Difference between revisions of "Testing, if form exists"

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{{Warning|This method has some limitations:
 
{{Warning|This method has some limitations:
 
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*At any time should not exist more than one instance of that form class.
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*'''Not''' ''more than one instance'' of that form class should exist at any time.
*Reference to any created form of that class should be stored at single global variable.
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*Reference to any created form of that class should be stored in ''a single global'' variable.
 
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Revision as of 15:51, 31 October 2017

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Sometimes a form may be launched from several places in a program. If it already exists, it only needs to be brought to the front. If not, it needs to be created.

This method is only needed if the form is not auto created (it should be listed under Project|Project Options|Forms|Available forms).

The easiest way is:

if (MyForm = nil) then Application.CreateForm(TMyForm, MyForm);
MyForm.Show;

Use CloseAction := caFree in the form's OnClose event.

procedure TMyForm.Formclose(Sender: Tobject; var Closeaction: Tcloseaction);
begin
  CloseAction := caFree;
  MyForm := nil;
End;

This method is taken from forum discussions.

Warning-icon.png

Warning: This method has some limitations:

  • Not more than one instance of that form class should exist at any time.
  • Reference to any created form of that class should be stored in a single global variable.