C# 检查TreeView是否选择了任何节点？

我在我的aspx页面上有一个treeview控件和一个按钮。根据treeview节点的选择，我想显示和隐藏该按钮。但是当最初加载页面时，没有任何已选择的节点处于生成异常的状态。有人能告诉我，我如何找到是否已选择任何节点吗

  //Here I want to check is there any selected node "ApplicationTree.Nodes.Count>0"
         <%if(ApplicationTree.Nodes.Count>0)
               {%>                         
                            <%
//Here it is generating exception because initially no any node is selected
              IsReviewPending = view_access.IsWaitingForViewAccess(ApplicationTree.SelectedNode.Value, Session["empCode"].ToString());
              if (IsReviewPending)
              {
                  CanReviewAccess = true;
              }
              else 
              {
                  CanReviewAccess = false;
              }                    
                                      %>  
                  <%if(CanReviewAccess)
                    {%>
                <asp:Button ID="btn_Review_Access" OnClick="btn_Review_Access_Click" runat="server" BackColor="#C6304A" ForeColor="White" Text="Confirm Access Review" Width="200px"  CssClass="center3" />                 
                  <%} %>

                                 <%} %>

//这里我想检查是否有任何选定的节点“ApplicationTree.Nodes.Count>0”
0)
{%>                         

我找到了解决方案：）

//这是我的代码

这是因为您试图访问该节点的空值。可能引入空检查可以解决您的问题。我没有上下文意识，但如果SelectedNode为空，是否希望完全忽略此操作？如果是，则引入if（ApplicationTree.SelectedNode！-null）会解决你的问题的不，我试过了，但同样的例外！！！谢谢你的支持

    //Here is my Code
     <%
             bool HasSelectedNode = false;
//i iterated through the overall nodes of the tree and checked any of the node is selected or not 
             for (int i = 0; i < ApplicationTree.Nodes.Count;i++ )
             {
             if(ApplicationTree.Nodes[i].Selected==true)
             {
                 HasSelectedNode = true;
             }
             }
              %>
         <%if(HasSelectedNode)
           {%>                         
                        <%
          IsReviewPending = view_access.IsWaitingForViewAccess(ApplicationTree.SelectedNode.Value, Session["empCode"].ToString());
             //  IsReviewPending = true;
          if (IsReviewPending)
          {
              CanReviewAccess = true;
          }
          else 
          {
              CanReviewAccess = false;
          }                    
                                  %>  
              <%if(CanReviewAccess)
                {%>
            <asp:Button ID="btn_Review_Access" OnClick="btn_Review_Access_Click" runat="server" BackColor="#C6304A" ForeColor="White" Text="Confirm Access Review" Width="200px"  CssClass="center3" />                 
              <%} %>

                             <%} %>