为什么页面重新加载后，dataset或datatable会为空？
像这样定义datatable,然后，在按钮的点击事件bFindSave_Click中，datatable内容却为空了，这是怎么回事？
public partial class AuthorizePurchaseOrder : Page
{
private readonly DatabaseHelper db = new DatabaseHelper();
private DataTable dt = new DataTable();
protected void FindPurchase(string Condition)
{
var sb = new StringBuilder();
sb.Append("select code,b.realname Petitioner,c.realname,applydate,recorddate");
sb.Append(
",(case state when 0 then '未提交' when 1 then '已提交' when 2 then '已审核' when 3 then '已完成' when 10 then '已作废' end ) state");
sb.Append(",state stateid");
sb.Append(" from tb_Purchase a,tb_user b,tb_user c");
sb.Append(" where a.petitioner=b.userid and a.userid=c.userid");
sb.Append(Condition);
dt1 = db.ExecuteDataSet(sb.ToString()).Tables[0];
uwgPurchase.DataKeyField = "code";
dt1.PrimaryKey = new[] {dt1.Columns["code"]};
uwgPurchase.DataBind();
ViewState["dt1"] = dt1;
}
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
FindPurchase("");
}
}
protected void bFindSave_Click(object sender, EventArgs e)
{
var sb = new StringBuilder();
foreach (DataRow c in dt1.Rows) //此时，dt1为空了。
{
switch (c.RowState)
{
case (DataRowState.Added):
break;
case (DataRowState.Modified):
// sb.Append(" update tb_Purchase set state=1 where code='"+c.Cells.FromKey("code")+"' and state=0");
break;
case (DataRowState.Deleted):
sb.Append(" delete from tb_Purchase where code='" + c["code",DataRowVersion.Original] + "' and state=0");
sb.Append(" delete from tb_PurchaseList where code='" + c["code", DataRowVersion.Original] + "'");
break;
}
}
var id = Convert.ToInt32(hfID.Value);
foreach (DataRow c in dt.Rows)
{
switch (c.RowState)
{
case (DataRowState.Added):
id++;
sb.Append(" insert into tb_PurchaseList(code,id,commoditycode,quantity,comment)");
sb.Append(" values('" + hfCode.Value + "'," + id + ",'" + c["code"] + "'," +
c["quantity"]);
sb.Append(",'" + c["comment"] + "')");
break;
case (DataRowState.Modified):
sb.Append(" update tb_PurchaseList");
sb.Append(" set CommodityCode='" + c["code"] + "'");
sb.Append(",quantity=" + c["quantity"] + ",comment='" + c["comment"] +
"'");
sb.Append(" where code='" + hfCode.Value + "'");
sb.Append(" and id=" + c["id"]);
break;
case (DataRowState.Deleted):
sb.Append(" delete from tb_purchaselist");
sb.Append(" where code='" + hfCode.Value + "'");
sb.Append(" and id=" + c["id", DataRowVersion.Original]);
break;
}
}
if (sb.Length>0)
db.ExecuteNonQuery(sb.ToString());
}
}
[解决办法]
protected void Page_Load(object sender, EventArgs e)
{
// !IsPostBack 只有第一次加载页面时执行里面的代码，如果你的按钮要多次点击都想有DataTable 就不能用 IsPostBack
//if (!IsPostBack)
//{
FindPurchase("");
// }
}
另外你声明的貌似是 private DataTable dt = new DataTable();
而 赋值的却是 dt1 = db.ExecuteDataSet(sb.ToString()).Tables[0];
没有报错吗？
