CTreeCtrl: prevent expanded node from collapsing

>>>> It is very easy to mess things up when you begin handling individual events in a tree control.  
That is true though it must not happen. In the last years I saw at least 5 implementations of a class derived from CListCtrl which uses the usual way via parent notification for handling the double-click and not doing it in PreTranslateMessage.

The problem (and benefit) of handling events in PreTranslateMessage is that it is a very early time where you would get the trigger (only catching mouse events would be earlier) but - as the name says - where the design only had intended a *translation* and not a handling. If you catch the WM_LBUTTONDBLCLK in PreTranslateMessage the function doesn't know more that a double-click happened somewhere at the list-control. You would need to find out by means of HitTest where the click actually happened and whether it is the situation where you want to prevent the collapsing. If so, you have to do all other actions the tree-control now would do automatically yourself, e. g. high-liting or selecting the current item. All these actions may cause other events to some other items what can produce the same mess of individual handling of events which you wanted to prevent. Also if double-clicking on an item should cause some further actions like showing additional informations or invoke a dialog you now must handle this in a very basic event handler. Of course you can do that calling virtual functions and other high-level and high-logic member function but you should never forget that after all actions you invoked you would return to the very basic PreTranslateMessage where you now stop any further handling of the current double-click by returning HANDLED=TRUE.

Generally, I admit that by overriding PreTranslateMessage you may have fast success where you may experience some more troubles when installing a normal double-click notification handler. But it is similar to virginity. You can loose it only once. If later you or others will derive again from the class and have a normal notification handler, they won't get notifications. And hopefully they will remember or find out that there is a PreTranslateMessage which is responsible for the abnormal behavior.

Here's what I'm doing now:

void CUserOptions::OnNMDblclkTree1(NMHDR *pNMHDR, LRESULT *pResult)
{
      // TODO: Add your control notification handler code here

      HTREEITEM ht = m_optionList.GetSelectedItem();

      if ( m_treeOptionUsers == ht )
            if (m_optionList.GetItemState( ht, TVIS_EXPANDED ))
            {
                  
                  return;
            }
      else
            m_optionList.Expand(ht, TVE_EXPAND);


      *pResult = 0;
}

Again, I'm trying to keep the parent nodes expanded (I'm only showing one parent node for clarity).

>>>>      if ( m_treeOptionUsers == ht )
>>>>             if (m_optionList.GetItemState( ht, TVIS_EXPANDED ))
>>>>             {
>>>>                   
>>>>                   return;
>>>>             }
>>>>       else
>>>>             m_optionList.Expand(ht, TVE_EXPAND);

Looks as if the 'else' would belong to the wrong if ....

I've tried it both places and neither works.  The node still expands and collapses like normal.  I need it to NOT collapse.

Thanks, Dan, that was just what I needed.  Any advise on suppressing the flicker that occurs when the control redraws?

You could try LockWindowUpdate() on the tree control.

http://msdn.microsoft.com/en-us/library/dd145034(VS.85).aspx

I've never tried it. The flicker could act as a visual cue that the user should not try to collapse those items. You might even want to add

    MessageBeep(-1);

As further indication that your program is working as designed and is not broken. Users expect trees to be fully collapsable and expandable. I've found that when your program does things that are not expected, you can expect tech support phone calls. :-)

The below code successfully prevents from any collapsing and it doesn't flicker either.

The difference to above codes is that I handled the TVN_ITEMEXPANDING notification and not the TVN_ITEMEXPANDED notification. The second needs to expand an already collapsed branch while the first is sent *prior*  to the expanding.

void TestMfcDlg::OnTvnItemexpandingTree1(NMHDR *pNMHDR, LRESULT *pResult)
{
    LPNMTREEVIEW pNMTreeView = reinterpret_cast<LPNMTREEVIEW>(pNMHDR);
    if ((pNMTreeView->action & TVE_COLLAPSE) != 0)
        *pResult = 1;   // stop collapsing
    else
        *pResult = 0;
}
                                              

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Yes.  As I mentioned in my comment, I tried that first.  However, I muffed the coding.

dhenderson12,
Your best bet is to handle the TVN_ITEMEXPANDING message, checking for TVE_COLLAPSE and setting *pResult to 1 if so, and 0 otherwise.

If you have multiple levels in the tree, and you want to allow the lower levels to collapse, then you should also check

    pNMTreeView->itemNew.hItem

...and if it is one that you want to allow to collapse, theh set *pResult to 0 on those (and set *pResult to 1 for the item that you do not want to allow to collapse).

I'd also still recommend the beep whenever you do not honor a U/I request to collpase.