truffle框架创建合约实例代码
truffle框架来创建合约实例的代码如下:
import React, { Component } from "react";
import SimpleStorageContract from "./contracts/SimpleStorage.json";
import getWeb3 from "./utils/getWeb3";
import truffleContract from "truffle-contract";
import "./App.css";
class App extends Component {
state = { storageValue: 0, web3: null, accounts: null, contract: null };
componentDidMount = async () => {
try {
// Get network provider and web3 instance.
const web3 = await getWeb3();
// Use web3 to get the user's accounts.
const accounts = await web3.eth.getAccounts();
// Get the contract instance.
const Contract = truffleContract(SimpleStorageContract);
Contract.setProvider(web3.currentProvider);
const instance = await Contract.deployed();
// Set web3, accounts, and contract to the state, and then proceed with an
// example of interacting with the contract's methods.
this.setState({ web3, accounts, contract: instance }, this.runExample);
} catch (error) {
// Catch any errors for any of the above operations.
alert(
`Failed to load web3, accounts, or contract. Check console for details.`
);
console.log(error);
}
};
runExample = async () => {
const { accounts, contract } = this.state;
// Stores a given value, 5 by default.
await contract.set(5, { from: accounts[0] });
// Get the value from the contract to prove it worked.
const response = await contract.get();
// Update state with the result.
this.setState({ storageValue: response.toNumber() });
};
render() {
if (!this.state.web3) {
return <div>Loading Web3, accounts, and contract...</div>;
}
return (
<div className="App">
<h1>Good to Go!</h1>
<p>Your Truffle Box is installed and ready.</p>
<h2>Smart Contract Example</h2>
<p>
If your contracts compiled and migrated successfully, below will show
a stored value of 5 (by default).
</p>
<p>
Try changing the value stored on <strong>line 37</strong> of App.js.
</p>
<div>The stored value is: {this.state.storageValue}</div>
</div>
);
}
}
export default App;