Elucidate delegates C#

Question

Hi, I'm a naive to C#, trying to understand Delegate. I have read few articles describing delegate as - Type-safe function pointer - Used to define callback functions (methods that have something to-return) - Call multiple methods on single event As C# is Object-Oriented & every object can be related to a real world entity, i believe delegates in real-world are 'people from one country/ team/ organization' > Trump says North Korea **delegates** will deliver letter from Kim Jong Un about summit. > Delegates from Microsoft talk about Github acquisition. So delegate will have same parameters and return type as of underlying method the delegate refers to. As per https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/delegates/#delegates-overview 1. Delegates allow methods to be passed as parameters. - We can also pass methods as parameters to other methods. Console.WriteLine(foo.ToString()); 2. Delegates can be used to define callback methods. - Methods with return keyword perform as delegates, because delegate is just a bridge between callee and caller methods. 3. Delegates can be chained together; for example, multiple methods can be called on a single event. - As methods can also be chained. Caller method() { // Callee method1(); Callee method2(); // Callee method3(); } which could also be invkoed from single event I assume, we see delegates working in background when we copy/cut & paste files/folders from Source to Destination . Because files are moved from source to Destination but how does progress-bar window know about current fileName & amount of progress to be filled in progress-bar .? So, Why & When to use delegate? (As delegate points to a function which has required functionality to execute, why can't i call a function directly instead calling delegate?) P.S @all C# corner members/ users - Please help me to understand delegate in & out. Thanks in advance.

James Axsom · Answer

Using your scenario with Trump and North Korea: North Korea would take the role of a publisher. The United State and /or any other country may take the role of a subscriber. North Korea would announce to the world the following: When the summit takes place Where the summit takes place Let’s assume North Korea has decided to announce and publish details about the summit. “Hey World! Its me Kim! There’s going to be summit!” The subscribers who have a stake in the summit hear this. Each subscriber handles North Korea’s published announcement differently. Let’s examine how each subscriber take the data from North Korea and handles it: 1 St Subscriber: Singapore Oh my! North Korea has announced the summit. It going to take place in my country. On 12 June 2018. I think I’ll prepare a place in my country for this to happen. I’ll prepare Sentosa Island. There is hotel there called Capella Hotel. It will all be already on 12 June. 2 nd Subscriber: United States Ok! That is great! Peace at last and a new friendship which may bring stability to the world. I’ll get Donald Trump ready for the summit. I’ll get him nice suit, fuel up air force one with aviation fuel and prepare a dialog all ready to go on 12 June. 3 rd Subscriber: South Korea Wow! Could this really be happening? What if things go wrong? I’ll hope for the best but prepare for the worse. I’ll put military on alert but won’t tell anybody about that. In the meantime, I’ll dispatch a huge public relations committee to bask in the glow of the summit. All other countries in the world hear Kim’s announcement but they don’t have a stake in the event. So, they ignore, Kim. “Ok! Good Luck!” As you can see each subscriber handled Kim’s announcement differently with their own implementation. Here is a project. I attached a project that address what you want to learn. I developed it in Visual Studio 2017, Community Edition. This edition is free at Microsoft’s website. You can download it and use it. Unpack the zip file and copy it to folder. Open Visual Studio and open the solution file, (the *sln file). Hope this helps.

Sahil Sharma · Answer

I'll try to explain it in simple terms. Delegate is a function pointer that means a variable to hold a function and execute it later. Example: If I need to store an integer value and to use it later, I'll write: int x = 5; while (x { Console.Write(x); x++; } Similarly, if I need to hold a function in a variable and use it later, I'll write: public void Show() { Console.Write( "Hello" ); } public delegate void FuntionHolder (); //Delegated way to hold a function FunctionHolder functionHolder = new FunctionHolder(Show); functionHolder(); //Function Execution Coming back to your question about why do we need to use delegates, if you have worked with ASP.NET WebForms which is a event-driven framework, delegates are extensively used in it. One simple example about delegate usage is Publisher-Subscriber pattern . Let's say I ask to write a program to execute ten different functions (same structure) on a single button click. How will you do that? Either yopu can call ten functions individualy or attach them to a delegate and simply invoke the delegate. This is why and where we use delegates. Cheers!