Methods marked with the System.Runtime.InteropServices.DllImportAttribute attribute use Platform Invocation Services to access unmanaged code and should not be exposed. Keeping them private or internal makes sure that their access is controlled and properly managed.

This rule raises an issue when a method declared with DllImport is public or protected.

Noncompliant Code Example

using System;
using System.Runtime.InteropServices;

namespace MyLibrary
{
    public class Foo
    {
        [DllImport("kernel32.dll", CharSet = CharSet.Unicode)]
        public static extern bool RemoveDirectory(string name);  // Noncompliant
    }
}

Compliant Solution

using System;
using System.Runtime.InteropServices;

namespace MyLibrary
{
    public class Foo
    {
        [DllImport("kernel32.dll", CharSet = CharSet.Unicode)]
        private static extern bool RemoveDirectory(string name);
    }
}

Deprecated

This rule is deprecated; use {rule:csharpsquid:S4200} instead.