DevChain

No gas needed. Accounts are only for identification purposes.

See the dapp in action

DEMO: A voting dapp

Step 1

Open the BUIDL IDE tool in any browser. http://buidl.secondstate.io/

Step 2

2.1 Copy and paste the following code to the contract section of BUIDL.

The smart contract is very simple. It provides the text and image url to be voted on, and keeps a record of votes. The vote() method is called by voters to vote thumb up or down.

pragma solidity >= 0.4.0;

contract Vote {

    string public greeting;
    string public photoUrl;
    mapping (address => int) votes;
    uint ups;
    uint downs;

    constructor(string _greeting, string _photoUrl) public {
        greeting = _greeting;
        photoUrl = _photoUrl;
    }

    function vote (int _choice) public {
        require (votes[msg.sender] == 0);
        require (_choice == 1 || _choice == -1);
        votes[msg.sender] = _choice;
        if (_choice == 1) ups++;
        if (_choice == -1) downs++;
    }

    function getVotes () view public returns (uint, uint) {
        return (ups, downs);
    }

    function getVote (address _addr) view public returns (int) {
        return votes[_addr];
    }
}

2.2 Click on Compile and you will see the following. Enter your text and image URL to be voted on, and then click on deploy on chain.

The contract is now deployed on the DevChain, and you can call its functions directly from inside BUIDL.

2.3 Go to the dapp section. Click on the Resources tab, and add the following as resources.

• CSS: https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css

• JavaScript: https://code.jquery.com/jquery-3.4.1.min.js

2.4 Next, copy and paste the following HTML code into the HTML editor.

<div class="container">
   <br/>
   <div class="jumbotron">
      <p class="lead" id="greeting"></p>
      <div id="imageDiv" style="display:none">
         <img id="image" src="" class="img-fluid img-thumbnail"/>
      </div>
      <hr/>
      <p id="votes" style="display:none">
         <span id="ups"></span> voted 👍 |
         <span id="downs"></span> voted 👎
      </p>
      <form id="form" class="form-inline" style="display:none">
         <button id="voteUp" type="button" onclick="return vote(1);" class="btn btn-secondary mb-2">👍</button>
         <button id="voteDown" type="button" onclick="return vote(-1);" class="btn btn-secondary mb-2">👎</button>
      </form>
      <div id="formSubmitted" style="display:none">Please wait 2 seconds ...</div>
      <div id="myVoteUp" style="display:none">You have already voted 👍</div>
      <div id="myVoteDown" style="display:none">You have already voted 👎</div>
   </div>
</div>

2.5 Copy and paste the following JavaScript code into the JS editor.

var instance = null;
window.addEventListener('web3Ready', function() {
  var contract = web3.ss.contract(abi);
  instance = contract.at(cAddr);
  reload();
});

function reload() {
    instance.greeting(function (e, r) {
        $("#greeting").html(r);
    });
    instance.photoUrl(function (e, r) {
        if (!e && r) {
            $("#imageDiv").css("display", "block");
            $("#image").attr("src", r);
        }
    });
    instance.getVotes(function (e, r) {
        if (!e && (r[0] > 0 || r[1] > 0)) {
            $("#votes").css("display", "block");
            $("#ups").text(r[0]);
            $("#downs").text(r[1]);
        }
    });

    $("#form").css("display", "none");
    $("#formSubmitted").css("display", "none");
    web3.ss.getAccounts(function (e, address) {
        if (!e) {
            instance.getVote(address, function (ee, r) {
                if (r == 1) {
                    $("#myVoteUp").css("display", "block");
                } else if (r == -1) {
                    $("#myVoteDown").css("display", "block");
                } else {
                    $("#form").css("display", "block");
                }
            });
        }
    });
}

function vote (choice) {
    web3.ss.getAccounts(function (e, address) {
        if (!e) {
            $("#form").css("display", "none");
            $("#formSubmitted").css("display", "block");
            instance.vote(choice, function (ee, result) {
                if (ee) {
                    window.alert("Failed for " + address);
                }
            });
            setTimeout(function () {
                reload ();
            }, 2 * 1000);
        }
    });
    return false;
}

2.6 Click on Run to see the dapp in action! You can now vote thumb up or down inside BUIDL.

2.7 Finally, you can publish the dapp.

Just click on the Publish button and give the dapp a name. Once published, you can share the published URL to the public to vote on your issue! Notice that the DevChain requires no gas to operate. So the user can vote from any of the auto-created or imported DevChain accounts.