为了在通用类型或方法"Nullable< T>"中将其用作参数"T"，类型"MyObject"必须是不可为空的值类型. [英] The type 'MyObject' must be a non-nullable value type in order to use it as parameter 'T' in the generic type or method 'Nullable<T>'

问题描述

我正在使用.net framework 4.5

我收到以下错误

错误CS0453类型'MyObject'必须是不可为空的值类型，以便将其用作通用类型或方法'Nullable'中的参数'T'

Error CS0453 The type 'MyObject' must be a non-nullable value type in order to use it as parameter 'T' in the generic type or method 'Nullable'

  public async Task<Nullable<MyObject>> MyMethod(string myParamter)
    {}

我也尝试过

  public async Task<MyObject?> MyMethod(string myParamter)
    {}

如果我将其设置为可为空，那么为什么出现此错误消息的情况下方法名称下方的红线

If I set the thing as nullable then why do I get the red line below the method name with this error message

stackoverflow

The stackoverflow answer is easy, make the return type nullable but for me Visual studio doesn't allow it.

推荐答案

由于MyObject是一个对象，并且对象根据定义可以为空，因此按顺序使用Nullable<T> struct或?运算符是没有用的支持空值.

Since MyObject is an object, and objects are nullable by definition, there is no use to use the Nullable<T> struct or ? operator in order to support null values.

Nullable<T>用于结构(例如DateTime)和值类型(例如int，float等).

Nullable<T> is for structs (like DateTime) and value types like int, float, etc.

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