Powershell GetType

Question

我想检查一下是否存在某种类型。例如：

Add-Type -TypeDefinition '
public class Test{
    public static int aaa(){
        return 1;
    }
}'

[test]::aaa() # 1

[type]::GetType('test') # empty

但是GetType()不适用于我的“test”类型。

Answer 1

您可以测试类型是否已经存在于

if (-not ('Test' -as [type])) {
# or 
# if (-not ([System.Management.Automation.PSTypeName]'Test').Type) {
    Add-Type -TypeDefinition '
    public class Test{
        public static int aaa(){
            return 1;
        }
    }'
}

我不知道为什么[type]::GetType('test')不起作用，但是

("Test" -as [type])

是否工作并返回$null或

IsPublic IsSerial Name                                     BaseType                                                                                                               
-------- -------- ----                                     --------                                                                                                               
True     False    Test                                     System.Object

Answer 2

补充西奥的有用答案，这无疑显示了最好的解决方案(-as [Type])，与为什么失败

• System.Type.GetType() 只从加载自磁盘或保存到磁盘的程序集中查找类型--也就是说，从先前存在的程序集文件加载的类型或动态创建的程序集中的类型也(可选)持久化到磁盘。
• 相反，当您在[Type]::GetType()中动态定义类型时，它们是在动态、内存中的程序集中创建的，这些程序集是而不是，因此E 229 PowerShell E 133看不到它们E 234。请注意，这同样适用于：

- Types created with [`Add-Type`](https://learn.microsoft.com/powershell/module/microsoft.powershell.utility/add-type) `-TypeDefinition` or `-MemberDefinition`

- Types created with the (PSv5+) `class` and `enum` keywords, i.e. custom PowerShell classes and enumerations.

但是，[Type]::GetType()提供了重载功能，可以将自定义程序集-解析器功能连接到类型查找过程中，即在其他地方查找程序集中的类型。

这大概是PowerShell在幕后使用的(包括)在查找过程中只使用内存中的动态程序集的方法，它在以下上下文中起作用(一般情况下是不敏感的，比如PowerShell )：

• 在最明显的形式中，在类型中，文字类型是 ([<typeName>])，因此您可以将您的Test类型称为[Test]。

- Such type literals therefore also work with `-is`, the [type(-inheritance) / interface test operator](https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_Type_Operators), so you can test a given object for being of or deriving from the given type / implementing the given interface type.

- Caveat: If the type name inside `[...]` isn't recognized as a loaded or dynamically declared type, an _exception_ occurs, which surfaces as a _statement-terminating error_ in PowerShell.

• 在-as**，的上下文中，[条件类型转换操作符**](https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_Type_Operators)，如Theo's refers ('<typeName>' -as [type])中所示，[type]再次引用System.Type。

- This approach tests if the string contains a type name that refers to a loaded type that can therefore be converted to a type-_information_ object.
- If so, such a type-information object is returned (the equivalent of `[Test]`, in your example); if not, `$null` is returned
- In a Boolean context such as an `if` conditional, a type-information object getting returned is implicitly `$true`, where as `$null` is implicitly `$false` - see the bottom section of [this answer](https://stackoverflow.com/a/53108138/45375) for the exact rules of implicit to-Boolean conversion), so the `-as [type]` approach is the most convenient way to test a type's presence.

• 当您将[type]：转换为时，类型名称字符串转换为 [type] 'Test'。

- Unlike the `-as` approach, this approach triggers an _exception_ that surfaces as a _statement-terminating error_ in PowerShell.
- The (more verbose and less efficient) equivalent of `if ('Test' -as [type]) ...` is

if ($(try { [type] 'Test' } catch { $null })) ...

关于名称空间的说明

• 使用class enum 和enum创建的类型具有无命名空间组件E 2106，因此仅以它们自己的名称引用类型就足够了，如D 107。
• 通过Add-Type创建的类型

- via **`-TypeDefinition`** (arbitrary C# code):

    - Whether you need a namespace qualifier depends on whether you enclose the new type's declaration in a `namespace <identifier> { ... }` construct or not.

- via **`-MemberDefinition`** (C# code for declaring static methods, typically for [P/Invoke](https://en.wikipedia.org/wiki/Platform_Invocation_Services) calls):

    - You _do_ need a namespace qualifier to refer to the resulting type, namely either the one you've specified explicitly via the `-Namespace` parameter or the the implicitly used `Microsoft.PowerShell.Commands.AddType.AutoGeneratedTypes.WinApi` namespace.

    - You can bypass having to refer to the type by namespace-qualified name by using the `-PassThru` switch and saving the type-definition object in a variable, which allows you to call its static methods directly via that variable.