Setting CTreeCtrl item's checkbox to partial state

First I add TVS_EX_PARTIALCHECKBOXES to the CTreeCtrl's extended styles:

TreeView_SetExtendedStyle(tree->GetSafeHwnd(), TVS_EX_PARTIALCHECKBOXES, TVS_EX_PARTIALCHECKBOXES);

Now how do I actually set any item to this state? There doesn't appear to be any documentation about that. I guessed that since checking and unchecking works by changing the item's state image to 1 or 2, I can try my luck with 3:

tree->SetItemState(tree->GetFirstVisibleItem(), INDEXTOSTATEIMAGEMASK(3), TVIS_STATEIMAGEMASK);

Of course that would have been too easy, it just made the image disappea开发者_运维百科r.

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Maybe you need to use tree->SetCheck() instead of tree->SetItemState(), Try setting check state to 2.