调用 C# 代码时,PowerShell $null 不再为 null [英] PowerShell $null is not null any more when calling into C# code
问题描述
在 PowerShell 中可以定义 C# 代码并执行它.将 $null 传入以下最简单的函数表明非 null 被传入函数
In PowerShell one can define C# code and execute it. Passing in $null into the following simplest function shows that not null gets passed into the function
Add-Type -TypeDefinition @"
public static class foo
{
public static void fooo(string a)
{
if(a!=null)
{
System.Console.WriteLine("Not Null. Is '" + a + "'");
}
}
}
"@ -Language CSharp
如下调用会导致输出 Not Null.是 ''.这表明 $null 在 C# 中不为 null.'IsNullOrEmpty' 或 'IsNullOrWhiteSpace' 之类的方法返回 true,因此 PowerShell 必须隐式地将 $null 转换为字符串.
Calling it as follows leads to the output Not Null. Is ''. This shows that $null was not null in C#. Methods like 'IsNullOrEmpty' or 'IsNullOrWhiteSpace' return true, so PowerShell must have implicitly converted the $null into a string.
[foo]::fooo($Null)
任何想法为什么会发生这种情况,除了在 C# 中调用 String.IsNullOrEnpty 之外,是否还有更好的解决方法?注意:这与指定的Add_Type"的 C# 语言无关.我使用的是 PowerShell V5.
Any ideas why this is happening and if there is a better fix apart from rather calling String.IsNullOrEnpty in C#? NB: This happens irrespective of the C# language specified 'Add_Type'. I'm using PowerShell V5.
推荐答案
显然,解决方案是如果您将 $null
传递给 [String]
参数,想要一个 $null
[String]
".应该使用一个特殊的 [NullString]
类.
Evidently the solution is "don't pass $null
to a [String]
parameter if you want a $null
[String]
". There is a special [NullString]
class that should be used instead.
PS > [foo]::fooo($Null)
Not Null. Is ''
PS > [foo]::fooo([NullString]::Value)
PS >
我在 PowerShell 文档中找不到任何提到需要使用 [NullString]
的地方,NullString
类的源代码 包括解释其用途的任何注释.
I can't find any mentions of the need to use [NullString]
in the PowerShell documentation, nor does the source code for the NullString
class include any comments explaining its purpose.
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