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PONullReferenceException on DropDownList.Items.FindByValue()
 

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  1. PONullReferenceException on DropDownList.Items.FindByValue()
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    <p>I hope someone can help me solve a little mystery....</p> <p>This code is in production, and working there. The issue is occuring on my localhost <em>(I'm testing a change I made before I release to staging).</em> This was working until 2 days ago and I have no idea why it would spontaneously stop working.</p> <p>(This is a .NET 3.5 Web Forms app)</p> <p>I have a list of "Organizations" that may have reported an incident. The list is populated from the Organization table in my database.</p> <pre><code>&lt;asp:DropDownList ID="Organizations" runat="server" Width="205" AutoPostBack="True" DataTextField="Name" DataValueField="Id"&gt;&lt;/asp:DropDownList&gt; </code></pre> <p>Here's the code to bind the list:</p> <pre><code>Organizations.DataSource = _service.ListOrganizations() .Where(o =&gt; o.IsDeleted == false &amp;&amp; o.ReportedBy == true) .OrderBy(o =&gt; o.Name); Organizations.DataBind(); Organizations.Items.Insert(0, new ListItem("Please make a selection", "-1")); // Find the "VICTIM...." items ListItem victim = Organizations.Items.FindByText("VICTIM"); ListItem guardian = Organizations.Items.FindByText("VICTIM'S PARENT/GUARDIAN"); ListItem child = Organizations.Items.FindByText("VICTIM'S SON/DAUGHTER"); ListItem partner = Organizations.Items.FindByText("VICTIM'S SPOUSE/DOMESTIC PARTNER"); ListItem unknown = Organizations.Items.FindByText("UNKNOWN"); // Move the "VICTIM...." items to the top of the list, under the default item Organizations.Items.Remove(victim); Organizations.Items.Remove(child); Organizations.Items.Remove(guardian); Organizations.Items.Remove(partner); Organizations.Items.Remove(unknown); Organizations.Items.Insert(1, victim); Organizations.Items.Insert(2, guardian); Organizations.Items.Insert(3, child); Organizations.Items.Insert(4, partner); Organizations.Items.Insert(5, unknown); </code></pre> <p>When I click on the "edit" icon to view/edit the details of a Case and my app tries to populate the form I get a NullReferenceException when it tries to set the SelectedIndex of the Organizations list.</p> <pre><code>Organizations.SelectedIndex = Organizations.Items.IndexOf(Organizations.Items.FindByValue(organizationId)); </code></pre> <p>If I set a breakpoint on this line (above) I can expand the Items collection and see that it does contain valid data and I can even locate the ListItem that matches the organizationId we are looking for. However, as soon as I hit F10 an exception is thrown. </p> <p>I broke this line up more to pinpoint which part is throwing the exception.</p> <pre><code>ListItem li = Organizations.Items.FindByValue(organizationId.Trim()); int idx = Organizations.Items.IndexOf(li); </code></pre> <p>I called Trim() on the organizationId just in case there were any white spaces that shouldn't be there. Organizations.Items.FindByValue(organizationId.Trim()); throws the exception. This makes no sense to me. If the item is in the list, why is it not found?</p> <p><strong>Screen Shots</strong></p> <p><img src="https://i.stack.imgur.com/OKJ9u.jpg" alt="Breakpoint: view organizationId"></p> <p>Here you can see the ListItem we're trying to select. It does exist in the Items collection.</p> <p><img src="https://i.stack.imgur.com/j98im.jpg" alt="Breakpoint: view ListItem in Items collection, it does exist"></p> <p>I thought maybe it was happening for just one Case, but it's not. I have attempted to edit multiple Cases and the same thing happens when the form is populated, no matter which Case I tried to edit.</p> <p>All advice/ideas are welcome. Thank you in advance for any assistance. </p> <h2>EDITS</h2> <p>(1) <em>"Can you tell exactly which exception is thrown?"</em> ...Here is the exception detail <img src="https://i.stack.imgur.com/qZtj8.jpg" alt="The exception detail"></p> <p>(2) Property or indexer 'System.Web.UI.WebControls.ListControl.SelectedItem' cannot be assigned to -- it is read only</p> <pre><code>Organizations.SelectedItem = Organizations.Items.FindByValue(organizationId); </code></pre> <p>(3) I get the same result if I modify the code to this (below)...it throws the same exception</p> <pre><code>ListItem li = Organizations.Items.FindByValue(organizationId); </code></pre> <p>(4) <em>"Did you try to parse it to int did you try to check it's length?"</em> <img src="https://i.stack.imgur.com/hglIB.jpg" alt="organizationId"></p> <p>(5) Here's the matching ListItem <img src="https://i.stack.imgur.com/0eDYD.jpg" alt="ListItem"></p> <p>(6) Just modified the code to <code>Organizations.Items.FindByValue(organizationId).Selected = true;</code> The exception is thrown on that line now. I rebooted my machine just for giggles, that also had no effect.</p>
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    1. COFindByValue shouldn't throw an exception, it should just return `null`. Can you tell exactly which exception is thrown?
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    2. COTo @freefaller's point, it could be that the internals of IndexOf are throwing a `NullReferenceException` with a `null` argument. You could test that by separating the IndexOf and FindByValue calls.
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    3. CO@freefaller I added a screenshot of the exception detail
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