Developing Asp.net pages for the IPAD ~fixing the postback issue

Dkultra — Fri, 29 Apr 2011 20:34:00 GMT

Today I will discuss and solve the challenges that an asp.net developer will face while creating aspx pages with master pages for the IPAD or IPAD 2. The obstacle that asp.net developers have is that when an aspx page is in full screen and the user does nothing for about two minutes all postbacks, but the first, that are not submits will fail to happen. A postback example would be while selecting a new value on a dropdown the selected index changed event is supposed to fire when autopostback="true", assuming that there is a defined method in the code behind, which is wired-up to the event. A person only has search the net for the IPAD cache, viewstate and asp.net issues to find this problem.

With the popularity of the IPAD and the premium for real estate on a mobile device this is an option for .net developers not wanting to learn Objective-C.

JavaScript and Reflection to the rescue!

Add the following code to the masterpage or page with the issue

function Xjump(sender, method) {

document.getElementById('<%=SenderX.ClientID %>').value = sender;

document.getElementById('<%=MethodX.ClientID %>').value = method;

document.forms[0].submit();

}

</script>

Call the following code during the page load, which is in the masterpage or a base page.

public partial class YourAspPage

{

protected void Page_Load(object sender, EventArgs e)

{

Housekeaping();

}

This code is assuming that the above code is in the masterpage hence, the Masterpage.findcontrol() .

protected virtual void Housekeaping()

{

var senderX = this.MasterPage.FindControl("SenderX") as HtmlInputHidden;

var method = this.MasterPage.FindControl("MethodX") as HtmlInputHidden;

if (!string.IsNullOrWhiteSpace(senderX.Value))

{

CallBaseMethod(senderX.Value, method.Value);

senderX.Value = string.Empty;

method.Value = string.Empty;

}

The following code will execute the desired method

public void CallBaseMethod(string sender, string methodAndArgs)

{

var oPage = this.GetType().GetFields(BindingFlags.NonPublic | BindingFlags.Instance |

BindingFlags.FlattenHierarchy);

var obj = oPage.Where(w => w.Name == sender).FirstOrDefault().GetValue(this)

List<object> lstO = new List<object>();

lstO.Add(obj); //sender

var spl = methodAndArgs.Split(',').ToList();

string method;

if (spl.Count() > 1)

{

method = spl[0];

for (int i = 1; i < spl.Count(); i++)

{

lstO.Add(spl[i]);

}

else

{

method = methodAndArgs;

lstO.Add(null); //args

}

this.GetType().GetMethod(method, BindingFlags.NonPublic | BindingFlags.Instance |

BindingFlags.FlattenHierarchy).Invoke(this, lstO.ToArray());

}

Asp.net code

<asp:DropDownList ID="ddl" runat="server" CausesValidation="false"

DataTextField="X" DataValueField="X"

onchange="Xjump(ddl','ddl_SelectedIndexChanged')"

OnDataBound="ddlDataBound"/>

Notice the onchange JavaScript function, XJump's Parameter are the ID and the serverside method we want called, which has no parameters.

The following is an example with a server side method that has parameters.

Unfortunately in order to get sorting to work for a grid view, we need to use asp: TemplateFields instead of asp: BoundFields.

<asp:TemplateField SortExpression="ColumnName">

Column Title </a>

</HeaderTemplate>

<asp:Label ID="lblbla" runat="server" Text='<%#Bind("ColumnName") %>' />

</ItemTemplate>

</asp:TemplateField>

The Code Behind method for the sort

protected virtual void Sort(object sender, string Column)

{

var gv = (GridView)sender;

if (gv.SortDirection == SortDirection.Ascending)

{

gv.Sort(Column, SortDirection.Descending);

}

else

{

gv.Sort(Column, SortDirection.Ascending);

}

In conclusion, we end up manually doing some of what asp.net should do for us, but this is far better than having to write the pages in strait html and JavaScript.

Another Standard Deviation Extension for LINQ

Dkultra — Fri, 03 Oct 2008 21:16:00 GMT

Just wanted to post my SDev extension for linq

HopeFully someone will find it helpfull

Happy coding all

Module Module1

<Runtime.CompilerServices.Extension()> _

Function StDev(Of T)(ByVal Values As System.Collections.Generic.IEnumerable(Of T), ByVal selector As Func(Of T, Double))

Return Statistics.StDev(Values.Select(selector).ToList())

End Function

End Module

Public Class Statistics

Public Shared Function StDev(ByVal Values As System.Collections.Generic.List(Of Double))

Dim n = Values.Count()

Dim SigXSquare = (From i In Values Select i * i).Sum()

Dim SigX = Values.Sum()

Dim SigSquareX = SigX * SigX

Dim MySTDev As Double = ((n * SigXSquare) - SigSquareX) / (n * (n - 1))

Dim root = Math.Sqrt(MySTDev)

Return root End Function

End Class

Writing basics for computer people

Dkultra — Wed, 23 Jan 2008 18:30:00 GMT

Friends, we as developers, programmers and all the in betweens need to sharpen our communication skills.

After taking a year of English composition in the distant past, I see numerous examples of posts or articles that could be improved with some basic writing guidelines. The first guideline would be to stop using the singular word you. For example, a post on a forum asks: I’m having rounding problems with SQL Server; a possible answer would be: You should pull back the value as a string and then convert the string value in the code behind. Does this not sound better: a person could pull back the value as a string and then convert the value in the code behind? The difference is that “a person” refers not only to the author of the post but also, the readers of the post. Another approach is to eliminate the reference to who is reading the post and just write the solution such as in the post that this example comes from: http://forums.asp.net/t/1199940.aspx

More Guidelines to come

Happy coding.

Lloyd McGhee

First a thanks

Dkultra — Wed, 23 Jan 2008 18:28:00 GMT

First, I would like to Thank Joe for setting up this Blog since, a great place to share my thoughts and ideas has not presented itself until now.

Lloyd McGhee