c# - PInvoke 创建桌面

Question

我正在尝试以传递标志的方式 PInvoke CreateDesktop 以由子进程继承桌面。声明如下:

[DllImport("user32", EntryPoint = "CreateDesktopW", CharSet = CharSet.Unicode, SetLastError = true)]
        public static extern IntPtr CreateDesktop(string lpszDesktop, IntPtr lpszDevice, IntPtr pDevmode, int dwFlags,
                                                  int dwDesiredAccess, [MarshalAs(UnmanagedType.LPStruct)] SECURITY_ATTRIBUTES lpsa);

        [StructLayout(LayoutKind.Sequential)]
        public struct SECURITY_ATTRIBUTES
        {
            public int nLength;
            public IntPtr lpSecurityDescriptor;
            public int bInheritHandle;
        }

我按如下方式使用它:

Win32.SECURITY_ATTRIBUTES sa = new Win32.SECURITY_ATTRIBUTES();
            sa.nLength = Marshal.SizeOf(sa);
            sa.bInheritHandle = 1;
            testDesktopHandle = Win32.CreateDesktop(name, IntPtr.Zero, IntPtr.Zero, 0, Win32.GENERIC_ALL, sa);

不幸的是，它不起作用，我收到以下错误:

System.Runtime.InteropServices.MarshalDirectiveException: Cannot marshal 'parameter #6': Invalid managed/unmanaged type combination (this value type must be paired with Struct).

知道我做错了什么吗？

Answer 1

尝试将参数 #6 更改为

static extern IntPtr CreateDesktop(..., [In] ref SECURITY_ATTRIBUTES lpsa);

(这会编译并且不会在运行时抛出异常，但我仅使用伪造参数对其进行了测试。)

与CreateDesktop的C++声明比较:

HDESK WINAPI CreateDesktop(..., __in_opt LPSECURITY_ATTRIBUTES lpsa);
                                  ↑      ↑ ↑
                                  [In] ref SECURITY_ATTRIBUTES lpsa

LP 代表“长指针”，即 LPSECURITY_ATTRIBUTES 是指向 SECURITY_ATTRIBUTES 结构的指针。因此，在 C# 中，您需要通过引用传递您的结构实例(值类型)。