一、Event是在程序中一个发布-订阅风格的事件系统用来发送和响应应用程序级别的事件。

import { Events } from 'ionic-angular';

constructor(public events: Events) {}

// 第一个页面(当user创建时)
function createUser(user) {
  console.log('User created!')
  events.publish('user:created', user);
}

// 第二个页面（监听user创建事件）
events.subscribe('user:created', (userEventData) => {
  // userEventData 是一个数组, so grab our first and only arg
  console.log('Welcome', userEventData[0]);
});


二、成员变量
1、subscribe(topic, handler)
事件订阅的主题，事件将触发他提供的方法。
topic  string  订阅的主题
handler  function  事件处理方法


2、unsubscribe(topic,handler)
取消签署的主题，你的handler将不再接收publish到主题事件
会返回true如果handler被移除


3、publish(topic, eventData)
提交一个event给指定的topic

 
/*
 * $Id: Events.java,v 1.5 2005/11/29 16:00:17 blowagie Exp $
 * $Name:  $
 *
 * This code is part of the 'iText Tutorial'.
 * You can find the complete tutorial at the following address:
 * http://itextdocs.lowagie.com/tutorial/
 *
 * This code is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 *
 * itext-questions@lists.sourceforge.net
 */
package com.lowagie.examples.directcontent.pageevents;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.EmptyStackException;
import java.util.HashMap;
import java.util.Iterator;
import java.util.TreeSet;

import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;

import com.lowagie.text.Chunk;
import com.lowagie.text.Document;
import com.lowagie.text.DocumentException;
import com.lowagie.text.ElementTags;
import com.lowagie.text.PageSize;
import com.lowagie.text.Paragraph;
import com.lowagie.text.Rectangle;
import com.lowagie.text.TextElementArray;
import com.lowagie.text.markup.MarkupTags;
import com.lowagie.text.pdf.BaseFont;
import com.lowagie.text.pdf.PdfContentByte;
import com.lowagie.text.pdf.PdfPageEventHelper;
import com.lowagie.text.pdf.PdfTemplate;
import com.lowagie.text.pdf.PdfWriter;
import com.lowagie.text.xml.SAXmyHandler;
import com.lowagie.text.xml.TagMap;
import com.lowagie.text.xml.XmlPeer;

/**
 * Example that takes an XML file, converts it to PDF and adds all kinds of
 * extra's, such as an alternating header, a footer with page x of y, a page
 * with metadata,...
 */
public class Events {

	/**
	 * This is an example of a PageEvents class you should write.
	 * This is an inner class to keep all the code of the example in one file.
	 * If you want to use a PageEvent, you may want to put the code in a separate class.
	 */

	class MyPageEvents extends PdfPageEventHelper {

		/** we will keep a list of speakers */
		TreeSet speakers = new TreeSet();

		/** This is the contentbyte object of the writer */
		PdfContentByte cb;

		/** we will put the final number of pages in a template */
		PdfTemplate template;

		/** this is the BaseFont we are going to use for the header / footer */
		BaseFont bf = null;

		/** this is the current act of the play */
		String act = "";
		
		/**
		 * Every speaker will be tagged, so that he can be added to the list of speakers.
		 * @see com.lowagie.text.pdf.PdfPageEventHelper#onGenericTag(com.lowagie.text.pdf.PdfWriter, com.lowagie.text.Document, com.lowagie.text.Rectangle, java.lang.String)
		 */
		public void onGenericTag(PdfWriter writer, Document document,
				Rectangle rect, String text) {
			speakers.add(new Speaker(text));
		}

		/**
		 * The first thing to do when the document is opened, is to define the BaseFont,
		 * get the Direct Content object and create the template that will hold the final
		 * number of pages.
		 * @see com.lowagie.text.pdf.PdfPageEventHelper#onOpenDocument(com.lowagie.text.pdf.PdfWriter, com.lowagie.text.Document)
		 */
		public void onOpenDocument(PdfWriter writer, Document document) {
			try {
				bf = BaseFont.createFont(BaseFont.HELVETICA, BaseFont.CP1252,
						BaseFont.NOT_EMBEDDED);
				cb = writer.getDirectContent();
				template = cb.createTemplate(50, 50);
			} catch (DocumentException de) {
			} catch (IOException ioe) {
			}
		}

		/**
		 * Every ACT is seen as a Chapter. We get the title of the act, so that
		 * we can display it in the header.
		 * @see com.lowagie.text.pdf.PdfPageEventHelper#onChapter(com.lowagie.text.pdf.PdfWriter, com.lowagie.text.Document, float, com.lowagie.text.Paragraph)
		 */
		public void onChapter(PdfWriter writer, Document document,
				float paragraphPosition, Paragraph title) {
			StringBuffer buf = new StringBuffer();
			for (Iterator i = title.getChunks().iterator(); i.hasNext();) {
				Chunk chunk = (Chunk) i.next();
				buf.append(chunk.content());
			}
			act = buf.toString();
		}

		/**
		 * After the content of the page is written, we put page X of Y
		 * at the bottom of the page and we add either "Romeo and Juliet"
		 * of the title of the current act as a header.
		 * @see com.lowagie.text.pdf.PdfPageEventHelper#onEndPage(com.lowagie.text.pdf.PdfWriter, com.lowagie.text.Document)
		 */
		public void onEndPage(PdfWriter writer, Document document) {
			int pageN = writer.getPageNumber();
			String text = "Page " + pageN + " of ";
			float len = bf.getWidthPoint(text, 8);
			cb.beginText();
			cb.setFontAndSize(bf, 8);
			cb.setTextMatrix(280, 30);
			cb.showText(text);
			cb.endText();
			cb.addTemplate(template, 280 + len, 30);
			cb.beginText();
			cb.setFontAndSize(bf, 8);
			cb.setTextMatrix(280, 820);
			if (pageN % 2 == 1) {
				cb.showText("Romeo and Juliet");
			} else {
				cb.showText(act);
			}
			cb.endText();
		}

		/**
		 * Just before the document is closed, we add the final number of pages to
		 * the template.
		 * @see com.lowagie.text.pdf.PdfPageEventHelper#onCloseDocument(com.lowagie.text.pdf.PdfWriter, com.lowagie.text.Document)
		 */
		public void onCloseDocument(PdfWriter writer, Document document) {
			template.beginText();
			template.setFontAndSize(bf, 8);
			template.showText(String.valueOf(writer.getPageNumber() - 1));
			template.endText();
		}

		/**
		 * Getting the list of speakers.
		 * @return	a list of speakers and the number of occurances.
		 */
		public TreeSet getSpeakers() {
			return speakers;
		}
	}

	/**
	 * Gets a PageEvents object.
	 * @return a new PageEvents object
	 */
	public MyPageEvents getPageEvents() {
		return new MyPageEvents();
	}
	/**
	 * Gets a Handler object.
	 * @param document  the document on which the handler operates
	 * @return a Handler object
	 * @throws IOException
	 */
	public MyHandler getXmlHandler(Document document) throws IOException {
		try {
			return new MyHandler(document, new RomeoJulietMap());
		} catch (DocumentException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}
		return null;
	}
	
	/**
	 * Converts a play in XML into PDF.
	 * @param args no arguments needed
	 */
	public static void main(String[] args) {

		System.out.println("Romeo and Juliet");

		// step 1: creation of a document-object
		Document document = new Document(PageSize.A4, 80, 50, 30, 65);

		try {
			// step 2:
			// we create a writer that listens to the document
			// and directs a XML-stream to a file
			PdfWriter writer = PdfWriter.getInstance(document,
					new FileOutputStream("RomeoJuliet.pdf"));

			// create add the event handler
			MyPageEvents events = new Events().getPageEvents();
			writer.setPageEvent(events);

			// step 3: we create a parser and set the document handler
			SAXParser parser = SAXParserFactory.newInstance().newSAXParser();

			// step 4: we parse the document
			parser.parse("playRomeoJuliet.xml", new Events().getXmlHandler(document));

			document.newPage();
			Speaker speaker;
			for (Iterator i = events.getSpeakers().iterator(); i.hasNext();) {
				speaker = (Speaker) i.next();
				document.add(new Paragraph(speaker.getName() + ": "
						+ speaker.getOccurrance() + " speech blocks"));
			}
			document.close();

		} catch (Exception e) {
			e.printStackTrace();
			System.err.println(e.getMessage());
		}
	}

	/**
	 * Special implementation of het XML handler.
	 * It adds a paragraph after each SPEAKER block and
	 * avoids closing the document after the final closing tag.
	 */
	class MyHandler extends SAXmyHandler {

		/**
		 * We have to override the constructor
		 * @param document	the Document object
		 * @param tagmap	the tagmap
		 * @throws IOException
		 * @throws DocumentException
		 */
		public MyHandler(Document document, HashMap tagmap) throws DocumentException, IOException {
			super(document, tagmap);
		}

		/**
		 * We only alter the handling of some endtags.
		 * @param uri	the uri of the namespace
		 * @param lname	the local name of the tag
		 * @param name	the name of the tag
		 */
		public void endElement(String uri, String lname, String name) {
			if (myTags.containsKey(name)) {
				XmlPeer peer = (XmlPeer) myTags.get(name);
				// we don't want the document to be close
				// because we are going to add a page after the xml is parsed
				if (isDocumentRoot(peer.getTag())) {
					return;
				}
				handleEndingTags(peer.getTag());
				// we want to add a paragraph after the speaker chunk
				if ("SPEAKER".equals(name)) {
					try {
						TextElementArray previous = (TextElementArray) stack
								.pop();
						previous.add(new Paragraph(16));
						stack.push(previous);
					} catch (EmptyStackException ese) {
					}
				}
			} else {
				handleEndingTags(name);
			}
		}
	}

	/**
	 * Normally you either choose to use a HashMap with XmlPeer objects,
	 * or a TagMap object that reads a TagMap in XML.
	 * Here we used a hybrid solution (for educational purposes only!)
	 * with on one side the tags in the XML tagmap, on the other side
	 * an XmlPeer object that overrides the properties of one of the tags.
	 */

	class RomeoJulietMap extends TagMap {

		/**
		 * Constructs a TagMap based on an XML file
		 * and/or on XmlPeer objects that are added.
		 * @throws IOException
		 */
		public RomeoJulietMap() throws IOException {
			super(new FileInputStream("tagmapRomeoJuliet.xml"));
			XmlPeer peer = new XmlPeer(ElementTags.CHUNK, "SPEAKER");
			peer.addValue(MarkupTags.CSS_KEY_FONTSIZE, "10");
			peer.addValue(MarkupTags.CSS_KEY_FONTWEIGHT, MarkupTags.CSS_VALUE_BOLD);
			peer.addValue(ElementTags.GENERICTAG, "");
			put(peer.getAlias(), peer);
		}
	}

	/**
	 * This object contains a speaker and a number of occurrances in the play
	 */

	class Speaker implements Comparable {

		// name of the speaker
		private String name;

		// number of occurrances
		private int occurrance = 1;

		/**
		 * One of the speakers in the play.
		 * @param name
		 */
		public Speaker(String name) {
			this.name = name;
		}

		/**
		 * Gets the name of the speaker.
		 * @return a name
		 */
		public String getName() {
			return name;
		}

		/**
		 * Gets the number of occurances of the speaker.
		 * @return a number of textblocks
		 */
		public int getOccurrance() {
			return occurrance;
		}

		/**
		 * There is something odd going on in this compareTo.
		 * Do you see it?
		 * @param o an other speaker object
		 * @see java.lang.Comparable#compareTo(java.lang.Object)
		 */
		public int compareTo(Object o) {
			Speaker otherSpeaker = (Speaker) o;
			if (otherSpeaker.getName().equals(name)) {
				this.occurrance += otherSpeaker.getOccurrance();
				otherSpeaker.occurrance = this.occurrance;
				return 0;
			}
			return name.compareTo(otherSpeaker.getName());
		}
	}
}

Using Touch Events

Events client
This sample client demonstrates how to connect to a peer to receive block

events. Block events come in the form of either full blocks as they have been

committed to the ledger or filtered blocks (a minimal set of information about

the block) which includes the transaction ids, transaction statuses, and any

chaincode events associated with the transaction.
Events service interface
Starting with v1.1, two new event services are available:
service Deliver {
    // deliver first requires an Envelope of type ab.DELIVER_SEEK_INFO with Payload data as a marshaled orderer.SeekInfo message,
    // then a stream of block replies is received.
    rpc Deliver (stream common.Envelope) returns (stream DeliverResponse) {
    }
    // deliver first requires an Envelope of type ab.DELIVER_SEEK_INFO with Payload data as a marshaled orderer.SeekInfo message,
    // then a stream of **filtered** block replies is received.
    rpc DeliverFiltered (stream common.Envelope) returns (stream DeliverResponse) {
    }
}

This sample demonstrates connecting to both of these services.
General use
cd fabric/examples/events/eventsclient
go build

You will see the executable eventsclient if there are no compilation errors.
Next, to start receiving block events from a peer with TLS enabled, run the

following command:
CORE_PEER_LOCALMSPID=<msp-id> CORE_PEER_MSPCONFIGPATH=<path to MSP folder> ./eventsclient -channelID=<channel-id> -filtered=<true or false> -tls=true -clientKey=<path to the client key> -clientCert=<path to the client TLS certificate> -rootCert=<path to the server root CA certificate>

If the peer is not using TLS you can run:
CORE_PEER_LOCALMSPID=<msp-id> CORE_PEER_MSPCONFIGPATH=<path to MSP folder> ./eventsclient -channelID=<channel-id> -filtered=<true or false> -tls=false

The peer will begin delivering block events and print the output to the console.
Example with the e2e_cli example
The events client sample can be used with TLS enabled or disabled. By default,

the e2e_cli example will have TLS enabled. In order to allow the events client

to connect to peers created by the e2e_cli example with TLS enabled, the easiest

way would be to map 127.0.0.1 to the hostname of the peer that you are

connecting to, such as peer0.org1.example.com. For example on *nix based

systems this would be an entry in /etc/hosts file.
If you would prefer to disable TLS, you may do so by setting

CORE_PEER_TLS_ENABLED=false in docker-compose-cli.yaml and

base/peer-base.yaml as well as

ORDERER_GENERAL_TLS_ENABLED=false inbase/docker-compose-base.yaml.
Next, run the e2e_cli example.
Once the “All in one” command:
./network_setup.sh up

has completed, attach the event client to peer peer0.org1.example.com by doing

the following:

If TLS is enabled:

to receive full blocks:



CORE_PEER_LOCALMSPID=Org1MSP CORE_PEER_MSPCONFIGPATH=$GOPATH/src/github.com/hyperledger/fabric/examples/e2e_cli/crypto-config/peerOrganizations/org1.example.com/peers/peer0.Org1.example.com/msp ./eventsclient -server=peer0.org1.example.com:7051 -channelID=mychannel -filtered=false -tls=true -clientKey=$GOPATH/src/github.com/hyperledger/fabric/examples/e2e_cli/crypto-config/peerOrganizations/org1.example.com/users/Admin@Org1.example.com/tls/client.key -clientCert=$GOPATH/src/github.com/hyperledger/fabric/examples/e2e_cli/crypto-config/peerOrganizations/org1.example.com/users/Admin@Org1.example.com/tls/client.crt -rootCert=$GOPATH/src/github.com/hyperledger/fabric/examples/e2e_cli/crypto-config/peerOrganizations/org1.example.com/users/Admin@Org1.example.com/tls/ca.crt


to receive filtered blocks:

CORE_PEER_LOCALMSPID=Org1MSP CORE_PEER_MSPCONFIGPATH=$GOPATH/src/github.com/hyperledger/fabric/examples/e2e_cli/crypto-config/peerOrganizations/org1.example.com/peers/peer0.Org1.example.com/msp ./eventsclient -server=peer0.org1.example.com:7051 -channelID=mychannel -filtered=true -tls=true -clientKey=$GOPATH/src/github.com/hyperledger/fabric/examples/e2e_cli/crypto-config/peerOrganizations/org1.example.com/users/Admin@Org1.example.com/tls/client.key -clientCert=$GOPATH/src/github.com/hyperledger/fabric/examples/e2e_cli/crypto-config/peerOrganizations/org1.example.com/users/Admin@Org1.example.com/tls/client.crt -rootCert=$GOPATH/src/github.com/hyperledger/fabric/examples/e2e_cli/crypto-config/peerOrganizations/org1.example.com/users/Admin@Org1.example.com/tls/ca.crt


If TLS is disabled:

to receive full blocks:



CORE_PEER_LOCALMSPID=Org1MSP CORE_PEER_MSPCONFIGPATH=$GOPATH/src/github.com/hyperledger/fabric/examples/e2e_cli/crypto-config/peerOrganizations/org1.example.com/peers/peer0.Org1.example.com/msp ./eventsclient -server=peer0.org1.example.com:7051 -channelID=mychannel -filtered=false -tls=false


to receive filtered blocks:

CORE_PEER_LOCALMSPID=Org1MSP CORE_PEER_MSPCONFIGPATH=$GOPATH/src/github.com/hyperledger/fabric/examples/e2e_cli/crypto-config/peerOrganizations/org1.example.com/peers/peer0.Org1.example.com/msp ./eventsclient -server=peer0.org1.example.com:7051 -channelID=mychannel -filtered=true -tls=false