Delegates and Lambda Expressions notes

 Delegate: pointer to a function

Eg. Photo class -> Load and Save methods

Photofilters -> Contains different types of filters. Eg., BWFilter, Contrast, Brightness, Resize etc

PhotoProcessor -> Takes the path, loads a photo, applies some filters and saves the Photo.

If a developer wants to develop a new filter, he has to download the code, create the filter and then make changes to PhotoProcessor.

Instead of PhotoProcessor taking the actual filters class, will take a PhotoFilterHandler delegate and will take as parameter.

public delegate PhotoFilterHandler(Photo photo);

public Photo process(string path, PhotoFilterHandler filter){

photo.Load(path);

 filter(photo);

photo.Save();

}


while implementing it

create an instance photoprocessor class.

Create an instance of PhotoFilterHandler

var filterHandler = photoFilter.ApplyBWFilter;

filterHandler += photoFilter.ApplyBrightnessFilter;

filterHandler += Resize;

photoProcessor.process("c:\\photos\\photo1.png", filterHandler);

static void Resize(Photo photo){

Console.WriteLine("Apply Resize");

}



Lambda Expressions

args => expression

No arguments

() => expression

One argument

x => expression

Two or more

(x, y, z) => expression

Action<> and Func<> are delegates

Action only input

Func<int, int>

A function taking an integer as argument and returning an int as output. 

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