我有一个 singleton 表单名称 FCD 无法访问已处理的 object 的问题。 Object 名称：'FCD'。

Question

code error here this is an other form who content a button to lunch the FCD form

private void Button1_Click(object sender, EventArgs e)
    {

        f = FCD.getInstance();
        f.Show();
   

    }

and the class FDC is

public partial class FCD : Form
{
    private static FCD instance=null;
    private FCD()
    {
        InitializeComponent();
        load();
    }

    public static FCD getInstance()
    {
        if(instance == null)
        {
            instance = new FCD();
        }
        return instance;
    }

the problem is when i execute the form fcd it work for the first time when i close it i try again and they give me this problem

Answer 1

Check if instance IsDisposed . Try the following:

Change from :

public static FCD getInstance()
{
    if(instance == null)
    {
        instance = new FCD();
    }
    return instance;
}

To :

public static FCD getInstance()
{
    if(instance == null || instance.IsDisposed)
    {
        instance = new FCD();
    }
    return instance;
}

Answer 2

so after a big discussion i found this solution

private void Button1_Click(object sender, EventArgs e)
    {
        if(f!=null)
        if (f.IsDisposed)
        {
            FCD.setInstanceNull();
        }

        f = FCD.getInstance();
        f.Show();
       
   

    }

and i add a methode who set instance = null if form closed

    public static void setInstanceNull()
    {
        instance = null;

    }