将T类型的泛型属性转换为已知的继承类型 [英] Cast generic property of type T up to a known inheriting type

问题描述

出现以下编译器错误

无法将类型'T'转换为
'ProjectReportingHandler'

为行

  var projectReport = （ProjectReportingHandler）result.Report; 
  

试图编译时：

{
// Report stuff
}

public abstract class ProjectReportingHandler：ReportingHandler
{
//报告内容
//项目特定报告内容
}

公共类ReportInstance< T>
其中T：ReportingHandler
{
public T Report {get;私人设置; }
}

公共类ReportLibraryEntry< T>
其中T：ReportingHandler
{
public ReportInstance< T> Create（）
{
ReportInstance< T> result = new ReportInstance< T>（）;

if（result.Report是ProjectReportingHandler）
{
var projectReport =（ProjectReportingHandler）result.Report;
//执行项目报告
}

返回结果;




$ b $ p
$ b

任何想法如何转换链接泛型类型属性 result.Report 添加到 ProjectReportingHandler ？

认为其中T：ReportingHandler 可以确保这是可能的：（$ / b
$ b

编辑：我似乎得到了一个

  public ReportInstance< T>创建（）报告实例< T>结果=新的ReportInstance< T>（）; 
 
 ReportingHandler report = result.Report; 
 if（report是ProjectReportingHandler） 
 {
 var projectReport =（ProjectReportingHandler）报告; 
 //完成项目报告
} 
 
返回结果; 
} 
  

为什么选择了一个可以解决问题的答案？（

）

解决方案

您可以通过首先投射结果来作弊。报告给一个对象，然后传给一个ProjectReportingHandler。

I'm getting the following compiler error

Cannot convert type 'T' to 'ProjectReportingHandler'

for the line

var projectReport = (ProjectReportingHandler)result.Report;

when trying to compile:

public abstract class ReportingHandler
{
    // Report stuff
}

public abstract class ProjectReportingHandler: ReportingHandler
{
    // Report stuff
    // Project specific report stuff
}

public class ReportInstance<T>
    where T : ReportingHandler
{
    public T Report { get; private set; }
}

public class ReportLibraryEntry<T>
        where T : ReportingHandler
{
    public ReportInstance<T> Create()
    {
        ReportInstance<T> result = new ReportInstance<T>();

        if (result.Report is ProjectReportingHandler)
        {
            var projectReport = (ProjectReportingHandler)result.Report;
            // do stuff with project reports
        }

        return result;
    }
}

Any ideas how to cast the linked generic type property result.Report to a ProjectReportingHandler?

I would have thought the where T : ReportingHandler would have ensured this was possible :(

EDIT: I seem to be getting a few responses that say my accepted answer is incorrect. It works, and I implemented it as follows:

public ReportInstance<T> Create()
{
    ReportInstance<T> result = new ReportInstance<T>();

    ReportingHandler report = result.Report;
    if (report is ProjectReportingHandler)
    {
        var projectReport = (ProjectReportingHandler)report;
        // do stuff with project reports
    }

    return result;
}

Why the down votes for an answer that worked? :(

解决方案

You can "cheat" by first casting result.Report to an object, and then to a ProjectReportingHandler.

这篇关于将T类型的泛型属性转换为已知的继承类型的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！