在前端页面调用合约写入数据时不会立即返回结果,这时需要再调用获取数据的函数,使用起来非常不便,这时event就可以很好解决这样的问题。
合约代码:
声明event事件:
event Deposit(address indexed _from, bytes32 indexed _id, uint _value);
触发event事件:
emit Deposit(, _id, );
pragma solidity >=0.6.0 <0.9.0;
contract Demo {
uint256 demoIndex = 0;
event DemoIndexInc(uint256 indexed index);
function getDemoIndex() public view returns (uint256) {
return demoIndex;
}
function incDemoIndex() public {
demoIndex = demoIndex+1;
emit DemoIndexInc(demoIndex);
}
}
H5代码:
订阅event事件:
<script src="./dist/"></script>
<script type="text/javascript">
const addEventWatchTx = async () => {
var web3 = new Web3(ethereum)
var metaTxContract = new (MetaTxABI, contractAddr)
({
filter:{},
fromBlock: 'latest'
}, function(error, event){})
.on('data', function(event){
(event); // same results as the optional callback above
})
.on('changed', function(event){
('emove event from local database');
})
.on('error', );
}
</script>