Extension methods -asp.net mvc

Extension Methods in asp.net mvc

why to use extension method ?

well, in a simple statement I would say extension methods are used to get rid of writing html source code for views in asp.net mvc

let's take an example

suppose you are building a html table with several rows and cols in view
eg:

<table><tr><td>...</td></tr></table>
now you need to use table structure in various places in your application so without re writing this just create one extension method and put you structure over there
like this :

namespace ExtensionMethods.Common
{
public static class Helpers
    {

        public static string table(this HtmlHelper helper, string itemfirst, string itemsecond)
        {
            return String.Format("<table><tr><td>{0}</td></tr><tr><td>{1}</td></tr></table>", itemfirst, itemsecond);
        }
      
}
}
note:static class only can have static functions.
so now when you implement table structure into your view,you just need to add appropriate namespace for my case this was
"ExtensionMethods.Common".

as shown below :

Now whenever you need this structure just imports the appropriate namespace and then call extension method by passing parameters within it.

and you will see items witin table structure in your application.

outputcaching with authorize filter

Hi guys,after a long time I am back to blogging,today I am going to explain about how to use outputcaching with authorizefilter.

for outputcaching you can refer by previous blog.
(outputcaching is also a kind of filter)

Filters in asp.net mvc : 

Authorize filter
Raises before any action execute and authorize the current user.
Action filter
two method overridden from actionfilterattribute class
onactionexecuting : before action get executed.
onactionexecuted : after action get executed.
Result Filter
two method overriden from actionfilterattribute class
onresultexecuting : before result get executed,
eg: when you return view() from any action this method executed before this.
onresultexecuted : after result get executed.

Exception filter
whenever action throws any exception.
class for this filter is HandleErrorAttribute.

Note: controller inherited from controllerbase class in which it implements filter attribute so ultimately your controller can also implement these attributes.
Eg:

[Athorize]
your action..

Using outputcaching with Authorize filter :

Problem : 

if we use both of these filters in the worst case the unauthorize users even can view the cached content of authorize users,to avoid we need to use a custom class which

implements authorizefilterattribute class.

public class EnhancedAuthorizeAttribute : AuthorizeAttribute
{
public bool AlwaysAllowLocalRequests = false;
protected override bool AuthorizeCore(System.Web.HttpContextBase httpContext)
{
if (AlwaysAllowLocalRequests && httpContext.Request.IsLocal)
return true;
// Fall back on normal [Authorize] behavior
return base.AuthorizeCore(httpContext);
}
}

[EnhancedAuthorize(Roles = "admin", AlwaysAllowLocalRequests = true)]
Now, this will grant login only for admin roles and not to any other role.

but I achieve this wtih athorize attribute

eg:
 [Authorize(Roles="admin")]
 [OutputCache(Duration=30,VaryByParam="None")]

note : order is a property of filter base class which defines the order of filter execution but by default filter are put on stack for execution which means the last one will be executed first.

using delegates and events in c#

What is a delegate ? 
Delegate is a function pointer means it can point to those function which are having identical signature with delegate.
you can also call delegate as a interface of methods as this acts same as interface in c# but that implemented for classes and this is implemented for methods.

Process to create a delegate:
1)declaration
2)instantiation
3)invocation

Example :

Consider the following code:

  delegate string StrDelegate();//declaration
   public class Custom
    {
        public string strmethod()
        {
            return "This is string ";
        }
    }
    class Program
        {
        static void Main(string[] args)
        {
            Custom objcustom = new Custom();
            StrDelegate strdelegate = new  StrDelegate(objcustom.strmethod); //instantiation
            string message=strdelegate(); //invocation
            Console.Write(message);
            Console.Read();
        }
       }
so what happened in this above code,well first we define a delegate with its signature,in this case its return type is string and no arguments. then we create instance of delegate which is strdelegate now this can point to (reference to) all those function which having same signature as in our case function is strmethod() and at the last we invoke this and receive this in message.

Advantages:
The main advantage of delegate is multi cast.
you can call number of function with matching singature with single instance of delegate but point to remember is that its return type should be void because there are many

methods and if we pass return type then each one will return some value and finally delegate instance will hold the last one method's value.

example

in our previous example i added the following :

        public void strmethodmulticast()
        {
           console.write("This is string multicast");

        }

in set of methods and

StrDelegate strdelegate = null;
            strdelegate += new StrDelegate(objcustom.strmethod);
            strdelegate += new StrDelegate(objcustom.strmethodmulticast);

this in Static Void Main

also changed the return type of delegate to void.


What are events 
event is a way for a class to provide notifications to clients of that class when some interesting thing happens to an object of that class.
you can also consider events as variable type of delegates ? why lets look at event declaration.

public event StrDelegate customevent;

Just need to put event keyword before delegate name and your event created.
events are handled by delegates which are called event handlers.

consider the following code:

 btnsubmit.Click+=new EventHandler(custommethod);

I created a button on form and its object 'btnsubmit' now avaiable on code behind as you know, now when click event raises in above it is being handled by EventHandler
delegate and method  'custommethod'  do the desire operation which is having the same signature as in EventHandler delegate (object sender//to raise event,Eventargs e// to receive other information)

public void custommethod(object sender, EventArgs e)
    {
        txtsubmit.Text = "This is called on button click";

    }

and hence on click event of button the above method is called which changes the text of txtsubmit.

dropdown not working in ie7 and ie8

If you have created dropdownlist and either its not visible or not visible onchange event of other dropdown
Then one of possible solution this is as follows:

Possible Cause :
if you use firebug and see html for dropdown you will notice that 'option' is not well formed in html for this dropdown.

One of Solution to Resolve this Problem:

If you have used something like this

for (i = 1; i <= day_length; i++)
{

doc.innerHTML += "<OPTION value=\"" + i + "\">" + i + "</OPTION>";
}
and adding items to dropdown (doc) dynamically with some values(eg: i in this case) replace this with

addOption(doc, i, i);

function addOption(selectbox,text,value )
{
var optn = document.createElement("OPTION");
optn.text = text;
optn.value = value;
selectbox.options.add(optn);
}

this add option adds all of those values which you want (eg: i ) and this will event work in ie 7 ,ie8.

It worked for me hope same would for you..

Cheers...

Error 3205 Too Many Backup Devices Specified.

Cause:
This error occured because of you sqlserver is not compatiable with current backup version



Solution:

1)first run SELECT @@version and find the version

2)exit from current sqlserver and connect with other server for which your backup file(.bak) is compatiable.

RouteExistingFiles and IgnoreRoute in asp.net mvc

How to Use RouteExistingFile and IgnoreRoute in asp.net mvc.

RouteExistingFile is a property of Routecollection class Which is True or false.
eg: routes.RouteExistingFiles = true

as you can see all css have been acting as route and hence no longer available for Home/
whenever you write this it routes the files present on your harddisk which in turns acts as a route.
for example if you have css in /content/file.css and you make RouteExistingFiles true then it will match
{controller}/{action} url for file.css and this will no longer available for existing pages.

Only two cases are possible to get file.css
1)if you directly hit that file eg:/content/file.css
2)if you use routes.Ignore route.

Case 1 is quite simple

Case 2 routes.IgnoreRoute is and extended method which accepts routes to be ignored and below will
ignore the route matching for css.
eg:
routes.IgnoreRoute("{Content}/{file.css}")

as shown in above figure now those files present on hard drive not acting as route and available for pages.

Thanks friends see you soon

Avoid css,Html errors-Asp.net

Do you receiving css+ html errors when compiling asp.net application,and want to remove these validation errors its quite easy do following:

Goto Tools>options>css specific now uncheck the show errors

&      Tools>options>validations uncheck show errors for (netscape7,opera7,ie6) from dropdown.

Thanks