c# - .NET GridView 行在回发时为空

Question

在回发后填充 GridView 的行后，我很难对其进行迭代。

总之，有两个下拉列表确定应在 GridView 中显示的数据。该页面最初仅加载两个下拉列表，此阶段没有 GridView。从下拉列表中选择值后，用户通过按钮提交页面。然后后面的代码调用 db 以检索数据并将其绑定到 GridView。我设法让这个工作！

问题是 GridView 有一列，用户可以在其中编辑 itemtemplate 中保存的文本框中的值。如果用户更改文本框中的值并提交页面，当我尝试迭代 GridView 的行时，它告诉我没有要迭代的行。当我可以在前端看到可用的行和数据时，我很困惑为什么会发生这种情况。

但是，如果我们删除涉及用户选择下拉菜单的步骤并且在初始 page_load 上填充 GridView，我实际上可以遍历行。

因此，如果 GridView 绑定在按钮单击事件中，就好像 ViewState 没有保留回发之间的行数。

有人可以向我解释一下，这是怎么回事。

这是VB.NET中的代码：

Protected Sub Me_Load(ByVal sender As Object, ByVal e As EventArgs) _
Handles Me.Load

End Sub

Protected Sub BtnGetData_Click(ByVal sender As Object, ByVal e As EventArgs) _
Handles BtnGetData.Click

    Dim ddlFirstValue As Integer = DropDownListOne.SelectedValue
    Dim ddlSecondValue As Integer = DropDownListSecond.SelectedValue
    MyGridView.DataSource = GetData(ddlFirstValue, ddlSecondValue)
    MyGridView.DataBind()

End Sub

Protected Sub BtnSubmit_Click(ByVal sender As Object, ByVal e As EventArgs) _
Handles BtnSubmit.Click

    For Each row As GridViewRow In MyGridView.Rows 'this returning 0 rows
        'Do something
    Next

End Sub

score 0 · Accepted Answer

我认为我们可能需要更多数据来描述为什么在您的特定情况下会发生这种行为。例如，您可能会考虑发布您的 ASPX (XHTML) 文件，以便我们更好地了解您的具体情况。

虽然我可能不完全理解您的需求，但您想要的似乎是可能的。下面是我整理的一个人为的示例，以大致模拟我对您的情况的理解。

我提交的代码允许用户：

打开带有空 GridView 的页面
从下拉列表中选择权重过滤器（尚无回发）
从另一个下拉列表中选择成本过滤器（尚无回发）
按下获取数据按钮以填充 GridView
在每个 GridView 行上的描述字段的文本框中键入信息
点击提交按钮
通过服务器端对文字控件的修改来观察用户的选择

由于处理发生在服务器上，我认为这段代码表明应该可以以规定的方式修改 GridView 并读取 GridView 的更改。

如果此代码没有描述您的情况，请添加评论，以便社区可以为您提供更好的帮助：

ASPX 模拟文件

<%@ Page Language="VB" AutoEventWireup="false" 
CodeFile="Default.aspx.vb" Inherits="_Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>
    Demo of using DropDown Lists to Filter Data for 
    Editable DataGrid
    </title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:Literal ID="theLiteral" runat="server" />
    </div>
    <br />
    <div>
        <asp:GridView ID="myGridView" runat="server" 
        AutoGenerateColumns="false" 
        DataKeyNames="weight, cost, Description">
            <Columns>               
                <asp:BoundField DataField="weight" HeaderText="Weight" /> 
                <asp:BoundField DataField="cost" HeaderText="Cost" /> 
                <asp:TemplateField HeaderText="Description">
                    <ItemTemplate>
                        <asp:TextBox runat="server" ID="descId"
                        Text='<%# Bind("Description") %>' />                          
                    </ItemTemplate>
                </asp:TemplateField>
            </Columns>
        </asp:GridView><br />
        Get Items With Weight >=:<br />
        <asp:DropDownList ID="DropDownListOne" runat="server">
            <asp:ListItem Text="1" Value="1" />            
            <asp:ListItem Text="2" Value="2" />      
            <asp:ListItem Text="5" Value="5" />                  
        </asp:DropDownList><br />
        Get Items With Cost >=:<br />
        <asp:DropDownList ID="DropDownListSecond" runat="server">
            <asp:ListItem Text="1" Value="1" />            
            <asp:ListItem Text="5" Value="5" />      
            <asp:ListItem Text="51" Value="51" />    
            <asp:ListItem Text="101" Value="101" />                                
        </asp:DropDownList><br />
        <asp:Button ID="BtnGetData" runat="server" Text="Get Data" /><br />
        <asp:Button ID="BtnSubmit" runat="server" Text="Submit" /><br />
    </div>
    </form>
</body>
</html>

模拟文件背后的代码

' Just some DataItem to stick in an IEnumerable Array to be 
' bound to CreativeInCode's MyGridView
public Class InventoryItem
    Public Sub New (
        ByVal iWeight As Integer, 
        ByVal iCost As Integer, 
        ByVal iDescription As String) 

        weight = iWeight
        cost = iCost
        description = iDescription
    End Sub

    ' Automatic VB.NET properties can be read about here:
    ' http://msdn.microsoft.com/en-us/library/dd293589.aspx
    Public Property weight As Integer
    Public Property cost As Integer
    Public Property description As String
End Class

' The code behind for Default.aspx starts here
Partial Class _Default
    Inherits System.Web.UI.Page

    ' Data to play with 
    Public storeItems As InventoryItem() = 
    {
        New InventoryItem(10, 20, "PaperWeight"), 
        New InventoryItem(1, 1, "Feather"), 
        New InventoryItem(2000, 20000, "Used SUV"), 
        New InventoryItem(3, 50, "Biology TextBook"), 
        New InventoryItem(1, 200, "Professional Isolation Headphones"), 
        New InventoryItem(1, 100, "Caviar (Does this Need to Be Refrigerated?)")
    }

    ' Function to simulate retrieval from DataBase
    Protected Function GetData( _ 
        ByVal weight As Integer, 
        ByVal cost As INteger
    ) As IEnumerable(Of InventoryItem)
        ' Example of LINQ can be found here
        ' http://msdn.microsoft.com/en-us/vstudio/bb688088.aspx
        ' I believe LINQ is the way of the future
        Dim returnValue As IEnumerable(Of InventoryItem) = 
            From items In storeItems
            Where (items.weight >= weight) AndAlso (items.cost >= cost)
            Select items
        Return returnValue
    End Function

     ' CreativeInCode's STuff starts here
    Protected Sub Me_Load(ByVal sender As Object, ByVal e As EventArgs) _ 
        Handles Me.Load 

    End Sub 

    Protected Sub BtnGetData_Click(ByVal sender As Object, ByVal e As EventArgs) _ 
        Handles BtnGetData.Click 

        Dim ddlFirstValue As Integer = DropDownListOne.SelectedValue 
        Dim ddlSecondValue As Integer = DropDownListSecond.SelectedValue                 
        MyGridView.DataSource = GetData(ddlFirstValue, ddlSecondValue) 
        myGridView.DataBind()

    End Sub 

    ''' <summary>
    ''' Made some modifications to CreativeInCode's function to 
    ''' dump the output to the user
    ''' </summary>                
    Protected Sub BtnSubmit_Click(ByVal sender As Object, ByVal e As EventArgs) _ 
        Handles BtnSubmit.Click 

        Dim outputToUser As String = _
            "The user put the following values in the GridView:<br />" 
        For Each row As GridViewRow In MyGridView.Rows 'this returning 0 rows 
            'Do something 

            ' This is just here to make a good place to set a 
            ' breakpoint            
            Dim weightStr As String = row.Cells(0).Text
            Dim costStr As String = row.Cells(1).Text
            Dim tbDescription As TextBox = row.FindControl("descId")
            Dim description As String = tbDescription.Text

            outputToUser &= 
                String.Format(
                    "weight={0}, cost={1}, description={2}<br />", _
                    weightStr, _ 
                    costStr, _
                    description
                )           
        Next 

        ' Show the user the changes she/he made to the GridView
        theLiteral.Text = outputToUser
    End Sub 
End Class

c# - .NET GridView 行在回发时为空

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