使用web3.js監聽以太坊智能合約event

傳送門: 柏鏈項目學院

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使用web3.js監聽以太坊智能合約event

  當咱們在前端頁面調用合約時發現有些數據不會當即返回，這時還須要再調用更新數據的函數。那麼這樣的方法使用起來很是不便，監聽event就能夠很好的解決這樣的問題，下面咱們來看看如何監聽event。如下內容基於web3.js1.0版本，版本不一樣可能會代碼差別。

1. 修改geth啓動參數

• 所有參數以下

geth --datadir ./data --networkid 15 --port 30303 --rpc --rpcaddr 0.0.0.0 --rpcport 8545 --rpcvhosts "*" --rpcapi 'db,net,eth,web3,personal' --rpccorsdomain "*" --ws --wsaddr "localhost" --wsport "8546" --wsorigins "*" --nat "any" --nodiscover --dev --dev.period 1 console 2> 1.log

• 主要增長了下列參數

--ws --wsaddr "localhost" --wsport "8546" --wsorigins "*"

2. 在geth上部署map3合約

• 合約代碼以下

pragma solidity ^0.4.24;

contract Map3 {
 
    mapping(string => string) map;
    
    event orderlog(string indexed action, string indexed key, string value);
    
    function getvalue(string key) public constant returns (string) {
        return map[key];
    }
    
    function setvalue(string key, string value) public {
        emit orderlog("setvalue haha", key, value);
        map[key] = value;
    }
}

3. 編寫用於監聽合約event的js代碼

• map_event.js代碼以下

var Web3 = require("web3")

var web3;

if (typeof web3 !== 'undefined') {
    web3 = new Web3(web3.currentProvider);
} else {
    web3 = new Web3(new Web3.providers.WebsocketProvider("ws://127.0.0.1:8546"));
}
        
var contractAbi = [
        {
                "constant": false,
                "inputs": [
                        {
                                "name": "key",
                                "type": "string"
                        },
                        {
                                "name": "value",
                                "type": "string"
                        }
                ],
                "name": "setvalue",
                "outputs": [],
                "payable": false,
                "stateMutability": "nonpayable",
                "type": "function"
        },
        {
                "constant": true,
                "inputs": [
                        {
                                "name": "key",
                                "type": "string"
                        }
                ],
                "name": "getvalue",
                "outputs": [
                        {
                                "name": "",
                                "type": "string"
                        }
                ],
                "payable": false,
                "stateMutability": "view",
                "type": "function"
        },
        {
                "anonymous": false,
                "inputs": [
                        {
                                "indexed": true,
                                "name": "action",
                                "type": "string"
                        },
                        {
                                "indexed": true,
                                "name": "key",
                                "type": "string"
                        },
                        {
                                "indexed": false,
                                "name": "value",
                                "type": "string"
                        }
                ],
                "name": "orderlog",
                "type": "event"
        }
];

var contractaAddress = "0x31bd7af45b90811f23fa748fbf1940dc8b3d9dcb";
        
MyContract = new web3.eth.Contract(contractAbi, contractaAddress);
                //console.log(MyContract.events.orderlog);
        
var myEvent = MyContract.events.orderlog({
        filter:{},
        fromBlock: 0
}, function(error, event){})
        .on('data', function(event){
        console.log(event); // same results as the optional callback above
})
        .on('changed', function(event){
                    // remove event from local database
        })        
    .on('error', console.error);
    

/*
    MyContract.getPastEvents('allEvents', {
        filter: {},
        fromBlock: 0,
        toBlock: 'latest'
    }, function(error, events){ console.log(events); })
    .then(function(events){
        console.log(events) // same results as the optional callback above
    });
*/

4. 運行map_event.js監聽event

• 方法以下

npm init -y
npm install web3 --save
node map_event.js

5. 調用map3合約中的setvalue函數觸發event

• 在remix中調用setvalue時的監聽效果
  

  當合約被調用時，前端頁面須要當即更新數據，監聽event就能夠實現這樣的效果。

• 所有代碼地址：https://github.com/zhenyuss/eth_event.git

• Solidity Event是如何實現的：https://www.liangzl.com/get-article-detail-11825.html

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