"未将对象引用设置到对象的实例"这个错误要如何解决?

Question

这个是页面文件
<%@ Control Language="C#" AutoEventWireup="true" CodeFile="LeftNav.ascx.cs" Inherits="LeftNav" %>
<%@ Register Assembly="ComponentArt.Web.UI" Namespace="ComponentArt.Web.UI" TagPrefix="ComponentArt" %><table class="HeadingCell" style="width:100%;height:25px;" cellpadding="0" cellspacing="0">
              <tr>
                <td class="HeadingCellText">系统导航菜单</td>
              </tr>
            </table>
        <ComponentArt:NavBar id="NavBar1" Width="200" Height="450" 
     CssClass="NavBar" 
      DefaultItemLookID="TopItemLook"
      SiteMapXmlFile="Xml/navData.xml"
      ExpandSinglePath="true"
      FullExpand="true"
      ImagesBaseUrl="images/"
      ShowScrollBar="false"
      ExpandTransition="Fade"
      ExpandDuration="200"
      CollapseTransition="Fade"
      CollapseDuration="200"
      ScrollUpImageUrl="scrollup.gif"
      ScrollUpHoverImageUrl="scrollup_hover.gif"
      ScrollUpActiveImageUrl="scrollup_active.gif"
      ScrollDownImageUrl="scrolldown.gif"
      ScrollDownHoverImageUrl="scrolldown_hover.gif"
      ScrollDownActiveImageUrl="scrolldown_active.gif"
      ScrollUpImageWidth="16"
      ScrollUpImageHeight="16"
      ScrollDownImageWidth="16"
      ScrollDownImageHeight="16"
      runat="server" >
   
    <ItemLooks>
      <ComponentArt:ItemLook LookID="TopItemLook" CssClass="TopItem" HoverCssClass="TopItemHover" LeftIconUrl="top_folder.gif" LabelPaddingLeft="15" LeftIconWidth="30" LeftIconHeight="24" />
      <ComponentArt:ItemLook LookID="Level2ItemLook" LabelPaddingLeft="10" CssClass="Level2Item" HoverCssClass="Level2ItemHover" LeftIconWidth="16" LeftIconHeight="16" />
      <ComponentArt:ItemLook LookID="EmptyLook" CssClass="Empty" />
    </ItemLooks>
    <ServerTemplates>
        <ComponentArt:NavigationCustomTemplate id="CalendarTemplate">
          <Template>
           <table width="100%" cellpadding="0" cellspacing="0" border="0">
           <tr>
              <td style="padding-top:2px;">
                <ComponentArt:Calendar id="Calendar1" runat="server"
                  ControlType="Calendar"
                  CalendarTitleCssClass="title" 
                  DayHeaderCssClass="dayheader" 
                  DayCssClass="day" 
                  DayHoverCssClass="dayhover" 
                  OtherMonthDayCssClass="othermonthday" 
                  SelectedDayCssClass="selectedday" 
                  CalendarCssClass="calendar" 
                  NextPrevCssClass="nextprev" 
                  MonthCssClass="month"
                  SwapSlide="Linear"
                  SwapDuration="200"
                  DayNameFormat="FirstLetter"
                  PrevImageUrl="images/cal_prevMonth.gif" 
                  NextImageUrl="images/cal_nextMonth.gif"
                  >
                </ComponentArt:Calendar>
              </td>
            </tr>
            </table>
          </Template>
        </ComponentArt:NavigationCustomTemplate>              <ComponentArt:NavigationCustomTemplate id="FolderListTemplate">
          <Template>
            <ComponentArt:TreeView id="TreeView1" Width="197" Height="282" 
              AutoScroll="true"
              DragAndDropEnabled="true" 
              NodeEditingEnabled="true" 
              KeyboardEnabled="true"
              CssClass="TreeView" 
              NodeCssClass="TreeNode" 
              HoverNodeCssClass="HoverTreeNode"
              SelectedNodeCssClass="SelectedTreeNode"
              NodeEditCssClass="NodeEdit"
              DefaultImageWidth="16" 
              DefaultImageHeight="16"
              ExpandCollapseImageWidth="15"
              ExpandCollapseImageHeight="15"
              CollapseImageUrl="images/exp.gif" 
              ExpandImageUrl="images/col.gif" 
              NodeIndent="16" 
              ItemSpacing="3" 
              NodeLabelPadding="3"
              ParentNodeImageUrl="images/folders.gif" 
              LeafNodeImageUrl="images/folder.gif" 
              ShowLines="false" 
              LineImagesFolderUrl="images/lines/"
              EnableViewState="false"
              
              runat="server">
              <ServerTemplates>
                <ComponentArt:NavigationCustomTemplate id="UnreadItemsTemplate">
                  <Template>
                    <div style="padding-left:1px;"><b><%# DataBinder.Eval(Container.DataItem, "Text") %></b>
                      <font color="blue">(<%# Container.Attributes["UnreadItems"] %>)</font>
                    </div>
                  </Template>
                </ComponentArt:NavigationCustomTemplate>                <ComponentArt:NavigationCustomTemplate id="InfoItemsTemplate">
                  <Template>
                  <b><%# DataBinder.Eval(Container.DataItem, "Text") %></b>
                  <font color="green">[<%# Container.Attributes["InfoItems"] %>]</font>
                  </Template>
                </ComponentArt:NavigationCustomTemplate>
              </ServerTemplates>          
            </ComponentArt:TreeView>
          </Template>
        </ComponentArt:NavigationCustomTemplate>      
    </ServerTemplates>
    </ComponentArt:NavBar>以下是c#文件
protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
        {
            Calendar1.SelectedDate = DateTime.Today.Date;
        }    }
为什么在Calendar1.SelectedDate = DateTime.Today.Date;中会出现未将对象引用设置到对象的实例的错误?

Answer 1

日期控件用的是第三方控件,可能是少了命名空间(using里面加)

Answer 2

我加了,可还是这个错误!我断点查看了一下,Calendar1为null,这是怎么回事啊,我面页面中明明有了Calendar1啊

Answer 3

我把Calendar1放到NavBar1外时,程序就可以了,把放回到NavBar1控件里时又找不到这个Calendar1了,请问,这件要如何解决呢?

Answer 4

可能是Calendar1是NavBar1下的子控件,可以试下用FindControl方法:
(Calendar)NavBar1.FindControl("Calendar1").SelectedDate...

Answer 5

你的CALENDAR控件没有初始化，然后又被调用了，把程序逻辑改下
在调用控件时做个判断是否为NULL，如果为NULL就进行初始化再调用。

Answer 6

乱七八糟的，这样写当然会出错。你的代码是复制的？？？？ 如果你是自己敲出来的，明显你按Calendar1后面按个点不会出来提示。。
而且ComponentArt的日期控件默认就是选今天，你那句代码等于没用。
控件自带的Demo上就有例子和现成的代码

Answer 7

NavBar1.Items[i].Items[j].........FindControl("Calendar1") i和j去 SiteMapXmlFile="Xml/navData.xml"   这个XML文件里找,如果只有一层就只写到i，两层就写到j，3层继续。比如官方的demo里面的是 
NavBar1.Items[3].Items[0].FindControl("Calendar1") 

Answer 8

感谢各位的帮忙!谢谢syeerzy(快乐永远*先天下之乐而乐*后天下之忧而忧*)!你的方法可以!非常感谢你的帮忙,解决了我的大问题!我要清楚这个用法,是其它地方还要用到,如里面的treeview等!再次感谢!