Observer implementation

Question

I want a button that when it's pushed a new string is shown in the textboxes.

What am I doing wrong?

Can someone enlighten me? Why doesn't this code work?

namespace WindowsFormsApplication1 { public partial class Form1 : Form { public event Startdelegate StartEvent; myButton button; newTb[] tb; public Form1() { InitializeComponent(); button = new myButton(); button.Parent = this; button.Location = new Point(120, 0); button.Text = "click on me!!!"; tb = new newTb[8]; for (int i = 0; i <= 80; i += 15) { tb[i / 15] = new newTb(); tb[i / 15].Parent = this; tb[i / 15].Location = new Point(i + i, i + i); // button.Subscribe(tb[i / 15]); } button.Click += new EventHandler(button_Click); } private void button_Click(object sender, EventArgs e) { button.s = "this is clicking"; //button.Notify(); } } public class myButton : Button, IObservable<newTb> { public string s; private List<IObserver<newTb>> observers; public myButton() { observers = new List<IObserver<newTb>>(); } public IDisposable Subscribe(IObserver<newTb> observer) { if (!observers.Contains(observer)) { observers.Add(observer); } return new Unsubscriber(observers, observer); } protected void Notify(newTb tb) { foreach (IObserver<newTb> observer in observers) { observer.OnNext(tb); } } #region Unsubscriber private class Unsubscriber : IDisposable { private List<IObserver<newTb>> observers; private IObserver<newTb> observer; public Unsubscriber(List<IObserver<newTb>> observers, IObserver<newTb> observer) { this.observers = observers; this.observer = observer; } public void Dispose() { if (observer != null && observers.Contains(observer)) { observers.Remove(observer); } } } #endregion class newTb : TextBox, IObserver<string> { string s; public void OnCompleted() { } public void OnError(Exception error) { } public void OnNext(string value) { this.Text = value; } } } }

+1 Just so that you can have some points to open another bounty :-) — SKG
– SKG, Commented Sep 10, 2010 at 17:38
If the answer is correct, then you should mark the question as answered so that the bounty can be awarded. — Erik Funkenbusch
– Erik Funkenbusch, Commented Sep 10, 2010 at 17:49
but it's not it's another way of imlpment i want to implment as they do in msdn in my own example — yoav.str
– yoav.str, Commented Sep 10, 2010 at 18:00
You really should work on code readability. Mind that there are some naming conventions in C#, i.e. type name should start with upper case letter. I am afraid that if you would use FxCop or StyleCop to check this code out, it will give you enormous number of errors. — Paweł Dyda
– Paweł Dyda, Commented Sep 11, 2010 at 17:08

Frederic Torres · Accepted Answer · 2010-09-08 14:21:23Z

According to http://msdn.microsoft.com/en-us/library/dd783449.aspx

The IObserver and IObservable interfaces provide a generalized mechanism for push-based notification, also known as the observer design pattern. The IObservable interface represents the class that sends notifications (the provider); the IObserver interface represents the class that receives them (the observer).

T represents the class that provides the notification information.

In your case the information you pass is a message (a string). In your sample you were passing the control newTB

With the following declaration

 public class ObservableButton : Button, IObservable<string> {} public class ObserverTextBox : TextBox, IObserver<string> {}

Every thing fall into places.

The method Notify of the classObservableButton can be written this way.

 public void Notify(string text) { foreach (IObserver<string> observer in _Observers) { observer.OnNext(text); } }

Here the full source code

using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Windows.Forms; namespace ObservableDemo { public class ObservableButton : Button, IObservable<string> { private List<IObserver<string>> _Observers; public ObservableButton() { _Observers = new List<IObserver<string>>(); } IDisposable IObservable<string>.Subscribe(IObserver<string> observer) { if (!_Observers.Contains(observer)) { _Observers.Add(observer); } return new Unsubscriber(_Observers, observer); } public void Notify(string text) { foreach (IObserver<string> observer in _Observers) { observer.OnNext(text); } } private class Unsubscriber : IDisposable { private List<IObserver<string>> observers; private IObserver<string> observer; public Unsubscriber(List<IObserver<string>> observers, IObserver<string> observer) { this.observers = observers; this.observer = observer; } public void Dispose() { if (observer != null && observers.Contains(observer)) { observers.Remove(observer); } } } } } using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Windows.Forms; namespace ObservableDemo { public class ObserverTextBox : TextBox, IObserver<string> { private IDisposable unsubscriber; void IObserver<string>.OnCompleted() { } void IObserver<string>.OnError(Exception error) { } void IObserver<string>.OnNext(string value) { this.Text = value; this.Refresh(); } public virtual void Subscribe(IObservable<string> provider) { if (provider != null) unsubscriber = provider.Subscribe(this); } public virtual void Unsubscribe() { unsubscriber.Dispose(); } } } using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Windows.Forms; namespace ObservableDemo { public partial class Form1 : Form { ObservableButton button; public Form1() { InitializeComponent(); button = new ObservableButton(); button.Parent = this; button.Location = new Point(120, 0); button.Text = "click on me!!!"; button.Click += new EventHandler(button_Click); for (int i = 0; i < 8; i++) { ObserverTextBox tb = new ObserverTextBox(); tb.Parent = this; tb.Location = new Point(0 , 30+(i*30)); tb.Width = 300; tb.Subscribe(button); } } private void button_Click(object sender, EventArgs e) { button.Notify(String.Format("{0} this is the message", DateTime.Now)); } void Form1_Load(object sender, System.EventArgs e) { } } }

thank u it works can you in-light with some facts I don't understand where i got wrong
Actually I also have a problem with the IObserver/IObservable pattern. I will try to write your problem from scratch tonight.
I changed may answer with this time something that make sense

Paweł Dyda · Accepted Answer · 2010-09-11 17:04:41Z

I believe this could be your problem:

class newTb : TextBox, IObserver<string>

Because what you what you wanted to observe based on this sample:

observers = new List<IObserver<newTb>>();

is actually IObserver<newTb>, which is different type than IObserver<string>. Your newTb class does not implement first interface, it only implements the latter. Not sure why this compiles (if it does), though.

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