DBNull转换成String时出错

[sdgqx]

我的语句是这样的:
da1.SelectCommand.CommandText = "select * from bzj_jbxx where dhhm='" + Request.QueryString("dhhm") + "'"
da1.Fill(DataSet21, "bzj_jbxx")
Try
txtDhhm.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("dhhm")
txtJdm.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("jdm")
txtYhmc.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("yhmc")
txtJmc.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("jmc")
txtAcc_nbr.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("acc_nbr_97")
txtIdCard.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("id_card")
txtAddr.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("addr")
txtYhzh.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("yhzh")
txtZhmc.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("zhmc")
txtAmt_f.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("amt_f")
txtZhye.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("zhye")
txtIP.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("ip")
txtPos.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("pos")
txtMark97.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("mark_97")
txtModi_id.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("modi_staff")

Catch ex As Exception
Response.Write(ex.ToString)

错误信息是:
System.InvalidCastException: 从类型“DBNull”到类型“String”的强制转换无效。 at Microsoft.VisualBasic.CompilerServices.StringType.FromObject(Object Value) at test.allinfo.Page_Load(Object sender, EventArgs e) in c:\inetpub\wwwroot\test\allinfo.aspx.vb:line 119

应该是空值的转换有问题了
到底应该怎样解决呢?

[zjf_dl]

txtDhhm.Text = iif(isdbnull(DataSet21.Tables("bzj_jbxx").Rows(0).Item("dhhm")),"",DataSet21.Tables("bzj_jbxx").Rows(0).Item("dhhm"))

[JafyLiu]

加判断
xx = yy==DBNull.Value?"":yy.ToString();

[zl13]

Convert.IsDbNull()判断一下是不是dbnull类型，或者在sql语句中,case TableField when null then ''
end as a

[aoyo]

要判断一下字段内容是否是DBNull.Value，在赋值

[zl13]

错了，
case TableField when null then '' else TableField end as a

[rickjelly2004]

da1.SelectCommand.CommandText = "select * from bzj_jbxx where dhhm='" + Request.QueryString("dhhm") + "'"
da1.Fill(DataSet21, "bzj_jbxx")
Try
txtDhhm.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("dhhm") & ""
txtJdm.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("jdm") & ""
txtYhmc.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("yhmc") & ""
txtJmc.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("jmc") & ""
txtAcc_nbr.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("acc_nbr_97")
txtIdCard.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("id_card")
txtAddr.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("addr")
txtYhzh.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("yhzh")
txtZhmc.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("zhmc")
txtAmt_f.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("amt_f")
txtZhye.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("zhye")
txtIP.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("ip")
txtPos.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("pos")
txtMark97.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("mark_97")
txtModi_id.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("modi_staff")

Catch ex As Exception
Response.Write(ex.ToString)

[rickjelly2004]

说白了
就是每个后面加
txtDhhm.Text = DataSet21.Tables("bzj_jbxx").Rows(0).Item("dhhm") & ""

& ""

就不会报错了

[henryfan1]

如果是DBNull值，直接ToString()应该可以了

[hjxlovetear]

直接在sql里加ISNULL(字段名,'')不就得了