将我的ICollection<T>分配给ICollection属性

Question

是的，我知道ICollection和ICollection<T>是两种不同的东西。让我描述一下我在尝试什么..。

这就是我想要做的：

public class SubmissionListViewModel
{
    public ICollection<ProjectSubmissionViewModel> Submissions { get; set; }

    public ReportBase GetContribAuthorsReport()
    {
        var report = new ContribAuthorsReport{ ReportType = "CSV" };

        var chapAffil = new ChapterAffiliates {ReportItems = Submissions};

        report.ReportSections.Add(chapAffil);
        // AT this point, I would expect report.ReportSections.First().ReportItems 
        // to have the records from Submissions, but I have `null`.

        return report;
    }
}

问题：为什么report.ReportSections.First().ReportItems为空？(请参见上文代码中的注释。)

下面是如何定义ContribAuthorsReport和ChapterAffiliates：

public class ContribAuthorsReport : ReportBase
{
    public ContribAuthorsReport()
    {
        ReportSections = new List<ReportSectionBase>();
    }

    public override string ReportName { get { return "Contributing Affiliates' Contact Information"; } }
}

public class ChapterAffiliates : ReportSectionBase
{
    public override string ReportSectionName { get { return "Chapter Affiliates"; } }

    // This is what I have now
    new public ICollection<ProjectSubmissionViewModel> ReportItems { get; set; }

    // This won't compile
    //public override ICollection<ProjectSubmissionViewModel> ReportItems { get; set; }

    // This would compile, but breaks GetContribAuthorsReport()
    //public override ICollection ReportItems { get; set; }

}

我将拥有继承自ReportSectionBase的其他类，这些类将具有不同的ICollection模型。我认为这个问题源于如何定义基类。(见下文)

我的基类。

public abstract class ReportBase
{
    virtual public string ReportType { get; set; }

    virtual public string ReportName { get; set; }

    public ICollection<ReportSectionBase> ReportSections { get; set; }

}

public abstract class ReportSectionBase 
{
    virtual public string ReportSectionName { get; set; }

    virtual public ICollection ReportItems { get; set; }
} 

更新：最终结果-以下是我现在使用的内容。

public class ReportBase
{
    public ReportBase()
    {
        ReportSections = new List<IReportSection>();
    }

    public string ReportType { get; set; }

    public string ReportName { get; set; }

    public ICollection<IReportSection> ReportSections { get; set; }

}
public interface IReportSection
{
    string ReportSectionName { get; }

    ICollection ReportItems { get; set; }
}

public class ReportSection<T> : IReportSection
{
    public string ReportSectionName { get; set; }

    public ICollection<T> ReportItems { get; set; }

    ICollection IReportSection.ReportItems
    {
        get { return ReportItems as ICollection; }
        set { ReportItems = value as ICollection<T>; }
    }
}

这样我就可以很容易地定义一个报告：

public ReportBase GetContribAuthorsReport
(
    ICollection<ProjectAffiliateViewModel> projectAffiliates, 
    ICollection<SubmissionAffiliateViewModel> submissionAffiliates
)
{
    var caReport = new ReportBase { ReportType = "CSV", ReportName = "Reviewers' Contact Information" };

    caReport.ReportSections.Add(new ReportSection<ProjectAffiliateViewModel> { ReportItems = projectAffiliates });
    caReport.ReportSections.Add(new ReportSection<SubmissionAffiliateViewModel> { ReportItems = submissionAffiliates });

    return caReport;
}

Answer 1

因为使用new隐藏集合，所以方法不是虚拟的，这意味着当您使用ReportSectionBase变量时，它将不会使用您的新集合。

解决这一问题的最简单方法是将抽象类更改为接口，这允许您对基类进行显式实现，但也可以公开泛型集合。

public abstract class ReportBase
{
    virtual public string ReportType { get; set; }

    virtual public string ReportName { get; set; }

    public ICollection<IReportSection> ReportSections { get; set; }

}

public interface IReportSection
{
    string ReportSectionName { get; }

    ICollection ReportItems { get; set; }
}

public class ContribAuthorsReport : ReportBase
{
    public ContribAuthorsReport()
    {
        ReportSections = new List<IReportSection>();
    }

    public override string ReportName { get { return "Contributing Affiliates' Contact Information"; } }
}

public class ChapterAffiliates : IReportSection
{
    public string ReportSectionName { get { return "Chapter Affiliates"; } }

    public ICollection<ProjectSubmissionViewModel> ReportItems { get; set; }

    ICollection IReportSection.ReportItems {
        get { return ReportItems as ICollection; }
        set { ReportItems = value as ICollection<ProjectSubmissionViewModel>; }
    }

}

Answer 2

问题是ChapterAffiliates类隐藏了从ReportSectionBase继承的ReportItems属性。见修饰符。当通过集合访问实例时，引用的类型为ReportSectionBase。因此，尚未设置ReportItems属性。访问ReportItems实例的ChapterAffiliates属性的唯一方法是对ChapterAffiliates类型的引用进行访问。

ChapterAffiliates a = new ChapterAffiliates { ReportItems = Submissions};
ReportSectionBase b = new ChapterAffiliates { ReportItems = Submissions};

// a.ReportItems == Submissions; returns true
// b.ReportItems == null; returns true
// ((ChapterAffiliates) b).ReportItems == Submissions; returns true 

要解决这个问题，我将使您的ReportSectionBase成为一个泛型类。类型参数将指定ReportItems的类型。这样，您不需要将集合变为虚拟的，因为它将在基类中提供。而且，它保证了所有类型的安全。在我看来这是件好事。

public abstract class ReportBase<TReportSection, TReportItem> where TReportSection : ReportSectionBase<TReportItem>
{
    public virtual string ReportType { get; set; }
    public virtual string ReportName { get; set; }
    public ICollection<TReportSection> ReportSections { get; set; }
}

public abstract class ReportSectionBase<TReportItem>
{
    public virtual string ReportSectionName { get; set; } 
    public ICollection<TReportItem> ReportItems { get; set; }
}

public class ChapterAffiliates : ReportSectionBase<ProjectSubmissionViewModel>
{
    public override string ReportSectionName { get { return "Chapter Affiliates"; } }             
}

public class ContribAuthorsReport : ReportBase<ChapterAffiliates, ProjectSubmissionViewModel>
{
    public ContribAuthorsReport()
    {
        ReportSections = new List<ChapterAffiliates>();
    }

    public override string ReportName { get { return "Contributing Affiliates' Contact Information"; } }
}

此外，考虑不要公开可设置的集合属性。在MSDN收集指南中不建议这样做。