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PODataSource containing a null value makes ComboBox fail
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  1. PODataSource containing a null value makes ComboBox fail
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    copied!<p>I've thrown myself headfirst into C# and .Net 2.0 using Linq, and I'm having a few problems debugging some of the problems, namely the following:</p> <p>I have a ComboBox control (<code>cmbObjects</code>) I want to populate with a set of objects retrieved using Linq. I've written a helper method to populate a <code>List&lt;T&gt;</code> generic:</p> <pre><code>class ObjectProvider { public static List&lt;T&gt; Get&lt;T&gt;(bool includeNull) where T : class, new() { List&lt;T&gt; list = new List&lt;T&gt;(); LutkeDataClassesDataContext db = ConnectionManager.GetConnection(); IQueryable&lt;T&gt; objects = db.GetTable&lt;T&gt;().AsQueryable(); if (includeNull) list.Add(null); foreach (T o in objects) list.Add(o); return list; } public static List&lt;T&gt; Get&lt;T&gt;() where T : class, new() { return Get&lt;T&gt;(false); } } </code></pre> <p>I verified the results when calling the function with true or false - the <code>List</code> does contain the right values, when passing <code>true</code>, it contains <code>null</code> as the first value, followed by the other objects.</p> <p>When I assign the <code>DataSource</code> to the <code>ComboBox</code> however, the control simply refuses to display any items, including the <code>null</code> value (not selectable):</p> <pre><code>cmbObjects.DataSource = ObjectProvider.Get&lt;Car&gt;(true); </code></pre> <p>Passing in <code>false</code> (or no parameter) does work - it displays all of the objects.</p> <p>Is there a way for me to specify a "null" value for the first object without resorting to magic number objects (like having a bogus entry in the DB just to designate a N/A value)? Something along the lines of a nullable would be ideal, but I'm kind of lost.</p> <p>Also, I've tried adding <code>new T()</code> instead of <code>null</code> to the list, but that only resulted in an <code>OutOfMemoryException</code>.</p>
 

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