C# と VB.NET の質問掲示板

やってみた。

namespace CppFormApp {

  using namespace System;
  ...

  ref class Calc {
  public:
    static void plus(int x, int y);
  };

  /// <summary>
  /// Form1 の概要
  /// </summary>
  public ref class Form1 : public System::Windows::Forms::Form
  {
    ...
    private: System::Windows::Forms::Button^  button1;
    public: System::Windows::Forms::TextBox^  textBox1; // textBox1をpublicにしとく
    ...
    private: System::Void button1_Click(System::Object^  sender, System::EventArgs^  e) {
      Calc::plus(1,2); // 1+2 をけーさんしろ
    }
  };

  void Calc::plus(int x, int y) {
    // Applicationが管理するFormから"Form1"を探しだし、そいつのtextBox1 にコタエを書く。
    ((CppFormApp::Form1^)Application::OpenForms[L"Form1"])->textBox1->Text = (x+y).ToString();
  }
}

別解:

ref class Form1 : ... {
    public: void setText(String^ str) {
      textBox1->Text = str;
    }

    public: static Form1^ target;

    private: System::Void button1_Click(System::Object^  sender, System::EventArgs^  e) {
      target = this;
      Calc::plus(1,2);
    }
};

void Calc::plus(int x, int y) {
  Form1::target->setText((x+y).ToString());
}