Windows Forms 디자이너 - The class Form1 can be designed, but is not the first class in the file.

다음과 같은 질문이 있군요,

C# Winform 작업을 하다가 처음 보는 오류를 접했습니다
; https://forum.dotnetdev.kr/t/c-winform/1219

클래스 Form1은(는) 디자인 가능하지만 파일의 첫 번째 클래스가 아닙니다. Visual Studio에서 디자이너는 파일의 첫 번째 클래스를 사용해야 합니다. 파일에서 첫 번째 클래스가 되도록 해당 클래스 코드를 이동한 다음 디자이너를 다시 로드하십시오.

The class Form1 can be designed, but is not the first class in the file. Visual Studio requires that designers use the first class in the file. Move the class code so that it is the first class in the file and try loading the designer again.     
 
at System.ComponentModel.Design.Serialization.CodeDomDesignerLoader.EnsureDocument(IDesignerSerializationManager manager)
at System.ComponentModel.Design.Serialization.CodeDomDesignerLoader.PerformLoad(IDesignerSerializationManager manager)
at Microsoft.VisualStudio.Design.Serialization.CodeDom.VSCodeDomDesignerLoader.PerformLoad(IDesignerSerializationManager serializationManager)
--- End of stack trace from previous location where exception was thrown ---
at Microsoft.VisualStudio.Design.Serialization.CodeDom.VSCodeDomDesignerLoader.PerformLoad(IDesignerSerializationManager serializationManager)
at System.ComponentModel.Design.Serialization.BasicDesignerLoader.BeginLoad(IDesignerLoaderHost host)  

using System.Windows.Forms;

namespace WindowsFormsApp1
{
    public class MyType
    {
        public int Age;
    }

    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
    }
}

using System.Windows.Forms;

namespace WindowsFormsApp1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
    }

    public class MyType
    {
        public int Age;
    }
}