从代码隐藏中展开ASP.Net TreeView节点

Question

我在学习如何访问ASP.Net母版页的控件并尝试展开特定的TreeView节点。我正在从另一个不是母版页的页面执行此操作。

objContentPlaceHolder，objLoginView和objTreeView都具有通过使用调试器确认的值。

你可以看看这段代码，让我们知道为什么for循环中的代码没有执行吗？它到达for循环，但只是在该点跳过for循环。

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load 

    Dim objContentPlaceHolder As ContentPlaceHolder 
    Dim objLoginView As LoginView 
    Dim objTreeView As TreeView 

    objContentPlaceHolder = CType(Master.FindControl("ContentPlaceHolderBody"), ContentPlaceHolder) 

    If Not objContentPlaceHolder Is Nothing Then 

     objLoginView = CType(objContentPlaceHolder.FindControl("loginViewMain"), LoginView) 

     If Not objLoginView Is Nothing Then 
      objTreeView = CType(objLoginView.FindControl("TreeViewMain"), TreeView) 

      ' Make sure all nodes for Maintenance are expanded. 
      '-------------------------------------------------- 
      For Each treenode As TreeNode In objTreeView.Nodes 
       If treenode.Text = "Maintenance" Then 
        treenode.Expand() 
       End If 
      Next treenode 
     End If 
    End If 
End Sub 

*更新*

我改变了页面加载事件处理程序，以一个PreRenderComplete事件处理程序，你会相信它的工作？不知道为什么PreRender没有，但那是它。再次感谢所有人的帮助。

Answer 1

public Sub TreeView_TreeNodeDataBound(ByVal sender As Object, ByVal e As TreeNodeEventArgs ) 
     dim mapNode as SiteMapNode = e.Node.DataItem as SiteMapNode 
     If mapNode.Title = "Maintenance" then 
      e.Node.Expand() 
     End if 
    End Sub 

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load 

     Dim objContentPlaceHolder As ContentPlaceHolder 
     Dim objLoginView As LoginView 
     Dim objTreeView As TreeView 

     objContentPlaceHolder = CType(Master.FindControl("ContentPlaceHolderBody"), ContentPlaceHolder) 

     If Not objContentPlaceHolder Is Nothing Then 

      objLoginView = CType(objContentPlaceHolder.FindControl("loginViewMain"), LoginView) 

      If Not objLoginView Is Nothing Then 
       objTreeView = CType(objLoginView.FindControl("TreeViewMain"), TreeView) 
       objTreeView.TreeNodeDataBound += TreeView_TreeNodeDataBound 
      End If 
     End If 
    End Sub 

希望这将有助于

Answer 2

从你的榜样，它看起来像你的逻辑是只检查根节点。在处理分层数据时，您需要使用递归逻辑来确保整个结构得到评估。

像这样的东西是你所需要的：

Protected Sub btnSearch_Click(sender As Object, e As EventArgs) 
    For Each node As TreeNode In TreeView1.Nodes 
     ExpandNodeByValue("Maintenance", node) 
    Next 
End Sub 

Private Sub ExpandNodeByValue(value As String, parentNode As TreeNode) 
    For Each childNode As TreeNode In parentNode.ChildNodes 
     If childNode.Value.ToLower() = value.ToLower() Then 
      childNode.Expand() 
     End If 
     If childNode.ChildNodes.Count > 0 Then 
      ExpandNodeByValue(value, childNode) 
     End If 
    Next 
End Sub 

我也建议使用的DirectCast代替CType，至少暂时，以确保控制被发现。你会这样实现：

Dim objTreeView as TreeView = DirectCast(objLoginView.FindControl("TreeViewMain"), TreeView) 
If objTreeView IsNot Nothing Then 
    'The control was found 
End If