DllImport is not found C++ - dllimport

Question

I am having trouble with using the DllImport function!
using namespace System;
using namespace System::Runtime::InteropServices;
[DllImport("user32.dll")]
It will show me no attribute when run. I am using a Windows Form with C++. And I am really noob with WindowsForms.
namespace Projekt3{
using namespace System;
using namespace System::ComponentModel;
using namespace System::Collections;
using namespace System::Collections::Generic;
using namespace System::Windows::Forms;
using namespace System::Data;
using namespace System::Drawing;
using namespace System::Runtime::InteropServices;
using namespace System::Threading::Tasks;
using namespace System::IO;
using namespace std;
public ref class next : public System::Windows::Forms::Form
{
[DllImport("user32.dll")]
public static extern IntPtr FindWindow(String sClassName, String sAppName);
[DllImport("user32.dll")]
private static extern bool RegisterHotKey(IntPtr hWnd, int id, int fsModifiers, int vk);
[DllImport("user32.dll")]
private static extern bool UnregisterHotKey(IntPtr hWnd, int id);
public:
next(void)
{
InitializeComponent();
//
//TODO: Konstruktorcode hier hinzufügen.
//
}
public: enum fsmodifiers
{
NOMOD = 0x0000,
ALT = 0x0001,
CTRL = 0x0002,
SHIFT = 0x0004,
WIN = 0x0008,
};

Answer 1

Your code works perfectly well, in so far as we can see it. For example, this program
using namespace System;
using namespace System::Runtime::InteropServices;
[DllImport("user32.dll")]
extern int MessageBox(System::IntPtr hwnd, System::String^ text, System::String^ caption,
unsigned int uType);
int main(array<System::String ^> ^args)
{
MessageBox((System::IntPtr)0, "foo", "bar", 0);
return 0;
}
produces the expected message box.
It is very much worth pointing out that using p/invoke from C++/CLI seems like a very pointless exercise. You can link to unmanaged code directly. It would be much more natural for this C++/CLI program to be written like so:
#include <Windows.h>
int main(array<System::String ^> ^args)
{
MessageBoxA(0, "foo", "bar", MB_OK);
return 0;
}