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为什么当对象类型为IList时,我得到的“foreach语句无法对”object“类型的变量进行操作

list c#

TrashMachine139 · 技术社区 · 3 年前

namespace NS
{
    using System;
    using System.Collections;
    using System.Collections.Generic;
    using System.Linq;
    
    public class Accelerator 
    {
        public string AccName { get; set; }    
    }
    public class DeviceInfo
    {
        public int Ram { get; set; }
        public List<Accelerator> Accelerator { get; set; }
    }
    
    public class SolutionPods
    {
        public DeviceInfo DeviceInfo { get; set; }
    }
    
    public class Solution
    {
        public List<SolutionPods> SolutionPods { get; set; }
    }

    public class HelloWorld
    {
        public static void Main(string[] args)
        {
            var acc1 = new Accelerator { AccName = "accelerator Name" };
            List<Accelerator> accList1 = new List<Accelerator>();
            accList1.Add(acc1);
            
            var devInfo1 = new DeviceInfo { Ram = 64, Accelerator = accList1 };
            
            var solComponet = new SolutionPods { DeviceInfo = devInfo1 };
            List<SolutionPods> SCList = new List<SolutionPods>();
            SCList.Add(solComponet);
            var solution = new Solution { SolutionPods = SCList };
            

            foreach (var solutionComponet in solution.SolutionPods)
            {
                var solutionInformation = solutionComponet.DeviceInfo;
                foreach (var solutionProperty in solutionInformation.GetType().GetProperties())
                {
                    var solutionValue = solutionProperty.GetValue(solutionInformation);
                    if (solutionValue is IList)
                    {
                        Console.WriteLine("IList found");
                        
                        // System.Collections.Generic.List`1[NS.Accelerator]
                        Console.WriteLine(solutionValue);
                        
                        /*
                        /tmp/AFBHdRy49g.cs(64,43): error CS1579: foreach statement cannot operate on variables of type 'object' because 'object' does not contain a public instance definition for 'GetEnumerator'
                        */
                        foreach (var s in solutionValue)
                        {
                            Console.WriteLine(s);
                        }
                    }
                }
            }
            Console.WriteLine("Setup Complete");
        }
    }
}

我不是真的抓到了一张名单吗?或者我需要将对象转换为不同的形式,使其具有GetEnumerator属性吗?

2 回复 | 直到 3 年前

StriplingWarrior 3 年前

在C#中,一旦声明了变量,它就会保持其声明的类型。就你而言 var solutionValue 使用推断的类型 object Property.GetValue() 返回。

当遇到以下条件时,编译器不会实现类型收缩:

if (solutionValue is IList)

if (solutionValue is IList solutions)
{
   ...
   foreach (var s in solutions)

Ondrej Tucny 3 年前

编译器执行类型检查所提供的值是否(静态)为 IEnumerable . 一 object 不是。A. (IList)solutionValue 是的。

if (solutionValue is IList list) // joining a type test and a cast
{
    foreach (var s in list) // here list is an IList
    {
        Console.WriteLine(s);
    }
}