javascript - Is there a knockoutjs computed equivalent in C#? -

i use knockout.js lot , love concept of computed observable.
idea computed observable defined function of other observable , takes dependence on observable variable used inside of it.
allow interesting scenarios dependent variables update once single observable change impact other computed variables.

http://knockoutjs.com/documentation/computedobservables.html

question :does c# have equivalent using either standard libraries or open source library?

answer : yes, there is.

interface inotifypropertychanged doing that, in system.componentmodel namespace.
interface contains propertychanged event, trigger when property changed.

c# 4 , below example

public class datacs4 : inotifypropertychanged {     #region inotifypropertychanged members      public event propertychangedeventhandler propertychanged;     protected virtual void onpropertychanged(string propertyname)     {         propertychangedeventhandler handler = propertychanged;         if (handler != null)             handler(this, new propertychangedeventargs(propertyname));     }      #endregion      // represent observable     private int firstnumber;     public int firstnumber     {         { return firstnumber; }         set         {             if (value == firstnumber)                 return;              this.firstnumber = value;             onpropertychanged("firstnumber");             onpropertychanged("sum");         }     }      // represent observable     private int secondnumber;     public int secondnumber     {         { return secondnumber; }         set         {             if (value == secondnumber)                 return;              this.secondnumber = value;             onpropertychanged("secondnumber");             onpropertychanged("sum");         }     }      // represent computed     public int sum { { return firstnumber + secondnumber; } } } 

this simple example sum 2 integers
have firstnumber property, (which consider knockout observable)
have secondnumber property (which consider knockout observable)
, have sum property (which consider knockout computed).

now every time change either firstnumber or secondnumber (by calling corresponding set functions), notifying subscribers properties (this done calling onpropertychanged method)

also calling onpropertychanged sum property notify subscribers property value of property has changed.

note common pattern when using wpf + mvvm pattern.

when using c# 5.0 or c# 6.0, benefits new features make code little easier

c# 5.0 example

public class datacs5 : inotifypropertychanged {     #region inotifypropertychanged members      public event propertychangedeventhandler propertychanged;      protected virtual void onpropertychanged([callermembername]string propertyname = null)     {         propertychangedeventhandler handler = propertychanged;         if (handler != null)             handler(this, new propertychangedeventargs(propertyname));     }      #endregion      // represent observable     private int firstnumber;     public int firstnumber     {         { return firstnumber; }         set         {             if (value == firstnumber)                 return;              this.firstnumber = value;             onpropertychanged();             onpropertychanged("sum");         }     }      // represent observable     private int secondnumber;     public int secondnumber     {         { return secondnumber; }         set         {             if (value == secondnumber)                 return;              this.secondnumber = value;             onpropertychanged();             onpropertychanged("sum");         }     }       // represent computed     public int sum { { return firstnumber + secondnumber; } } } 

there 2 changes here

1. protected virtual void onpropertychanged([callermembername]string propertyname = null), putting attribute before parameter of method, compiler know name of property called method automatiilcay, without passing property name manually, can write following statement.
2. onpropertychanged(); represent second modification.

note: callermembername attribute exists in system.runtime.compilerservices namespace

c# 6.0 example

with c# 6.0 simplify implemenation of onpropertychanged method.

public class datacs6 : inotifypropertychanged {     #region inotifypropertychanged members      public event propertychangedeventhandler propertychanged;      // c# 6.0     protected void onpropertychanged([callermembername] string propertyname = null)     {         propertychanged?.invoke(this, new propertychangedeventargs(propertyname));     }      #endregion      // represent observable     private int firstnumber;     public int firstnumber     {         { return firstnumber; }         set         {             if (value == firstnumber)                 return;              this.firstnumber = value;             onpropertychanged();             onpropertychanged("sum");         }     }      // represent observable     private int secondnumber;     public int secondnumber     {         { return secondnumber; }         set         {             if (value == secondnumber)                 return;              this.secondnumber = value;             onpropertychanged();             onpropertychanged("sum");         }     }      // represent computed     public int sum => firstnumber + secondnumber; } 

reference

update
responding following comment :

interesting! here have manage dependencies yourself. have trigger property changed sum. in knockout figures out properties shall trigger property changed on computed. way of doing that?

i think have 2 options (at least)

1. propertychanged library on github.
   description of library :

   injects inotifypropertychanged code properties @ compile time

   here new code after download library nuget

   [propertychanged.implementpropertychanged] public class data {     public int firstnumber { get; set; }      public int secondnumber { get; set; }      public int sum => secondnumber + firstnumber; } 

   2.postsharp library

cheers !.