在PowerShell中调用泛型静态方法

Question

如何在Powershell中调用自定义类的通用静态方法？

鉴于以下课程:

public class Sample
{
    public static string MyMethod<T>( string anArgument )
    {
        return string.Format( "Generic type is {0} with argument {1}", typeof(T), anArgument );
    }
}

这被编译成一个程序集'Classes.dll'并加载到PowerShell中,如下所示:

Add-Type -Path "Classes.dll"

调用MyMethod方法最简单的方法是什么？

Answer 1

正如@Athari所说,调用MyMethod的最简单方法是使用MakeGenericMethod.由于他实际上没有说明如何做到这一点,这里有一个经过验证的工作代码示例:

$obj = New-Object Sample

$obj.GetType().GetMethod("MyMethod").MakeGenericMethod([String]).Invoke($obj, "Test Message")
$obj.GetType().GetMethod("MyMethod").MakeGenericMethod([Double]).Invoke($obj, "Test Message")

与输出

Generic type is System.String with argument Test Message
Generic type is System.Double with argument Test Message

Answer 2

您可以调用泛型方法,请参阅PowerShell中的非通用类上的调用通用方法.

这不是直截了当的,你需要使用MakeGenericMethod函数.如果方法没有覆盖,则非常简单,如果方法没有覆盖则会变得更难.

以防万一,从那里复制粘贴的代码:

## Invoke-GenericMethod.ps1 
## Invoke a generic method on a non-generic type: 
## 
## Usage: 
## 
##   ## Load the DLL that contains our class
##   [Reflection.Assembly]::LoadFile("c:\temp\GenericClass.dll")
##
##   ## Invoke a generic method on a non-generic instance
##   $nonGenericClass = New-Object NonGenericClass
##   Invoke-GenericMethod $nonGenericClass GenericMethod String "How are you?"
##
##   ## Including one with multiple arguments
##   Invoke-GenericMethod $nonGenericClass GenericMethod String ("How are you?",5)
##
##   ## Ivoke a generic static method on a type
##   Invoke-GenericMethod ([NonGenericClass]) GenericStaticMethod String "How are you?"
## 

param(
    $instance = $(throw "Please provide an instance on which to invoke the generic method"),
    [string] $methodName = $(throw "Please provide a method name to invoke"),
    [string[]] $typeParameters = $(throw "Please specify the type parameters"),
    [object[]] $methodParameters = $(throw "Please specify the method parameters")
    ) 

## Determine if the types in $set1 match the types in $set2, replacing generic
## parameters in $set1 with the types in $genericTypes
function ParameterTypesMatch([type[]] $set1, [type[]] $set2, [type[]] $genericTypes)
{
    $typeReplacementIndex = 0
    $currentTypeIndex = 0

    ## Exit if the set lengths are different
    if($set1.Count -ne $set2.Count)
    {
        return $false
    }

    ## Go through each of the types in the first set
    foreach($type in $set1)
    {
        ## If it is a generic parameter, then replace it with a type from
        ## the $genericTypes list
        if($type.IsGenericParameter)
        {
            $type = $genericTypes[$typeReplacementIndex]
            $typeReplacementIndex++
        }

        ## Check that the current type (i.e.: the original type, or replacement
        ## generic type) matches the type from $set2
        if($type -ne $set2[$currentTypeIndex])
        {
            return $false
        }
        $currentTypeIndex++
    }

    return $true
}

## Convert the type parameters into actual types
[type[]] $typedParameters = $typeParameters

## Determine the type that we will call the generic method on. Initially, assume
## that it is actually a type itself.
$type = $instance

## If it is not, then it is a real object, and we can call its GetType() method
if($instance -isnot "Type")
{
    $type = $instance.GetType()
}

## Search for the method that:
##    - has the same name
##    - is public
##    - is a generic method
##    - has the same parameter types
foreach($method in $type.GetMethods())
{
    # Write-Host $method.Name
    if(($method.Name -eq $methodName) -and
    ($method.IsPublic) -and
    ($method.IsGenericMethod))
    {
        $parameterTypes = @($method.GetParameters() | % { $_.ParameterType })
        $methodParameterTypes = @($methodParameters | % { $_.GetType() })
        if(ParameterTypesMatch $parameterTypes $methodParameterTypes $typedParameters)
        {
            ## Create a closed representation of it
            $newMethod = $method.MakeGenericMethod($typedParameters)

            ## Invoke the method
            $newMethod.Invoke($instance, $methodParameters)

            return
        }
    }
}

## Return an error if we couldn't find that method
throw "Could not find method $methodName"

Answer 3

这是PowerShell的限制,无法直接在PowerShell V1或V2 AFAIK中完成.

顺便说一句,你的通用方法并不是通用的.不应该是:

public static string MyMethod<T>(T anArgument)
{ 
   return string.Format( "Generic type is {0} with argument {1}", 
                         typeof(T), anArgument.ToString()); 
} 

如果您拥有此代码并希望从PowerShell中使用它,请避免使用泛型方法或编写非泛型C#包装器方法.