I agree, they all seem to allow reusing multiple “classes” of behaviour. There are differences, though, and understanding these will probably aid your decision. Before providing a brief summary/highlight of each feature and examples of suitable usage, let’s just summarize on the conclusion of each. Conclusion / typical usage: @Delegate: Used to add all the … Read more
The error is somewhere in your … — that error means that your ListViewController class didn’t get closed, so the extension is being interpreted as nested inside, like this: class ListViewController { … extension ListViewController { } } Find the missing closing brace and you should solve the problem.
Delegates are just a way to pass around a function in a variable. You pass a delegated function to do a callback. Such as when doing asynchronous IO, you pass a delegated function (a function you have written with the delegate parameter) that will be called when the data has been read off the disk.
Simple answer: the code needing to perform the action doesn’t know the method to call when it’s written. You can only call the method directly if you know at compile-time which method to call, right? So if you want to abstract out the idea of “perform action X at the appropriate time” you need some … Read more
The RemoveAll() methods accept a Predicate<T> delegate (until here nothing new). A predicate points to a method that simply returns true or false. Of course, the RemoveAll will remove from the collection all the T instances that return True with the predicate applied. C# 3.0 lets the developer use several methods to pass a predicate … Read more
Best would be to have the dictionary strongly typed, but if you assign the lambda to a specific lambda (delegate) first, it should work (because the compiler then knows the delegate format): Action<bool> inp = InProgress => base.InProgress = InProgress; dict.Add(“InProgress”, inp); Or by casting it directly, same effect dict.Add(“InProgress”, (Action<bool>)(InProgress => base.InProgress = InProgress)); … Read more
The line self.MessageTextField.delegate = self causes the error since you try to assign self as the delegate of a UITextField. But your ViewController is not a UITextFieldDelegate. To make your class this kind of delegte, you need to adopt the UITextFieldDelegate protocol. This can be achieved by adding it to the list of protocols and … Read more
A protocol, declared with the (@protocol syntax in Objective-C) is used to declare a set of methods that a class “adopts” (declares that it will use this protocol) will implement. This means that you can specify in your code that, “you don’t care which class is used as long as it implements a particular protocol”. … Read more
A “callback” is a term that refers to a coding design pattern, available in any language that has function pointers, or an analogue to function pointers (which is kinda what a delegate is) In this pattern, you pass a pointer to a function to another function, so that within the called function, it can “call … Read more
Fwiw, neither example uses standard .NET conventions. The EventHandler<T> generic should declare the event: public event EventHandler<EmployeeEventArgs> Leave; The “On” prefix should be reserved for a protected method that raises the event: protected virtual void OnLeave(EmployeeEventArgs e) { var handler = Leave; if (handler != null) handler(this, e); } You don’t have to do it … Read more