eth智能合约---一个简单的投票

目的

学习智能合约的开发以及使用流程

期望

1. A发起智能合约,设定选择项目(比如 1,2,3,4)
2. A设定那些人可以进行投票,先对可以进行投票的人授权
3. 已经被授权的人可以投票,没被授权的人投票无效
4. 计算最终那个选项投票数最多

合约代码

pragma solidity ^0.4.16;

/// @title Voting with delegation.
contract Ballot {
    // This declares a new complex type which will
    // be used for variables later.
    // It will represent a single voter.
    struct Voter {
        uint weight; // weight is accumulated by delegation
        bool voted;  // if true, that person already voted
        address delegate; // person delegated to
        uint vote;   // index of the voted proposal
    }

    // This is a type for a single proposal.
    struct Proposal {
        bytes32 name;   // short name (up to 32 bytes)
        uint voteCount; // number of accumulated votes
    }

    address public chairperson;

    // This declares a state variable that
    // stores a `Voter` struct for each possible address.
    mapping(address => Voter) public voters;

    // A dynamically-sized array of `Proposal` structs.
    Proposal[] public proposals;

    /// Create a new ballot to choose one of `proposalNames`.
    function Ballot(bytes32[] proposalNames) public {
        chairperson = msg.sender;
        voters[chairperson].weight = 1;

        // For each of the provided proposal names,
        // create a new proposal object and add it
        // to the end of the array.
        for (uint i = 0; i < proposalNames.length; i++) {
            // `Proposal({...})` creates a temporary
            // Proposal object and `proposals.push(...)`
            // appends it to the end of `proposals`.
            proposals.push(Proposal({
                name: proposalNames[i],
                voteCount: 0
            }));
        }
    }

    // Give `voter` the right to vote on this ballot.
    // May only be called by `chairperson`.
    function giveRightToVote(address voter) public {
        // If the argument of `require` evaluates to `false`,
        // it terminates and reverts all changes to
        // the state and to Ether balances. It is often
        // a good idea to use this if functions are
        // called incorrectly. But watch out, this
        // will currently also consume all provided gas
        // (this is planned to change in the future).
        require(
            (msg.sender == chairperson) &&
            !voters[voter].voted &&
            (voters[voter].weight == 0)
        );
        voters[voter].weight = 1;
    }

    /// Delegate your vote to the voter `to`.
    function delegate(address to) public {
        // assigns reference
        Voter storage sender = voters[msg.sender];
        require(!sender.voted);

        // Self-delegation is not allowed.
        require(to != msg.sender);

        // Forward the delegation as long as
        // `to` also delegated.
        // In general, such loops are very dangerous,
        // because if they run too long, they might
        // need more gas than is available in a block.
        // In this case, the delegation will not be executed,
        // but in other situations, such loops might
        // cause a contract to get "stuck" completely.
        while (voters[to].delegate != address(0)) {
            to = voters[to].delegate;

            // We found a loop in the delegation, not allowed.
            require(to != msg.sender);
        }

        // Since `sender` is a reference, this
        // modifies `voters[msg.sender].voted`
        sender.voted = true;
        sender.delegate = to;
        Voter storage delegate_ = voters[to];
        if (delegate_.voted) {
            // If the delegate already voted,
            // directly add to the number of votes
            proposals[delegate_.vote].voteCount += sender.weight;
        } else {
            // If the delegate did not vote yet,
            // add to her weight.
            delegate_.weight += sender.weight;
        }
    }

    /// Give your vote (including votes delegated to you)
    /// to proposal `proposals[proposal].name`.
    function vote(uint proposal) public {
        Voter storage sender = voters[msg.sender];
        require(!sender.voted);
        require(sender.weight == 1);
        sender.voted = true;
        sender.vote = proposal;

        // If `proposal` is out of the range of the array,
        // this will throw automatically and revert all
        // changes.
        proposals[proposal].voteCount += sender.weight;
    }

    /// @dev Computes the winning proposal taking all
    /// previous votes into account.
    function winningProposal() public view
            returns (uint winningProposal_)
    {
        uint winningVoteCount = 0;
        for (uint p = 0; p < proposals.length; p++) {
            if (proposals[p].voteCount > winningVoteCount) {
                winningVoteCount = proposals[p].voteCount;
                winningProposal_ = p;
            }
        }
    }

    // Calls winningProposal() function to get the index
    // of the winner contained in the proposals array and then
    // returns the name of the winner
    function winnerName() public view
            returns (bytes32 winnerName_)
    {
        winnerName_ = proposals[winningProposal()].name;
    }
}

使用流程-发布

首先你要搭建一个私链的环境(当然如果你是土豪,可以直接使用公链),具体怎么搭建可以参考
搭建以太坊私链
在钱包选择contracts(合同),点击deploy new contract(发布一个新的合同)

第二步,把上面的代码复制其中,等待编译后.右面选择函数名字,以及设置投票选择的分类(这里我用1,2,3,4代替)

然后发布

等待一个块产生后(在钱包主页面查看),合同就生成了,如下.

使用流程-授权

用刚才创建合同的账号,给让参与投票的账号授权,点击进入合同.

选择give right to vote.填写参与者的地址.

使用流程-投票

选择投票函数,填写要投票的选项(这里是从0开始的计算.所以0表示上面投票给了1选项.当然上面的选择可以不用数字比如 水果 [苹果,西红柿,西瓜],那么0就表示苹果,1表示西红柿. 而且这里的值不在数字的范围内是会报错的.)

使用流程-查看结果

1.可以根据选项查看投票的数量
2.查看那个选项得票率最高
3.根据用户查看他投那个选项的票,以及是否授权等

关联的所有交易查看

以上参考网络上的一个只能合约做了修改(修复了之前那个人的错误),还加入了自己的解释. 里面还包含了可以委托没有讲.
个人总结:

1. 其实智能合约一定是基于交易的,而且里面除了自己的变量设定之外.只能调用连上的部分东西
2. 虽然是图灵完备,但是功能有限
3. 每次交易数据状态完全存储,感觉这个会是智能合约的痛
   4.去中心化以及永不丢失的优点,必然会让很多缺点暴露无疑.