找不到类型或命名空间名称“T”（您是不是缺少 using 指令或程序集引用？）

Posted 2023-03-31

【中文标题】找不到类型或命名空间名称“T”（您是不是缺少 using 指令或程序集引用？）

【英文标题】：The type or namespace name 'T' could not be found (are you missing a using directive or an assembly reference?)找不到类型或命名空间名称“T”（您是否缺少 using 指令或程序集引用？）

【发布时间】：2012-05-01 16:39:21

【问题描述】：

我正在尝试来自singleton base class article 的一些代码。但是当我编译时，它给了我那个错误信息。我确保项目的目标框架是完整的 4.0，而不是 4.0 客户端框架。代码有什么问题？

代码如下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Globalization;
using System.Reflection;

namespace ConsoleApplication1

    public abstract class SingletonBase<t> where T : class
    
        /// <summary>
        /// A protected constructor which is accessible only to the sub classes.
        /// </summary>
        protected SingletonBase()  

        /// <summary>
        /// Gets the singleton instance of this class.
        /// </summary>
        public static T Instance
        
            get  return SingletonFactory.Instance; 
        

        /// <summary>
        /// The singleton class factory to create the singleton instance.
        /// </summary>
        class SingletonFactory
        
            // Explicit static constructor to tell C# compiler
            // not to mark type as beforefieldinit
            static SingletonFactory()  

            // Prevent the compiler from generating a default constructor.
            SingletonFactory()  

            internal static readonly T Instance = GetInstance();

            static T GetInstance()
            
                var theType = typeof(T);

                T inst;

                try
                
                    inst = (T)theType
                      .InvokeMember(theType.Name,
                        BindingFlags.CreateInstance | BindingFlags.Instance
                        | BindingFlags.NonPublic,
                        null, null, null,
                        CultureInfo.InvariantCulture);
                
                catch (MissingMethodException ex)
                
                    throw new TypeLoadException(string.Format(
                      CultureInfo.CurrentCulture,
                      "The type '0' must have a private constructor to " +
                      "be used in the Singleton pattern.", theType.FullName)
                      , ex);
                

                return inst;
            
        
    

    public sealed class SequenceGeneratorSingleton : SingletonBase<SequenceGeneratorSingleton>
    
        // Must have a private constructor so no instance can be created externally.
        SequenceGeneratorSingleton()
        
            _number = 0;
        

        private int _number;

        public int GetSequenceNumber()
        
            return _number++;
        
    

    class Program
    
        static void Main(string[] args)
        
            Console.WriteLine("Sequence: " + SequenceGeneratorSingleton.Instance
                .GetSequenceNumber().ToString());  // Print "Sequence: 0"

        
    

【参考方案1】：

是t的情况吗？应该是T。无论如何，它需要在整个班级中保持一致，并且大写是惯例。

【参考方案2】：

public abstract class SingletonBase<t> where T : class

应该是：

public abstract class SingletonBase<T> where T : class

C# 区分大小写，因此编译器将 where T : class 视为引用未知的泛型类型参数，因为您在类型声明中使用了小写的 t，SingletonBase<t>。