当ERP的财务模块与生产，供应链模块集成时，这些模块过帐时会产生会计凭证。如果能在产生会计凭证前可预览一下凭证，那对用户而言是一个很友好的设计。如下图所示，贷项通知单过帐前，可通过预览凭证，知晓即将产生的会计凭证。

点击预览凭证按钮，可看到即将产生的会计凭证：

为达到此目的，分享一下对系统的修改。

首先是业务单据重写按钮事件，

protected override void OnPreviewVoucher(Dictionary<string, VoucherEntity> voucherList)
{
     base.OnPreviewVoucher(voucherList);
     if (_expenseRemibursementEntity.Amount > 0)
     {
         VoucherEntity voucher = _expenseRemibursementManager.CreateExpenseRemibursementVoucherForPreview( _expenseRemibursementEntity);
         if (voucher != null)
             voucherList.Add(VOUCHER_KEY, voucher);
     }
}

通过重写这个方法，基类可获取当前业务单据产生的会计凭证。产生会计凭证的方法原型如下：

public VoucherEntity CreateExpenseRemibursementVoucherForPreview(ExpenseRemibursementEntity ExpenseRemibursement)
{
     VoucherEntity voucher = null;
     using (DataAccessAdapter adapter = GetCompanyDataAccessAdapter(sessionId))
     {
          try
          {
              adapter.StartTransaction(IsolationLevel.ReadCommitted, "CreateExpenseRemibursementVoucherForPreview");
              ExpenseRemibursementEntity clonedAdjustment = (ExpenseRemibursementEntity)Shared.CloneEntity(ExpenseRemibursement);
              IFiscalPeriodManager fiscalPeriodManager = ClientProxyFactory.CreateProxyInstance<IFiscalPeriodManager>();
              ExcludeIncludeFieldsList fieldsList = new ExcludeIncludeFieldsList(false);
              fieldsList.Add(FiscalPeriodFields.Period);
              fieldsList.Add(FiscalPeriodFields.FiscalYear);
              fieldsList.Add(FiscalPeriodFields.PeriodNo);
              FiscalPeriodEntity fiscalPeriod = fiscalPeriodManager.GetValidFiscalPeriod(sessionId, clonedAdjustment.AppliedDate, fieldsList, true);
             
              clonedAdjustment.Period = fiscalPeriod.Period;
              clonedAdjustment.FiscalYear = fiscalPeriod.FiscalYear;
              clonedAdjustment.PeriodNo = fiscalPeriod.PeriodNo;
              voucher=GenerateVoucher(sessionId, clonedAdjustment);
            }
            finally
            {
                adapter.Rollback();
            }
      }
      return voucher;
}

这里有一个细节是并没有对当前的业务实体(business object)直接操作，而是对它的一个深拷贝进行操作。这样对这个拷贝的对象进行的操作都不会影响到原来的业务实体。

其次，需要增加一个MDI界面，主界面用于承载会计凭证界面，子窗体为会计凭证界面。为达到这个目的，我们将会计凭证界面作为子窗体载入到一个新创建的MDI主窗体界面中：

standardFunctionForm = null;
Form form = ComponentCommon.MainForm.GetStandardFunctionForm(primaryKeys[0]);
if (form != null)
  standardFunctionForm = form as FunctionFormBase;
standardFunctionForm.Owner = this;
standardFunctionForm.TopLevel = false;
standardFunctionForm.AutoScroll = true;
standardFunctionForm.HideBindingNavigator = true;
standardFunctionForm.HideStatusStrip = true;
standardFunctionForm.AllowAdd = false;
standardFunctionForm.AllowDelete = false;
standardFunctionForm.AllowEdit = false;
standardFunctionForm.AllowPost = false;
standardFunctionForm.SupportAdd = false;
standardFunctionForm.SupportDelete = false;
standardFunctionForm.SupportEdit = false;
standardFunctionForm.SupportApproval = false;
standardFunctionForm.SupportPost = false;
standardFunctionForm.SupportImport = false;
standardFunctionForm.SupportExport = false;
standardFunctionForm.Show();
standardFunctionForm.SaveLayoutOnClose = SaveLayouts.Never;
Dictionary<string, string> refNo = new Dictionary<string, string>();
refNo.Add(primaryKeys[1], RefNo);
standardFunctionForm.FindAndLoadData(refNo);

这里面可以看到，为什么要用一个MDI主界面来载入会计凭证窗体，是为了在不破坏原有功能的情况下，可定制它的部分功能。比如这个预览凭证窗体，不需要保存数据或过帐等操作，于是看到上面的代码中，我们将SupportEdit=false表示不需要编辑功能。

最后三句是MDI子窗体载入数据，通过传入键值对来完成数据的加载。FindAndLoadData方法会调用内部LoadData：

protected override EntityBase2 LoadData(Dictionary<string, string> refNo)
{
    base.LoadData(refNo);
    string RefNo = string.Empty;
    if (refNo.TryGetValue("RefNo", out RefNo))
    {
         IPrefetchPath2 prefetchPath = new PrefetchPath2((int)EntityType.ExpenseRemibursementEntity);
         prefetchPath.Add(ExpenseRemibursementEntity.PrefetchPathExpenseRemibursementDetail);
         _expenseRemibursementEntity = _expenseRemibursementManager.GetExpenseRemibursement(Shared.CurrentUserSessionId, RefNo, prefetchPath);
    }
    else
    {
        _expenseRemibursementEntity = new ExpenseRemibursementEntity();
    }
    return _expenseRemibursementEntity;
}
这样我们就完成了财务模块的凭证预览功能。