Tag Archives: workaround

Infragistics WebDataGrid stalls on paging large datasets

A common scenario while using Infragistics WebDataGrid is to have an unbound column, whose cell’s value is determined at runtime in InitializeRow event, something like

Private Sub xmyGrid_InitializeRow(ByVal sender As Object, ByVal e As GridControls.RowEventArgs) Handles xmyGrid.InitializeRow
   '... some code
   e.Row.Items(0).Value = SomeCalculatedData
   '... some more code
End Sub

This works fine if you bind the grid to a small data set (and you should!) But if, due to circumstances out of your control, you bind it to a dataset with tens of thousand of records you might be screwed. Even if you enable paging (and you most definitely should!) you may find yourself living in a shotgun shack in a situation that changing page takes forever and eventually crashes. If you do – change the above line to 

e.Row.Items(0).Text = SomeCalculatedData

note using of .Text property, which is String, instead of .Value which is Object. Since you’re assigning the calculated data for presentation only – no need to change underlying value – and this makes all the difference.

Canvas for Pebble: How to hide time in all-day events

If you wish to create a custom watchface for Pebble Smartwatch but want it to have some more advanced features than very cool Watchface Generator offers then amazing Android app Canvas for Pebble is definitely for you.

Using it you can have your Pebble watchface to display weather, location, temperature, of course date and time, etc. etc. in highly customizable formats.

One cool thing it allows you to show – next calendar events from your Google calendar. As with everything else it’s a highly customizable entry. For example three (out of much more) options are:

%a – abbreviated day of the week
%R – start time of the event in 24-hour-format
%ET – event title

So if you format the calendar field as "%a %R: %ET" your Pebble will display something like "Mon 12:30: Visit from Elvis". Unfortunately if calendar event is an all-day event (e.g. national holiday) – start time of the event (%R) always displays as “00:00” making your event look like "Tue 00:00: Day of the Tentacle". It would be really nice if we could hide the time for all-day events.

Fortunately one of the things Canvas allows you to do is conditional formatting. It does this in a form of {text1#condition#text2} where if condition is true – text1 is displayed, otherwise text2 is displayed (which is optional and can be omitted).

I noticed that for all-day events, event duration (represented in Canvas as %ED) is always 24 hours (duh). So I replaced the above format for calendar event with this one: %a{ %R#%ED<24}: %ET. The code in braces means “if event duration is less than 24 hours – show event start time, otherwise don’t show anything”. And the result is in images above.

TSQL: NOT IN doesn’t work

If you encounter a weird scenario when query

SELECT Something FROM Table1 WHERE SomethingElse IN (SELECT Lookup FROM Table2)

work perfectly, but the opposite query

SELECT Something FROM Table1 WHERE SomethingElse NOT IN (SELECT Lookup FROM Table2)

doesn’t return any results – and you know for a fact that there’re results – check values returned by the subquery. Chances are there’re NULLs among those values. If that’s the case – NOT IN won’t return any results.

As a quick workaround you can add IS NOT NULL condition to the subquery:

SELECT Something FROM Table1
WHERE SomethingElse NOT IN (SELECT Lookup FROM Table2 WHERE Lookup IS NOT NULL)

and this should do the trick.

Credit: This Stack Overflow answer.

How to make “scrollIntoView” apply to IFRAME only

Let’s say you have a really long HTML page with scrollbars, for the sake of argument something like this:

<div>aaaa</div>
<div>aaaa</div>
<div>aaaa</div>
...more content...
<div id="xB">bbbb</div>
<div>aaaa</div>
<div>aaaa</div>
<div>aaaa</div>
...much more content...

And somewhere, perhaps on pageload, you want to make sure that highlighted element is visible to the user, so to scroll it into view you execute

document.getElementById("xB").scrollIntoView();

And it works fine and well – the needed element is automatically displayed on top of the page. But what if this page is in an IFRAME and the parent page has a large scrollable content of it’s own:
Continue reading →

Infragistics WebSplitter: Set SplitterBar’s CSS class in clinet-side JavaScript

Hello there. Haven’t written in a while, been busy participating in Stack Overflow community, but this little bit I found interesting.

Infragistics has a cool versatile Web Splitter control in their ASP.NET suite, but recently I encountered a shortcoming – there’s no way to set a CSS class for splitter bar on client-side via JavaScript. On server-side you can do something like

xMySplitter.SplitterBar.CssClass = "hiddenElement";

On client-side – you can get the CSS class via

var sCss = $find('xMySplitter').get_splitterBarCss()

but there’s no counterpart set_splitterBarCss() method. Continue reading →

Solution for SqlDataReader.ReadColumnHeader NullReferenceException

This post related to the previous one, but I decided to write a separate article because it seems to be a common problem.

Sometimes when you use SqlDataReader, you would get an exception:

NullReferenceException {“Object reference not set to an instance of an object.”}
at System.Data.SqlClient.SqlDataReader.ReadColumnHeader(Int32 i)
at System.Data.SqlClient.SqlDataReader.ReadColumn(Int32 i, Boolean setTimeout)
at System.Data.SqlClient.SqlDataReader.GetInt32(Int32 i)

And the maddening thing – it doesn’t happen often, just every once in a while. And it happens at different times too, sometimes reader would read 100 records, sometimes 200 etc.

One possible case – SqlDataReader is losing its connection. And one possible reason for that – connection goes out of scope.

Consider following scenario – you have a function that returns SqlDataReader:

Function GetTheReader() as SqlDataReader
   Dim oConn As New SqlConnection("Connection String") : oConn.Open()
   Dim oComm As New SqlCommand("Stored Procedure", oConn)

   Dim oReader As SqlDataReader = oComm.ExecuteReader(CommandBehavior.CloseConnection)

   Return oReader
End Function

And you use it like this:

Dim oReader as SqlDataReader = GetTheReader()
'Begin use reader - loop, read data etc.

The problem with this approach that connection used to create the reader is stored in a private variable inside of `GetTheReader` function and when the function exits – the variable goes out of scope. Eventually, sooner or later Garbage Collector will collect it and close and dispose of connection – and at this time your SqlDataReader will fail.

The solution? Either use SqlDataReader at the same scope level you created it, or, if you do need to use function – pass connection object into it as one of the parameters, so it would remain valid after function exits.

When SqlDataReader is missing rows

I have a very basic scenario:

  1. Execute TSQL Stored procedure
  2. Return a DataReader
  3. Read data from the Reader

This is ADO.NET 101. There is one problem: DataReader loses rows. This problem has haunted me forever, extensive research and numerous suggestion didn’t help, even though the code is extremely basic:

Get the reader:

m_dbSel.CommandType = CommandType.StoredProcedure
m_dbSel.CommandText = "SP_Name"
oResult = m_dbSel.ExecuteReader()

Pass the reader to class constructor to fill Generic List (of Integer): 

Public Sub New(i_oDataReader As Data.SqlClient.SqlDataReader)

    m_aFullIDList = New Generic.List(Of Integer)

    While i_oDataReader.Read
        m_aFullIDList.Add(i_oDataReader.GetInt32(0))
    End While

    m_iTotalNumberOfRecords = m_aFullIDList.Count

End Sub

This problem occurs when number of rows returned by the reader is relatively large (over 600,000 records). If this happens – number of rows added to the list from the reader is inconsistent, but always less than real one. Most often “magic” number of 524289 rows is returned.

Well, this is no longer a mystery, thanks to the great people from Stack Overflow @RBarryYoung, @granadaCoder and especially @MartinSmith who was the first to point me in the right direction – and here it is.

Even though the problem is with SqlDataReader – it is happening because it is used in conjunction with Generic List. List, as you may know has a flexible Capacity for number of elements it can store. When count of elements exceeds capacity – capacity increases and always to a power of 2. E.g.

When the count exceeds 4 elements – capacity is set to 8 (2^3)
When the count exceeds 8 elements – capacity is set to 16 (2^4)
When the count exceeds 16 elements – capacity is set to 32 (2^5)

etc..

This is what makes Generic List such a powerful tool, used by many large scale .NET projects, e.g. bingogodz.com. And ordinary this is not a problem. Unfortunately this is not the case when it is used together with SqlDataReader. When count of items in the List exceeds 524,288 (2^19) and its capacity is set to 1,048,576 (2^20) – SqlDataReader’s Read method suddenly returns False even though not all records have been read. No exception is thrown, it simple stops.

The only possible workaround I’ve found so far (I am still looking for better ones) is to pre-set List capacity in advance. Since, when using DataReader, you do not know number of rows, you’re left either with hardcoding the number or running another DB query to retrieve number of rows via something like COUNT(*). Like I said, I don’t like this workaround, please let me know if you find a better one.

UPDATE: Finally figured it out: http://stackoverflow.com/a/18520609/961695

WebHierarchicalDataGrid: get_scrollTop() returns incorrect value

Infragistics WebHierarchicalDataGrid has a neat client-side built-in function get_scrollTop() – it is used if at any point you need to retrieve current vertical scroll position of the grid (e.g. to use it in your own calculations to display something at a specific position on the grid – tooltip, help, additional info etc.)

Unfortunately the function has a bug: its value only set if user actually manually scrolls the grid: using mouse and scrollbar on the right, keyboard etc. If no scrolling user-interaction is involved and scroll position changes due to other means (e.g. displayed data size changes) – the function retains original value, throwing all your calculation out of whack. Continue reading →

ADO.NET DataTable: Change Column DataType after table is populated with data

Sometimes there is a need to change DataType of ADO.NET DataTable column. If your table is populated as a result of some database operation – you don’t know in advance what type the columns will be. And by design you cannot change the type of the column after the table is populated. Conudrum. Catch 22. Tough luck.

But wait, there’s light at the end of the tunnel. You cannot change the type of the existing column, but you can create a new one. Continue reading →

Disable WebDataTree in client-side JavaScript

Let’s say you’re using Infrafitics WebDataTree’s server-side SelectionChanged event to perform some action when user selects a tree node. Now let’s say there’re times when you need to disable tree-selection (for example another control, e.g. WebDataGrid is being updated and clicking tree node during update will mess things up). Also you need to do it in client-side JavaScript (e.g. if that second control is inside of UpdatePanel – server-side updates will not affect controls outside the panel).

What to do? WebDataTree doesn’t have CSOM set_enabled() method and if you use client-side DOM’s:

$find('xMyTree').get_element().setAttribute('disabled','true');

tree may take appearance of being disabled in some browsers, but user can still select nodes.

Fortunately there is a solution (thanks Bhadresh from Infragisitcs techsupport for suggesting it). WebDataTree has SelectionType property (0 = None, 1 = Single, 2 = Multiple) that controls how many nodes can be selected in the tree. It also has a counterpart in client-side JavaScript set_selectionType(), so in order to disable selection simple use command

$find('xMyTree').set_selectionType(0);

Later on selection can be re-enabled either by passing 1 to above function or even server-side by calling

xMyTree.SelectionType = NavigationControls.NodeSelectionTypes.Single