分配我的ICollection <T> 到ICollection属性

Question

Yes, I know that ICollection and ICollection<T> are two different things. Let me describe what I'm trying though...

This is what I would like to do:

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;
    }
}

Question: Why is report.ReportSections.First().ReportItems null? (See comments in code above.)

Here is how ContribAuthorsReport and ChapterAffiliates are defined:

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; }

}

I will have other classes that inherit from ReportSectionBase, that will have different models for the ICollection. I believe that this issue stems from how I have the base classes defined. (See below)

My base classes.

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; }
} 

UPDATE: Final Result - Here is what I'm using now.

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>; }
    }
}

This allows me to define a report as easy as this:

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

The problem is that your ChapterAffiliates class hides the ReportItems property inherited from ReportSectionBase. See the MSDN documentation on the new modifier . When accessing the instance through the collection, the reference is of type ReportSectionBase. Therefore, the ReportItems property has NOT been set. The only way to access the ReportItems property of the ChapterAffiliates instance is to access it on a reference of type ChapterAffiliates.

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 

To solve this, I would make your ReportSectionBase a generic class. The type argument would specify the type of your ReportItems. This way, you do not need to make the collection virtual, as it will be provided in the base class. Also, it keeps everything type safe. Which is a good thing in my opinion.

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"; } }
}

Also, consider not exposing settable collection properties. It is not recommended in MSDN collection guidelines .

Answer 2

Because you shadow the collection with new the method is not virtual, this means when you are using a ReportSectionBase variable it will not use your new collection.

The easiest way to solve this is change your abstract class to a interface, this allows you to do a explicit implementation of the base class but also expose your generic collection.

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>; }
    }

}