请教一个MDI窗口的问题？

Question

我在菜单中写的打开子窗口事件：
form1:=tform1.create(self);
form1.show;
每次点菜单都会新建一个子窗口，能否只建一个子窗口就行了。

Answer 1

if not Assigned(form1) then
  form1 := tform1.create(self);
form1.show;或者
if form1 = nil then
  form1 := tform1.create(self);
form1.show;

Answer 2

给你一个通用函数：procedure OpenForm(FormClass: TFormClass; var fm; AOwner:TComponent);
var
  i: integer;
  Child:TForm;
begin
  for i := 0 to Screen.FormCount -1 do
      if Screen.Forms[i].ClassType=FormClass then
      begin
        Child:=Screen.Forms[i];
        if Child.WindowState=wsMinimized then
           ShowWindow(Child.handle,SW_SHOWNORMAL)
        else
           ShowWindow(Child.handle,SW_SHOWNA);
        if (not Child.Visible) then Child.Visible:=True;
        Child.BringToFront;
        Child.Setfocus;
        TForm(fm):=Child;
        exit;
      end;
  Child:=TForm(FormClass.NewInstance);
  TForm(fm):=Child;
  Child.Create(AOwner);
end;这样你每次调用即可：如：  OpenForm(TfrmChild1,frmChild1, self);别忘了在close的时候：  Action:=caFree;

Answer 3

使用下面的函数就行了
procedure OpenForm(FormClass: TFormClass; var fm; AOwner:TComponent);
var
  i: integer;
  Child:TForm;
begin
  for i := 0 to Screen.FormCount -1 do
      if Screen.Forms[i].ClassType=FormClass then
      begin
        Child:=Screen.Forms[i];
        if Child.WindowState=wsMinimized then
           ShowWindow(Child.handle,SW_SHOWNORMAL)
        else
           ShowWindow(Child.handle,SW_SHOWNA);
        if (not Child.Visible) then Child.Visible:=True;
        Child.BringToFront;
        Child.Setfocus;
        TForm(fm):=Child;
        exit;
      end;
  Child:=TForm(FormClass.NewInstance);
  TForm(fm):=Child;
  Child.Create(AOwner);
end;

Answer 4

if not Assigned(form1) then
  form1 := tform1.create(Application);
form1.show;