How i can open a form and close it by one button [closed]

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It seems you have to implement the following logic:

  1. If there’s an opened Form2 instance, close it
  2. Otherwise create and show the new Form2 instance.

If it’s your case we should look for the opened Form2 instance(s) first; and only then create it with new (if required)

  using System.Linq;

  ... 

  // Search: do we have opened Form2 instances?
  Form2 openform = Application
    .OpenForms        // among all opened forms 
    .OfType<Form2>()  // of type Form2
    .LastOrDefault(); // in case we have several instances, let's choose the last one

  if (null == openform) {   // no Form2 instance has been found
    openform = new Form2(); 

    openform.Show();
  }   
  else {                    // Instance (openform) has been found 
    openform.Close(); // Or openform.Hide();   
  }

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