Postback Event when using SharePoint:PeopleEditor

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I'm using the SharePoint PeopleEditor to select a user and when the user is selected I want to populate a few fields with information about that user, I retrieve the data from AD. The problem I had was how do I make the PeopleEditor send a signal to my code that a value has been set?! There is no event on the PeopleEditor control which is fired when a value is set.

I first asked myself this question about a month ago, but as I have been unable to find an answer I added a button to my form which says "Retrieve Userinformation". This is not the normal way of UI design and during a demo for the customer today they made a remark about it, so I decided to take another look at this problem.

It took me almost an hour to realize that there is a property called AutoPostBack on some server controls. When you set this property a Postback will be generated when a value is set in the control. As you may understand from my lack of knowledge in this area ASP.NET UI design is not my primary competence, but in most cases I know enough to get the job done.

<SharePoint:PeopleEditor AutoPostBack="true" ID="peUser" runat="server" />

In the case of the PeopleEditor this means that when you type a username and click Check names (or hit enter) or use the Addressbook to select a user you will receive a generic postback, no specific event i raised by the page is reloaded. Therefore you can have code in your Page_Load which checks if a value has been selected and take some action.

string accountName = null;
if (peUser.ResolvedEntities.Count > 0)
{
PickerEntity entity = (PickerEntity)peUser.ResolvedEntities[0];

    accountName = entity.Key;
int pos = accountName.IndexOf('\\');
accountName = accountName.Substring(pos + 1);

    // take some action based on accountName

}

In essence the AutoPostBack acts as an event generator which lets you perform an action when the value of the control is set. A discussion about AutoPostBack can be found at https://www.dotnetspider.com/kb/Article195.aspx, this is not PeopleEditor specific.