAsset>();
private ICollection<FPTManagedStrategyAsset> wrstrats = Array.Empty<FPTManagedStrategyAsset>();

Answer 2

好吧，您始终可以null在添加前进行检查。或者，您可以将其变成属性：

private ICollection<FPTAssetClassAsset> wrassets
{ 
    get { return _wrassets == null ? new List<FPTAssetClassAsset>() : _wrassets; }
}
private ICollection<FPTAssetClassAsset> _wrassets;

Answer 3

在foreach循环之前初始化您的集合，这样它们将始终具有一个值：

private ICollection<FPTAssetClassAsset> wrassets = new Collection<FPTAssetClassAsset>();
private ICollection<FPTFundAsset> wrfunds = new Collection<FPTFundAsset>();
private ICollection<FPTManagedStrategyAsset> wrstrats = new Collection<FPTManagedStrategyAsset>();