public static string setText(string str)

{

    return str;

}

//通过反射打开Dll窗体

private void button1_Click(object sender, EventArgs e)

{

    //dll命名空间名

    string dllName = "DllDemo";

    //dll类名

    string dllClassName = "DllDemo.Form1";

    //载入并创建实例转为Form类型

    Form frm = Assembly.Load(dllName).CreateInstance(dllClassName) as Form;

    frm.ShowDialog();

}

//通过反射调用Dll中的方法

private void button2_Click(object sender, EventArgs e)

{

    //dll文件路径

    string dllName = "DllDemo";

    //dll类名

    string dllClassName = "DllDemo.Form1";

    //加载dll文件

    var assembly = Assembly.Load(dllName);

    //获取类

    Type type = assembly.GetType(dllClassName);

    //创建该类型的实例

    object obj = Activator.CreateInstance(type);

    //获取该类的方法

    string str = type.InvokeMember("setText", BindingFlags.InvokeMethod | BindingFlags.Public | BindingFlags.Static, null, null, new object[] { textBox1.Text }).ToString();

    MessageBox.Show(str);

    //缩写

    string returnStr = Assembly.Load(dllName)

                      .GetType(dllClassName)

                      .InvokeMember(

                                    "setText"

                                    , BindingFlags.InvokeMethod | BindingFlags.Public | BindingFlags.Static

                                    , null

                                    , null

                                    , new object[] { textBox1.Text }  //传入方法参数

                                    )

                      .ToString();

    MessageBox.Show(returnStr);

}