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| 1 | +using System; |
| 2 | +using System.Collections.Generic; |
| 3 | + |
| 4 | +namespace ObserverPattern |
| 5 | +{ |
| 6 | +class JobPost |
| 7 | +{ |
| 8 | + public string Title { get; private set; } |
| 9 | + |
| 10 | + public JobPost(string title) |
| 11 | + { |
| 12 | + Title = title; |
| 13 | + } |
| 14 | +} |
| 15 | +class JobSeeker : IObserver<JobPost> |
| 16 | +{ |
| 17 | + public string Name { get; private set; } |
| 18 | + |
| 19 | + public JobSeeker(string name) |
| 20 | + { |
| 21 | + Name = name; |
| 22 | + } |
| 23 | + |
| 24 | + //Method is not being called by JobPostings class currently |
| 25 | + public void OnCompleted() |
| 26 | + { |
| 27 | + //No Implementation |
| 28 | + } |
| 29 | + |
| 30 | + //Method is not being called by JobPostings class currently |
| 31 | + public void OnError(Exception error) |
| 32 | + { |
| 33 | + //No Implementation |
| 34 | + } |
| 35 | + |
| 36 | + public void OnNext(JobPost value) |
| 37 | + { |
| 38 | + Console.WriteLine("Hi {0} ! New job posted: {1}", Name, value.Title); |
| 39 | + } |
| 40 | +} |
| 41 | + |
| 42 | +class JobPostings : IObservable<JobPost> |
| 43 | +{ |
| 44 | + private List<IObserver<JobPost>> mObservers; |
| 45 | + private List<JobPost> mJobPostings; |
| 46 | + |
| 47 | + public JobPostings() |
| 48 | + { |
| 49 | + mObservers = new List<IObserver<JobPost>>(); |
| 50 | + mJobPostings = new List<JobPost>(); |
| 51 | + } |
| 52 | + |
| 53 | + public IDisposable Subscribe(IObserver<JobPost> observer) |
| 54 | + { |
| 55 | + // Check whether observer is already registered. If not, add it |
| 56 | + if (!mObservers.Contains(observer)) |
| 57 | + { |
| 58 | + mObservers.Add(observer); |
| 59 | + } |
| 60 | + return new Unsubscriber<JobPost>(mObservers, observer); |
| 61 | + } |
| 62 | + |
| 63 | + private void Notify(JobPost jobPost) |
| 64 | + { |
| 65 | + foreach(var observer in mObservers) |
| 66 | + { |
| 67 | + observer.OnNext(jobPost); |
| 68 | + } |
| 69 | + } |
| 70 | + |
| 71 | + public void AddJob(JobPost jobPost) |
| 72 | + { |
| 73 | + mJobPostings.Add(jobPost); |
| 74 | + Notify(jobPost); |
| 75 | + } |
| 76 | + |
| 77 | +} |
| 78 | + |
| 79 | +internal class Unsubscriber<JobPost> : IDisposable |
| 80 | +{ |
| 81 | + private List<IObserver<JobPost>> mObservers; |
| 82 | + private IObserver<JobPost> mObserver; |
| 83 | + |
| 84 | + internal Unsubscriber(List<IObserver<JobPost>> observers, IObserver<JobPost> observer) |
| 85 | + { |
| 86 | + this.mObservers = observers; |
| 87 | + this.mObserver = observer; |
| 88 | + } |
| 89 | + |
| 90 | + public void Dispose() |
| 91 | + { |
| 92 | + if (mObservers.Contains(mObserver)) |
| 93 | + mObservers.Remove(mObserver); |
| 94 | + } |
| 95 | +} |
| 96 | + |
| 97 | + |
| 98 | + class Program |
| 99 | + { |
| 100 | + static void Main(string[] args) |
| 101 | + { |
| 102 | +//Create Subscribers |
| 103 | +var johnDoe = new JobSeeker("John Doe"); |
| 104 | +var janeDoe = new JobSeeker("Jane Doe"); |
| 105 | + |
| 106 | +//Create publisher and attch subscribers |
| 107 | +var jobPostings = new JobPostings(); |
| 108 | +jobPostings.Subscribe(johnDoe); |
| 109 | +jobPostings.Subscribe(janeDoe); |
| 110 | + |
| 111 | +//Add a new job and see if subscribers get notified |
| 112 | +jobPostings.AddJob(new JobPost("Software Engineer")); |
| 113 | + |
| 114 | +//Output |
| 115 | +// Hi John Doe! New job posted: Software Engineer |
| 116 | +// Hi Jane Doe! New job posted: Software Engineer |
| 117 | + |
| 118 | +Console.ReadLine(); |
| 119 | + } |
| 120 | + } |
| 121 | +} |
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