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<span class="productTitle">ExpTreeLib Demo</span><br />
<span class="topicTitle">LVColSorter</span><br />
<p>
<a href="../Exp_Index.htm">ExpLib and Demo Package</a><--
<a href="ExpDemo_Index.htm">Exp Demo Index</a><--
LVColSorter
--><a href="../ExpTreeLib/ExpLib_Index.htm">ExpTreeLib Index</a>
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<h3><a id = "BkMrk_1">Summary</a></h3>
<p>LVColSorter is a Class to be used as a ListViewItemSorter. As with any
ListViewItemSorter, it responds to Mouse Clicks on the ColumnHeaders of the
ListView by Sorting the contents of the ListView in order of the contents of the
ListViewItem.SubItems displayed in the Clicked Column. LVColSorter has the
following additional features:</p>
<ul>
<li>Displays a Sort Glyph in the Sorted ColumnHeader. That Glyph indicates the
direction of Sort that the <i>next</i> Click on that Column will Sort.</li>
<li>Column(0) Sorting is a special case.
<ul>
<li>If the ListViewItem.Tag is set and if the Object in that .Tag supports the IComparable Interface, then
Column(0) will be Sorted on that Tag.</li>
<li>If the ListViewItem.Tag is not set (is Nothing) or if it does not support the
IComparable Interface, then Column(0) will be sorted on the .Tag or .Text
Property of ListViewItem.SubItem(0). Note that the ListViewItem and its'
SubItems(0) have separate .Tag Properties.</li>
<li>If neither of the .Tag Properties is usable for sorting, then LVColSorter will
Sort using the .Text Property.</li>
</ul></li>
<li>Sorts on the .Tag Property of the SubItems corresponding to the Clicked
ColumnHeader, if present and if of a type that
supports the IComparable Interface. If no .Tag is present, Sort will be on the
.Text Property of the SubItem.</li>
<li>If the Clicked Column is not Column(0) then Column(0) is used as a Secondary
Sort Key, following Column(0) rules.</li>
</ul>
<h3><a id = "BkMrk_2">Why .Tags and Why is Column(0) special?</a></h3>
<p>A common way of linking the individual ListViewItems to their original data
source (eg - a Class instance or a DataRow) is to set the .Tag Property of the
ListViewItem to that original data source. If it is important to Sort the
original data source, it is also likely that it will support the IComparable
Interface and may well support Sorting by its' own Sort rules. Typically, the
ListView is populated in some Sorted order, typically in the Sort order of the
original data source. Sorting Column(0) by the original data source items, will
restore the original Sort order of the ListView.</p>
<p>Using Column(0) as the Secondary Sort Key will ensure that when the ListView is
sorted by some other Column, items with equal values in the Sort Column will
also be displayed in the original sort order, grouped by unique values in the
Sort Column.</p>
<p>All of these conditions are true for ListViews in the Demo Forms which always have a
CShItem in the .Tag of each ListViewItem and alway build the ListView in the
Sort order of those CShItems. Note that CShItems have a rather complex Sort
which is similar to Windows Explorer's order.</p>
<p>The Textual representation of many Types is not necessarily Sortable by normal
alphnumeric Sorting. For example the common US representation of a Date is
"MM/dd/yyyy". Dates in this form are not directly sortable. In cases where the
.Text Property, as displayed in the ListView, is not sortable by an alphanumeric
sort, setting the original value into the .Tag Property of the corresponding
SubItem will allow LVColSorter to sort by that value rather than the .Text
Property. In the case of a Date displayed in "MM/dd/yyyy" format, set the
SubItem.Tag Property to the actual <code>Date</code> value.</p>
<h3><a id = "BkMrk_3">Usage</a></h3>
<p>Ensure that the ListView's Sort Property is set to "None" - LVColSort will take care of it.</p>
<p>To take full advantage of LVColSort, set the .Tag Properties as described above.
The below example illustrates, assuming that "item" is a CShItem:</p>
<code><pre>
Dim lvi As New ListViewItem(item.DisplayName)
lvi.Tag = item
lvi.SubItems.Add(item.CreationTime.ToString("MM/dd/yyyy HH:mm:ss"))
lvi.SubItems(lvi.SubItems.Count - 1).Tag = item.CreationTime
</pre></code>
<p>To use LVColSorter, simply assign a New instance of LVColSorter to the ListView's
ListViewColumnSorter Property. </p>
<code>
<pre> ListView1.ListViewItemSorter = New LVColSorter(ListView1)
</pre></code>
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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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