ch19.htm

24小时学会vc++

		<TD ALIGN="LEFT" VALIGN="TOP"><B>Message</B></TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><B>Function</B></TD>
	</TR>
	<TR ALIGN="LEFT" rowspan="1">
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>IDC_TREE</TT></TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>TVN_BEGINDRAG</TT></TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>OnBegindragTree</TT></TD>
	</TR>
	<TR ALIGN="LEFT" rowspan="1">
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>CAboutDlg</TT></TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>WM_MOUSEMOVE</TT></TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>OnMouseMove</TT></TD>
	</TR>
	<TR ALIGN="LEFT" rowspan="1">
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>CAboutDlg</TT></TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>WM_LBUTTONUP</TT></TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>OnLButtonUp</TT></TD>
	</TR>
</TABLE>
</P>
<P>The source code for the three functions is provided in Listing 19.6.
<H4><FONT COLOR="#000077">TYPE: Listing 19.6. Functions used to implement simple
drag and drop.</FONT></H4>
<PRE><FONT COLOR="#0066FF"><TT>void CAboutDlg::OnBegindragTree(NMHDR* pNMHDR, LRESULT* pResult)</TT>
<TT>{</TT>
<TT>    NM_TREEVIEW* pNMTreeView = (NM_TREEVIEW*)pNMHDR;</TT>
<TT>    m_dragItem = pNMTreeView-&gt;itemNew.hItem;</TT>
<TT>    if( m_tree.GetParentItem( m_dragItem ) != NULL )</TT>
<TT>    {</TT>
<TT>        CImageList* pDragImage;</TT>
<TT>        pDragImage = m_tree.CreateDragImage( m_dragItem );</TT>
<TT>        m_tree.SelectItem( m_dragItem );</TT>
<TT>        pDragImage-&gt;BeginDrag( 0, CPoint(0,0) );</TT>
<TT>        pDragImage-&gt;DragEnter( &amp;m_tree, pNMTreeView-&gt;ptDrag );</TT>
<TT>        SetCapture();</TT>
<TT>        m_bIsDragging = TRUE;</TT>
<TT>        delete pDragImage;</TT>
<TT>    }</TT>
<TT>    *pResult = 0 ;</TT>
<TT>}</TT>
<TT>void CAboutDlg::OnMouseMove(UINT nFlags, CPoint point)</TT>
<TT>{</TT>
<TT>    if( m_bIsDragging != FALSE )</TT>
<TT>    {</TT>
<TT>        CPoint      ptTree( point );</TT>
<TT>        MapWindowPoints( &amp;m_tree, &amp;ptTree, 1 );</TT>
<TT>        CImageList::DragMove( ptTree );</TT>
<TT>        UINT uHitTest = TVHT_ONITEM;</TT>
<TT>        m_dragTarget = m_tree.HitTest( ptTree, &amp;uHitTest );</TT>
<TT>    }</TT>
<TT>    CDialog::OnMouseMove(nFlags, point);</TT>
<TT>}</TT>
<TT>void CAboutDlg::OnLButtonUp(UINT nFlags, CPoint point)</TT>
<TT>{</TT>
<TT>    if( m_bIsDragging != FALSE )</TT>
<TT>    {</TT>
<TT>        CImageList::DragLeave( &amp;m_tree );</TT>
<TT>        CImageList::EndDrag();</TT>
<TT>        ReleaseCapture();</TT>
<TT>        m_bIsDragging = FALSE;</TT>
<TT>        if( m_dragTarget != NULL )</TT>
<TT>        {</TT>
<TT>            HTREEITEM hParent;</TT>
<TT>            hParent = m_tree.GetParentItem( m_dragTarget );</TT>
<TT>            CString szLabel = m_tree.GetItemText( m_dragItem );</TT>
<TT>            if( hParent != NULL )</TT>
<TT>                m_tree.InsertItem( szLabel, 1, 1, hParent,</TT>
<TT>                                   m_dragTarget );</TT>
<TT>            else</TT>
<TT>                m_tree.InsertItem( szLabel, 1, 1, m_dragTarget,</TT>
<TT>                                   TVI_FIRST );</TT>
<TT>            m_tree.DeleteItem( m_dragItem );</TT>
<TT>        }</TT>
<TT>    }</TT>
<TT>    else</TT>
<TT>        CDialog::OnLButtonUp(nFlags, point);</TT>
</FONT></PRE>
<P><TT>}</TT> The source code in Listing 19.6 is all you need to perform a drag-and-drop
operation inside a single control. The drag sequence begins with the tree view control
sending the <TT>TVN_DRAGBEGIN</TT> to the control's parent--in this case, the TreeEx
About dialog box. The MFC framework translates this message into a <TT>CAboutDlg::OnBegindragTree</TT>
function call. Inside this function, the handle to the drag item is stored in <TT>m_dragItem</TT>.


<BLOCKQUOTE>
	<P>
<HR>
<B> </B><FONT COLOR="#000077"><B>Just a Minute:</B></FONT><B> </B>In this example,
	you aren't dragging items at the first, or root level, so <TT>GetParentItem</TT>
	is used to get a handle to the drag item's parent; if <TT>NULL</TT> is returned,
	the item is at the root level, and the drag never starts. 
<HR>


</BLOCKQUOTE>

<P>As the mouse is moved across the screen during the drag and drop, <TT>WM_MOUSEMOVE</TT>
messages are sent to the dialog box, just as in the ListEx example from Hour 18.</P>
<P>At some point, the user releases the left mouse button, resulting in a <TT>WM_LBUTTONUP</TT>
message, which is translated into a call to the <TT>CAboutDlg::OnLButtonUp</TT> function.
If a drag and drop is in progress, the operation is completed by calling the <TT>DragLeave</TT>
and <TT>EndDrag</TT> functions. The mouse capture is released, and the <TT>m_bIsDragging</TT>
flag is set to <TT>FALSE</TT>.</P>
<P>The completion of a drag and drop is slightly more complicated in a tree view
control than in a list view control. If the drop target is a second-level item, the
drag item is inserted just after the drop target. If the drop target is a root-level
item, the drag item is inserted as the first child item. These calls to the <TT>InsertItem</TT>
function use a fourth parameter, which is a handle for the item just before the new
item. This parameter can be one of three predefined values:

<UL>
	<LI><TT>TVI_FIRST</TT> inserts the item as the first child, as used in this example.
	<LI><TT>TVI_LAST</TT> inserts the item as the last child.
	<LI><TT>TVI_SORT</TT> sorts the item alphabetically.
</UL>

<P>After the drag item has been inserted in a new position, the old position is removed
using the <TT>DeleteItem</TT> function. In order to implement a copy-drag, just eliminate
the call to <TT>DeleteItem</TT>.
<H3><FONT COLOR="#000077"><B>Performing In-Place Label Editing</B></FONT></H3>
<P>Like the list view control, the tree view control offers a built-in Edit control
that you can use to edit items contained in the control. In order to take advantage
of this capability, the tree view control must have its Edit labels property checked.</P>
<P>In addition to setting the tree view control style, there are two messages that
relate to label editing:

<UL>
	<LI><TT>TVN_BEGINLABELEDIT</TT>, which is sent just before the label editing begins.
	<LI><TT>TVN_ENDLABELEDIT</TT>, which is sent after editing is completed or after
	the user has cancelled the editing operation.
</UL>

<P>These messages are handled exactly as they are for a list view control. When you
receive <TT>TVN_BEGINLABELEDIT</TT>, you can prevent a label from being edited by
setting <TT>*pResult</TT> to <TT>TRUE</TT>, and you can allow editing to proceed
by setting <TT>*pResult</TT> to <TT>FALSE</TT>. In addition, you can use the <TT>TVN_BEGINLABELEDIT</TT>
message to take control of the tree view's edit control.</P>
<P>The <TT>TVN_ENDLABELEDIT</TT> message is used exactly like the <TT>LVN_ENDLABELEDIT</TT>
message is used with a list view control.


<BLOCKQUOTE>
	<P>
<HR>
<B> </B><FONT COLOR="#000077"><B>CAUTION:</B></FONT><B> </B>If you use the newly
	edited label text in your application, make sure to look out for situations in which
	the user has cancelled the label editing operation. When this happens, the <TT>TV_ITEM</TT>
	<TT>pszText</TT> member variable is set to <TT>NULL</TT>, or the <TT>iItem</TT> member
	variable is set to <TT>-1</TT>. 
<HR>


</BLOCKQUOTE>

<P>Add new message-handling functions for the label editing messages using the values
in Table 19.6.
<H4><FONT COLOR="#000077">Table 19.6. Message-handling functions used for label editing.</FONT></H4>
<P>
<TABLE BORDER="1">
	<TR ALIGN="LEFT" rowspan="1">
		<TD ALIGN="LEFT" VALIGN="TOP"><B>Class Name</B></TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><B>Object ID</B></TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><B>Message</B></TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><B>Function</B></TD>
	</TR>
	<TR ALIGN="LEFT" rowspan="1">
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>CAboutDlg</TT></TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>IDC_TREE</TT></TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>TVN_BEGINLABELEDIT</TT></TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>OnBeginlabeleditTree</TT></TD>
	</TR>
	<TR ALIGN="LEFT" rowspan="1">
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>CAboutDlg</TT></TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>IDC_TREE</TT></TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>TVN_ENDLABELEDIT</TT></TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>OnEndlabeleditTree</TT></TD>
	</TR>
</TABLE>
</P>
<P>The source code for these functions is provided in Listing 19.7.
<H4><FONT COLOR="#000077">TYPE: Listing 19.7. Functions used to implement simple
drag and drop.</FONT></H4>
<PRE><FONT COLOR="#0066FF"><TT>void CAboutDlg::OnBeginlabeleditTree(NMHDR* pNMHDR, LRESULT* pResult)</TT>
<TT>{</TT>
<TT>    *pResult = FALSE;</TT>
<TT>}</TT>

<TT>void CAboutDlg::OnEndlabeleditTree(NMHDR* pNMHDR, LRESULT* pResult)</TT>
<TT>{</TT>
<TT>    *pResult = TRUE;</TT>
</FONT></PRE>
<P><TT>}</TT> Compile and run the TreeEx project. Experiment with editing item labels,
drag and drop, and removing items in the About dialog box.
<H2><FONT COLOR="#000077"><B>Summary</B></FONT></H2>
<P>In this hour, you learned about the tree view control and created two examples:
a tree view used as an SDI main view and a tree view control in a dialog box. You
also learned about drag and drop as well as edit notifications.
<H2><FONT COLOR="#000077"><B>Q&amp;A</B></FONT></H2>

<DL>
	<DD><B>Q How can I allow or deny label editing based on the text the user has entered
	into a label?</B><BR>
	<BR>
	<B>A</B> When you receive the <TT>TVN_ENDLABELEDIT</TT> message, you can check the
	value stored in the <TT>pszText</TT> member of the item structure. If the string
	is valid, set <TT>*pResult</TT> to <TT>TRUE</TT>, otherwise, set it to <TT>FALSE</TT>
	to reject the change.<BR>
	<BR>
	<B>Q How can I force the tree view control to scroll to a particular position?</B><BR>
	<BR>
	<B>A</B> You can force a particular item to be visible by calling the <TT>CTreeCtrl::EnsureVisible</TT>
	function:
</DL>



<BLOCKQUOTE>
	<PRE><FONT COLOR="#0066FF"><TT>m_tree.EnsureVisible(hItem);</TT></FONT></PRE>

</BLOCKQUOTE>

<PRE><FONT COLOR="#0066FF"><TT></TT></FONT></PRE>

<DL>
	<DD>The tree view control will scroll if necessary to display the item referred to
	by <TT>hItem</TT>. If the item is hidden under a parent, the tree will be expanded
	to show the item.
</DL>

<H2><FONT COLOR="#000077"><B>Workshop</B></FONT></H2>
<P>The Workshop is designed to help you anticipate possible questions, review what
you've learned, and begin thinking ahead to putting your knowledge into practice.
The answers to the quiz are in Appendix B, &quot;Quiz Answers.&quot;
<H3><FONT COLOR="#000077"><B>Quiz</B></FONT></H3>

<DL>
	<DD>1. What messages are sent when a user edits a tree view label?<BR>
	<BR>
	2. What messages must be handled to implement drag and drop?<BR>
	<BR>
	3. Why are two image list indexes specified when adding an item that displays an
	image to a tree view control?<BR>
	<BR>
	4. What <TT>CTreeCtrl</TT> member function is used to remove all items in a tree
	view control?<BR>
	<BR>
	5. How do you change the properties for a tree view control that is part of the <TT>CTreeView</TT>
	class?<BR>
	<BR>
	6. What properties are available specifically for tree view controls, and what are
	their equivalent window styles?<BR>
	<BR>
	7. How are individual tree view items referred to?<BR>
	<BR>
	8. What is the size of the images used by the tree view control?<BR>
	<BR>
	9. How do you insert an item as the first child under a parent?
</DL>

<H3><FONT COLOR="#000077"><B>Exercises</B></FONT></H3>

<DL>
	<DD>1. Modify the <TT>CAboutDlg</TT> so that you can add an item to the tree view
	control.<BR>
	<BR>
	2. Add an additional item to the <TT>IDB_TREE</TT> image list. Use the new image
	list item when a top-level tree view control item is selected.<FONT COLOR="#000077"></FONT>
</DL>

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