考虑以下Asp.net页面代码:
<head runat="server">
<title></title>
<script type="text/javascript">
function showhide(master, detail) {
var src = $(master).children()[0].src;
if (src.endsWith("plus.png"))
src = src.replace('plus.png', 'minus.png');
else
src = src.replace('minus.png', 'plus.png');
$(master).children()[0].src = src;
$(detail).slideToggle("normal");
}
</script>
</head>
<body>
<form id="form1" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server">
<Scripts>
<asp:ScriptReference Path="~/scripts/jquery-1.6.2.min.js" ScriptMode="Release" />
</Scripts>
</asp:ScriptManager>
<div>
<asp:SqlDataSource ID="sqlDsCustomers" runat="server" ConnectionString="<%$ ConnectionStrings:Northwind %>"
SelectCommand="SELECT [Customers].[CustomerID], [Customers].[CompanyName], COUNT([OrderID]) TotalOrders FROM [Customers] INNER JOIN [Orders] ON [Customers].[CustomerID]=[Orders].[CustomerID] Group By [Customers].[CustomerID], [Customers].[CompanyName]">
</asp:SqlDataSource>
<asp:GridView Width="100%" AllowPaging="True" ID="gvCustomers" AutoGenerateColumns="False"
DataSourceID="sqlDsCustomers" runat="server" ShowHeader="False" OnRowCreated="gvCustomers_RowCreated">
<Columns>
<asp:TemplateField>
<ItemTemplate>
<div class="group" id='<%#String.Format("customer{0}",Container.DataItemIndex) %>'
onclick='showhide(<%#String.Format(""#customer{0}"",Container.DataItemIndex) %>,<%#String.Format(""#order{0}"",Container.DataItemIndex) %>)'>
<asp:Image ID="imgCollapsible" CssClass="first" ImageUrl="~/Assets/img/plus.png"
Style="margin-right: 5px;" runat="server" /><span class="header">
<%#Eval("CustomerID")%>
:
<%#Eval("CompanyName")%>
(<%#Eval("TotalOrders")%>Orders) </span>
</div>
<div id='<%#String.Format("order{0}",Container.DataItemIndex) %>' class="order">
<asp:GridView AutoGenerateColumns="false" CssClass="grid" ID="ddd" runat="server"
ShowHeader="true" EnableViewState="false">
<RowStyle CssClass="row" />
<AlternatingRowStyle CssClass="altrow" />
<Columns>
<asp:TemplateField ItemStyle-CssClass="rownum">
<ItemTemplate>
<%# Container.DataItemIndex + 1 %>
</ItemTemplate>
</asp:TemplateField>
<asp:BoundField HeaderText="Order ID" DataField="OrderID" ItemStyle-Width="80px" />
<asp:BoundField HeaderText="Date Ordered" DataField="OrderDate" DataFormatString="{0:MM/dd/yyyy}"
ItemStyle-Width="100px" />
<asp:BoundField HeaderText="Date Required" DataField="RequiredDate" DataFormatString="{0:MM/dd/yyyy}"
ItemStyle-Width="110px" />
<asp:BoundField HeaderText="Freight" DataField="Freight" DataFormatString="{0:c}"
ItemStyle-Width="50px" ItemStyle-HorizontalAlign="Right" />
<asp:BoundField HeaderText="Date Shipped" DataField="ShippedDate" DataFormatString="{0:MM/dd/yyyy}"
ItemStyle-Width="100px" />
</Columns>
</asp:GridView>
</div>
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
</div>
<asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Button" />
</form>
和后面的代码:
protected void Page_Load(object sender, EventArgs e)
{
}
protected void gvCustomers_RowCreated(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow)
{
string custID = ((DataRowView)e.Row.DataItem)["CustomerID"].ToString();
using (DataClassesDataContext dc=new DataClassesDataContext())
{
List<Order> ord = (from o in dc.Orders
where o.CustomerID == custID.Trim()
select o).ToList();
GridView ctrl = e.Row.FindControl("ddd") as GridView;
ctrl.DataSource = ord;
}
}
}
protected void Button1_Click(object sender, EventArgs e)
{
Response.Redirect("Default.aspx");
}
问题是当我单击Button1重定向到另一个页面gvCustomers_RowCreated raise，我得到Null引用错误。为什么这个事件在回发后引发?
编辑1):
我删除了SqlDataSource并在后面的代码中绑定GridView，像这样:
public partial class Default2 : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
using (DataClassesDataContext dc=new DataClassesDataContext())
{
var query = dc.ExecuteQuery<clsRetern>("SELECT [Customers].[CustomerID], [Customers].[CompanyName], COUNT([OrderID]) TotalOrders FROM [Customers] INNER JOIN [Orders] ON [Customers].[CustomerID]=[Orders].[CustomerID] Group By [Customers].[CustomerID], [Customers].[CompanyName]").ToList();
List<clsRetern> ret = new List<clsRetern>();
foreach (var item in query)
{
clsRetern r = new clsRetern();
r.CompanyName = item.CompanyName;
r.CustomerID = item.CustomerID;
r.TotalOrders = item.TotalOrders;
ret.Add(r);
}
gvCustomers.DataSource = ret;
gvCustomers.DataBind();
}
}
}
protected void gvCustomers_RowCreated(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow)
{
string custID = ((clsRetern)e.Row.DataItem).CustomerID.Trim();
using (DataClassesDataContext dc=new DataClassesDataContext())
{
List<Order> ord = (from o in dc.Orders
where o.CustomerID == custID.Trim()
select o).ToList();
GridView ctrl = e.Row.FindControl("ddd") as GridView;
ctrl.DataSource = ord;
}
}
}
protected void Button1_Click(object sender, EventArgs e)
{
Response.Redirect("Default.aspx",true);
}
}
public class clsRetern
{
public string CustomerID { get; set; }
public string CompanyName { get; set; }
public int TotalOrders { get; set; }
}
我尝试了Response.Redirect("Default.aspx");，但问题仍然存在。
如果你了解ASP。NET页面模型，那么这个问题不应该出现在你身上。每次请求到ASP。. NET页时，将创建一个新的页对象以及整个控件树，并在回发场景中使用视图状态管理状态。因此，在您的示例中，每当发生回发时，都会创建一个新的页面和网格视图。网格视图的数据将保存在新的视图状态中，网格将绑定到该数据。
无论是否显式调用DataBind，只要创建网格行，就会引发RowCreated事件。该事件的目的是为了让用户可以调整UI(网格视图单元格)——例如，如果需要，可以将一些控件推入网格视图单元格。无论post-back场景如何，都应该发生相同的情况，否则这些动态控件将不会被创建。通常，这些控件将使用view-state恢复其状态，并且您可以将网格视图UI(控件树)恢复为第一页循环时的状态。
这是因为即使你触发Response.Redirect, Page_Load事件仍然会被引发，如果你的GridView绑定代码不在!IsPostBack内，该代码将被击中。
试试这个。
protected void Page_Load(object sender, EventArgs e)
{
try
{
if (!IsPostBack)
{
//bind gridview here
}
}
catch (Exception exception)
{
//Elmah.ErrorSignal.FromCurrentContext().Raise(exception);
}
}
精明?
将EnableViewState=False添加到page指令中，以防止每次回发时都运行"RowCreated"