Monthly Archives: August 2012

Infragistics: Detect type of AJAX callback

This post continues topic started in “WHDG: Correctly detect Async Callback“. Back then I described a way to correctly detect server-side when an infragistics control (WebHierarchicalDataGrid) issues an async callback.

But what if you need to detect actual type of the call and distinguish paging from sorting from filtering from row expanding? Well, where there is will there is way. Infragistics says there’s no build-in flag indicating AJAX action, but we can determine the action by intercepting and interpreting HTTP Request object.

First let’s define a return type in form of an Enum describing all possible outcomes (it’s always good to work strongly typed values):

   NON_AJAX = 0
   PAGING = 1
   SORTING = 2
End Enum

And now actual function. In the previous post I described that presence of AJAX call can be determined if key starting with "__IGCallback" is present in Request.Form collection. By interpreting actual value of Request item with that key we can determine type of AJAX call. For example, when grid’s row is expanding during load-on-demand, it contains JSON data "eventName":"Populating","type":"loadOnDemand" so our function simple has to catch it:

Function GetGridAjaxCallType() As GRID_AJAX_CALL_TYPE
   Dim sIgCallBackKey As String = HttpContext.Current.Request.Form.AllKeys.SingleOrDefault(Function(S As String) S IsNot Nothing AndAlso S.StartsWith("__IGCallback"))
   Dim sIgCallBackRequest As String

   If sIgCallBackKey <> "" Then
      sIgCallBackRequest = HttpContext.Current.Request.Form(sIgCallBackKey)

      'Detecting Child Populating.
      If sIgCallBackRequest.Contains("""eventName"":""Populating"",""type"":""loadOnDemand""") Then Return GRID_AJAX_CALL_TYPE.CHILD_POPULATING

   End If

End Function

The function tries to locate "__IGCallback" key in HTTP request (Line 2), if the key present – function reads actual Request value (Line 6) and if Load-on-demand populating is detected (Line 9) – returns result saying so, otherwise returned result indicated non-ajax call.

This example implements only one detection – Load-on-demand populating, I will leave it to you to add sorting/filtering/paging detection. Once implemented – usage is pretty straightforward:

If Not IsPostBack Then
   End If
End if

Active CSS selector not working correctly for Input Button in IE

CSS has a cool selector called “:active“, it can be used for example to select a button when it is pressed. Let’s say you have an HTML markup like this:

<input type="button" class="mybutton" value="Click me" />

and you define CSS selector like this:

.mybutton:active {background-color:red}

the button will change its background color to red when clicked and only for the duration of the click (while the mouse button is down) as soon as mouse button is released – background color is reverted to original.

This works fine in all modern browsers and supposed to work in Internet Explorer since version 8. And it works – well kind of – only you click the button but not the button label (text of the button). If you click actual text – style does not change.

Weird, but with IE weird is often normal. To alleviate the problem use button HTML element instead of input:

<button type="button" class="mybutton">Click me"</button>

With this markup CSS described above works universally.

Of course if you need to target browser below IE8, CSS selector approach does not work, you have to resort to JavaScript:

<input type="button" style="background-color:white" value="Click Me" onmousedown="'green'" onmouseup="'white'" />

Solution: WebDataGrid loses styles after postback

Infragistics WebDataGrid control offers very flexible styling option – you can set font, color, size of almost any element from column to individual cell. Here is an example of basic markup that sets CSS classes of overall grid control, grid header, grid odd row and grid even row:

<ig:WebDataGrid ID="xMyGrid" runat="server"
   CssClass = "GridStyle"
   HeaderCaptionCssClass = "GridHeaderCellStyle"
   ItemCssClass = "GridCellStyle"
   AltItemCssClass = "GridAltCellStyle" 

And corresponding example of CSS class for even row:

tbody > tr.GridAltCellStyle > td
   font-family:Verdana, Geneva, sans-serif;
   padding: 2px 2px 2px 2px;
   border-bottom: none;
   border-right: 1px solid rgb(190,198,178);

(For a complete grid styling reference take a look at this styling guide)

And it all works fine, your grid renders so beautifully, Picasso would cry. But only on initial page load. And here comes dreadful postback. Continue reading →

Position:Absolute within Position:Absolute

Let’s say we have a basic HTML layout: a container DIV and within it another DIV and an image:

<div id="xdivContainer">
   <div id="xdivMenu" style="position:absolute"></div>
   <img id="ximgIcon" src="icon.gif" />

Inner (child) div is positioned absolutely and we want to place it at the coordinates of the image (think popup menu appearing on icon click). A very basic JavaScript function obtains position of the image:

// Class placeholder for coordinates
function CTopLeft(i_nTop, i_nLeft) {
   this.nTop = i_nTop;
   this.nLeft = i_nLeft;

// obtain position of a DOM element
function GetTopLeft(i_oElem) {
   var cTL = new CTopLeft(0, 0);
   var oElem = i_oElem;

   while (oElem) {
      cTL.nLeft += oElem.offsetLeft;
      cTL.nTop += oElem.offsetTop;
      oElem = oElem.offsetParent;
   return cTL;

As you can see it simple collects offset positions of the HTML element, combining them into absolute coordinates. So to absolutely position our child DIV at the coordinates of the image we can call it like this (I am using $() notation as a shortcut for document.getElementById)

var oPos = GetTopLeft($('ximgIcon'));
$('xdivMenu') = oPos.nTop + 'px';
$('xdivMenu').style.left = oPos.nLeft + 'px'

And it works fine. Until container DIV is in turn absolutely positioned: Continue reading →

Jelly Bean: Android 4.1 on Kindle Fire

And the saga continues. Tired of Ice Cream Sandwich I decided to step up. Turning my Kindle Fire into a Jelly Bean device (same Android version run by Google’s Nexus 7) is a snap. Just go to this XDA thread and download bright shiny new CyanogenMod 10.

Jelly Bean on Kindle Fire

It runs much smoother than ICS, seems a lot faster and more streamlined. There’re a lot of small things (like lockscreen trailing your finger) that make everyday tablet use a lot more enjoyable.

Jelly Bean on Kindle Fire Got a few new features as well, Google Now being one of the coolest one. As you continue to use your tablet, it learns your ways and begins supply you with useful array of information – from weather and traffic of your commute, to appointments and your favorite sports teams.

It doesn’t support Flash anymore, but with the advance of HTML5 Flash becomes more and more irrelevant in such areas as gaming and video. Major apps (Google Chrome, ROM Manager, Titanium Backup etc.) love Jelly Bean and runs perfect under Android 4.1.

Even new Optimum app released exclusively for Kindle Fire runs fine under Jelly Bean (yes sometimes I get so lazy so even finding a TV remote seems as too much of an effort and on Kindle I can watch my cable without getting up).

So, if you haven’t already done so – do yourself a favor and turn your Kindle fire from nothing more than an Amazon shopping cart into a full blown Android tablet, capable of many amazing things.

Disclaimer: Do it at your own risk. I am speaking from personal experience, but I am not responsible if you brick your device.