TVM_EXPAND message

The TVM_EXPAND message expands or collapses the list of child items associated with the specified parent item, if any. You can send this message explicitly or by using the TreeView_Expand macro.



Action flag. This parameter can be one or more of the following values:


Collapses the list.


Collapses the list and removes the child items. The TVIS_EXPANDEDONCE state flag is reset. This flag must be used with the TVE_COLLAPSE flag.


Expands the list.


Version 4.70. Partially expands the list. In this state the child items are visible and the parent item's plus sign (+), indicating that it can be expanded, is displayed. This flag must be used in combination with the TVE_EXPAND flag.


Collapses the list if it is expanded or expands it if it is collapsed.



Handle to the parent item to expand or collapse.

Return value

Returns nonzero if the operation was successful, or zero otherwise.


Expanding a node that is already expanded is considered a successful operation and SendMessage returns a nonzero value. Collapsing a node returns zero if the node is already collapsed; otherwise it returns nonzero. Attempting to expand or collapse a node that has no children is considered a failure and SendMessage returns zero.

When an item is first expanded by a TVM_EXPAND message, the action generates TVN_ITEMEXPANDING and TVN_ITEMEXPANDED notification codes and the item's TVIS_EXPANDEDONCE state flag is set. As long as this state flag remains set, subsequent TVM_EXPAND messages do not generate TVN_ITEMEXPANDING or TVN_ITEMEXPANDED notifications. To reset the TVIS_EXPANDEDONCE state flag, you must send a TVM_EXPAND message with the TVE_COLLAPSE and TVE_COLLAPSERESET flags set. Attempting to explicitly set TVIS_EXPANDEDONCE will result in unpredictable behavior.

The expand operation may fail if the owner of the treeview control denies the operation in response to a TVN_ITEMEXPANDING notification.


Minimum supported client

Windows Vista [desktop apps only]

Minimum supported server

Windows Server 2003 [desktop apps only]