已经可见的窗体不能显示为模式对话框

Question

In my program I open every form with the help of ShowDialog and close previous one with the help of:

this.Hide();
...some code...
this.Close();

But when I want to open Form for a second time, I get the error that is in the title. What can it be? Maybe it's because I use Singleton patter for that form that I want to open for a second time.

Answer 1

Instead of continually showing forms using ShowDialog you can just create new instances of each form as you need them. For example

using(Form frm = new Form1)
{
   DialogResult dr = frm.ShowDialog(this)
   if(dr == DialogResult.Cancel)
   {
     ...
   }
}

or

Form frm = new Form1();
DialogResult dr = frm.ShowDialog(this);
if(dr == DialogResult.Cancel)
{
  ...
}
frm.Dispose();

See this answer