Asp – Double postback causes SelectedIndexChanged to fire which fires AutoPostback

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I have a Gridview in a UpdateTemplate. I have four template fields in the four different columns. Each TemplateField has an UpdatePanel with a control in it. All the columns are sortable and the Gridview is page-able. Three of the template fields has DropDowns in the UpdatePanel and one has a Textbox, all these controls have AutoPostBack = True. All the UpdatePanels have UpdateMode = Conditional and ChildrenAsTriggers = false.

When I click sort or change page index and the results have not returned and do it again(click sort or page index) while it is busy the SelectedIndexChanged and TextChanged events fires on some of the controls.

It seems that depending on when I do this some of the results has been refreshed and there events don't fire but some are still busy, and the second Postback halts the first one and thinks that the values have changed and fires there respective AutoPostBackt events. When all the events fired the grid then displays the intended result set that was expected from the first sort or page index change.

Best Answer

Is there a question here?

One thing you can do is add a "busy" display while waiting for the first Ajax call and disable the controls that would cause another postback. Remember what the first A stand for in AJAX: asynchronous.

Related Solutions

How to get an UpdatePanel to intercept a CompositeControl’s DropDownList

Ok so this may not be the best answer, but I think the problem you're having it that the UpdatePanel just can't see the child control's event. Good news is, it's easy to fix. Say you have a control (CatchMyEvent, which by the way is a crazy clever name) and it has a DropDownList on it. Now you want the parent page to see the SelectedIndexChanged event fire on that list and update a label to match the SelectedItem.Text. As it is, the parent can't really do that. So let's change that:

public partial class CatchMyEvent : System.Web.UI.UserControl
{
    public delegate void ChangedIndex(object sender, EventArgs e);
    public event ChangedIndex SelectedIndexChanged;

    protected override void OnInit(EventArgs e)
    {
        base.OnInit(e);
        dropDownListThrow.SelectedIndexChanged += new EventHandler(dropDownListThrow_SelectedIndexChanged);
        labelOutput.Text = "no";
    }

    public void dropDownListThrow_SelectedIndexChanged(object sender, EventArgs e)
    {
        labelOutput.Text = ((DropDownList)sender).SelectedItem.Text;
        if(SelectedIndexChanged != null)
        {
            SelectedIndexChanged(sender, e);
        }
    }
}

Basically all I did is have the control capture the DropDownList's SelectedIndexChanged event and fired it so that any parent page or control could see it. Essentially all I've done is passed it on. Now on the parent page, it's really easy to capture.

You just need to add an UpdatePanel with a trigger that holds:

<asp:AsyncPostBackTrigger ControlID="catchMyEventMain" EventName="SelectedIndexChanged" />

...and of course add this to the code behind for the parent page:

protected override void OnInit(EventArgs e)
{
    base.OnInit(e);
    catchMyEventMain.SelectedIndexChanged += dropDownListThrow_SelectedIndexChanged;
}

public void dropDownListThrow_SelectedIndexChanged(object sender, EventArgs e)
{        
    labelSelectedValue.Text = ((DropDownList)sender).SelectedItem.Text;
}

Where the label is the before mentioned label. And then let the magic happen.

Also two notes:

1) Don't be an idiot like I was when testing this and forget to set the AutoPostBack property on the DropDownList to true.

2) Make sure the label is in the UpdatePanel's ContentTemplate.

Hope this helps.

Asp – Why would a child control of a child update panel update both parent and child if each is set to conditional

Is the parent update panel actually updating, i.e. the contents are changing?

I would expect that the OnLoad function of the parent update panel would never run except on the actual page load

This is a false, but unfortunately common assumption. Remember that even though it's an asynchronous postback, the entire page and control lifecycle is executed for every control, including Load and Init. It's just like you were requesting the page normally.

The difference is that it's only the UpdatePanel's region of the page that would be updated, not the entire UI.

For more on how UpdatePanels work there is a great article on ASP.Net Ajax documentation site.

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