Use managed equivalents of win32 api

Cause

A platform invoke method is defined and a method with the equivalent functionality exists in the .NET Framework class library.

Rule Description

A platform invoke method is used to call an unmanaged DLL function and is defined using the System.Runtime.InteropServices.DllImportAttribute attribute, or the Declare keyword in Visual Basic. An incorrectly defined platform invoke method can lead to runtime exceptions because of issues such as a misnamed function, faulty mapping of parameter and return value data types, and incorrect field specifications, such as the calling convention and character set. If available, it is generally simpler and less error prone to call the equivalent managed method than to define and call the unmanaged method directly. Calling a platform invoke method can also lead to additional security issues that need to be addressed.

How to Fix Violations

To fix a violation of this rule, replace the call to the unmanaged function with a call to its managed equivalent.

When to Exclude Warnings

Exclude a warning from this rule if the suggested replacement method does not provide the needed functionality.

Example

The following example shows a platform invoke method definition that violates the rule. In addition, the calls to the platform invoke method and the equivalent managed method are shown.

Imports System
Imports System.Runtime.InteropServices
Imports System.Text

Namespace UsageLibrary

   Class NativeMethods

      Private Sub New()
      End Sub

      ' The following method definitions violate the rule.

      <DllImport("kernel32.dll", CharSet := CharSet.Auto, _ 
         SetLastError := True)> _ 
      Friend Shared Function ExpandEnvironmentStrings _ 
         (lpSrc As String, lpDst As StringBuilder, nSize As Integer) _ 
         As Integer
      End Function

      Friend Declare Auto Function ExpandEnvironmentStrings2 _ 
         Lib "kernel32.dll" Alias "ExpandEnvironmentStrings" _ 
         (lpSrc As String, lpDst As StringBuilder, nSize As Integer) _ 
         As Integer

   End Class

   Public Class UseNativeMethod

      Shared Sub Main()
      
         Dim environmentVariable As String = "%TEMP%"
         Dim expandedVariable As New StringBuilder(100)

         ' Call the unmanaged method.
         NativeMethods.ExpandEnvironmentStrings( _ 
            environmentVariable, _ 
            expandedVariable, _ 
            expandedVariable.Capacity)

         ' Call the unmanaged method.
         NativeMethods.ExpandEnvironmentStrings2( _ 
            environmentVariable, _ 
            expandedVariable, _ 
            expandedVariable.Capacity)

         ' Call the equivalent managed method.
         Environment.ExpandEnvironmentVariables(environmentVariable)

      End Sub

   End Class

End Namespace

using System;
using System.Runtime.InteropServices;
using System.Text;

namespace UsageLibrary
{
   internal class NativeMethods
   {
      private NativeMethods() {}

      // The following method definition violates the rule.
      [DllImport("kernel32.dll", CharSet = CharSet.Auto, 
          SetLastError = true)]
      internal static extern int ExpandEnvironmentStrings(
         string lpSrc, StringBuilder lpDst, int nSize);
   }

   public class UseNativeMethod
   {
      public void Test()
      {
         string environmentVariable = "%TEMP%";
         StringBuilder expandedVariable = new StringBuilder(100);

         // Call the unmanaged method.
         NativeMethods.ExpandEnvironmentStrings(
            environmentVariable, 
            expandedVariable, 
            expandedVariable.Capacity);

         // Call the equivalent managed method.
         Environment.ExpandEnvironmentVariables(environmentVariable);
      }
   }
}

Related Rules

Call GetLastError immediately after pinvoke

Move pinvokes to native methods class

PInvoke entry points should exist

PInvokes should not be visible

Specify marshaling for pinvoke string arguments