MDI子窗体问题

子窗体名称.hide
或者子窗体名称.visual:=false;

你试过没有
MDI子窗体是不允许使用这种方法的

子窗体名称.hide
或者子窗体名称.visual:=false;

ShowWindow(Form1.MDIChildren[要隐藏的子窗体].Handle, SW_Hide);

要显示：
SetWindowPos(Form1.MDIChildren[要隐藏的子窗体].Handle, HWND_TOP, 0, 0, 0, 0, SWP_NOSIZE or SWP_NOMOVE or SWP_SHOWWINDOW);

The ShowWindow function sets the specified window's show state. BOOL ShowWindow(    HWND hWnd, // handle of window
    int nCmdShow // show state of window
   );
ParametershWndIdentifies the window. nCmdShowSpecifies how the window is to be shown. This parameter is ignored the first time an application calls ShowWindow, if the program that launched the application provides a STARTUPINFO structure. Otherwise, the first time ShowWindow is called, the value should be the value obtained by the WinMain function in its nCmdShow parameter. In subsequent calls, this parameter can be one of the following values: Value Meaning
SW_HIDE Hides the window and activates another window.
SW_MAXIMIZE Maximizes the specified window.
SW_MINIMIZE Minimizes the specified window and activates the next top-level window in the Z order.
SW_RESTORE Activates and displays the window. If the window is minimized or maximized, Windows restores it to its original size and position. An application should specify this flag when restoring a minimized window.
SW_SHOW Activates the window and displays it in its current size and position.
SW_SHOWDEFAULT Sets the show state based on the SW_ flag specified in the STARTUPINFO structure passed to the CreateProcess function by the program that started the application.
SW_SHOWMAXIMIZED Activates the window and displays it as a maximized window.
SW_SHOWMINIMIZED Activates the window and displays it as a minimized window.
SW_SHOWMINNOACTIVE Displays the window as a minimized window. The active window remains active.
SW_SHOWNA Displays the window in its current state. The active window remains active.
SW_SHOWNOACTIVATE Displays a window in its most recent size and position. The active window remains active.
SW_SHOWNORMAL Activates and displays a window. If the window is minimized or maximized, Windows restores it to its original size and position. An application should specify this flag when displaying the window for the first time.
Return ValuesIf the window was previously visible, the return value is nonzero.
If the window was previously hidden, the return value is zero. ResThe first time a program calls ShowWindow, it uses the WinMain function's nCmdShow parameter as its nCmdShow parameter. Subsequent calls to ShowWindow must use one of the values in the given list, instead of the one specified by the WinMain function's nCmdShow parameter.
As noted in the discussion of the nCmdShow parameter, the nCmdShow value is ignored in the first call to ShowWindow if the program that launched the application specifies startup information in the STARTUPINFO structure. In this case, ShowWindow uses the information specified in the STARTUPINFO structure to show the window. On subsequent calls, the application must call ShowWindow with nCmdShow set to SW_SHOWDEFAULT to use the startup information provided by the program that launched the application. For example, Program Manager specifies that applications start with a minimized main window. This behavior is designed for the following situations: ?Applications create their main window by calling CreateWindow with the WS_VISIBLE flag set.
?Applications create their main window by calling CreateWindow with the WS_VISIBLE flag cleared, and later call ShowWindow with the SW_SHOW flag set to make it visible.  See AlsoCreateProcess, CreateWindow, ShowOwnedPopups, STARTUPINFO, WinMain

在子窗体的close事件里Action:=caFree;
子窗体:=NIL;

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在子窗体的close事件里Action:=caFree;
Show时动态创建

窗体已经创建好了才能SHOW的吧MDI窗体包含很很多子窗体
在你关闭一个子窗体的时候，他要消失或释放，这个看你怎么处理
但是当用户再点击按纽要显示这个窗体时候
如果子窗体被释放要重新创建并显示
如果子窗体未被释放要显示在最前面现在我要做一个子窗体类
让其他的子窗体都从我这个类继承出去
而不是TFORM

问题已经解决
谢谢各位关注特将代码上传，供大家观看unit fChildForm;interface
uses Forms,fMenuAboutForm,Menus,fIAddDeleteMenu,fIIUD,Dialogs,messages,fINextPrev;type
TChildForm = class(TForm,IIUD)
private
  state:integer;
  lastLeft:integer;
  lastTop:integer;
  lastWidth:integer;
  lastHeight:integer;
public
  friendMenuItem : TMenuItem;
  parent : IAddDeleteMenu;
  constructor create(var theParent :IAddDeleteMenu);
  destructor destroy();  procedure notify(Sender: TObject);virtual;
  procedure closeOperation(Sender: TObject; var Action: TCloseAction);virtual;
  procedure addVO(); virtual;
  procedure updateVO(); virtual;
  procedure deleteVO(); virtual;  procedure moveNext(); virtual;
  procedure movePrev(); virtual;  procedure WndProc(var message:Tmessage);override;end;
implementationprocedure TChildForm.WndProc(var message:TMessage);
begin   if (message.Msg = WM_SYSCOMMAND) and ((message.WParam = 61488) or (message.WParam = 61490)) then
       begin
          if state = 0 then //原壮
             begin
                //存储原尺寸
                lastLeft := self.Left;
                lastTop := self.Top;
                lastWidth := self.Width;
                lastHeight := self.Height;
                //设置最大尺寸
                self.Width := parent.getWorkWidth ;
                self.Height := parent.getWorkHeight ;
                self.Left := 0;
                self.Top := 0;
                state := 1;//状态为最大化
             end
          else
             begin
                self.Left := lastLeft;
                self.Top := lastTop;
                self.Width := lastWidth;
                self.Height := lastHeight;
                state := 0;//状态为原态
             end;
       end
   else
      inherited WndProc(message);
end;

在closeing事件中写
action：=free
子窗体：=nil

发错了，不好意思
这个问题我用单例模式已经解决了
unit fSubject;interfaceuses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, DB, ADODB, ExtCtrls,  dxtrprds, Grids, DBGridEh ,
  Menus, dxmdaset, StdCtrls,fChildForm,fIAddDeleteMenu,fSubjectVO, RzPanel,
  fDataModule, DBActns, ActnList;type
  TSubjectSetForm = class(TChildForm)
    ctlDBGridEh: TDBGridEh;
    DataSource: TDataSource;
    Label1: TLabel;
    RzPanel1: TRzPanel;
    ADOQuery: TADOQuery;
    procedure FormCreate(Sender: TObject);
    class function getInstance(var theParent :IAddDeleteMenu):TSubjectSetForm;
  private
  constructor create(var theParent :IAddDeleteMenu);
    { Private declarations }
  public
     procedure closeOperation(Sender: TObject; var Action: TCloseAction);override;
     destructor destroy();     procedure addVO(); override;
     procedure updateVO(); override;
     procedure deleteVO(); override;     procedure moveNext(); override;
     procedure movePrev(); override;
    { Public declarations }
  end;

var subjectSetForm : TSubjectSetForm;
implementation
uses fAddUpdateSubjectForm,fSubjectDAO;{$R *.dfm}procedure TSubjectSetForm.moveNext();
begin
   if self.ADOQuery.RecordCount >0 then
   begin
      ADOQuery.Next ;
      if ADOQuery.Eof then
         ADOQuery.First;
   end;
end;procedure TSubjectSetForm.movePrev();
begin
   if self.ADOQuery.RecordCount >0 then
   begin
      ADOQuery.Prior  ;
      if ADOQuery.Bof then
         ADOQuery.Last ;   end;
end;class function TSubjectSetForm.getInstance(var theParent :IAddDeleteMenu):TSubjectSetForm;
begin
   if subjectSetForm = nil then
         subjectSetForm := create(theParent);
   Result := subjectSetForm;end;procedure TSubjectSetForm.closeOperation(Sender: TObject; var Action: TCloseAction);
begin
   subjectSetForm := nil;
   inherited;
end;constructor TSubjectSetForm.create(var theParent : IAddDeleteMenu);
begin
   inherited create(theParent);
   subjectSetForm := self;
   ADOQuery.Connection := ZDataModule.sqlConnection;
   ADOQuery.SQL.Text  := 'select subject_id ,memo  from subject';
   ADOQuery.Active := true;
end;destructor TSubjectSetForm.destroy();
begin
    inherited;
end;
procedure TSubjectSetForm.addVO();
var  subjectSetForm:TAddUpdateSubject;
begin
     subjectSetForm := TAddUpdateSubject.create();
     subjectSetForm.ShowModal;
     ADOQuery.Close;
     ADOQuery.Open;
end;procedure TSubjectSetForm.updateVO();
var subjectVO:TSubjectVO;
var subjectEditForm:TAddUpdateSubject;
begin   if self.ADOQuery.RecordCount  >0 then
   begin
       subjectVO := TSubjectVO.Create();
       subjectVO.setSubjectID(ctlDBGridEh.Fields[0].AsInteger  );
       subjectVO.setMemo(ctlDBGridEh.Fields[1].AsString);
       subjectEditForm := TAddUpdateSubject.create(subjectVO);
       subjectEditForm.ShowModal;
       ADOQuery.Close;
       ADOQuery.Open;
       subjectVO.Free;
   end;end;procedure TSubjectSetForm.deleteVO();
var subject_id :Integer;
begin
   if self.ADOQuery.RecordCount  >0 then
   begin
       if application.MessageBox('确定删除指定的科目吗？','删除确认',MB_OKCANCEL) = IDCANCEL THEN
          exit;
       subject_id := ctlDBGridEh.Fields[0].AsInteger;
       ZDataModule.SubjectDAO.deleteSubjectVO(subject_id);
       ADOQuery.Close;
       ADOQuery.Open;
   end;
end;procedure TSubjectSetForm.FormCreate(Sender: TObject);
begin
    ADOQuery.Active := true;
end;end.

调试易

MDI子窗体问题

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