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What is the difference between an asynchronous and synchronous event receivers?

Posted By :Faizal     Posted Date :August 22, 2010    Points :10   Category :SharePoint 
An asynchronous event occurs after an action has taken place, and a synchronous event occurs before an action has take place. For example, an asynchronous event is ItemAdded, and its sister synchronous event is ItemAdding

You can also find related Interview Question to What is the difference between an asynchronous and synchronous event receivers?  below: 

What is different between an asynchronous and synchronous event receivers?

  
Asynchronous events can trap an item,document library or site when it is added,deleted or updatedeg.itemAdded,ItemUpdated,ItemDeleted.

Synchronous events can trap an item,document library or site before it is deleted,updated.
Eg.ItemAdding,ItemUpdating. (More...)

the difference between a delegate and an event

  
the difference between a delegate and an event

Hi


Here is the difference between a delegate and an event.

Delegate:

public class VikramDel

{

public delegate void VikramExampleDelegate(int num1,string str1);

public VikramExampleDelegate VikramDeleageteCallback;

}

Event:

public class VikramEvent

{

public delegate void VikramExampleEvent(int num1,string str2);

public event VikramExampleEvent VikramEventCallback;

}

So syntax wise there is only one difference that we have to use the event keyword with the event.

So the question comes why do we have a keyword when the same work can be done without using it. But there is a reason for the existence of the keyword event. Lets take an example how would a client work with this class

VikramDel V = new VikramDel();

V.VikramDeleageteCallback +=new

VikramDel.VikramExampleDelegate (this.VikDelegate);

Here we are adding a new target to the invocation list of the delegate. The same code will work with the other class also without any problem

VikramEvent V = new VikramEvent();

V.VikramEventCallback + =new

VikramEvent.VikramExampleEvent(this.VikDelegate);

But consider a case where by instead of adding a new target to the invocation list of the delegate if I simply set a delegate to a new delegate (The difference is with the + sign being not there).

VikramDel V = new VikramDel();

V.VikramDeleageteCallback =new

VikramDel.VikramExampleDelegate (this.VikDelegate);

This code will work fine here but the same will not work with an event.

So what it means is that if we use the event keyword no client class can set it to null. This is very important. Multiple clients can use the same delegate. After multiple client have added a function to listen to the callback of the delegate. But now one of the client sets the delegate to null or uses the = sign to add a new call back. This means that the previous invocation list will not be used any more. Hence all the previous client will not get any of the callback even if they have registered for the call back.

Hence we can say that the even keyword adds a layer of protection on the instance of the delegate. The protection prevents any client to reset the delegate invocation list. They can only add or remove the target from the invocation list. (More...)

What is the difference between Page_init and Page_Load event?

  
Page_init - This is the first event to occur in the lifecycle of ASP.NET. This event fires only the first time the page is loaded and from the next time on a postback Page_init is not fired.

Page_Load - This is the event where most of our work will be done, this event occurs
when all objects/controls on the page are created and will be available for use. (More...)

what is the main difference between delegate and an event in c#?

  
Delegates and Events Both are related.

Dalegete is a function pointer which can able to store the address of any function with same prototype.

Event is a function handler which can handles or run the functions in same prototype of its delegate.

For handling events delegate is used. (More...)

What is the difference between method activity and event activity in WorkFlow ?

  
A method activity is one that performs an action, such as creating or updating a task. An event activity is one that runs in response to an action occurring. (More...)

What are event receivers?

  
Event receivers are classes that inherit from the SpItemEventReciever or SPListEventReciever base class (both of which derive out of the abstract base class SPEventRecieverBase), and provide the option of responding to events as they occur within SharePoint, such as adding an item or deleting an item.
(More...)

What base class do event receivers inherit from?

  
Event receivers either inherit from the SPListEventReciever base class or the SPItemEventReciever base class, both which derive from the abstract base class SPEventReceiverBase.
(More...)

What are event receivers?

  
Ans. Event receivers are classes that inherit from the SpItemEventReciever or SPListEventReciever base class (both of which derive out of the abstract base class SPEventRecieverBase), and provide the option of responding to events as they occur within SharePoint, such as adding an item or deleting an item. (More...)

What is the difference between method activity and event activity in WorkFlow ?


  

A method activity is one that performs an action, such as creating or updating a task. An event activity is one that runs in response to an action occurring (More...)

What are event receivers?

  
Event receivers are classes that inherit from the SpItemEventReciever or SPListEventReciever base class (both of which derive out of the abstract base class SPEventRecieverBase), and provide the option of responding to events as they occur within SharePoint, such as adding an item or deleting an item. (More...)

What base class do event receivers inherit from?

  

Event receivers either inherit from the SPListEventReciever base class or the SPItemEventReciever base class, both which derive from the abstract base class SPEventReceiverBase.
(More...)

Difference between event and delegate?

  
event:
1) Data member of a type(class/structure)
2)Declared inside a type(class/structure)

delegates.

delegate:
1)Datatype(reference type) that holds references of methods with
some signatures.also called as function pointer.
2)It may or may not be declared inside a class.
(More...)

Difference Between LinkedLabel Clicked event and LinkedLabel LinkClicked event

  
No difference ,between LinkedLabel Clicked event and LinkedLabel LinkClicked event.
If you use two Events in your Project ,LinkedLabel Clicked event triggers,LinkedLabel LinkClicked event doesn't trigger. (More...)

Difference Between Event Receiver and Workflow

  
Event Receiver:
.Can only be created in Microsoft Visual Studio.
.Can be executed post or prior the event.
.Support varieties different events include delete.

Workflow:
.Can be created in SharePoint Designer, Microsoft Office Visio and Microsoft Visual Studio.
.Can only be executed post the event.
.Support manual started, item created and item updated.
(More...)

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