如何解决dbgrid的空字段值怎么导到excel中的问题

Question

这段代码当中，如果下面8个字段都不是空的就可以完全导出。
当其中某个字段是空的话就出现错误，请高手指点如何解决从dbgrid中把数据到到excel完整的处理过程。谢谢！！！
下面为本人的写的部分代码：
procedure Tkfb_query.Button8Click(Sender: TObject);
var
  XL,Sheet: Variant;
  FileName: String;
  i,row: integer;begin      if DM.kfb_hetongchaxun.Active =true then
       begin
          if DM.kfb_hetongchaxun.RecordCount >0 then
           begin
           Screen.Cursor:=crSqlWait;
        try
          FileName:=ExtractFilePath(Application.ExeName)+'合同信息.xls';
          XL:=CreateOLEObject('Excel.Application');
          XL.WorkBooks.open(FileName);
          Sheet:=XL.WorkBooks[1].WorkSheets['合同信息'];
          Sheet.Activate;
          except
         MessageDlg('【合同信息】文件不存在或已经被破坏！'+#13+'无法完成导出。',mtWarning,[mbOk],0);
        Screen.Cursor:=crDefault;
        Exit;
        end;
     try
        row:=8;//the  number of row
        for i:=1 to DM.kfb_hetongchaxun.RecordCount  do
         begin
          Sheet.Cells[row,1]:=Trim(DM.kfb_hetongchaxun.FieldValues['编号']);//
          Sheet.Cells[row,2]:=Trim(DM.kfb_hetongchaxun.FieldValues['负责人']);//
          Sheet.Cells[row,3]:=Trim(DM.kfb_hetongchaxun.FieldValues['校内单位']);//
          Sheet.Cells[row,4]:=Trim(DM.kfb_hetongchaxun.FieldValues['合同编号']);//
          Sheet.Cells[row,5]:=DM.kfb_hetongchaxun.FieldValues['项目名称'];//
          Sheet.Cells[row,6]:=DM.kfb_hetongchaxun.FieldValues['项目性质'];//
          Sheet.Cells[row,7]:=DM.kfb_hetongchaxun.FieldValues['合作单位'];//
          Sheet.Cells[row,8]:=DM.kfb_hetongchaxun.FieldValues['合同额'];
          row:=row+1;
          DM.kfb_hetongchaxun.Next;//the  next of master table
         end;
          XL.visible:=true;
         Screen.Cursor:=crDefault;
         except
         MessageDlg('导出Excel错误！',mtError,[mbOk],0);
         Screen.Cursor:=CrDefault;
        end;
    end;
    end;
end;

Answer 1

procedure Tkfb_query.Button8Click(Sender: TObject);
var
  XL,Sheet: Variant;
  FileName: String;
  i,row: integer;begin      if DM.kfb_hetongchaxun.Active =true then
       begin
          if DM.kfb_hetongchaxun.RecordCount >0 then
           begin
           Screen.Cursor:=crSqlWait;
        try
          FileName:=ExtractFilePath(Application.ExeName)+'合同信息.xls';
          XL:=CreateOLEObject('Excel.Application');
          XL.WorkBooks.open(FileName);
          Sheet:=XL.WorkBooks[1].WorkSheets['合同信息'];
          Sheet.Activate;
          except
         MessageDlg('【合同信息】文件不存在或已经被破坏！'+#13+'无法完成导出。',mtWarning,[mbOk],0);
        Screen.Cursor:=crDefault;
        Exit;
        end;
     try
        row:=8;//the  number of row
        for i:=1 to DM.kfb_hetongchaxun.RecordCount  do
         begin
          if varisnull(Trim(DM.kfb_hetongchaxun.FieldValues['编号'])) then
             Sheet.Cells[row,1]:=''
          else
             Sheet.Cells[row,1]:=Trim(DM.kfb_hetongchaxun.FieldValues['编号']);//
          if varisnull(DM.kfb_hetongchaxun.FieldValues['负责人']) then 
             Sheet.Cells[row,2]:=''
          else 
             Sheet.Cells[row,2]:=Trim(DM.kfb_hetongchaxun.FieldValues['负责人']);//
          if varisnull(DM.kfb_hetongchaxun.FieldValues['校内单位']) then
             Sheet.Cells[row,3]:=''
          else
             Sheet.Cells[row,3]:=Trim(DM.kfb_hetongchaxun.FieldValues['校内单位'])//
          if varisnull(DM.kfb_hetongchaxun.FieldValues['合同编号']) then
             Sheet.Cells[row,4]:=''
          else
             Sheet.Cells[row,4]:=Trim(DM.kfb_hetongchaxun.FieldValues['合同编号']);//
          if varisnull(DM.kfb_hetongchaxun.FieldValues['项目名称']) then
             Sheet.Cells[row,5]:=''
          else        
             Sheet.Cells[row,5]:=DM.kfb_hetongchaxun.FieldValues['项目名称'];//
          if varisnull(DM.kfb_hetongchaxun.FieldValues['项目性质']) then   
             Sheet.Cells[row,6]:=''
          else
             Sheet.Cells[row,6]:=DM.kfb_hetongchaxun.FieldValues['项目性质'];//
          if varisnull(DM.kfb_hetongchaxun.FieldValues['合作单位']) then
             Sheet.Cells[row,6]:=''  
          else   
             Sheet.Cells[row,7]:=DM.kfb_hetongchaxun.FieldValues['合作单位'];//
          if varisnull(DM.kfb_hetongchaxun.FieldValues['合同额']) then
             Sheet.Cells[row,8]:=0
          else
             Sheet.Cells[row,8]:=DM.kfb_hetongchaxun.FieldValues['合同额'];
          row:=row+1;
          DM.kfb_hetongchaxun.Next;//the  next of master table
         end;
          XL.visible:=true;
         Screen.Cursor:=crDefault;
         except
         MessageDlg('导出Excel错误！',mtError,[mbOk],0);
         Screen.Cursor:=CrDefault;
        end;
    end;
    end;
end;

Answer 2

当我动态写标题事出现错误！！
求高手再指点！！！！
           //写入标题
              range :=varexcel.workbooks[1].worksheets[1].columns;
              for i:=0 to kfb_query.ListBox2.items.count -1 do
                 begin
              varexcel.workbooks[1].worksheets[1].cell[2,i+1].value := kfb_query.ListBox2.items.strings[i];//              varexcel.workbooks[1].worksheets[1].cell[2,i+1] :=Trim(kfb_query.ListBox2.items[i]);              varexcel.workbooks[1].worksheets[1].cell[2,i+1].Font.bold :=true;
//              range.columns[i+1].columnwidth := DM.kfb_hetongchaxun.FieldByName(Trim(kfb_query.ListBox2.items[i])).Displaywidth;
              range.columns[i+1].columnwidth := DM.kfb_hetongchaxun.FieldByName(kfb_query.ListBox2.items.strings[i]).Displaywidth;
              range.columns[i+1].HorizontalAlignment :=xlCenter;
               end;