- Declaring Events
- C# Delegate Example
- Delegates and Events
- C# Event Example: EventHandler - Dot Net Perls
He has over 17 years of software industry experience in various roles including Lead Software Architect, Principal Software Engineer, and Product Manager. Nish is an industry acknowledged expert in the Microsoft technology stack. In addition, he has over published technology articles on CodeProject. Nish is vastly experienced in team management, mentoring teams, and directing all stages of software development.
If you are interested in hiring Nish as a consultant, you can reach him via his google email id voidnish. Event handling in C. To bubble or tunnel basic WPF events. Simple CRUD with the. Event handling in VB. Dejan Dimeski Oct Member 8-Mar Member 6-May Starting to think people post kid pics in their profiles because that was the last time they were cute - Jeremy. Mico Perez 7-Aug Mark McClure Apr Paul French Apr Member 1-Nov Albert Pascual 6-Apr Andrew Phillips May Nish Nishant May Article Alternatives Comments 28 Add your own alternative version Tagged as. Events and event handling in C Nish Nishant , 16 Oct Events and event handling in C Member Aug 3: Thanks for posting a very nice article.
My vote of 3 chait Dec 2: Nice one but not for the beginners. Excellent article Dejan Dimeski Oct Exactly mentioning what prerequisites and knowledge you need to understand the material. It would we very good if there is also "in real world" example. Not quite as simple as I wished for a first example Timok1A 5-Aug Hello, This is a very good article with lots of explanations, but I feel it is is still a little bit more complex that it would need to as a first event example in C. I have written a simpler version here: Simplistic event example in C I suggest to come back here once you have tried the most simple version.
Thank you Member 8-Mar Nish, I got it running in Silverlight with Blend 4.
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Only had to add a static TextBlock in the class declaration space above MainPage to replace the Console output. My vote of 5 naymyohaen Nov Your program only uses one event function. That is to show people they can add more subscriptions to the event. You just add your method to the event without worrying about who is already hooked in to the event. Hi I just wonder why you have so many static functions etc. My vote of 4 Mico Perez 7-Aug My vote of 4 bindum31 6-Jul 3: Your article helps me a lot to learn event handling in C.
Can you talk more clearly about paramenter object and eventargs and more example for them binhcoolfreestyles Mar Can you talk more clearly about paramenter object and eventargs and more example for them. Can you talk more clearly about paramenter object and eventargs and more example for them Mark McClure Apr I agree, this would helpful.
Declaring Events
The fact is that i am using System. Can you show your solution? Time wait for none but wait for Disable event temporarily RomanskiSt Apr 2: I would like to disable the ItemCheck event for a ListView item while assigning the Checked property manually: The second is DelegateArticle. SecondDelegate which has two char parameters, and doesn't return anything because the return type is specified as void. Note that the delegate keyword doesn't always mean that a delegate type is being declared.
The same keyword is used when creating instances of the delegate type using anonymous methods. The types declared here derive from System. MulticastDelegate , which in turn derives from System. In practice, you'll only see delegate types deriving from MulticastDelegate. The difference between Delegate and MulticastDelegate is largely historical; in betas of. You can pretty much pretend that they're only one type. Any delegate type you create has the members inherited from its parent types, one constructor with parameters of object and IntPtr and three extra methods: Invoke , BeginInvoke and EndInvoke.
C# Delegate Example
We'll come back to the constructor in a minute. The methods can't be inherited from anything, because the signatures vary according to the signature the delegate is declared with.
Using the sample code above, the first delegate has the following methods:. As you can see, the return type of Invoke and EndInvoke matches that of the declaration signature, as are the parameters of Invoke and the first parameters of BeginInvoke. We'll see the purpose of Invoke in the next section, and cover BeginInvoke and EndInvoke in the section on advanced usage. It's a bit premature to talk about calling methods when we don't know how to create an instance, however.
We'll cover that and more in the next section. Now we know how a delegate type is declared and what it contains, let's look at how to create an instance of such a type, and what we can do with it. My article on closures talks about the features of C 2. By concentrating on the explicit manner of creating instances in C 1. When you understand the basics, it's clearly worth knowing the features these later versions provide - but if you try to use them without having a firm grasp on the basics, you may well get confused.
As mentioned earlier, the key points of data in any particular delegate instance are the method the delegate refers to, and a reference to call the method on the target. For static methods, no target is required.
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The CLR itself supports other slightly different forms of delegate, where either the first argument passed to a static method is held within the delegate, or the target of an instance method is provided as an argument when the method is called. See the documentation for System.
Delegate for more information on this if you're interested, but don't worry too much about it. So, now that we know the two pieces of data required to create an instance along with the type itself, of course , how do we tell the compiler what they are? We use what the C specification calls a delegate-creation-expression which is of the form new delegate-type expression.
Delegates and Events
The expression must either be another delegate of the same type or a compatible delegate type in C 2. Creating copies of a delegate is fairly rare, so we will concentrate on the more common form. A few examples are listed below:. The constructor we mentioned earlier has two parameters - an object and an IntPtr. The object is a reference to the target or null for static methods and the IntPtr is a pointer to the method itself.
One point to note is that delegate instances can refer to methods and targets which wouldn't normally be visible at the point the call is actually made. For instance, a private method can be used to create a delegate instance, and then the delegate instance can be returned from a public member. Alternatively, the target of an instance may be an object which the eventual caller knows nothing about. However, both the target and the method must be accessible to the creating code. In other words, if and only if you can call a particular method on a particular object, you can use that method and target for delegate creation.
Access rights are effectively ignored at call time. Delegate instances are called just as if they were the methods themselves. For instance, to call the delegate referred to by variable d1 above, we could write:. The method referred to by the delegate instance is called on the target object if there is one , and the result is returned. Producing a complete program to demonstrate this without including a lot of seemingly irrelevant code is tricky.
However, here's a program which gives one example of a static method and one of an instance method. StaticMethod could be written as just StaticMethod in the same way that within an instance method you could write InstanceMethod instead of this. InstanceMethod - I've included the class name just to make it clear how you would reference methods from other classes. The C syntax is just a short-hand for calling the Invoke method provided by each delegate type. These are explained later. Delegates can be combined such that when you call the delegate, a whole list of methods are called - potentially with different targets.
When I said before that a delegate contained a target and a method, that was a slight simplification.
C# Event Example: EventHandler - Dot Net Perls
That's what a delegate instance representing one method contains. For the sake of clarity, I'll refer to such delegate instances as simple delegates. The alternative is a delegate instance which is effectively a list of simple delegates, all of the same type i. I'll call these combined delegates. Combined delegates can themselves be combined together, effectively creating one big list of simple delegates in the obvious fashion.
It's important to understand that delegate instances are always immutable. This is just like strings: PadLeft for instance, it doesn't actually change the string you call it on - it just returns a new string with the appropriate padding. Combining two delegate instances is usually done using the addition operator, as if the delegate instances were strings or numbers. Subtracting one from another is usually done with the subtraction operator.
Note that when you subtract one combined delegate from another, the subtraction works in terms of lists. This documentation is archived and is not being maintained. We recommend using Visual Studio Hooking Up to Events Visual Studio. You can then modify this reference, as the text is already selected in the Code Editor. Otherwise, automatic event hook up is complete at this point.
To hook up to an event Create a C Windows application.