求高手指点，if的替换
if (txt_number.Text.Trim() != "")
  {
  if (sqlwhere == "")
  {
  sqlwhere = " where PONumber like '%" + txt_number.Text.Trim() + "%'";
  }
  else
  {
  sqlwhere += " and PONumber like '%" + txt_number.Text.Trim() + "%'";
  }
  }

  if (txt_chestno.Text.Trim() != "")
  {
  if (sqlwhere == "")
  {
  sqlwhere = "where PackNo like '%" + txt_chestno.Text.Trim() + "%'";
  }
  else
  {
  sqlwhere += " and PackNo like '%" + txt_chestno.Text.Trim() + "%'";
  }
  }
  if (cob_model.Text.Trim() != "")
  {
  if (sqlwhere == "")
  {
  sqlwhere = "where ProductModel like '%" + cob_model.Text.Trim() + "%'";
  }
  else
  {
  sqlwhere += " and ProductModel like '%" + cob_model.Text.Trim() + "%'";
  }
  }
  if (sqlwhere == "")
  {
  sqlwhere = "where ProjectType ='" + cob_select.Text.Trim() + "'";
  }
  else
  {
  sqlwhere += " and ProjectType ='" + cob_select.Text.Trim() + "'";
  }



这段代码可以写成别的形式吗？不用if语句，用别的方法能实现现在的目的吗？

------解决方案--------------------
switch()
{case}
------解决方案--------------------
因为要对每一个text进行判断拼接，也只能这样了
或者你搞个foreach遍历所有组件，判断是不是你需要的，然后拼接，可以在textbox的tag属性中保存一些信息，根据此信息得到你要的内容进行拼接
------解决方案--------------------

C# code

//这样是不是清爽多了？
sqlwhere  += " where 1=1 "

if (txt_number.Text.Trim() != "")
  {
  sqlwhere += " and PONumber like '%" + txt_number.Text.Trim() + "%'";
  }

  if (txt_chestno.Text.Trim() != "")
  {
   sqlwhere += " and PackNo like '%" + txt_chestno.Text.Trim() + "%'";
  }
  if (cob_model.Text.Trim() != "")
  {
  sqlwhere += " and ProductModel like '%" + cob_model.Text.Trim() + "%'";
  }

  sqlwhere += " and ProjectType ='" + cob_select.Text.Trim() + "'";