C# Event Processing ppt

8/18/2019 C# Event Processing ppt

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C# Event Processing

Model

Solving The Mystery


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Introduction

C# is a modern programming languagesupported y an e$tensive set o %PI structuresand classes& i&e&' The &(et )ramewor*

C# supports event+driven programmingnormally associated with Microsot ,indowsapplications&

"ne normally thin*s o events as einggenerated y -.I components /ut any o0ect can generate an 1event2 i it3s

programmed to do so/


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C# Event Processing Macro View

-enerally spea*ing' two logicalcomponents are required to implementthe event processing model4 56 %n event producer 7or pulisher6

86 %n event consumer 7or suscrier6

Each logical components has assigned

responsiilities Consider the ollowing diagram


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"0ect 97Event Suscrier6

"0ect %7Event Pulisher6

Suscrier :ist7"0ect 96

Event !andler Code

"0ect 9 suscries to event7or events6 generated y "0ect %&

"0ect % maintains alist o suscriers or

each pulishaleevent

,hen an Event occursnoti;cation is sent to allthe suscriers on thelist or that particularevent/

"0ect 9 processes theevent noti;cation in itsevent handler code



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:et3s map "0ect % and "0ect 9 to some amiliar o0ect types/

Main%pp7Event Suscrier6

9utton7Event Pulisher6

Suscrier :ist7Main%pp&on9uttonClic*6

on9uttonClic*

Main%pp suscries to 9utton3sClic* event

9utton maintains alist o suscriers o

itsClic* event

,hen a Clic* eventoccurs noti;cation is sentto all the suscriers onthe list/

Main%pp processes theClic* noti;cation in itson9uttonClic* event

handler code


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These two diagrams hide a lot o details !ow is the suscrier list maintained<

!ow is the event generated<

!ow is noti;cation sent to eachsuscrier<

,hat is an event = really<

!ow can you add custom eventprocessing to your programs<

This presentation attempts to answerthese questions in a clear manner/


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The &(et %PI contains lots o classes thatgenerate di>erent types o events/ Most are -.I related

Can you thin* o a ew< It also contains lots o ?elegates

Can you name at least one<

:et3s ta*e a closer loo* at the C# eventprocessing model


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Required Components

To implement custom event processing inyour programs you need to understandhow to create the ollowing componenttypes4 ?elegates Event -enerating "0ects 7pulishers6

Events Event (oti;cation Methods

Event !andling "0ects 7suscriers6 Event !andler Methods


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Required Components

@ou will also need to *now how to passinormation related to the eventetween the event generating o0ect

and the suscrier o0ect The Event%rgs class can e used as+is or

suclassed The Event%rgs class captures generic

inormation aout an o0ect and the eventthat occured


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Role of Each Component- elegate -

?elegate ?elegate types represent reerences to

methods with a particular parameter list

and return type E$ample

Event!andler7"0ect sender' Event%rgs e6

Represents a method that has two parameters'the ;rst one eing o type "0ect and the second

eing o type Event%rgs& Its return type is void& %ny method' so long as its signature matches

that e$pected y the delegate' can e handledy the delegate&


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9ut 0ust what is a delegate< % delegate is a reerence type o0ect&

% delegate e$tends either the

System&?elegate or Multicast?elegateclass ?epends on whether one 7?elegate6 or more

7Multicast?elegate6 suscriers are involved

@ou do not e$tend ?elegate orMulticast?elegate The C# compiler does it or you


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The delegate o0ect contains thesuscrier list& It is actually implemented as a lin*ed list

where each node o the list contains apointer to a suscrier3s event handlermethod

?elegates are types = li*e classes E$cept = you declare them with the

delegate *eyword and speciy the typeso methods they can reerence


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Role of Each Component- Pu!lisher -

% pulisher is any class that can ;re an eventand send event noti;cations to interestedsuscriers

% pulisher class contains the ollowing critical

elements4 %n event ;eld

This is what suscriers suscrie to/ %n event noti;cation method

This activates the suscrier noti;cationprocess when the event occurs

%nd some means o generating the event orrecogniAing the event in question has occurred This usually happens in a method as well


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Role of Each Component- Event -

%n event is a ;eld in a class

Events are declared with the event*eyword

Events must e a delegate type ?elegates' rememer' are o0ects that

contain a list o pointers to suscriermethods that delegate can process

%n event ;eld will e null until the ;rstsuscrier suscries to that event @ou3ll see what I mean y this in a moment


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Role of Each Component- Event "otification Method -

In addition to an event ;eld a pulisherwill have a method whose 0o it is tostart the suscrier noti;cation process

when the event in question occurs %n event noti;cation method is 0ust a

normal method

It usually has a parameter o Event%rgs

or a user+de;ned sutype o Event%rgs& 9ut it can have any numer and type o

parameters you require


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Role of Each Component- u!scri!er -

% suscrier is a class that registers itsinterest in a pulisher3s events

% suscrier class contains one or more

event handler methods


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Role of Each Component- Event $andler Method -

%n event handler methods is anordinary method that is registered witha pulisher3s event&

The event handler method3s signaturemust match the signature required ythe pulisher3s event delegate&


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An Custom Event E%ample

- Elapsed Minute &imer -

This e$ample includes ;ve separatesource ;les4 ?elegate&cs

Pulisher&cs Suscrier&cs

MinuteEvent%rgs&cs

Main%pp&cs


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using SystemB

namespace CustomEventE$ample

pulic delegate void ElapsedMinuteEvent!andler7"0ect sender'MinuteEvent%rgs e6B

D end CustomEventE$ample namespace


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using SystemB


pulic class MinuteEvent%rgs 4 Event%rgs

private ?ateTime dateFtimeB

pulic MinuteEvent%rgs7?ateTime dateFtime6 this&dateFtime G dateFtimeB D

pulic int Minute get return dateFtime&MinuteB D

D DD


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using SystemB


pulic class Pulisher

pulic event ElapsedMinuteEvent!andler MinuteTic*B

pulic Pulisher76 Console&,rite:ine7HPulisher CreatedH6B D

pulic void countMinutes76 int currentFminute G ?ateTime&(ow&MinuteB

while7true6 i7currentFminute G ?ateTime&(ow&Minute6Console&,rite:ine7HPulisher4 JDH' ?ateTime&(ow&Minute6B

onMinuteTic*7new MinuteEvent%rgs7?ateTime&(ow66B currentFminute G ?ateTime&(ow&MinuteB Dend i

D end while D end countMinutes method

pulic void onMinuteTic*7MinuteEvent%rgs e6 i7MinuteTic* G null6 MinuteTic*7this' e6B D D end onMinuteTic* method D end Pulisher class de;nitionD end CustomEventE$ample namespace


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using SystemB


pulic class Suscrier

private Pulisher pulisherB

pulic Suscrier7Pulisher pulisher6 this&pulisher G pulisherB suscrieToPulisher76B Console&,rite:ine7HSuscrier CreatedH6B D

pulic void suscrieToPulisher76 pulisher&MinuteTic* KG new ElapsedMinuteEvent!andler7minuteTic*!andler6B D

pulic void minuteTic*!andler7"0ect sender' MinuteEvent%rgs e6

Console&,rite:ine7HSuscrier !andler Method4 JDH' e&Minute6B

D D end Suscrier class de;nitionD end CustomEventE$ample namespace


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using SystemB


pulic class Main%pp pulic static void Main76 Console&,rite:ine7HCustom Events are CoolH6B

Pulisher p G new Pulisher76B Suscrier s G new Suscrier7p6B p&countMinutes76B

D end main D end Main%pp class de;nition

D end CustomEventE$ample namespace


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C# Event Processing ppt