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POObjects need to be disposed in a specific order: is this a code smell?
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  1. POObjects need to be disposed in a specific order: is this a code smell?
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    copied!<p><strong>The context</strong></p> <p>I'm working with a Winforms application (.NET 3.5 SP1) which has the concept of workspaces, which can contain n number of panels. Each panel (derives from <code>Panel</code>) has view:</p> <pre> .-----------------------. |Workspace | |.--------. .--------. | ||Panel1 | |Panel2 | | ||.-----. | |.-----. | | |||View1| | ||View2| | | ||'-----' | |'-----' | | |'--------' '--------' | '-----------------------' </pre> <p>All panels get added to the <code>this.Controls</code> collection of the Workspace class (which derives from an <code>UltraTabPageControl</code>, an Infragistics GUI control). Each view is added to the <code>Controls</code> collection of their parent. So, when <code>Dispose</code> is called on the Workspace, the panels and views automatically get disposed, which is completely expected and desired.</p> <p>We have another concept called a <code>ViewManager</code>. It keeps track of all the <code>View</code> controls in the workspace, and is in charge of maintaining a single "master" view. Whenever a <code>View</code> is created, it registers itself with this manager. This adds the <code>View</code> to a list, and then runs some logic to determine the new "master" view and then calls a <code>Synchronize()</code> method on each View.</p> <p>The current design is that, whenever <code>View.Dispose()</code> is called, it unregisters itself from the <code>ViewManager</code>. This removes the <code>View</code> from the list, and then runs corresponding logic that checks for a new master, out of the remaining views.</p> <p><strong>The twist</strong></p> <p>When we are closing an entire workspace, there is one special <code>Panel</code> type that needs to be closed before other panels. So we have code in our <code>Dispose</code> method that looks like this:</p> <pre><code>protected override void Dispose(bool disposing) { var theSpecialPanel = GetSpecialPanel(); if (theSpecialPanel != null) { theSpecialPanel.Dispose(); } base.Dispose(disposing); } </code></pre> <p>If we take out that code, then other panels may be disposed before <code>theSpecialPanel</code>. This causes the logic that checks for a new master panel to be run, calls <code>Synchronize()</code> on each <code>View</code> including this special panel. This throws an </p> <p>"InvalidComObjectException: COM object that has been separated from its underlying RCW cannot be used."</p> <p><strong>The question</strong></p> <p>Is this design is a code smell? Is it strange to enforce that a specific object gets disposed before others?</p>
 

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