observer added

Author: maciej-nowak

observer/README.md

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+# observer
+
+This is repository of http://androidcode.pl blog. It shows uses of Observer in Android. It is a part of Design Patterns - Observer post in the blog.

observer/example/Main.java

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+public class Main {
+	
+	public static void main() {
+	ActionHouse house = new ActionHouse();
+	Auctions auctions = new Auctions();
+	Bids bids = new Bids();
+
+	//register
+	house.registerObserver(auctions);
+	house.registerBids(bids);
+
+	//new action coming from server and runs ActionHouse
+	house.newBid(bidEvent); //update Bids and Auctions modules
+	house.newAuction(auctionEvent); //update Auctions module
+	}
+}

observer/example/dummies/Auction.java

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+public class Auction {
+	
+	//body
+}

observer/example/dummies/Bid.java

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+public class Bid {
+	
+	//body
+}

observer/example/events/NewAuctionEvent.java

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+public class NewAuctionEvent {
+	
+	private Auction auction;
+	//other fields
+
+	public Auction getAuction() {
+		return auction;
+	}
+
+	//other methods
+}

observer/example/events/NewBidEvent.java

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+public class NewBidEvent {
+	
+	private Bid bid;
+	//other fields
+
+	public Bid getBid() {
+		return bid;
+	}
+
+	//other methods
+}

observer/example/observable/AuctionHouse.java

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+public class AuctionHouse implements Observable {
+
+    private List<Observer> observers;
+    //other fields
+
+    public AuctionHouse() {
+        observers = new ArrayList();
+    }
+
+    @Override
+    public void registerObserver(Observer observer) {
+        observers.add(observer);
+    }
+
+    @Override
+    public void unregisterObserver(Observer observer) {
+        observers.remove(observer);
+    }
+
+    @Override
+    public void notifyObservers() {
+        for(Observer observer : observers)
+            observer.update(this, null);
+    }
+
+    @Override
+    public void notifyObservers(Object args) {
+        for(Observer observer : observers)
+            observer.update(this, args);
+    }
+
+    public void newBid(NewBidEvent event) {
+        //check event details and add if is OK
+        Bid bid = event.getBid();
+        notifyObservers(bid);
+    }
+
+    public void newAuction(NewAuctionEvent auction) {
+        //check event details and add if is OK
+        Auction auction = event.getAuction();
+        notifyObservers(auction);
+    }
+
+    //others methods
+}

observer/example/observable/Observable.java

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+public interface Observable {
+	public void registerObserver(Observer observer);
+	public void unregisterObserver(Observer observer);
+	public void notifyObservers(Object args);
+	public void notifyObservers();
+}

observer/example/observers/Auctions.java

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+public class Auctions implements Observer {
+
+    private List<Auction> auctions;
+    //other fields
+
+    public Auction(List<Auction> auctions) {
+    this.auctions = auctions;
+    }
+
+    @Override
+    public void update(Observable observable, Object args) {
+        if(observable instanceof AuctionManager) {
+            if(args instanceof Auction) {
+                Auction auction = (Auction) args;
+                auctions.add(auction);
+                //refresh UI list
+            }
+            else if(args == instanceof Bid) {
+                Bid bid = (Bid) args;
+                int auctionIndex = auctions.indexOf(bid.getAuction());
+                if(auctionIndex != -1) {
+                    auctions.get(auctionIndex).addBid(bid);
+                    //refresh UI list
+                }
+            }
+        }
+    }
+
+    //other methods
+}

observer/example/observers/Bids.java

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+public class Bids implements Observer {
+
+    private Auction auction;
+    private List<Bid> bids;
+    //other fields
+
+    public Bids(Auction auction) {
+        this.auction = auction;
+        this.bids = auction.getBids();
+    }
+
+    @Override
+    public void update(Observable observable, Object args) {
+        if(observable instanceof AuctionManager) {
+            if(args instanceof Bid) {
+                Bid bid = (Bid) args;
+                if(bid.getAuction() == auction) {
+                    bids.add(bid);
+                    //refresh UI list
+                }
+            }
+        }
+    }
+
+    //other methods
+}

observer/example/observers/Observer.java

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+public interface Observer {
+	
+	public void update(Observable observable, Object args);
+}

observer/pattern/ConcreteObservable.java

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+public class ConcreteObservable implements Observable {
+
+	private List<Observer> observers;
+
+	//other fields
+
+	public ConcreteObservable() {
+		observers = new ArrayList();
+	}
+	
+	@Override
+	public void registerObserver(Observer observer) {
+		observers.add(observer);
+	}
+
+	@Override
+	public void unregisterObserver(Observer observer) {
+		observers.remove(observer);
+	}
+
+	@Override
+	public void notifyObservers() {
+		for(Observer observer : observers)
+			observer.update(this, null);
+	}
+
+	@Override
+	public void notifyObservers(Object object) {
+		for(Observer observer : observers)
+			observer.update(this, object);
+	}
+
+	public void method1() {
+		//do some work
+		notifyObservers();
+	}
+
+	public void method2() {
+		//do some work
+		Event event = new Event(); //args wrapped in event
+		notifyObservers(event);
+	}
+
+	//others methods
+}

observer/pattern/Observable.java

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+public interface Observable {
+	public void registerObserver(Observer observer);
+	public void unregisterObserver(Observer observer);
+	public void notifyObservers(Object args);
+	public void notifyObservers();
+}

observer/pattern/Observer.java

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+public interface Observer {
+	
+	public void update(Observable observable, Object args);
+}

observer/pattern/observers/Observer1.java

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+public class Observer1 implements Observer {
+	
+	@Override
+	public void update(Observable observable, Object object) {
+		if(observable instanceof ConcreteObservable) {
+			//do some work
+		}
+		else {
+			//do some work
+		}
+	}
+
+	//other methods
+}

observer/pattern/observers/Observer2.java

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+public class Observer2 implements Observer {
+	
+	@Override
+	public void update(Observable observable, Object object) {
+		if(observable instanceof ConcreteObservable) {
+			if(object instanceof Event) {
+				//do some work
+			}
+		}
+	}
+
+	//other methods
+}