Question

我尝试通过一些示例来了解在CheckBoxes分页时如何使GridView保持选中状态。

我试图通过GridView复制一个分页示例。我使用以下示例：

PostgreSQL - fetch the row which has the Max value for a column

唯一的区别是我使用自己的GridView如下：

<%@ Page Title="Home Page" Language="C#" MasterPageFile="~/Site.master" AutoEventWireup="true" 
    CodeBehind="Default.aspx.cs" Inherits="GridViewExample._Default" %>

<asp:Content ID="HeaderContent" runat="server" ContentPlaceHolderID="HeadContent">
</asp:Content>
<asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent">
<asp:GridView ID="gvCustomers" DataKeyNames="Key" PageSize="4" AllowPaging="true" OnPageIndexChanging="gvCustomersPageChanging" runat="server" AutoGenerateColumns="false">

    <Columns>

    <asp:TemplateField>
        <ItemTemplate>
        <asp:CheckBox ID="chkSelect" runat="server" Checked="false" Value='<%#Eval("Key") %>' />
        </ItemTemplate>
    </asp:TemplateField>


    <asp:TemplateField HeaderText="Key">
        <ItemTemplate>
        <%# Eval("Key") %>
        </ItemTemplate>
    </asp:TemplateField>

    <asp:TemplateField HeaderText="First Name">
        <ItemTemplate>
        <%# Eval("FirstName") %>
        </ItemTemplate>
    </asp:TemplateField>

     <asp:TemplateField HeaderText="Last Name">
        <ItemTemplate>
        <%# Eval("LastName") %>
        </ItemTemplate>
    </asp:TemplateField>

    </Columns>

    </asp:GridView>
</asp:Content>

这是数据加载逻辑：

protected void Page_Load(object sender, EventArgs e)
{
    BindData();
}

private void BindData()
{
    var customers = new List<Customer>{
        new Customer { FirstName = "Mohammad",  LastName = "Azam", Key = 1},
        new Customer { FirstName = "John",  LastName = "Doe",  Key = 2},
        new Customer { FirstName = "Mary",  LastName = "Kate",  Key = 3},
        new Customer { FirstName = "Jerry",  LastName = "Seinfeld",  Key = 4},
        new Customer { FirstName = "Alex",  LastName = "Rowe",  Key = 5},
        new Customer { FirstName = "James",  LastName = "Smith",  Key = 9},
        new Customer { FirstName = "Jerry",  LastName = "Grand",  Key = 10},
        new Customer { FirstName = "Thomas",  LastName = "Anders",  Key = 11},
        new Customer { FirstName = "Diter",  LastName = "Bolen",  Key = 12},
        new Customer { FirstName = "Ryan",  LastName = "McDonag",  Key = 13},
        new Customer { FirstName = "Stewart",  LastName = "Black",  Key = 14},
        new Customer { FirstName = "James",  LastName = "Soth",  Key = 15},
        new Customer { FirstName = "Alex",  LastName = "Bowldwin",  Key = 18},
        new Customer { FirstName = "Arnold",  LastName = "Strong",  Key = 19},
    };


    gvCustomers.DataSource = (from c in customers select c).ToList();

    gvCustomers.DataBind();
}

这是示例中的代码：

   private void RememberOldValues()
    {
        ArrayList categoryIDList = new ArrayList();
        int index = -1;
        foreach (GridViewRow row in gvCustomers.Rows)
        {
            index = (int)gvCustomers.DataKeys[row.RowIndex].Value;
            bool result = ((CheckBox)row.FindControl("chkSelect")).Checked;
            string id = ((CheckBox)row.FindControl("chkSelect")).ClientID;

            // Check in the Session
            if (Session["CHECKED_ITEMS"] != null)
                categoryIDList = (ArrayList)Session["CHECKED_ITEMS"];
            if (result)
            {
                if (!categoryIDList.Contains(index))
                    categoryIDList.Add(index);
            }
            else
                categoryIDList.Remove(index);
        }
        if (categoryIDList != null && categoryIDList.Count > 0)
            Session["CHECKED_ITEMS"] = categoryIDList;
    }

    private void RePopulateValues()
    {
        ArrayList categoryIDList = (ArrayList)Session["CHECKED_ITEMS"];
        if (categoryIDList != null && categoryIDList.Count > 0)
        {
            foreach (GridViewRow row in gvCustomers.Rows)
            {
                int index = (int)gvCustomers.DataKeys[row.RowIndex].Value;
                if (categoryIDList.Contains(index))
                {
                    CheckBox myCheckBox = (CheckBox)row.FindControl("chkSelect");
                    myCheckBox.Checked = true;
                }
            }
        }
    }

protected void gvCustomersPageChanging(object sender, GridViewPageEventArgs e)
{
  RememberOldValues();
  gvCustomers.PageIndex = e.NewPageIndex;
  BindData();
  RePopulateValues();
}

问题是即使我在调试以下行时选中了复选框：

bool result = ((CheckBox)row.FindControl("chkSelect")).Checked;

在RememberOldValues()方法中，result始终为假

为什么？有什么想法吗？

Answer 1

在Page_Load事件中，请将代码替换为下面的代码。

每次您浏览gridview时，页面都会回发并在达到PageIndexChanging事件之前重新绑定它，因为您始终在Page_Load事件中绑定gridview，这会将复选框重置为默认值虚假价值。使用下面的代码，它将永远不会在达到PageIndexChanging事件之前重新绑定，并且您的复选框值将被保留。

protected void Page_Load(object sender, EventArgs e)
{
     if (!Page.IsPostBack)
     {
       BindData();
     }
}

通过GridView进行分页时，GridVIew中的CheckBoxes不会保持选中状态

1 个答案: