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<span class="productTitle">ExpTreeLib</span><br />
<span class="topicTitle">Searching the Internal Tree</span><br />
<p>
<a href="../Exp_Index.htm">ExpLib and Demo Package</a><--
<a href="ExpLib_Index.htm">ExpTreeLib Index</a><--
Tree Search
--><a href="TechNote4.htm">Comparing PIDLs</a>
--><a href="../ExpDemo/ImprovingResponsiveness.htm">Improving Responsiveness</a>
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<p>
In the discussion below, text blocks marked like <span class="note">this text</span>
is additional information that is related to the main text, but may be skipped to
follow the main line of the discussion. Text in <b>bold</b> contains the main points
of the discussion.</p>
<h3><a id="TreeSearch_BkMk">Searching the Internal Tree</a></h3>
<p>All CShItems, like all ShellItems in the Shell Namespace, are contained in a
Folder (except the Desktop). Each Folder CShItem contains two Collections, one
for Folders and one for Files. Thus the tree consists of the Desktop CShItem,
which contains a Collection of Folder, each of which also contains a Collection
of Folders, and so on. The entire internal tree then consists of the Desktop
CShItem. All CShItems will reside in the Desktop or in one of the Folders
contained within one of the Folders contained by the Desktop.</p>
<p><b>Every CShItem has its' own PIDL Property containing an Absolute PIDL which
fully describes its' location in the Shell Namespace</b>. This Absolute PIDL
also fully describes its' location in the internal tree. Therefore, it is
possible to determine if one PIDL (PIDL_A) is an <b>Ancestor</b> of another PIDL
(PIDL_C) - that is - does PIDL_C fall somewhere under PIDL_A in the tree. It is
also possible to determine if PIDL_A is the Parent of PIDL_C where <b>Parent</b>
means that PIDL_C is directly contained within PIDL_A. It is also possible to
determine if PIDL_C is <b>Equal</b> to PIDL_A.</p>
<p>Given the nature of the internal tree, the following code is used to locate
a PIDL in the tree, returning Nothing if the PIDL does not exist in the
tree:</p>
<pre lang="vbnet">
Public Shared Function FindCShItem(ByVal BaseItem As CShItem, ByVal Abs As IntPtr) As CShItem
FindCShItem = Nothing
If IsEqual(BaseItem.PIDL, Abs) Then Return BaseItem
If BaseItem.FilesInitialized AndAlso IsAncestorOf(BaseItem.PIDL, Abs, True) Then
For Each FItem As CShItem In BaseItem.FileList
If IsEqual(FItem.PIDL, Abs) Then Return FItem
Next
End If
If BaseItem.FoldersInitialized Then
For Each DItem As CShItem In BaseItem.DirectoryList
If IsEqual(DItem.PIDL, Abs) Then Return DItem
If IsAncestorOf(DItem.PIDL, Abs) Then
Return FindCShItem(DItem, Abs)
End If
Next
End If
End Function
</pre>
<p>A few notes may be needed about the Code:</p>
<ul>
<li>This code is the base CShItem.FindCShItem used for all searches that do not expand the internal tree.</li>
<li>The Function is initially called with the Desktop as the BaseItem. The function
calls itself recursively to walk down the internal tree, only looking at Folders
that are known to be Ancestors of the desired item.</li>
<li>The Properties BaseItem.xxxInitialized return False if the application has
never, directly or indirectly, expressed an interest in that Collection of Files
and Folders. Remember we are not looking for the actual Files/Folders, just
their CShItems as they exist in the tree.</li>
<li>The IsAncestor call in line 4 prevents querying BaseItem.FileList unless the
BaseItem is the immediate (Parent) ancestor of Abs.</li>
<li>The functions
<see cref = "M:ExpTreeLib.CShItem.IsAncestorOf">
IsAncestorOf</see> and
<see cref = "M:ExpTreeLib.CShItem.IsEqual">
IsEqual</see> base their results on the Absolute PIDLs
that are given to them. These functions are the key to searching the tree and
are discussed on the <a href="TechNote4.htm">next page</a>.</li>
</ul>
<p>
</p>
<p>
<b>See Next:</b></p>
<p style="margin-left: 2em">
<a href="TechNote4.htm">Comparing PIDLs</a></p>
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After 30+ years working in the IT field, mostly managing SysAdmins, I have retired. One of my hobbies returns me to programming, basically just to keep my hand in.
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