PInvoke CreateDesktop

Question

我正在尝试以传递标志的方式PInvoke CreateDesktop以通过子进程继承桌面。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;
        }

我用它如下：

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).

任何想法我做错了什么？

Answer 1

尝试将参数＃6更改为

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

（这会在运行时编译并不会抛出异常，但我只是使用伪造的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。所以在C＃中你需要通过引用传递你的struct实例（值类型）。

Answer 2

请考虑使用以下原型：

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

然后调用它只是创建一个固定句柄：

        GCHandle handle = GCHandle.Alloc(myStruct);
        try {
            IntPtr pinnedAddress = handle.AddrOfPinnedObject();
        }
        finally {
            handle.Free();
        }

这对于使用结构调用PInvoke'd方法非常有效。