Assembly: System.Windows.Forms (in System.Windows.Forms.dll)
|TreeViewCancelEventArgs(TreeNode, Boolean, TreeViewAction)|
Initializes a new instance of theclass with the specified tree node, a value specifying whether the event is to be canceled, and the type of tree view action that raised the event.
Determines whether the specified object is equal to the current object.(Inherited from Object.)
Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection.(Inherited from Object.)
Serves as the default hash function. (Inherited from Object.)
Returns a string that represents the current object.(Inherited from Object.)
The following example demonstrates how to change the collapse state of a TreeView so that all the checked nodes are visible. First, all the nodes are collapsed, and a handler is added to the TreeView.BeforeExpand event. Next, all the nodes are expanded. The TreeView.BeforeExpand event handler determines whether a given node has child nodes that are checked. If a node does not have checked children, the expansion is canceled for that node. In order to allow normal node expansion when the plus sign next to a node is clicked, the TreeView.BeforeExpand event handler is then removed.
This behavior can also be implemented by handling the TreeView.BeforeCollapse event, as illustrated in the example for that topic.
For the complete example, see the TreeView.CheckBoxes reference topic.
Private Sub showCheckedNodesButton_Click(ByVal sender As Object, ByVal e As EventArgs) ' Disable redrawing of treeView1 to prevent flickering ' while changes are made. treeView1.BeginUpdate() ' Collapse all nodes of treeView1. treeView1.CollapseAll() ' Add the CheckForCheckedChildren event handler to the BeforeExpand event. AddHandler treeView1.BeforeExpand, AddressOf CheckForCheckedChildren ' Expand all nodes of treeView1. Nodes without checked children are ' prevented from expanding by the checkForCheckedChildren event handler. treeView1.ExpandAll() ' Remove the checkForCheckedChildren event handler from the BeforeExpand ' event so manual node expansion will work correctly. RemoveHandler treeView1.BeforeExpand, AddressOf CheckForCheckedChildren ' Enable redrawing of treeView1. treeView1.EndUpdate() End Sub 'showCheckedNodesButton_Click ' Prevent expansion of a node that does not have any checked child nodes. Private Sub CheckForCheckedChildren(ByVal sender As Object, ByVal e As TreeViewCancelEventArgs) If Not HasCheckedChildNodes(e.Node) Then e.Cancel = True End If End Sub 'CheckForCheckedChildren ' Returns a value indicating whether the specified ' TreeNode has checked child nodes. Private Function HasCheckedChildNodes(ByVal node As TreeNode) As Boolean If node.Nodes.Count = 0 Then Return False End If Dim childNode As TreeNode For Each childNode In node.Nodes If childNode.Checked Then Return True End If ' Recursively check the children of the current child node. If HasCheckedChildNodes(childNode) Then Return True End If Next childNode Return False End Function 'HasCheckedChildNodes
Available since 1.1
Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.