可访问性不一致:返回类型的可访问性低于方法C#

好吧,这真的很糟糕。我有一个私人会员,我想把它用到Form2。我已经创建了一个公共静态方法,这样我就可以将该成员放入Form2。

这是我的代码:

private static AppController appController;
private BreadRepository breadRep;
private CakeRepository cakeRep;
private SandwichRepository sandwichRep;

public Form1()
{
    InitializeComponent();

    breadRep = new BreadRepository();
    cakeRep = new CakeRepository();
    sandwichRep = new SandwichRepository();
    appController = new AppController(breadRep , sandwichRep, cakeRep);
}
public static AppController getController()
{
    return appController;
}

我已经尝试将Form1中的appController公开,但我收到了更多错误。现在我明白了:

可访问性不一致:返回类型“example_map.controller.AppController”的可访问性低于方法“example_map.Form1.getController()” 有什么想法吗?

更新:

这是我的AppController类:

class AppController
{
    private BreadRepository breadRep;
    private SandwichRepository sandwichRep;
    private CakeRepository cakeRep;
    public AppController(BreadRepository breadRep, SandwichRepository sandwichRep, CakeRepository cakeRep)
    {
        this.breadRep = breadRep;
        this.sandwichRep = sandwichRep;
        this.cakeRep = cakeRep;
    }

    public void writeToFile(String file)
    {
        StreamWriter wr = new StreamWriter(file);
        String writeMe = "";
        foreach(Bread e in breadRep.getAll())
        {
            writeMe = writeMe + e.getAll() + "\n";
        }
        foreach (Sandwich e in sandwichRep.getAll())
        {
            writeMe = writeMe + e.getAll() + "\n";
        }
        foreach (Cake e in cakeRep.getAll())
        {
            writeMe = writeMe + e.getAll() + "\n";
        }

        wr.Write(writeMe);
        wr.Close();
    }
}

我已将AppController更改为public,但再次出现更多错误。同样的错误,但对于breadRep、cakeRep和sandwichRep。