Question

I am working on an application that has a GridView item on an ASP.net page which is dynamically generated and does a partial post-back as items are updated within the grid-view. This partial post-back is causing the tab indices to be lost or at the very least ignored as the tab order appears to restart. The grid view itself already has the pre-render that is being caught to calculate the new values from the modified items in the grid-view. Is there a way to get what element had the focus of the page prior to the pre-render call? The sender object is the grid-view itself.

Answer 1

You can try using this function, which will return the control that caused the postback. With this, you should be able to reselect it, or find the next tab index.

    private Control GetControlThatCausedPostBack(Page page)
    {
        //initialize a control and set it to null
        Control ctrl = null;

        //get the event target name and find the control
        string ctrlName = Page.Request.Params.Get("__EVENTTARGET");
        if (!String.IsNullOrEmpty(ctrlName))
            ctrl = page.FindControl(ctrlName);

        //return the control to the calling method
        return ctrl;
    }

Here’s an instance where I had dynamically generated inputs that updated totals via AJAX on change. I used this code to determine the next tab index, based on the tab index of the control that caused the postback. Obviously, this code is tailored to my usage, but with some adjustments I think it could work for you as well.

int currentTabIndex = 1;
WebControl postBackCtrl = (WebControl)GetControlThatCausedPostBack(Page);                

foreach (PlaceHolder plcHolderCtrl in pnlWorkOrderActuals.Controls.OfType<PlaceHolder>())
{
    foreach (GuardActualHours entryCtrl in plcHolderCtrl.Controls.OfType<GuardActualHours>())
    {
        foreach (Control childCtrl in entryCtrl.Controls.OfType<Panel>())
        {
            if (childCtrl.Visible)
            {
                foreach (RadDateInput dateInput in childCtrl.Controls.OfType<RadDateInput>())
                {
                    dateInput.TabIndex = (short)currentTabIndex;
                    if (postBackCtrl != null)
                    {
                        if (dateInput.TabIndex == postBackCtrl.TabIndex + 1)
                            dateInput.Focus();
                    }
                    currentTabIndex++;
                }
            }                        
        }
    }
}