TreeView::BeforeCheck Event
Occurs before the tree node check box is checked.
Assembly: System.Windows.Forms (in System.Windows.Forms.dll)
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Setting the TreeNode::Checked property from within the BeforeCheck or AfterCheck event causes the event to be raised multiple times and can result in unexpected behavior. For example, you might set the Checked property in the event handler when you are recursively updating the child nodes, so that the user does not have to expand and check each one individually. To prevent the event from being raised multiple times, add logic to your event handler that only executes your recursive code if the Action property of the TreeViewEventArgs is not set to TreeViewAction::Unknown. |
For more information about how to handle events, see Consuming Events.
The following code example updates all the child tree nodes of a TreeNode when the user changes its checked state. This code requires that you have a Form with a TreeView that has TreeNode objects in its TreeNodeCollection. The TreeNodeCollection should have tree nodes with child nodes.
// Updates all child tree nodes recursively. void CheckAllChildNodes( TreeNode^ treeNode, bool nodeChecked ) { IEnumerator^ myEnum = treeNode->Nodes->GetEnumerator(); while ( myEnum->MoveNext() ) { TreeNode^ node = safe_cast<TreeNode^>(myEnum->Current); node->Checked = nodeChecked; if ( node->Nodes->Count > 0 ) { // If the current node has child nodes, call the CheckAllChildsNodes method recursively. this->CheckAllChildNodes( node, nodeChecked ); } } } // NOTE This code can be added to the BeforeCheck event handler instead of the AfterCheck event. // After a tree node's Checked property is changed, all its child nodes are updated to the same value. void node_AfterCheck( Object^ /*sender*/, TreeViewEventArgs^ e ) { // The code only executes if the user caused the checked state to change. if ( e->Action != TreeViewAction::Unknown ) { if ( e->Node->Nodes->Count > 0 ) { /* Calls the CheckAllChildNodes method, passing in the current Checked value of the TreeNode whose checked state changed. */ this->CheckAllChildNodes( e->Node, e->Node->Checked ); } } }
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.
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