C#•3y ago

How to subscribe an EventHandler? [Answered]

I don't understand how to subscribe this. I don't get it. I honestly don't even know why I used an EventHandler instead of an Action or something.

CharberryTree tree = new CharberryTree();
while (true)
tree.MaybeGrow();

public class CharberryTree
{
    public event EventHandler<RipenedEventArgs>? Ripened;

    public CharberryTree()
    {

    }
    private Random _random = new Random();
    public bool Ripe { get; set; }
    public void MaybeGrow()
    {
        // Only a tiny chance of ripening each time, but we try a lot!
        if (_random.NextDouble() < 0.00000001 && !Ripe)
        {
            Ripe = true;
            Ripened?.Invoke(this, new RipenedEventArgs(Ripe));
        }
    }
}

public class Notifier
{
    public Notifier(CharberryTree tree)
    {
        tree.Ripened += OnRipened();
    }
    public void OnRipened()
    {

    }
}

public class Harvester
{
    public Harvester(CharberryTree tree)
    {
        
    }
}

public class RipenedEventArgs : EventArgs
{
    public bool Ripe { get; set; }
    public RipenedEventArgs(bool ripe) => Ripe = ripe;
}

CharberryTree tree = new CharberryTree();
while (true)
tree.MaybeGrow();

public class CharberryTree
{
    public event EventHandler<RipenedEventArgs>? Ripened;

    public CharberryTree()
    {

    }
    private Random _random = new Random();
    public bool Ripe { get; set; }
    public void MaybeGrow()
    {
        // Only a tiny chance of ripening each time, but we try a lot!
        if (_random.NextDouble() < 0.00000001 && !Ripe)
        {
            Ripe = true;
            Ripened?.Invoke(this, new RipenedEventArgs(Ripe));
        }
    }
}

public class Notifier
{
    public Notifier(CharberryTree tree)
    {
        tree.Ripened += OnRipened();
    }
    public void OnRipened()
    {

    }
}

public class Harvester
{
    public Harvester(CharberryTree tree)
    {
        
    }
}

public class RipenedEventArgs : EventArgs
{
    public bool Ripe { get; set; }
    public RipenedEventArgs(bool ripe) => Ripe = ripe;
}

230 Replies

BigggMoustacheOP•3y ago

actually at this point I'm sure I'm doing the exercise wrong.

sibber•3y ago

tree.Ripened += OnRipened; you dont want to invoke the method, you want the method itself

BigggMoustacheOP•3y ago

yeah that's right. I just changed the EventHandler to an Action? also

sibber•3y ago

also Notifier should be called NotificationHandler, it doesnt notify anything sure

BigggMoustacheOP•3y ago

Oh really okay

sibber•3y ago

or preferably change the handler signature

BigggMoustacheOP•3y ago

Idk what that means lol

sibber•3y ago

    public void OnRipened(object? sender, RipenedEventArgs args)
    {

    }

    public void OnRipened(object? sender, RipenedEventArgs args)
    {

    }

BigggMoustacheOP•3y ago

Okay yeah I could have done that.

sibber•3y ago

the handler's signature has to match the event delegate's signature

BigggMoustacheOP•3y ago

yeah thanks. Give me one second to figure out next question.

sibber•3y ago

which is EventHandler<RipenedEventArgs>

BigggMoustacheOP•3y ago

Okay I remember reading that EventArgs is how data is passed

sibber•3y ago

yeah thats one way to pass data its the convention tho

BigggMoustacheOP•3y ago

and my interpretation was using that to pass the Ripe value of the tree did I do that correctly?

sibber•3y ago

sure yeah

BigggMoustacheOP•3y ago

okay I'm changing back to EventHandler then lol sec

sibber•3y ago

maybe name it IsRipe to be clearer

BigggMoustacheOP•3y ago

in the eventarg?

sibber•3y ago

and the class

BigggMoustacheOP•3y ago

cause the top portion is part copied from example ye i dun wanna do that lol

sibber•3y ago

ah fair

BigggMoustacheOP•3y ago

CharberryTree tree = new CharberryTree();
while (true)
 tree.MaybeGrow();
public class CharberryTree
{
 private Random _random = new Random();
 public bool Ripe { get; set; }
 public void MaybeGrow()
 {
 // Only a tiny chance of ripening each time, but we try a lot!
 if (_random.NextDouble() < 0.00000001 && !Ripe)
 {
 Ripe = true;
 }
 }
}

CharberryTree tree = new CharberryTree();
while (true)
 tree.MaybeGrow();
public class CharberryTree
{
 private Random _random = new Random();
 public bool Ripe { get; set; }
 public void MaybeGrow()
 {
 // Only a tiny chance of ripening each time, but we try a lot!
 if (_random.NextDouble() < 0.00000001 && !Ripe)
 {
 Ripe = true;
 }
 }
}

This is the reference it gave

Objectives:
• Make a new project that includes the above code.
• Add a Ripened event to the CharberryTree class that is raised when the tree ripens.
• Make a Notifier class that knows about the tree (Hint: perhaps pass it in as a constructor parameter) and subscribes to its Ripened event. Attach a handler that displays something like “A charberry fruit has ripened!” to the console window.
• Make a Harvester class that knows about the tree (Hint: like the notifier, this could be passed as a constructor parameter) and subscribes to its Ripened event. Attach a handler that sets the tree’s Ripe property back to false.
• Update your main method to create a tree, notifier, and harvester, and get them to work together to grow, notify, and harvest forever

Objectives:
• Make a new project that includes the above code.
• Add a Ripened event to the CharberryTree class that is raised when the tree ripens.
• Make a Notifier class that knows about the tree (Hint: perhaps pass it in as a constructor parameter) and subscribes to its Ripened event. Attach a handler that displays something like “A charberry fruit has ripened!” to the console window.
• Make a Harvester class that knows about the tree (Hint: like the notifier, this could be passed as a constructor parameter) and subscribes to its Ripened event. Attach a handler that sets the tree’s Ripe property back to false.
• Update your main method to create a tree, notifier, and harvester, and get them to work together to grow, notify, and harvest forever

This is the instruction and my first post is what I've done

sibber•3y ago

i think the harvester is the one that should subscribe to the event

BigggMoustacheOP•3y ago

So my problem with the EventHandler thing is I don't sub the event through the ctor like instructed

sibber•3y ago

wdym

BigggMoustacheOP•3y ago

the instruction suggest taking the tree through the other classes constructor to sub the event in the CharberryTree class

sibber•3y ago

yeah whats the problem with that

BigggMoustacheOP•3y ago

I'd have to set a property / field to hold the what the constructor paramter takes in, and then reference that in the class taking the EventArg? I'm just not sure how it works lol. The EventArg example didn't have any stuff poppin' in a constructors parameters.

sibber•3y ago

well you only need to subscribe to the event which you already did

public class Notifier
{
    public Notifier(CharberryTree tree)
    {
        tree.Ripened += OnRipened();
    }
    public void OnRipened()
    {

    }
}

public class Notifier
{
    public Notifier(CharberryTree tree)
    {
        tree.Ripened += OnRipened();
    }
    public void OnRipened()
    {

    }
}

so all thats left for this class is to print a message to the console saying the tree has ripened anyway gtg its 2 am goodluck

BigggMoustacheOP•3y ago

ty lol gn homie well I gott ajet anyways. I guess I'll finish this later too. xD. Thanks again homie.

CharberryTree tree = new CharberryTree();
while (true)
tree.MaybeGrow();

public class CharberryTree
{
    public event EventHandler<RipenedEventArgs> ?Ripened;

    public CharberryTree()
    {

    }
    private Random _random = new Random();
    public bool Ripe { get; set; }
    public void MaybeGrow()
    {
        // Only a tiny chance of ripening each time, but we try a lot!
        if (_random.NextDouble() < 0.00000001 && !Ripe)
        {
            Ripe = true;
            Ripened?.Invoke(this, new RipenedEventArgs(Ripe));
        }
    }
}

public class Notifier
{
    public CharberryTree Tree { get; set; }
    public Notifier(CharberryTree tree)
    {
        Tree = tree;
    }
    public void OnRipened(object sender, RipenedEventArgs args)
    {
        if (sender is CharberryTree) Console.WriteLine("Tree has ripened!");
    }
}

public class Harvester
{
    public CharberryTree Tree { get; set; }
    public Harvester(CharberryTree tree)
    {
        Tree = tree;
    }
    public void OnRipened(object sender, RipenedEventArgs args)
    {

    }
}

public class RipenedEventArgs : EventArgs
{
    public bool Ripe { get; set; }
    public RipenedEventArgs(bool ripe) => Ripe = ripe;
}

CharberryTree tree = new CharberryTree();
while (true)
tree.MaybeGrow();

public class CharberryTree
{
    public event EventHandler<RipenedEventArgs> ?Ripened;

    public CharberryTree()
    {

    }
    private Random _random = new Random();
    public bool Ripe { get; set; }
    public void MaybeGrow()
    {
        // Only a tiny chance of ripening each time, but we try a lot!
        if (_random.NextDouble() < 0.00000001 && !Ripe)
        {
            Ripe = true;
            Ripened?.Invoke(this, new RipenedEventArgs(Ripe));
        }
    }
}

public class Notifier
{
    public CharberryTree Tree { get; set; }
    public Notifier(CharberryTree tree)
    {
        Tree = tree;
    }
    public void OnRipened(object sender, RipenedEventArgs args)
    {
        if (sender is CharberryTree) Console.WriteLine("Tree has ripened!");
    }
}

public class Harvester
{
    public CharberryTree Tree { get; set; }
    public Harvester(CharberryTree tree)
    {
        Tree = tree;
    }
    public void OnRipened(object sender, RipenedEventArgs args)
    {

    }
}

public class RipenedEventArgs : EventArgs
{
    public bool Ripe { get; set; }
    public RipenedEventArgs(bool ripe) => Ripe = ripe;
}

My event in Notifier is not being called. it's getting to my Ripened?.Invoke() line and going back to the while loop at start I'm noticing my EventHandler<RipenedEventArgs> ?Ripened; is null when invoked and I'm not sure why that is either.

ero•3y ago

You never subscribe anything to tree.Ripened

BigggMoustacheOP•3y ago

CharberryTree tree = new CharberryTree();
while (true)
tree.MaybeGrow();

public class CharberryTree
{
    public event EventHandler<RipenedEventArgs> ?Ripened;

    public CharberryTree()
    {

    }
    private Random _random = new Random();
    public bool Ripe { get; set; }
    public void MaybeGrow()
    {
        // Only a tiny chance of ripening each time, but we try a lot!
        if (_random.NextDouble() < 0.00000001 && !Ripe)
        {
            Ripe = true;
            Ripened?.Invoke(this, new RipenedEventArgs(Ripe));
        }
    }
}

public class Notifier
{
    public CharberryTree Tree { get; set; }
    public Notifier(CharberryTree tree)
    {
        Tree = tree;
        tree.Ripened += OnRipened;
    }
    public void OnRipened(object sender, RipenedEventArgs args)
    {
        if (sender is CharberryTree) Console.WriteLine("Tree has ripened!");
    }
}

public class Harvester
{
    public CharberryTree Tree { get; set; }
    public Harvester(CharberryTree tree)
    {
        Tree = tree;
    }
    public void OnRipened(object sender, RipenedEventArgs args)
    {

    }
}

public class RipenedEventArgs : EventArgs
{
    public bool Ripe { get; set; }
    public RipenedEventArgs(bool ripe) => Ripe = ripe;
}

CharberryTree tree = new CharberryTree();
while (true)
tree.MaybeGrow();

public class CharberryTree
{
    public event EventHandler<RipenedEventArgs> ?Ripened;

    public CharberryTree()
    {

    }
    private Random _random = new Random();
    public bool Ripe { get; set; }
    public void MaybeGrow()
    {
        // Only a tiny chance of ripening each time, but we try a lot!
        if (_random.NextDouble() < 0.00000001 && !Ripe)
        {
            Ripe = true;
            Ripened?.Invoke(this, new RipenedEventArgs(Ripe));
        }
    }
}

public class Notifier
{
    public CharberryTree Tree { get; set; }
    public Notifier(CharberryTree tree)
    {
        Tree = tree;
        tree.Ripened += OnRipened;
    }
    public void OnRipened(object sender, RipenedEventArgs args)
    {
        if (sender is CharberryTree) Console.WriteLine("Tree has ripened!");
    }
}

public class Harvester
{
    public CharberryTree Tree { get; set; }
    public Harvester(CharberryTree tree)
    {
        Tree = tree;
    }
    public void OnRipened(object sender, RipenedEventArgs args)
    {

    }
}

public class RipenedEventArgs : EventArgs
{
    public bool Ripe { get; set; }
    public RipenedEventArgs(bool ripe) => Ripe = ripe;
}

If I understand correctly tree.Ripened += OnRipened; in the public Notifier(CharberryTree tree) subscribes the event? Sorry I forgot to update code

ero•3y ago

and what part of your code calls the Notifier constructor?

BigggMoustacheOP•3y ago

I thought the MaybeGrow() method did with Ripened.Invoke()

ero•3y ago

no, none of that code contains a call to any constructor

BigggMoustacheOP•3y ago

Oh I never made a Notifier or Harvester so I can't use them lol tyvm. Hey so quick question about what was happenig

BigggMoustacheOP•3y ago

before I created the new objects this was always null

BigggMoustacheOP•3y ago

I don't understand.

ero•3y ago

BigggMoustacheOP•3y ago

so the event being null is having nothing subscribed okay that's the first time I've ran into anything that was null because of a relationship to something else iirc so I have another question I guess well one moment let me collect mythoughts so the goal of the exercise is to have the tree ripen, notify, and havest (Ripe = false again) how to order events?

MODiX•3y ago

Ero#1111

REPL Result: Success

Foo foo = new();

foo.BarNull();
foo.Bar += (s, e) => { };
foo.BarNull();

class Foo
{
  public event EventHandler<string>? Bar;
  public void BarNull() => Console.WriteLine(Bar is null);
}

Foo foo = new();

foo.BarNull();
foo.Bar += (s, e) => { };
foo.BarNull();

class Foo
{
  public event EventHandler<string>? Bar;
  public void BarNull() => Console.WriteLine(Bar is null);
}

Console Output

True
False

True
False

Compile: 780.351ms | Execution: 89.895ms | React with ❌ to remove this embed.

ero•3y ago

i'm not super familiar with event patterns unfortunately

BigggMoustacheOP•3y ago

I'll be hoenst that shoots entirely over my head no problem. could you explain the thing?

ero•3y ago

what thing? i assume foo.Bar += (s, e) => { }; is what confuses you?

BigggMoustacheOP•3y ago

yes

ero•3y ago

just a very shorthand form of subscribing

BigggMoustacheOP•3y ago

I don't get the output lol so maybe the whole thing confuses xD

ero•3y ago

oh i was just showing whether foo.Bar was null or not showing that it is null before subscribing anything, and not null after

BigggMoustacheOP•3y ago

oh okay OH you were showing the error I had okay yeah tyvm. That was a new experience, where the relation itself is the content checked yeah that is illuminating. could you explain the shorthand? what is s, e?

ero•3y ago

like i'd personally just have Actions for this, i rarely use delegates or events sender and whatever type the EventHandler takes (in my case, string)

BigggMoustacheOP•3y ago

I used EventHandler because it seemed like the easiest way to share the Ripe property in the event

ero•3y ago

i just woulnd't even share it like why would another class care about my tree growing and ripening

BigggMoustacheOP•3y ago

well my goal was just to play with it because I'd never used it. well Harvester *will set *Ripe back to false so I was going to try to use the event data to determine that So just wanted to explore the functions I guess Why do you like Actions? Oh yeah I forgot EventHandler has two parameters

ero•3y ago

Tree tree = new Tree();
tree.OnRipen = _ => Console.WriteLine("My tree ripened!");

while (true)
  tree.TryGrow();


class Tree
{
  public bool IsRipe { get; set; }
  public Action<Tree>? OnRipen { get; set; }

  public void TryGrow()
  {
    if (Random.Shared.Next() < 0.00000001 && !IsRipe)
    {
      IsRipe = true;
      OnRipen?.Invoke(this);
    }
  }
}

Tree tree = new Tree();
tree.OnRipen = _ => Console.WriteLine("My tree ripened!");

while (true)
  tree.TryGrow();


class Tree
{
  public bool IsRipe { get; set; }
  public Action<Tree>? OnRipen { get; set; }

  public void TryGrow()
  {
    if (Random.Shared.Next() < 0.00000001 && !IsRipe)
    {
      IsRipe = true;
      OnRipen?.Invoke(this);
    }
  }
}

MODiX•3y ago

Ero#1111

REPL Error

An error occurred while sending a request to the REPL service. This may be due to a StackOverflowException or exceeding the 30 second timeout. Details: The request was canceled due to the configured HttpClient.Timeout of 100 seconds elapsing.

Tried to execute

this code

ero•3y ago

whoops, probability too small

BigggMoustacheOP•3y ago

It does seem easier overall to use lol

ero•3y ago

but maybe there are some patterns i don't know about

BigggMoustacheOP•3y ago

shrug idk either lol. I just know from example reference EventHandler was made to pass data around for you so I wanted to give it a go. I'll ask for criticism once complete in a minute or two.

BigggMoustacheOP•3y ago

CharberryTree tree = new CharberryTree();
Notifier notifier = new Notifier(tree);
Harvester harvester = new Harvester(tree);

while (true)
tree.MaybeGrow();

public class CharberryTree
{
    public event EventHandler<RipenedEventArgs> ?Ripened;

    public CharberryTree()
    {

    }
    private Random _random = new Random();
    public bool Ripe { get; set; }
    public void MaybeGrow()
    {
        // Only a tiny chance of ripening each time, but we try a lot!
        if (_random.NextDouble() < 0.00000001 && !Ripe)
        {
            Ripe = true;
            Ripened?.Invoke(this, new RipenedEventArgs(Ripe));
        }
    }
}

public class Notifier
{
    public CharberryTree Tree { get; set; }
    public Notifier(CharberryTree tree)
    {
        Tree = tree;
        tree.Ripened += OnRipened;
    }
    public void OnRipened(object sender, RipenedEventArgs args)
    {
        if (sender is CharberryTree) Console.WriteLine("Tree has ripened!");
    }
}

public class Harvester
{
    public CharberryTree Tree { get; set; }
    public Harvester(CharberryTree tree)
    {
        Tree = tree;
        tree.Ripened += OnRipened;
    }
    public void OnRipened(object sender, RipenedEventArgs args)
    {
        if (sender is CharberryTree && args.Ripe == true)
        {
            Console.WriteLine("Havesting Charberry.");
            Tree.Ripe = false;
        }
    }
}

public class RipenedEventArgs : EventArgs
{
    public bool Ripe { get; set; }
    public RipenedEventArgs(bool ripe) => Ripe = ripe;
}

CharberryTree tree = new CharberryTree();
Notifier notifier = new Notifier(tree);
Harvester harvester = new Harvester(tree);

while (true)
tree.MaybeGrow();

public class CharberryTree
{
    public event EventHandler<RipenedEventArgs> ?Ripened;

    public CharberryTree()
    {

    }
    private Random _random = new Random();
    public bool Ripe { get; set; }
    public void MaybeGrow()
    {
        // Only a tiny chance of ripening each time, but we try a lot!
        if (_random.NextDouble() < 0.00000001 && !Ripe)
        {
            Ripe = true;
            Ripened?.Invoke(this, new RipenedEventArgs(Ripe));
        }
    }
}

public class Notifier
{
    public CharberryTree Tree { get; set; }
    public Notifier(CharberryTree tree)
    {
        Tree = tree;
        tree.Ripened += OnRipened;
    }
    public void OnRipened(object sender, RipenedEventArgs args)
    {
        if (sender is CharberryTree) Console.WriteLine("Tree has ripened!");
    }
}

public class Harvester
{
    public CharberryTree Tree { get; set; }
    public Harvester(CharberryTree tree)
    {
        Tree = tree;
        tree.Ripened += OnRipened;
    }
    public void OnRipened(object sender, RipenedEventArgs args)
    {
        if (sender is CharberryTree && args.Ripe == true)
        {
            Console.WriteLine("Havesting Charberry.");
            Tree.Ripe = false;
        }
    }
}

public class RipenedEventArgs : EventArgs
{
    public bool Ripe { get; set; }
    public RipenedEventArgs(bool ripe) => Ripe = ripe;
}

Pobiega•3y ago

Re event vs action, there are a few tradeoffs events can have multiple listeners, for one

BigggMoustacheOP•3y ago

So I'll be honest I'm confused why in the public class Harvester method OnRipened using Tree.Ripe = false; sets the tree object bool of Ripe back to false sorry for interrupting Pobiega

Pobiega•3y ago

np and events sort of represent a less tightly coupled integration, imho

BigggMoustacheOP•3y ago

okay 1 listener on Action sounds weird, why is that?

Pobiega•3y ago

wdym? thats just how it is

BigggMoustacheOP•3y ago

lol okay idk

Pobiega•3y ago

`cs

Tree tree = new Tree();
tree.OnRipen = _ => Console.WriteLine("My tree ripened!");

while (true)
  tree.TryGrow();


class Tree
{
  public bool IsRipe { get; set; }
  public Action<Tree>? OnRipen { get; set; }

  public void TryGrow()
  {
    if (Random.Shared.Next() < 0.00000001 && !IsRipe)
    {
      IsRipe = true;
      OnRipen?.Invoke(this);
    }
  }
}

Tree tree = new Tree();
tree.OnRipen = _ => Console.WriteLine("My tree ripened!");

while (true)
  tree.TryGrow();


class Tree
{
  public bool IsRipe { get; set; }
  public Action<Tree>? OnRipen { get; set; }

  public void TryGrow()
  {
    if (Random.Shared.Next() < 0.00000001 && !IsRipe)
    {
      IsRipe = true;
      OnRipen?.Invoke(this);
    }
  }
}

this code that Ero posted for example once you set the OnRipen action, how would someone else add their listener to it? they can't. they'd replace the current one events support the += MyHandler tjhing out of the box

BigggMoustacheOP•3y ago

I didn't try the multidelegate(probably wrong word) or chaining thing that was talked of in book is that event specific?

Pobiega•3y ago

Action is a delegate type

BigggMoustacheOP•3y ago

OH okay

Pobiega•3y ago

nah you're correct events are supported by a multi delegate

BigggMoustacheOP•3y ago

okay thanks for that. why event vs eventhandler then?

Pobiega•3y ago

hm? well an event is an event honestly that part is a bit confusing

Pobiega•3y ago

https://docs.microsoft.com/en-us/dotnet/standard/events/

Handling and Raising Events

Learn to handle and raise .NET events, which are based on the delegate model. This model lets subscribers register with or receive notifications from providers.

Pobiega•3y ago

class Counter
{
    public event EventHandler ThresholdReached;

    protected virtual void OnThresholdReached(EventArgs e)
    {
        EventHandler handler = ThresholdReached;
        handler?.Invoke(this, e);
    }

    // provide remaining implementation for the class
}

class Counter
{
    public event EventHandler ThresholdReached;

    protected virtual void OnThresholdReached(EventArgs e)
    {
        EventHandler handler = ThresholdReached;
        handler?.Invoke(this, e);
    }

    // provide remaining implementation for the class
}

EventHandler is a type, much like Counter or string etc so to make an event, you say event MyEventType MyEventName;

BigggMoustacheOP•3y ago

right right

Pobiega•3y ago

the type declares what parameters a handler must have

BigggMoustacheOP•3y ago

Oh so it's a premade type of event

Pobiega•3y ago

but since its all delegates in the background, you can assign any method to be your "handler"

BigggMoustacheOP•3y ago

yeah okay

Pobiega•3y ago

EventHandler is a premade delegate type, yes

BigggMoustacheOP•3y ago

dude this is wild lol

Pobiega•3y ago

mhm it can be confusing but ITS ALL DELEGATES 😄

BigggMoustacheOP•3y ago

I know lmaooooo the book made sure to emphasize over and over that it was uh, delegates underneath

Pobiega•3y ago

essentially, use event for actual events, like OnRipened etc

BigggMoustacheOP•3y ago

made me think of inumerable under things so like Linq

Pobiega•3y ago

I tend to use Action like "events" when I do testing stubs since I know I will never ever have more than one "listener/handler"

BigggMoustacheOP•3y ago

okay yeah. I'm finding things up until this point were super easy but things like this are like, multi step processes you put on top of all the other stuff idk haha.

Pobiega•3y ago

I seem to recall you asking some questions before, so not "super easy" :p

BigggMoustacheOP•3y ago

I tried learning events a long time ago when I had a worse grasp of C# LOL yeah I'm just saying it's like a new layer of abstract concept to slap on the top of things

Pobiega•3y ago

haha yeah it pretty much is

BigggMoustacheOP•3y ago

could you offer whatever basic criticism of what I wrote?

CharberryTree tree = new CharberryTree();
Notifier notifier = new Notifier(tree);
Harvester harvester = new Harvester(tree);

while (true)
tree.MaybeGrow();

public class CharberryTree
{
    public event EventHandler<RipenedEventArgs> ?Ripened;

    public CharberryTree()
    {

    }
    private Random _random = new Random();
    public bool Ripe { get; set; }
    public void MaybeGrow()
    {
        // Only a tiny chance of ripening each time, but we try a lot!
        if (_random.NextDouble() < 0.00000001 && !Ripe)
        {
            Ripe = true;
            Ripened?.Invoke(this, new RipenedEventArgs(Ripe));
        }
    }
}

public class Notifier
{
    public CharberryTree Tree { get; set; }
    public Notifier(CharberryTree tree)
    {
        Tree = tree;
        tree.Ripened += OnRipened;
    }
    public void OnRipened(object sender, RipenedEventArgs args)
    {
        if (sender is CharberryTree) Console.WriteLine("Tree has ripened!");
    }
}

public class Harvester
{
    public CharberryTree Tree { get; set; }
    public Harvester(CharberryTree tree)
    {
        Tree = tree;
        tree.Ripened += OnRipened;
    }
    public void OnRipened(object sender, RipenedEventArgs args)
    {
        if (sender is CharberryTree && args.Ripe == true)
        {
            Console.WriteLine("Havesting Charberry.");
            Tree.Ripe = false;
        }
    }
}

public class RipenedEventArgs : EventArgs
{
    public bool Ripe { get; set; }
    public RipenedEventArgs(bool ripe) => Ripe = ripe;
}

CharberryTree tree = new CharberryTree();
Notifier notifier = new Notifier(tree);
Harvester harvester = new Harvester(tree);

while (true)
tree.MaybeGrow();

public class CharberryTree
{
    public event EventHandler<RipenedEventArgs> ?Ripened;

    public CharberryTree()
    {

    }
    private Random _random = new Random();
    public bool Ripe { get; set; }
    public void MaybeGrow()
    {
        // Only a tiny chance of ripening each time, but we try a lot!
        if (_random.NextDouble() < 0.00000001 && !Ripe)
        {
            Ripe = true;
            Ripened?.Invoke(this, new RipenedEventArgs(Ripe));
        }
    }
}

public class Notifier
{
    public CharberryTree Tree { get; set; }
    public Notifier(CharberryTree tree)
    {
        Tree = tree;
        tree.Ripened += OnRipened;
    }
    public void OnRipened(object sender, RipenedEventArgs args)
    {
        if (sender is CharberryTree) Console.WriteLine("Tree has ripened!");
    }
}

public class Harvester
{
    public CharberryTree Tree { get; set; }
    public Harvester(CharberryTree tree)
    {
        Tree = tree;
        tree.Ripened += OnRipened;
    }
    public void OnRipened(object sender, RipenedEventArgs args)
    {
        if (sender is CharberryTree && args.Ripe == true)
        {
            Console.WriteLine("Havesting Charberry.");
            Tree.Ripe = false;
        }
    }
}

public class RipenedEventArgs : EventArgs
{
    public bool Ripe { get; set; }
    public RipenedEventArgs(bool ripe) => Ripe = ripe;
}

OOHHH I asked earlier about that Tree.Ripe = false toward the bottom

Pobiega•3y ago

public event EventHandler<RipenedEventArgs> ?Ripened; that questionmark really bothers me its part of the type, not the name

BigggMoustacheOP•3y ago

Oh okay I always forget where those go tbh lol I thought it was for the variable specifically xD

Pobiega•3y ago

well it is, but its part of the type you are saying this variable is of type EventHandler<RipenedEventArgs>? so it can be null so, this seems okay. I'd perhaps change the Tree.Ripe = false to be tree.Harvest() or something depends on how you wanna divvie up your responsibliites

BigggMoustacheOP•3y ago

yeah ofc that makes sense

Pobiega•3y ago

should a tree know how to be harvested, or should a harvester know about trees?

BigggMoustacheOP•3y ago

OH BUT HEY that tree thing there how does referencing the class property change the other classes property

Pobiega•3y ago

hm? wdym

ero•3y ago

Exactly that way

Pobiega•3y ago

yeah exactly that way :p

BigggMoustacheOP•3y ago

Tree in that case is of the Harvester class

ero•3y ago

It's a reference

BigggMoustacheOP•3y ago

Pobiega•3y ago

its not a copy its a reference to the actual thing $refvsvalue

MODiX•3y ago

https://cdn.discordapp.com/attachments/364492811489509376/692833980650881084/pass-by-reference-vs-pass-by-value-animation.gif

BigggMoustacheOP•3y ago

shoot I did not realize that

ero•3y ago

Classes are always passed byref

BigggMoustacheOP•3y ago

I think I need a cheat sheet to put that on lol

Pobiega•3y ago

your "architecture" here is a bit unusual too in that your notifier/harvester both hold a hard ref to the tree instead of just registering their listeners and getting the tree that ripened from there what if you had one harvester responsible for 10 trees? the event args should contain the tree that ripened (its the sender in your case)

BigggMoustacheOP•3y ago

yeah yeah okay so just the constructor param is enough? well the Harvester uses the reference

ero•3y ago

Perhaps you'd want a static harvester class which acts as an extension on the tree

BigggMoustacheOP•3y ago

I don't understand that tbh but I'm excited to be exposed to the idea lol

Pobiega•3y ago

public class Harvester
{
    public Harvester(CharberryTree tree)
    {
        tree.Ripened += OnRipened;
    }

    public void OnRipened(object sender, RipenedEventArgs args)
    {
        if (sender is CharberryTree tree && args.Ripe == true)
        {
            Console.WriteLine("Havesting Charberry.");
            tree.Ripe = false;
        }
    }
}

public class Harvester
{
    public Harvester(CharberryTree tree)
    {
        tree.Ripened += OnRipened;
    }

    public void OnRipened(object sender, RipenedEventArgs args)
    {
        if (sender is CharberryTree tree && args.Ripe == true)
        {
            Console.WriteLine("Havesting Charberry.");
            tree.Ripe = false;
        }
    }
}

BigggMoustacheOP•3y ago

Also I tried using the sender object to get the tree and couldn't figure it out OH okay sender is not a reference to it

Pobiega•3y ago

obviously, since you register your handler in the ctor, this isn't super useful you'd probably move that out to a new method no it is, but its being sent as object so you do a typecheck

ero•3y ago

I said static extension for a reason

Pobiega•3y ago

if sender is CharberryTree tree yup

BigggMoustacheOP•3y ago

hmm that's cool okay can you give example of static here??

Pobiega•3y ago

your harvester doesnt really need to be what it is currently

BigggMoustacheOP•3y ago

oh?

Pobiega•3y ago

yeah all it does is change something on the source and print a message to the console

ero•3y ago

Ok i can't code this on my phone gimme a bit

Pobiega•3y ago

that could easily be a static method an extension method to register it with would be neat

BigggMoustacheOP•3y ago

Oh well I'm just following exercise instruction which was to make it a class

Pobiega•3y ago

yeah, thats fine

BigggMoustacheOP•3y ago

but I would love to know what you're talking about yeah dude I'm here to learn lmao, this is fucking great

Pobiega•3y ago

because most of the time, you'll want it to be a class

BigggMoustacheOP•3y ago

nice.

Pobiega•3y ago

its just that because this example is so simple, and doesnt need any instance data... I'm sure Ero will post the code once they write it up

BigggMoustacheOP•3y ago

Oh that's right lol. @Ero Take your time bud no rush. I really, really appreciate the instruction. so sender just grabs the object for a typecheck, it does not serve as a reference to the object as the type it is?

Pobiega•3y ago

Also, regardless of how helpful you are, you really need to watch your snark. You are way to snarky way to often.

BigggMoustacheOP•3y ago

so just to clarify, I can send bunches of EventArgs in params and set them, and they all get passed around with reference to the object they come from?

Pobiega•3y ago

? look at how you invoke the event Ripened?.Invoke(this, new RipenedEventArgs(Ripe)); the first parameter this is the sender that gets exposed to any listener as does the event args, but its the same eventargs being passed to all listeners, one by one

BigggMoustacheOP•3y ago

right. so I could put new RipenedEventArgs(Ripe, Age, Season, ...) in there?

Pobiega•3y ago

yeah your eventargs is just an object with a bunch of props on it "here is the info related to the event"

BigggMoustacheOP•3y ago

so its use is to pass all that around without needing a direct reference to the object? for decoupling?

Pobiega•3y ago

for example, on an "OnClick" event it contains the mouse location, what button was pressed, etc

BigggMoustacheOP•3y ago

Pobiega•3y ago

well you need the object ref to register the listener/handler but that might have happened via some abstraction yeah its a way to invert the dependency actually instead of your tree knowing about the harvester, its your harvester that knows about the tree at least initially

BigggMoustacheOP•3y ago

That's so cool. 'hey look over here. It's a sender with args lol

Pobiega•3y ago

do you know what the garbage collector is btw?

BigggMoustacheOP•3y ago

oh yes I meant to ask how that'd work here unsubscribing in practice

Pobiega•3y ago

yeah. unsubbing is the hard part events often lead to memory leaks, becuse if you dont unsub, the registered handler will keep the event source alive forever only when all the handlers get collected would the ref count reach 0 and the event source be collected

BigggMoustacheOP•3y ago

yeah all of that is wooshing I mean I vaguely get it lol

Pobiega•3y ago

the super simplified version of the garbage collector is that it just looks at how many references there are to an object

BigggMoustacheOP•3y ago

can you show me in my code where it'd be practical given some additional circumstance if necessary?

Pobiega•3y ago

if that number reaches 0, the object gets cleaned up ? what exactly?

BigggMoustacheOP•3y ago

in my exercise, where would I unsub the events, and if not anywhere, what premise would provide a practical place?

Pobiega•3y ago

uhm, well your tree grows forever in a while(true)

BigggMoustacheOP•3y ago

yeah I know lol

Pobiega•3y ago

so you dont have any leaks.

BigggMoustacheOP•3y ago

I'm just saying to further my practical understanding of the matter so it's less of a floaty abstraction

Pobiega•3y ago

imagine if you had multiple trees, and each tree had a chance to die each time it was harvested

BigggMoustacheOP•3y ago

Pobiega•3y ago

upon death, you'd want to unsub any and all listeners the common way to do this is to just assign null to the event

ero•3y ago

Tree tree =
  new Tree()
  .AddNotifier<MyRipenNotifier>()
  .AddHarvester<MyTreeHarvester>();

while (true)
  tree.TryGrow();

class Tree
{
  public bool IsRipe { get; set; }
  public EventHandler<RipenEventArgs>? OnRipen;

  public void TryGrow()
  {
    if (Random.Shared.Next() < 0.1 && !IsRipe)
    {
      IsRipe = true;
      OnRipen?.Invoke(this, new(IsRipe));
    }
  }
}

static class TreeFarm
{
  public static Tree AddNotifier<T>(this Tree tree) where T : IRipenNotifier
  {
    tree.OnRipen += T.OnNotify;
    return tree;
  }

  public static Tree AddHarvester<T>(this Tree tree) where T : IHarvester
  {
    tree.OnRipen += T.OnHarvest;
    return tree;
  }
}

interface IRipenNotifier
{
  static abstract void OnNotify(object? sender, RipenEventArgs e);
}

class MyRipenNotifier : IRipenNotifier
{
  public static void OnNotify(object? sender, RipenEventArgs e)
  {
    if (sender is not Tree tree)
      return;

    Console.WriteLine("Tree is now ripe!");
  }
}

interface IHarvester
{
  static abstract void OnHarvest(object? sender, RipenEventArgs e);
}

class MyTreeHarvester : IHarvester
{
  public static void OnHarvest(object? sender, RipenEventArgs e)
  {
    if (sender is not Tree tree)
      return;

    Console.WriteLine("Harvesting that tree!");
    tree.IsRipe = false;
  }
}

class RipenEventArgs : EventArgs
{
  public RipenEventArgs(bool isRipe)
  {
    Ripened = isRipe;
  }

  public bool Ripened { get; }
}

Tree tree =
  new Tree()
  .AddNotifier<MyRipenNotifier>()
  .AddHarvester<MyTreeHarvester>();

while (true)
  tree.TryGrow();

class Tree
{
  public bool IsRipe { get; set; }
  public EventHandler<RipenEventArgs>? OnRipen;

  public void TryGrow()
  {
    if (Random.Shared.Next() < 0.1 && !IsRipe)
    {
      IsRipe = true;
      OnRipen?.Invoke(this, new(IsRipe));
    }
  }
}

static class TreeFarm
{
  public static Tree AddNotifier<T>(this Tree tree) where T : IRipenNotifier
  {
    tree.OnRipen += T.OnNotify;
    return tree;
  }

  public static Tree AddHarvester<T>(this Tree tree) where T : IHarvester
  {
    tree.OnRipen += T.OnHarvest;
    return tree;
  }
}

interface IRipenNotifier
{
  static abstract void OnNotify(object? sender, RipenEventArgs e);
}

class MyRipenNotifier : IRipenNotifier
{
  public static void OnNotify(object? sender, RipenEventArgs e)
  {
    if (sender is not Tree tree)
      return;

    Console.WriteLine("Tree is now ripe!");
  }
}

interface IHarvester
{
  static abstract void OnHarvest(object? sender, RipenEventArgs e);
}

class MyTreeHarvester : IHarvester
{
  public static void OnHarvest(object? sender, RipenEventArgs e)
  {
    if (sender is not Tree tree)
      return;

    Console.WriteLine("Harvesting that tree!");
    tree.IsRipe = false;
  }
}

class RipenEventArgs : EventArgs
{
  public RipenEventArgs(bool isRipe)
  {
    Ripened = isRipe;
  }

  public bool Ripened { get; }
}

i think this requires .net 7 and preview lang though

Pobiega•3y ago

yup, static abstracts but its a nice example of how something like this could look in a "real" project given that your event handlers are simple generics + extension methods = superpowers

BigggMoustacheOP•3y ago

so on tree death I'd just Ripened = null and that'd fix it?

Pobiega•3y ago

for that case, yes there is a reverse thou, which is when the publisher (event source) lives longer than the subscriber if the subscriber upon death doesnt unsub itself

BigggMoustacheOP•3y ago

I was just about to ask that lol and @Ero I'll ask about your thing in a moment. Tyvm

ero•3y ago

I'ma go to sleep

BigggMoustacheOP•3y ago

❤️ okay. I appreciate the help bud.

Pobiega•3y ago

its only really a problem when the lifetimes of the subscriber and the publisher differ greatly

BigggMoustacheOP•3y ago

have a good night. why would sub need to keep reference of event around if source is gone? to use the data in the arg?

Pobiega•3y ago

no its the publisher that knows about the subscribers

BigggMoustacheOP•3y ago

oh okay

ero•3y ago

Yeah the order of execution here isn't really sensical

Pobiega•3y ago

once the source dies, the handler will not be invoked

ero•3y ago

A tree shouldn't have a harvester

Pobiega•3y ago

because the source is dead

BigggMoustacheOP•3y ago

yeah i get that

ero•3y ago

A harvester should be assigned the task of harvesting a number of trees

Pobiega•3y ago

this SO explains it fairly well https://stackoverflow.com/questions/4526829/why-and-how-to-avoid-event-handler-memory-leaks

BigggMoustacheOP•3y ago

NICE. getting pinned I'm looking at what Ero shared I've only used generics a couple times. This is super cool. What is being extended here though? Or were you just saying extensionmethods are based af? lol

ero•3y ago

Tree in TreeFarm

Pobiega•3y ago

extension methods are just static methods that "pretend" to be part of something else so intead of doing TreeFarm.AddNotifier(tree, ...) you can call tree.AddNotifier(...) its the exact same thing

BigggMoustacheOP•3y ago

Oh yeah okay

Pobiega•3y ago

they are very common in modern C#

BigggMoustacheOP•3y ago

yeah everything in there is new to me so it's more than a bit confusing xD

ero•3y ago

I guess they don't need to be extensions

BigggMoustacheOP•3y ago

Generics, Events, and ExtensionMethods are things I've only done a couple times

ero•3y ago

Could just be part of tree

BigggMoustacheOP•3y ago

I'm gonna copy it and step through it

Pobiega•3y ago

well you don't need to worry about this right now

BigggMoustacheOP•3y ago

oh well okay hahahaha

Pobiega•3y ago

your example is a bit contrived, and very simple

BigggMoustacheOP•3y ago

ero•3y ago

You probably can't copy it anyway

BigggMoustacheOP•3y ago

Oh 😭 lol

ero•3y ago

Unless you have a preview version of .net 7 downloaded and bs 2022 preview installed vs

BigggMoustacheOP•3y ago

That's a no lol

ero•3y ago

Then you'll have to wait until November lol

BigggMoustacheOP•3y ago

So what you folks are telling me is I did an okay job with this exercise and to move onto the next one? xD

Pobiega•3y ago

I refrain from commenting 😛

BigggMoustacheOP•3y ago

👀

ero•3y ago

Eh, it works, right?

BigggMoustacheOP•3y ago

lollllllllll

ero•3y ago

It's not something you would ever design in a real app

Pobiega•3y ago

Like, we don't know the exercise, only your code and as said, its a contrived example that is too simple to be realistic

ero•3y ago

I don't think there was a task

BigggMoustacheOP•3y ago

Objectives:
• Make a new project that includes the above code.
• Add a Ripened event to the CharberryTree class that is raised when the tree ripens.
• Make a Notifier class that knows about the tree (Hint: perhaps pass it in as a constructor 
parameter) and subscribes to its Ripened event. Attach a handler that displays something like “A 
charberry fruit has ripened!” to the console window.
• Make a Harvester class that knows about the tree (Hint: like the notifier, this could be passed as 
a constructor parameter) and subscribes to its Ripened event. Attach a handler that sets the tree’s 
Ripe property back to false.
• Update your main method to create a tree, notifier, and harvester, and get them to work together
to grow, notify, and harvest forever

Objectives:
• Make a new project that includes the above code.
• Add a Ripened event to the CharberryTree class that is raised when the tree ripens.
• Make a Notifier class that knows about the tree (Hint: perhaps pass it in as a constructor 
parameter) and subscribes to its Ripened event. Attach a handler that displays something like “A 
charberry fruit has ripened!” to the console window.
• Make a Harvester class that knows about the tree (Hint: like the notifier, this could be passed as 
a constructor parameter) and subscribes to its Ripened event. Attach a handler that sets the tree’s 
Ripe property back to false.
• Update your main method to create a tree, notifier, and harvester, and get them to work together
to grow, notify, and harvest forever

CharberryTree tree = new CharberryTree();
while (true)
 tree.MaybeGrow();
public class CharberryTree
{
 private Random _random = new Random();
 public bool Ripe { get; set; }
 public void MaybeGrow()
 {
 // Only a tiny chance of ripening each time, but we try a lot!
 if (_random.NextDouble() < 0.00000001 && !Ripe)
 {
 Ripe = true;
 }
 }
}

CharberryTree tree = new CharberryTree();
while (true)
 tree.MaybeGrow();
public class CharberryTree
{
 private Random _random = new Random();
 public bool Ripe { get; set; }
 public void MaybeGrow()
 {
 // Only a tiny chance of ripening each time, but we try a lot!
 if (_random.NextDouble() < 0.00000001 && !Ripe)
 {
 Ripe = true;
 }
 }
}

Pobiega•3y ago

alright given that description, yeah you did alright

BigggMoustacheOP•3y ago

NICE.

ero•3y ago

Yeah that's fine

Pobiega•3y ago

I'd remove the Tree prop from the harvester/notifier but other than that, 👍

BigggMoustacheOP•3y ago

heck yes

ero•3y ago

If anything make it a private field, but if it's not used, remove it completely

BigggMoustacheOP•3y ago

ya it's not used now I had confusion about sender before which is why I had it probably still have confusion about sender but that's okay lol ❤️ thanks again Ero and Pobiega. Maybbe someday your discord handles will be references in my resume. xD

Pobiega•3y ago

wtf :d don't

ero•3y ago

And isn't that truly why we're here

Pobiega•3y ago

thats not what a reference is, lol

ero•3y ago

*referenced

BigggMoustacheOP•3y ago

"Give three references of people you know who can attest the quality of your work" Uhhh.. @Pobiega#2671, uhhh...

Pobiega•3y ago

yeah, nah

BigggMoustacheOP•3y ago

lmao I know I know I kid.

Pobiega•3y ago

references on CVs need to be actual people you've worked with.

BigggMoustacheOP•3y ago

I'm just saying you folks are a large part of what's going to get me through this. ❤️

ero•3y ago

Hey I'm as real as any other person thank you

BigggMoustacheOP•3y ago

LOL

Pobiega•3y ago

I'm just a shared figment of both your imaginations

BigggMoustacheOP•3y ago

DUDE POBIEGA, I HAVE AN INTERESTING TWIST ON THAT THAT HAS IMPLICATIONS ABOUT THE NATURE OF BEING sorry, i dig philosophy though To Hegel, 'being' is the product of a social function, that is 'consciousness reflecting on consciousness' the object, that is subject, become subject of the subject.

Pobiega•3y ago

/close?

BigggMoustacheOP•3y ago

LOL okay fine.

Pobiega•3y ago

ero•3y ago

I was about to send that lmfao

BigggMoustacheOP•3y ago

haha ty again.

Accord•3y ago

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How to subscribe an EventHandler? [Answered]