begin
   SaveDialog1.FileName:=ActiveMDIChild.Caption;  //問题所在?
   IF saveDialog1.Execute Then
      Begin
        IF (FileExists(SaveDialog1.FileName)) and
          (ActiveMDIChild.Caption<>SaveDialog1.FileName) Then
          Begin
            IF (MessageDlg('文件'+SaveDialog1.FileName+'已存在,是否覆盖?',
               Mtconfirmation,[Mbyes,Mbno],0)=mryes) then
                 Begin
                   TMDIChildForm(ActiveMDIChild).Memo1.Lines.SaveToFile(SaveDialog1.FileName);
                   TMDIChildForm(ActiveMDIChild).Caption:=SaveDialog1.FileName;
                 End;
             end
             Else
               Begin
                  TMDIChildForm(ActiveMDIChild).Memo1.Lines.SaveToFile(SaveDialog1.FileName);
               End;
             end;
           end;我是個初學者,我不太清楚 TMDIChildForm(ActiveMDIChild) 里面的ACtiveMDICHild是用来做什麽的?我找不到它的聲明。我不知它从哪来的。。