只允許建立一次子視窗的 MDI 程式

bestlong

範例：

1. procedure OpenChildForm(FormClass: TFormClass; var Fm; AOwner:TComponent);
   
2. var
   
3.   I: Integer;
   
4.   Child: TForm;
   
5. begin
   
6.   for I := 0 to Screen.FormCount - 1 do
   
7.     if Screen.Forms[I].ClassType = FormClass then
   
8.     begin
   
9.       Child := Screen.Forms[I];
   
10.       if Child.WindowState = wsMinimized then
    
11.         ShowWindow(Child.Handle, SW_SHOWNORMAL)
    
12.       else
    
13.         ShowWindow(Child.handle,SW_SHOWNA);
    
14.       if (not Child.Visible) then Child.Visible := True;
    
15.         Child.BringToFront;
    
16.         Child.Setfocus;
    
17.         TForm(Fm) := Child;
    
18.         Exit;
    
19.     end;
    
20.   Child := TForm(FormClass.NewInstance);
    
21.   TForm(Fm) := Child;
    
22.   Child.Create(AOwner);
    
23. end;

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