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POArgumentOutOfRangeException when sorting a DataGridView using a custom IComparer
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copied!<h2>Setup</h2> <p>I have a piece of code that is sorting a DataGridView using a custom IComparer:</p> <pre><code>public class CustomComparer: IComparer { public int Compare(object x, object y) { DataGridViewRow row1 = (DataGridViewRow)x; DataGridViewRow row2 = (DataGridViewRow)y; if (row1.ReadOnly && row2.ReadOnly) { return 0; } else if (row1.ReadOnly && !row2.ReadOnly) { return 1; } else { return -1; } } </code></pre> <h2>Problem</h2> <p>Strangely, when I execute the following line (after populating the rows):</p> <pre><code>grid.Sort(new CustomComparer()); </code></pre> <p>I get an ArgumentOutOfRangeException with the message "Index was out of range. Parameter: index".</p> <h2>More Facts</h2> <p>Further investigation revealed the following:</p> <ul> <li>The DataGridView I'm sorting <em>doesn't</em> have a BindingSource on it - rows have been manually added.</li> <li>The Stack Trace of the error is only one level deep - it occurs on an InternalDictionary in mscorlib</li> <li>Strange fact #1 - This only happens if at any point, my custom comparer returns -1 for any of its comparisons</li> <li>If I change the Sort method to no longer use my CustomComparer, the exception is not thrown.</li> </ul> <h2>Workaround</h2> <p>This last fact led me to rewrite the Compare() method to defer to .NET's CompareTo method:</p> <pre><code>DataGridViewRow row1 = (DataGridViewRow)x; DataGridViewRow row2 = (DataGridViewRow)y; return row1.ReadOnly.CompareTo(row2.ReadOnly); </code></pre> <p>Which mysteriously <strong>worked</strong>. The exception is no longer thrown.</p> <p>So although I have a workaround, I wonder if anyone has any idea why this could possibly be a fix, and what the issue might have been in the first place. I've looked at the implementation of CompareTo and it <em>also</em> returns -1...</p>

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