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copied!<p>Change events are raised on every postback for which they're relevant - as described in the MSDN topic "<a href="http://msdn.microsoft.com/en-us/library/y3bwdsh3.aspx" rel="nofollow noreferrer">ASP.NET Web Server Control Event Model</a>."</p> <blockquote> <p>Change events in HTML server controls and Web server controls, such as the TextBox control, do not immediately cause a post. Instead, <strong>they are raised</strong> <strong>the next time a post occurs</strong>.</p> </blockquote> <p>When users click your 'Edit Artist' button, ASP.NET thinks <code>lbLinks.SelectedIndex</code> has changed, so it invokes its <code>SelectedIndexChanged</code> handler.</p> <p>The <em>reason</em> ASP.NET thinks the index has changed is this: when the page first loads, <code>lbLinks</code> doesn't have a selected index (or value) unless you say otherwise by explicitly setting it. Until you do that, the selected index is -1 and its selected value is an empty string. The selected value (in this case, an empty string) is written to view state when the page is rendered <em>so that ASP.NET can tell if the value has changed on postbacks</em>.</p> <p>You can observe this while debugging by inspecting your list boxes' selected indices and values before rendering, or you can use one of the online view state decoders (<a href="http://lachlankeown.blogspot.com/2008/05/online-viewstate-viewer-decoder.html" rel="nofollow noreferrer">like this one</a>) to see what's in your page when it's first written (though to read this, you need to know about <a href="http://msdn.microsoft.com/en-us/library/ms972976.aspx#viewstate_topic11" rel="nofollow noreferrer">the structure of serialized view state data</a>).</p> <p>When you next post back, the HTML <code><select></code> element <code>lbLinks</code> <em>has a non-empty value</em>, and it is submitted as part of the post data. Take a look at <code>Request.Form["lbLinks"]</code> and you'll see that it equals <code>lbLinks.Items[0].Value</code>.</p> <p>ASP.NET maps the posted value to <code>lbLinks.SelectedValue</code>, but it also knows that the selected value <em>used to be an empty string</em> - it gets the old value from view state. Since the two values are different, the process raises the control's selected index changed event, causing the undesirable behavior you've observed.</p> <p><a href="https://stackoverflow.com/questions/1733077/why-do-unrelated-autopostback-methods-get-called-when-an-asp-net-listbox-autopo/1752797#1752797">As boon suggested</a>, the solution is to always explicitly set the <code>SelectedIndex</code> for all your <code>ListBox</code> controls when you're using the <code>OnSelectedIndexChanged</code> event, even if you're just setting the index to zero.</p> <p>(The AutoPostBack setting is an unrelated red herring. If you remove it from both list boxes, their <code>OnSelectedIndexChanged</code> events will both fire every time you click the button.)</p>

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