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Cmdlet dynamic parameters

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Cmdlets can define parameters that are available to the user under special conditions, such as when the argument of another parameter is a specific value. These parameters are added at runtime and are referred to as dynamic parameters because they're only added when needed. For example, you can design a cmdlet that adds several parameters only when a specific switch parameter is specified.

Note

Providers and PowerShell functions can also define dynamic parameters.

Dynamic parameters in PowerShell cmdlets

PowerShell uses dynamic parameters in several of its provider cmdlets. For example, the Get-Item and Get-ChildItem cmdlets add a CodeSigningCert parameter at runtime when the Path parameter specifies the Certificate provider path. If the Path parameter specifies a path for a different provider, the CodeSigningCert parameter isn't available.

The following examples show how the CodeSigningCert parameter is added at runtime when Get-Item is run.

In this example, the PowerShell runtime has added the parameter and the cmdlet is successful.

Get-Item -Path cert:\CurrentUser -CodeSigningCert

Location   : CurrentUser
StoreNames : {SmartCardRoot, UserDS, AuthRoot, CA...}

In this example, a FileSystem drive is specified and an error is returned. The error message indicates that the CodeSigningCert parameter can't be found.

Get-Item -Path C:\ -CodeSigningCert

Get-Item : A parameter cannot be found that matches parameter name 'codesigningcert'.
At line:1 char:37
+  get-item -path C:\ -codesigningcert <<<<
--------
    CategoryInfo          : InvalidArgument: (:) [Get-Item], ParameterBindingException
    FullyQualifiedErrorId : NamedParameterNotFound,Microsoft.PowerShell.Commands.GetItemCommand

Support for dynamic parameters

To support dynamic parameters, the following elements must be included in the cmdlet code.

Interface

System.Management.Automation.IDynamicParameters. This interface provides the method that retrieves the dynamic parameters.

For example:

public class SendGreetingCommand : Cmdlet, IDynamicParameters

Method

System.Management.Automation.IDynamicParameters.GetDynamicParameters. This method retrieves the object that contains the dynamic parameter definitions.

For example:

 public object GetDynamicParameters()
 {
   if (employee)
   {
     context= new SendGreetingCommandDynamicParameters();
     return context;
   }
   return null;
}
private SendGreetingCommandDynamicParameters context;

Class

A class that defines the dynamic parameters to be added. This class must include a Parameter attribute for each parameter and any optional Alias and Validation attributes that are needed by the cmdlet.

For example:

public class SendGreetingCommandDynamicParameters
{
  [Parameter]
  [ValidateSet ("Marketing", "Sales", "Development")]
  public string Department
  {
    get { return department; }
    set { department = value; }
  }
  private string department;
}

For a complete example of a cmdlet that supports dynamic parameters, see How to Declare Dynamic Parameters.

See also