在MDI界面中，如何让子窗体唯一显示？(100分)

有多个不同的字窗体，不能有多个相同的子窗体同时被显示，如何检测某个子窗体是否
被显示，是否有函数可以调用。
另一问题：如何做像myie底部那样的按钮，就是每个字窗体创建后，底部会出现一个按
钮与之对。我在父窗体底部加了一个toolbar，每出现一个字窗体，便creat一个按钮，
关于按钮与子窗体的对应，各位有没有什么好的想法？

if frmXXX.Showed then ...

MDI窗口的单一显示
procedure TMainFrm.SB5Click(Sender: TObject);
begin
if FormPurStat = nil then
FormPurStat := TFormPurStat.Create(Application)
else
FormPurStat.Show;
end;
MDI窗口关闭时
procedure TFormPurStat.FormClose(Sender: TObject;
var Action: TCloseAction);
begin
FormPurStat := nil;
Action := caFree;
end;
另外，我觉得MYIE应该不是你所说的做法的，应该是用了PAGE控件

myie里的子窗体是单独的
怎么会是用的page？
你说的哪种page,怎么用啊
告诉我啊 大侠

用assigned这个函数，来判断是否已经运行！！

if not assigned(form1) then
begin
form1:=tform1.create(application);
form1.show;
end
else
//可以什么也不做！
showmessage('窗口已经运行！！');

好

//公用的打开子窗口的函数

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.ClassType=FormClass then
begin
Child:=Screen.Forms;
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;
另外用tabpage，如果把自窗体.parent:=tabsheet 可以不？我没有试过，你试一试，
如果可以告诉我啊。

实现MyIE的效果，使用下面的吧。把它存成一个Pas文件，然后创建一个Package，包含这个
文件，安装就行了，只需设置Align。

=================================================================
unit MdiTabs;

interface

uses
Windows, Messages, Classes, Controls, Graphics, Forms,
CommCtrl, ComCtrls, ImgList;

type

{ TMDITabs }

TMDITabOption = (amtCaption, amtIcon);
TMDITabOptions = set of TMDITabOption;

TMDITabs = class(TCustomTabControl)
private
FFormIconImages: TImageList;
FClientInstance: TFarProc;
FClientHandle: HWND;
FDefClientProc: TFarProc;
FOwnerForm: TForm;
FSyncTabs: Boolean;
FDestroyingChild: TForm;
FOptions: TMDITabOptions;
procedure AddFormIcon(AForm: TForm);
procedure MDIChildCreated;
procedure MDIChildDestroyed;
procedure MDIChildActivated;
procedure MDIClientProc(var Message: TMessage);
procedure SubClassMDIClient;
procedure SetOptions(const Value: TMDITabOptions);
protected
function CanChange: Boolean; override;
procedure Change; override;
procedure Loaded; override;
public
constructor Create(AOwner: TComponent); override;
destructor Destroy; override;
property DisplayRect;
procedure RefreshTabs;
published
property Align default alTop;
property Anchors;
property BevelEdges;
property BevelKind;
property BevelInner;
property BevelOuter;
property BiDiMode;
property Constraints;
property Enabled;
property Font;
property HotTrack;
property MultiLine;
property MultiSelect;
property OwnerDraw;
property ParentBiDiMode;
property Options: TMDITabOptions read FOptions write SetOptions
default [amtCaption, amtIcon];
property ParentFont;
property ParentShowHint;
property PopupMenu;
property RaggedRight;
property ScrollOpposite;
property ShowHint;
property Style default tsButtons;
property TabHeight;
property TabOrder;
property TabPosition;
property TabStop;
property TabWidth;
property Visible;
property OnChange;
property OnChanging;
property OnContextPopup;
property OnDrawTab;
property OnEnter;
property OnExit;
property OnMouseDown;
property OnMouseMove;
property OnMouseUp;
property OnResize;
end;

procedure Register;

implementation

const
sErrorOwnerMDIFormExpected = 'FormStyle 必须为 fsMDIForm';

procedure Register;
begin
RegisterComponents('WolfSoft', [TMdiTabs]);
end;

constructor TMDITabs.Create(AOwner: TComponent);
begin
inherited;
if (AOwner is TForm) then
if (TForm(AOwner).FormStyle = fsMDIForm) then
inherited Align := alClient
else
raise EComponentError.Create(sErrorOwnerMDIFormExpected)
else
raise EComponentError.Create(sErrorOwnerMDIFormExpected);
FOwnerForm := TForm(AOwner);
Align := alTop;
FFormIconImages := TImageList.Create(Self);
Images := FFormIconImages;
Style := tsButtons;
Height := 23;
FOptions := [amtCaption, amtIcon];
end;

destructor TMDITabs.Destroy;
begin
Destroying;
SetWindowLong(FClientHandle, GWL_WNDPROC, Longint(FDefClientProc));
FreeObjectInstance(FClientInstance);
Images := nil;
FFormIconImages.Free;
inherited;
end;

procedure TMDITabs.Loaded;
begin
inherited Loaded;
if FClientHandle = 0 then
if not (csDesigning in ComponentState) then
SubClassMDIClient;
end;

procedure TMDITabs.SubClassMDIClient;
begin
FClientHandle := FOwnerForm.ClientHandle;
FClientInstance := MakeObjectInstance(MDIClientProc);
FDefClientProc := Pointer(GetWindowLong(FClientHandle, GWL_WNDPROC));
SetWindowLong(FClientHandle, GWL_WNDPROC, Longint(FClientInstance));
end;

procedure TMDITabs.MDIClientProc(var Message: TMessage);
var
i: integer;
begin
if Message.Msg = WM_MDIDESTROY then
for i := 0 to Tabs.Count - 1 do
if TForm(Tabs.Objects).Handle = THandle(Message.wParam) then
begin
FDestroyingChild := TForm(Tabs.Objects);
Break;
end;
Message.Result := CallWindowProc(FDefClientProc, FClientHandle, Message.Msg, Message.WParam, Message.LParam);
case Message.Msg of
WM_MDICREATE:
MDIChildCreated;
WM_MDIDESTROY:
MDIChildDestroyed;
WM_MDIACTIVATE, WM_SETFOCUS:
MDIChildActivated;
end;
end;

procedure TMDITabs.AddFormIcon(AForm: TForm);
var
tempIcon: TIcon;
begin
if (AForm.Icon <> nil) and not AForm.Icon.Empty then
FFormIconImages.AddIcon(AForm.Icon)
else if (Application.Icon <> nil) and not Application.Icon.Empty then
FFormIconImages.AddIcon(Application.Icon)
else
begin
tempIcon := TIcon.Create;
try
tempIcon.Handle := LoadIcon(MainInstance, 'MAINICON');
if tempIcon.Handle = 0 then
tempIcon.Handle := LoadIcon(0, IDI_APPLICATION);
FFormIconImages.AddIcon(tempIcon);
finally
tempIcon.Free;
end;
end;
end;

procedure TMDITabs.MDIChildCreated;
var
ChildForm: TForm;
begin
FSyncTabs := True;
with FOwnerForm do
if MDIChildCount > Tabs.Count then
begin
ChildForm := MDIChildren[MDIChildCount - 1];
if amtCaption in Options then
Tabs.AddObject(ChildForm.Caption, ChildForm)
else
Tabs.AddObject('', ChildForm);
if amtIcon in Options then
AddFormIcon(ChildForm);
TabIndex := Tabs.Count - 1;
end;
FSyncTabs := False;
end;

procedure TMDITabs.MDIChildDestroyed;
var
i: integer;
begin
FSyncTabs := True;
for i := 0 to Tabs.Count do
if TForm(Tabs.Objects) = FDestroyingChild then
begin
Tabs.Delete(i);
Perform(TCM_REMOVEIMAGE, i, 0);
Break;
end;
FSyncTabs := False;
end;

procedure TMDITabs.MDIChildActivated;
var
i: integer;
begin
FSyncTabs := True;
for i := 0 to Tabs.Count - 1 do
if TForm(Tabs.Objects) = FOwnerForm.ActiveMDIChild then
begin
TabIndex := i;
Break;
end;
FSyncTabs := False;
end;

procedure TMDITabs.Change;
begin
if not FSyncTabs then
begin
if (TabIndex > -1) and (TabIndex < FOwnerForm.MDIChildCount) then
with TForm(Tabs.Objects[TabIndex]) do
begin
if WindowState = wsMinimized then
WindowState := wsNormal;
BringToFront;
SetFocus;
end;
inherited;
end;
end;

function TMDITabs.CanChange: Boolean;
begin
if FSyncTabs then
Result := True
else
Result := inherited CanChange;
end;

procedure TMDITabs.RefreshTabs;
var
i: integer;
begin
FFormIconImages.Clear;
for i := 0 to Tabs.Count - 1 do
begin
if amtCaption in Options then
Tabs := TForm(Tabs.Objects).Caption
else
Tabs := '';
if amtIcon in Options then
AddFormIcon(TForm(Tabs.Objects));
end;
end;

procedure TMDITabs.SetOptions(const Value: TMDITabOptions);
begin
if Value <> FOptions then
begin
FOptions := Value;
if [csDesigning, csLoading] * ComponentState = [] then
RefreshTabs;
end;
end;

end.

多人接受答案了。