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Expand branches during drag-drop

Thursday Aug 6th 1998 by Justin Rudd

Expand branches during drag-drop

"Here is a sample I whipped up over lunch and cleaned up after work. It demonstrates something that Outlook 97 and the IE 4.0 tree control do. When you drag an item and hold it over a closed node for 2 seconds it will expand it. I did it in a CTreeView derived class, but its pretty easy to understand. I used your drag-n-drop logic and just added in the timer logic."

The data members I used are


CImageList* m_pDragImage; HTREEITEM m_htiDrag, m_htiDrop, m_htiOldDrop; bool m_bLDragging; UINT m_idTimer;

Most of these are self explanatory from the drag and drop page. The new data members I added are m_htiOldDrop and m_idTimer. It should probably be called m_htiDropHilight, but I called it old drop because it is the old drop target. I keep track of the old drop target to fix a behavioral issue that IE 4.0 tree control doesn't have. Mainly, if you hilight and item and move it up and down a pixel or 2 ( where the hilight still remains ), my code would restart the timer. So I only start the timer if the drop target changed. m_idTimer is self-explanatory...it holds the ID returned by SetTimer. I use a hard-coded value of 1000 which would normally be the first dialog control ID, so you might want to change that to a const.

The following code might look a little weird in the OnMouseMove handler. What happens is on your initial mouse move action, m_htiOldDrop is NULL and gets set to whatever GetDropHilightItem returns. If it returns NULL, it will try to init it next time through. Once it gets initialized, the following check basically says, if we have a valid timer ID and the current item found through hit testing (hti) is equal to the old drop target kill the timer and start over. The behavior that this fixes is described above, but repeated here...with IE 4.0 installed, if you drag files from the listview in the right pane to the tree view in the left pane, you can have the selection hover over a closed node and it will expand automatically. One thing that it does is if you accidently shift the mouse while sitting there, as long as the hilight stays the same, it will still open it, it won't restart the timer like mine would before. But with this if statement and the data member m_htiOldDrop, I was able to get around this. So it will only kill the timer if you move back over the original drop target.

if( m_idTimer && hti == m_htiOldDrop ) { KillTimer( m_idTimer ); m_idTimer = 0; } if( !m_idTimer ) m_idTimer = SetTimer( 1000, 2000, NULL );

Now in response to the timer message, I basically just get the drop hilight item and check if it has children. If it does, I expand it.


void CDragView::OnTimer(UINT nIDEvent) { if( nIDEvent == m_idTimer ) { CTreeCtrl& theTree = GetTreeCtrl(); HTREEITEM htiFloat = theTree.GetDropHilightItem(); if( htiFloat && htiFloat == m_htiDrop ) { if( theTree.ItemHasChildren( htiFloat ) ) theTree.Expand( htiFloat, TVE_EXPAND ); } } CTreeView::OnTimer(nIDEvent); }

Justin has provided a zipped file that you can download (52k).

Here's some of the other code that help in the drag-drop.


void CDragView::OnBeginDrag(NMHDR* pNMHDR, LRESULT* pResult) { NM_TREEVIEW* pNMTreeView = (NM_TREEVIEW*)pNMHDR; m_htiDrag = pNMTreeView->itemNew.hItem; m_htiDrop = NULL; m_pDragImage = GetTreeCtrl().CreateDragImage( m_htiDrag ); if( !m_pDragImage ) return; m_bLDragging = true; CPoint pt(0,0); IMAGEINFO ii; m_pDragImage->GetImageInfo( 0, &ii ); pt.x = (ii.rcImage.right - ii.rcImage.left) / 2; pt.y = (ii.rcImage.bottom - ii.rcImage.top) / 2; m_pDragImage->BeginDrag( 0, pt ); pt = pNMTreeView->ptDrag; ClientToScreen( &pt ); m_pDragImage->DragEnter(NULL,pt); SetCapture(); *pResult = 0; } void CDragView::OnLButtonUp(UINT nFlags, CPoint point) { CTreeView::OnLButtonUp(nFlags, point); if( m_bLDragging ) { CTreeCtrl& theTree = GetTreeCtrl(); m_bLDragging = false; CImageList::DragLeave(this); CImageList::EndDrag(); ReleaseCapture(); delete m_pDragImage; theTree.SelectDropTarget(NULL); m_htiOldDrop = NULL; if( m_htiDrag == m_htiDrop ) return; HTREEITEM htiParent = m_htiDrop; while( (htiParent = theTree.GetParentItem(htiParent)) != NULL ) { if( htiParent == m_htiDrag ) return; } theTree.Expand( m_htiDrop, TVE_EXPAND ); HTREEITEM htiNew = CopyBranch( m_htiDrag, m_htiDrop, TVI_LAST ); theTree.DeleteItem(m_htiDrag); theTree.SelectItem( htiNew ); if( m_idTimer ) { KillTimer( m_idTimer ); m_idTimer = 0; } } } void CDragView::OnMouseMove(UINT nFlags, CPoint point) { CTreeView::OnMouseMove(nFlags, point); HTREEITEM hti; UINT flags; if( m_bLDragging ) { CTreeCtrl& theTree = GetTreeCtrl(); POINT pt = point; ClientToScreen( &pt ); CImageList::DragMove(pt); hti = theTree.HitTest(point,&flags); if( hti != NULL ) { CImageList::DragShowNolock(FALSE); if( m_htiOldDrop == NULL ) m_htiOldDrop = theTree.GetDropHilightItem(); theTree.SelectDropTarget(hti); m_htiDrop = hti; if( m_idTimer && hti == m_htiOldDrop ) { KillTimer( m_idTimer ); m_idTimer = 0; } if( !m_idTimer ) m_idTimer = SetTimer( 1000, 2000, NULL ); CImageList::DragShowNolock(TRUE); } } } HTREEITEM CDragView::CopyItem ( HTREEITEM hti, HTREEITEM htiNewParent, HTREEITEM htiAfter // = TVI_LAST ) { CTreeCtrl& theTree = GetTreeCtrl(); TVINSERTSTRUCT insert; ::ZeroMemory(&insert, sizeof(TVINSERTSTRUCT)); HTREEITEM htiNew = NULL; CString text; insert.item.hItem = hti; insert.item.mask = TVIF_CHILDREN|TVIF_HANDLE|TVIF_IMAGE|TVIF_SELECTEDIMAGE; theTree.GetItem(&(insert.item)); text = theTree.GetItemText( hti ); insert.item.cchTextMax = text.GetLength(); insert.item.pszText = text.LockBuffer(); insert.hParent = htiNewParent; insert.hInsertAfter = htiAfter; insert.item.mask = TVIF_IMAGE|TVIF_SELECTEDIMAGE|TVIF_TEXT; htiNew = theTree.InsertItem(&insert); text.UnlockBuffer(); theTree.SetItemData( htiNew, theTree.GetItemData( hti ) ); theTree.SetItemState( htiNew, theTree.GetItemState( hti, TVIS_STATEIMAGEMASK ), TVIS_STATEIMAGEMASK ); return htiNew; } HTREEITEM CDragView::CopyBranch ( HTREEITEM hti, HTREEITEM htiNewParent, HTREEITEM htiAfter // = TVI_LAST ) { CTreeCtrl& theTree = GetTreeCtrl(); HTREEITEM htiChild = NULL; HTREEITEM htiNew = CopyItem( hti, htiNewParent, htiAfter ); htiChild = theTree.GetChildItem( hti ); while( htiChild != NULL ) { CopyBranch( htiChild, htiNew ); htiChild = theTree.GetNextSiblingItem( htiChild ); } return htiNew; } void CDragView::OnDestroy() { CImageList* pImage = GetTreeCtrl().GetImageList( TVSIL_NORMAL ); delete pImage; if( m_idTimer ) { KillTimer( m_idTimer ); m_idTimer = 0; } CTreeView::OnDestroy(); }

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