CTreeCtrl的加号和减号为何不显示

Question

    TVS_HASBUTTONS、TVS_LINESATROOT都设为TRUE了，也试过Expand(hItem, TVE_EXPAND)、Expand(hItem, TVE_COLLACT)，都没用，还是不见加号和减号；   单文档、CFormView类，具体代码如下：
void CtestView::OnInitialUpdate()
{
CFormView::OnInitialUpdate();
GetParentFrame()->RecalcLayout();
ResizeParentToFit(); CTreeCtrl *pTree = (CTreeCtrl *)GetDlgItem(IDC_TREE1);
HTREEITEM hItem,hSubItem;
hItem = pTree->InsertItem(_T("Parent1"),TVI_ROOT);//在根结点上添加Parent1
hSubItem = pTree->InsertItem(_T("Child1_1"),hItem);//在Parent1上添加一个子结点
hSubItem = pTree->InsertItem(_T("Child1_2"),hItem,hSubItem);//在Parent1上添加一个子结点，排在Child1_1后面
hSubItem = pTree->InsertItem(_T("Child1_3"),hItem,hSubItem);
//pTree->Expand(hItem, TVE_EXPAND);
//pTree->Expand(hItem, TVE_COLLACT);
hItem = pTree->InsertItem(_T("Parent2"),TVI_ROOT,hItem);    
hItem = pTree->InsertItem(_T("Parent3"),TVI_ROOT,hItem); 
}

Answer 1

看看： 
                        tvi.cChildren=1;
                         tvi.mask |= TVIF_CHILDREN;

Answer 2

加上这个：
pTree->ModifyStyle(0, TVS_HASBUTTONS | TVS_HASLINES | TVS_LINESATROOT);