The Antidote to ASP.NET Smart Navigation, Part Deux

December 20, 2004

In The Antidote to ASP.NET Smart Navigation, I mentioned an article that contained a clever solution to the scrolling problem with long ASP.NET forms and postbacks. Well, I recently located an even better version of that solution from Scott Mitchell, aka the founder of 4GuysFromRolla. I refactored it a bit into this:

''' <summary>
''' automatically preserves postback scroll position
''' </summary>
Private Sub Page_PreRender(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.PreRender
  RegisterHiddenField("scrollLeft", Convert.ToString(Request.Form("scrollLeft")))
  RegisterHiddenField("scrollTop", Convert.ToString(Request.Form("scrollTop")))

  Dim sb As New System.Text.StringBuilder(1000)
  Dim nl As String = Environment.NewLine
  With sb
    .Append("<script language = ""javascript"">")
    .Append(String.Concat(nl, "<!--", nl))
    .Append("function SmartScroller_GetCoords() {")
    .Append(String.Concat(nl, "var scrollX, scrollY;", nl))
    .Append("if (document.all) {")
    .Append(String.Concat(nl, "if (!document.documentElement.scrollLeft)", nl))
    .Append("scrollX = document.body.scrollLeft;")
    .Append(String.Concat(nl, "else", nl))
    .Append("scrollX = document.documentElement.scrollLeft;")
    .Append(String.Concat(nl, "if (!document.documentElement.scrollTop)", nl))
    .Append("scrollY = document.body.scrollTop;")
    .Append(String.Concat(nl, "else", nl))
    .Append("scrollY = document.documentElement.scrollTop; }")
    .Append(String.Concat(nl, "else {", nl))
    .Append("scrollX = window.pageXOffset; scrollY = window.pageYOffset; }")
    .Append(String.Concat(nl, nl))
    .Append("document.getElementById('scrollLeft').value = scrollX;")
    .Append(nl)
    .Append("document.getElementById('scrollTop').value = scrollY;")
    .Append(String.Concat(nl, "}", nl))

    .Append(String.Concat(nl, "function SmartScroller_Scroll() {", nl))
    .Append("var x = document.getElementById('scrollLeft').value;")
    .Append(String.Concat(nl, "var y = document.getElementById('scrollTop').value;", nl))
    .Append("window.scrollTo(x, y); }")

    .Append(String.Concat(nl, nl, "window.onload = SmartScroller_Scroll;"))
    .Append(String.Concat(nl, "window.onscroll = SmartScroller_GetCoords;", nl))
    .Append("window.onclick = SmartScroller_GetCoords; window.onkeypress = SmartScroller_GetCoords;")
    .Append(String.Concat(nl, "// -->", nl))
    .Append("</script>")
  End With

  RegisterClientScriptBlock("scrollCode", sb.ToString)
End Sub

Works great! Of course, you can insert this script any number of ways: in an inherited base page, as a server control, or by directly inserting it into a single page.