web3.js与智能合约交互

智能合约示例：

pragma solidity ^0.5.2;

contract Coin {
    uint public val;
    
    event Set(uint val);
    function set(uint _val) public {
        val = _val;
        emit Set(_val);
    }
    function get() public view returns (uint) {
        return val;
    }
    
}

html页面（请先下载web3.min.js，并放置在与当前html页面同文件夹下）

<html>
  <head>
    <meta charset="UTF-8">
    <title>web3.js使用</title>
    <script src="web3.min.js"></script>
    <style type="text/css">
        span {
            display: inline-block;
        }
    </style>
  </head>

  <body>
    <h1>web3.js与智能合约交互</h1>
    <div id="info">444</div>
    <span>
        <input type="text" id="myVal"></input>
        <button onclick="setVal()">修改</button>
    </span>

    <script>
        //1、利用以太坊provider创建web3
        var web3 = new Web3(new Web3.providers.HttpProvider("http://127.0.0.1:7545"));
            
        //2、智能合约的abi，abi是由编译器生成的
        var abi = [
            {
                "constant": true,
                "inputs": [],
                "name": "val",
                "outputs": [
                    {
                        "name": "",
                        "type": "uint256"
                    }
                ],
                "payable": false,
                "stateMutability": "view",
                "type": "function"
            },
            {
                "constant": false,
                "inputs": [
                    {
                        "name": "_val",
                        "type": "uint256"
                    }
                ],
                "name": "set",
                "outputs": [],
                "payable": false,
                "stateMutability": "nonpayable",
                "type": "function"
            },
            {
                "constant": true,
                "inputs": [],
                "name": "get",
                "outputs": [
                    {
                        "name": "",
                        "type": "uint256"
                    }
                ],
                "payable": false,
                "stateMutability": "view",
                "type": "function"
            },
            {
                "anonymous": false,
                "inputs": [
                    {
                        "indexed": false,
                        "name": "val",
                        "type": "uint256"
                    }
                ],
                "name": "Set",
                "type": "event"
            }
        ];
        
        //3、根据abi获取合约
        var ZombieFactoryContract = web3.eth.contract(abi);
        //合约地址，发布之后在以太坊上生成的合约地址
        var contractAddress = "0x18b490cddf021886af0e5f3129468533c0026da2";
        //4、根据合约地址获取合约实例
        var ZombieFactory = ZombieFactoryContract.at(contractAddress);
        //5、监听合约中定义的事件, 执行UI操作，合约实例能访问合约中公共的函数以及事件
        var event = ZombieFactory.Set(function(error, result) {
            if (error) {
                return
            }
            //console.log("9999");
            //console.log(result.args.val.c);
            document.getElementById("info").innerHTML = ZombieFactory.get();
        });

        //
        function setVal(){
            /**
            *调用合约中的函数
            *方式1：不会更改状态变量的函数调用方法   ZombieFactory.get()
            *方式2：会更改状态变量的函数调用方法，需要发送交易     ZombieFactory.set.sendTransaction(函数参数, {from: web3.eth.accounts[0]})
            */
            ZombieFactory.set.sendTransaction(document.getElementById("myVal").value, {from: web3.eth.accounts[0]});
    }
    </script>
  </body>
</html>

--------------------------------------------

solidity语法：

a.sol合约文件

pragma solidity ^0.5.2;
contract A {
    uint public x;
    uint public amount;
    
    constructor(uint _x) public payable {
        x = _x;
    }
    
    function get() public view returns (uint) {
        return x;
    }
}

test.sol合约文件

pragma solidity ^0.5.2;

import "./er.sol";

contract Coin {

    uint public val;
    A a;
    
    event Set(uint val);
    function set(uint _val) public {
        val = _val;
        a = new A(_val);
        emit Set(_val);
    }
    function get() public view returns (uint) {
        return val + a.get();
    }
}

--------------------

solidity的payable使用

payable 方法是让 Solidity 和以太坊变得如此酷的一部分 —— 它们修饰的函数是一种可以接收以太的特殊函数。

在以太坊中，钱 (以太), 数据 (事务负载)，以及合约代码本身都存在于以太坊。你可以在调用函数的同时付钱给另外一个合约。

合约 OnlineStore.sol如下：

pragma solidity ^0.5.2;

contract a {
    function get() public payable {
        // 检查以确定0.001以太发送出去来运行函数
        require(msg.value == 0.001 ether);
        // 如果requiretongguo，执行函数向调用者发送数字内容
　　　　　// transferSomething(msg.sender);
    }
}

在这里，msg.value 是可以查看向合约发送了多少以太的方法，另外 ether 是一个內建单元。

这里发生的事是，一些人会从 web3.js 调用这个函数 (从DApp的前端)，像这样 :

// 假设 `OnlineStore` 在以太坊上指向你的合约:
OnlineStore.get.sendTransaction({from: web3.eth.accounts[0], value: web3.toWei(0.001, 'ether')})；//该函数返回一个256位的值，类似  0x3b57fabc53f0bc6d6dec107d3d0cea2e3409683cf105a2766bf867768c0d9cf1  这种

-----------------------------

合约本身也是一个账户，当我们调用合约里定义的payable函数时，就会向合约发送一定数量的以太，这些以太就保存在合约账户里，我们也可以从合约中将这些以太提取到指定账户，如下使用示例：

pragma solidity ^0.5.2;

contract Coin {
    uint public val;
    
    event Set(uint val);
    
    address public owner;
    constructor() public{
        owner = msg.sender;
    }
    function set(uint _val) public payable {
        val = _val;
        emit Set(_val);
    }
    function get() public view returns (uint) {
        return val;
    }
    
    function balanceOf() public view returns (uint) {
        return owner.balance;
    }
    
    function balanceOfContract() public view returns (uint) {
        return address(this).balance;
    }
    
}

<html>
  <head>
    <meta charset="UTF-8">
    <title>web3.js使用</title>
    <script src="web3.min.js"></script>
    <style type="text/css">
        span {
            display: inline-block;
        }
    </style>
  </head>

  <body>
    <h1>web3.js与智能合约交互</h1>
    <div id="info">444</div>
    <div id="balance">444</div>
    <span>
        <input type="text" id="myVal"></input>
        <button onclick="setVal()">update</button>
    </span>

    <script>
        //1、利用以太坊provider创建web3
        var web3 = new Web3(new Web3.providers.HttpProvider("http://127.0.0.1:7545"));
            
        //2、智能合约的abi，abi是由编译器生成的
        var abi = [
    {
        "constant": false,
        "inputs": [
            {
                "name": "_val",
                "type": "uint256"
            }
        ],
        "name": "set",
        "outputs": [],
        "payable": true,
        "stateMutability": "payable",
        "type": "function"
    },
    {
        "inputs": [],
        "payable": false,
        "stateMutability": "nonpayable",
        "type": "constructor"
    },
    {
        "anonymous": false,
        "inputs": [
            {
                "indexed": false,
                "name": "val",
                "type": "uint256"
            }
        ],
        "name": "Set",
        "type": "event"
    },
    {
        "constant": true,
        "inputs": [],
        "name": "balanceOf",
        "outputs": [
            {
                "name": "",
                "type": "uint256"
            }
        ],
        "payable": false,
        "stateMutability": "view",
        "type": "function"
    },
    {
        "constant": true,
        "inputs": [],
        "name": "balanceOfContract",
        "outputs": [
            {
                "name": "",
                "type": "uint256"
            }
        ],
        "payable": false,
        "stateMutability": "view",
        "type": "function"
    },
    {
        "constant": true,
        "inputs": [],
        "name": "get",
        "outputs": [
            {
                "name": "",
                "type": "uint256"
            }
        ],
        "payable": false,
        "stateMutability": "view",
        "type": "function"
    },
    {
        "constant": true,
        "inputs": [],
        "name": "owner",
        "outputs": [
            {
                "name": "",
                "type": "address"
            }
        ],
        "payable": false,
        "stateMutability": "view",
        "type": "function"
    },
    {
        "constant": true,
        "inputs": [],
        "name": "val",
        "outputs": [
            {
                "name": "",
                "type": "uint256"
            }
        ],
        "payable": false,
        "stateMutability": "view",
        "type": "function"
    }
];
        
        //3、根据abi获取合约
        var ZombieFactoryContract = web3.eth.contract(abi);
        //合约地址，发布之后在以太坊上生成的合约地址
        var contractAddress = "0xd6358db490163053a8a8c852c6397502278d0d97";
        //4、根据合约地址获取合约实例
        var ZombieFactory = ZombieFactoryContract.at(contractAddress);
        //5、监听合约中定义的事件, 执行UI操作，合约实例能访问合约中公共的函数以及事件
        var event = ZombieFactory.Set(function(error, result) {
            if (error) {
                return
            }
            //console.log("9999");
            //console.log(result.args.val.c);
            document.getElementById("info").innerHTML = ZombieFactory.get();
        });

        //
        function setVal(){
            /**
            *调用合约中的函数
            *方式1：不会更改状态变量的函数调用方法   ZombieFactory.get()
            *方式2：会更改状态变量的函数调用方法，需要发送交易     ZombieFactory.set.sendTransaction(函数参数, {from: web3.eth.accounts[0]})
            */
            ZombieFactory.set.sendTransaction(document.getElementById("myVal").value, {from: web3.eth.accounts[0], value: web3.toWei(0.001, 'ether')});
            
            console.log(web3.eth.getBalance("0xa6c07AE626F0BB30Fe77f3f924c37CCa59895BAc"));
       
            
    }
    </script>
  </body>
</html>