I want to save and retrieve data to an Ethereum Blockchain. I’m using the following code but I am not able to retrieve data. I am only getting the transaction the receipt. How to retrieve data?
Web3.js
export class AppComponent {
title = 'app';
dappUrl: string = 'http://myapp.com';
web3: any;
contractHash: string = '0x3b8a60616bde6f6d251e807695900f31ab12ce1a';
MyContract: any;
contract: any;
ABI: any = [{"constant":true,"inputs":[{"name":"idx","type":"uint256"}],"name":"getLocationHistory","outputs":[{"name":"delegate","type":"address"},{"name":"longitude","type":"uint128"},{"name":"latitude","type":"uint128"},{"name":"name","type":"bytes32"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"recentLocation","outputs":[{"name":"delegate","type":"address"},{"name":"longitude","type":"uint128"},{"name":"latitude","type":"uint128"},{"name":"name","type":"bytes32"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[{"name":"longitude","type":"uint128"},{"name":"latitude","type":"uint128"},{"name":"name","type":"bytes32"}],"name":"saveLocation","outputs":[],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[],"name":"getLastLocation","outputs":[{"components":[{"name":"delegate","type":"address"},{"name":"longitude","type":"uint128"},{"name":"latitude","type":"uint128"},{"name":"name","type":"bytes32"}],"name":"recentLocation","type":"tuple"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[{"name":"","type":"uint256"}],"name":"locations","outputs":[{"name":"delegate","type":"address"},{"name":"longitude","type":"uint128"},{"name":"latitude","type":"uint128"},{"name":"name","type":"bytes32"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"item","outputs":[{"name":"id","type":"bytes32"},{"name":"name","type":"bytes32"}],"payable":false,"stateMutability":"view","type":"function"},{"inputs":[{"name":"id","type":"bytes32"},{"name":"name","type":"bytes32"}],"payable":false,"stateMutability":"nonpayable","type":"constructor"}];
constructor(private route: ActivatedRoute) { }
@HostListener('window:load')
windowLoaded() {
this.checkAndInstantiateWeb3();
this.getLocation();
}
getLocationHistory() {
this.MyContract.methods
.getLocationHistory(0).send({
'from': '0x902D578B7E7866FaE71b3AB0354C9606631bCe03',
'gas': '44000'
}).then((result) => {
this.MyContract.methods.getLocationHistory(0).call()
.then(hello => {console.log('hello', hello)});
});
}
private checkAndInstantiateWeb3 = () => {
if (typeof window.web3 !== 'undefined') {
console.warn('Using web3 detected from external source.');
// Use Mist/MetaMask's provider
this.web3 = new Web3(window.web3.currentProvider);
} else {
console.warn(`No web3 detected. Falling back to http://localhost:8545.`);
this.web3 = new Web3(
new Web3.providers.HttpProvider('http://localhost:8545')
);
}
this.MyContract = new this.web3.eth.Contract(this.ABI, this.contractHash);
}
private getLocation(): void {
let query = this.route.snapshot.queryParams;
if (query.action && query.action === 'setLocation') {
this.setLocation();
}
}
private setLocation(): void {
navigator.geolocation.getCurrentPosition((position) => {
this.MyContract.methods.saveLocation(
position.coords.longitude, position.coords.latitude, window.web3.fromAscii("test")
).send({'from': '0x902D578B7E7866FaE71b3AB0354C9606631bCe03'}
).then((result) => {
console.log('saveLocation')
console.log(result)
});
this.getLocationHistory();
});
}
}
Solidity Contract
pragma solidity ^0.4.11;
/// @title QRCodeTracking with delegation.
contract QRCodeTracking {
struct Location {
address delegate;
uint128 longitude;
uint128 latitude;
bytes32 name;
}
struct Item {
bytes32 id;
bytes32 name;
}
Item public item;
Location[] public locations;
Location public recentLocation;
function QRCodeTracking(bytes32 id, bytes32 name) public {
// Limit gas
locations.length = 100;
item = Item({id: id, name: name});
}
function saveLocation (
uint128 longitude,
uint128 latitude,
bytes32 name
) public constant {
locations.push(Location({
delegate: msg.sender,
longitude: longitude,
latitude: latitude,
name: name
}));
}
function getLocationHistory(uint idx) constant
returns (address delegate, uint128 longitude, uint128 latitude, bytes32 name) {
Location storage loc = locations[idx];
return (loc.delegate, loc.longitude, loc.latitude, loc.name);
}
function getLastLocation() public
returns (Location recentLocation) {
recentLocation = locations[locations.length - 1];
return recentLocation;
}
}