TreeViewCancelEventArgs Class
Provides data for the BeforeCheck, BeforeCollapse, BeforeExpand, and BeforeSelect events of a TreeView control.
System::EventArgs
System.ComponentModel::CancelEventArgs
System.Windows.Forms::TreeViewCancelEventArgs
Assembly: System.Windows.Forms (in System.Windows.Forms.dll)
The TreeViewCancelEventArgs type exposes the following members.
| Name | Description | |
|---|---|---|
![]() | TreeViewCancelEventArgs | Initializes a new instance of the TreeViewCancelEventArgs class 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. |
| Name | Description | |
|---|---|---|
![]() | Equals(Object) | Determines whether the specified Object is equal to the current Object. (Inherited from Object.) |
![]() | Finalize | Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.) |
![]() | GetHashCode | Serves as a hash function for a particular type. (Inherited from Object.) |
![]() | GetType | Gets the Type of the current instance. (Inherited from Object.) |
![]() | MemberwiseClone | Creates a shallow copy of the current Object. (Inherited from Object.) |
![]() | ToString | Returns a string that represents the current object. (Inherited from Object.) |
For more information about handling events, see Consuming Events.
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: void showCheckedNodesButton_Click( Object^ /*sender*/, EventArgs^ /*e*/ ) { // 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. treeView1->BeforeExpand += 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. treeView1->BeforeExpand -= checkForCheckedChildren; // Enable redrawing of treeView1. treeView1->EndUpdate(); } // Prevent expansion of a node that does not have any checked child nodes. void CheckForCheckedChildrenHandler( Object^ /*sender*/, TreeViewCancelEventArgs^ e ) { if ( !HasCheckedChildNodes( e->Node ) ) e->Cancel = true; } // Returns a value indicating whether the specified // TreeNode has checked child nodes. bool HasCheckedChildNodes( TreeNode^ node ) { if ( node->Nodes->Count == 0 ) return false; System::Collections::IEnumerator^ myEnum = node->Nodes->GetEnumerator(); while ( myEnum->MoveNext() ) { TreeNode^ childNode = safe_cast<TreeNode^>(myEnum->Current); if ( childNode->Checked ) return true; // Recursively check the children of the current child node. if ( HasCheckedChildNodes( childNode ) ) return true; } return false; }
Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
