什么是[参数：NOTNULL]在C＃是什么意思？ [英] What does [param: NotNull] mean in C#?

问题描述

在实体框架的源$ C ​​$ C（<一个href=\"https://github.com/aspnet/EntityFramework/blob/dev/src/EntityFramework.Relational/Storage/RelationalConnection.cs#L74\">link)我发现这行：

In Entity Framework's source code (link) I found this line:

public virtual IRelationalTransaction Transaction 
{ get; [param: NotNull] protected set; }

的 [参数：NOTNULL] 部分看起来很奇怪，我。任何想法什么样的一个C＃语法的东西？我熟悉的属性和参数而不是这个组合。

The [param: NotNull] part looks very strange to me. Any idea what kind of a C# syntax is this? I'm familiar with attributes and param but not this combination.

NOTNULL的定义是这样的：

The definition of NotNull is this:

[AttributeUsage(
    AttributeTargets.Method | AttributeTargets.Parameter |
    AttributeTargets.Property | AttributeTargets.Delegate |
    AttributeTargets.Field)]
internal sealed class NotNullAttribute : Attribute
{
}

这我想像的要简单地用作 [NOTNULL] 但什么是参数在这里做什么？

Which I expected to be used simply as [NotNull] but what is param doing here?

推荐答案

当你标记与 NOTNULL 方法就意味着，该方法返回没有空对象：

When you mark method with NotNull it means, that method returns not null object:

[NotNull]
public object Get()
{
    return null; //error
}

当你标记二传手它同样 - 二传手返回NOT NULL（因为.NET转换属性get和set方法）

When you mark setter it does the same - setter returns not null (because .net converts properties to get and set methods).

public virtual IRelationalTransaction Transaction { get; [NotNull] protected set; }

等于：

[NotNull] 
public virtual void set_Transaction(IRelationalTransaction value) { ... }

所以，你需要添加参数：来一点，说：我的意思是 - 二传的参数不为null，集法不结果：

So, you need to add param: to point, that "i mean - parameter of setter is not null, not a result of set-method":

public virtual IRelationalTransaction Transaction { get; [param: NotNull] protected set; }

等于：

public virtual void set_Transaction([NotNull] IRelationalTransaction value) { ... }

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