通过新云链理解DAPP

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我将用一个实例，讲解什么是DAPP，即智能合约。

智能合约并不神秘

什么是智能合约:

  • 狭义智能合约: 部署在区块链上的代码, 直接会对链上数据直接更改
  • 广义智能合约: 一个完整的智能合约项目, 不仅包括狭义智能合约, 也包括客户端部分

传统业务: 客户发送数据给服务提供商的服务器, 服务器处理完将结果返回给你

智能合约项目: 唯一差别在于, 不存在所谓中心化的服务器, 客户将数据上传到区块链, 链上的矿工节点帮你处理数据.

项目名字： Super dictionary

下载连接:

功能： 搜索新云链上的词条， 没有词条，可以创建词条，储存在新云链上

页面.png

项目结构： 分为两个部分

智能合约部分:

位置: 部署在新云链上的代码

功能: 在新云链上进行增,删,改,查等基本操作

注意: 增删改等操作是合约上的内置函数,可以直接调用

本地客户端部分:

位置: 部署在本地电脑的客户端前端代码

功能: 图形界面的展示, 用户交互, 调用访问新云链的API
注意: 本地需要下载新云链官方提供的API, 如下代码:

npm i nebulas

狭义智能合约部分:

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"use strict";

var DictItem = function(text) {
	if (text) {
		var obj = JSON.parse(text);
		this.key = obj.key;
		this.value = obj.value;
		this.author = obj.author;
	} else {
	    this.key = "";
	    this.author = "";
	    this.value = "";
	}
};

DictItem.prototype = {
	toString: function () {
		return JSON.stringify(this);
	}
};

var SuperDictionary = function () {
    LocalContractStorage.defineMapProperty(this, "repo", {
        parse: function (text) {
            return new DictItem(text);
        },
        stringify: function (o) {
            return o.toString();
        }
    });
};
// 以下实现了`保存`和`获取`的方法. 
SuperDictionary.prototype = {
    init: function () {
        // todo
    },

    save: function (key, value) {

        key = key.trim();
        value = value.trim();
        if (key === "" || value === ""){
            throw new Error("empty key / value");
        }
        if (value.length > 64 || key.length > 64){
            throw new Error("key / value exceed limit length")
        }

        var from = Blockchain.transaction.from;
        var dictItem = this.repo.get(key);
        if (dictItem){
            throw new Error("value has been occupied");
        }

        dictItem = new DictItem();
        dictItem.author = from;
        dictItem.key = key;
        dictItem.value = value;

        this.repo.put(key, dictItem);
    },

    get: function (key) {
        key = key.trim();
        if ( key === "" ) {
            throw new Error("empty key")
        }
        return this.repo.get(key);
    }
};
module.exports = SuperDictionary;

本地客户端部分：

这里只展示前端页面的代码, 这里的API包名: nebpay 

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<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <meta name="viewport" content="width=device-width,initial-scale=1, maximum-scale=1, minimum-scale=1, user-scalable=no">

    <title>Super Dictionary</title>
    <link rel="stylesheet" href="lib/bootstrap-4.0.0-dist/css/bootstrap.min.css">
    <style>
        .logo {
            width: 60%;
            height: 500px;
            margin: auto;
        }

        .name {
            text-align: center;
            font-size: 66px;
            text-shadow: 3px 5px grey, 1px 1px #333;
        }

        .img {
            width: 48%;
            height: 53%;
            margin: auto;
            margin-top: 38px;
        }

        .img img {
            width: 100%;
            height: 100%;
        }

        .search {
            width: 60%;
            height: 100px;
            margin: auto;
        }

        .noExtension {
            width: 60%;
            height: 100px;
            margin: auto;
            font-size: 23px;
        }

        #search_value {
            width: 80%;
            height: 50px;
            box-shadow: 3px 5px grey, 1px 1px #333;
        }

        .search button {
            width: 18%;
            height: 50px;
            margin-left: 6px;
            box-shadow: 3px 5px grey, 1px 1px #333;
        }

         @keyframes rotate {
            0% { transform:rotateY(0deg);}
            25% { transform:rotateY(180deg);}
            50% { transform:rotateY(0deg);}
            75% { transform:rotateY(180deg);}
            100% { transform:rotateY(0deg);}
        }

        .logo_rotate {
			/*
            animation: rotate 10s infinite;
            animation-fill-mode: forwards;
            animation-timing-function: linear;
				*/
            /*  当动画结束时，让<div>元素保留上一个关键帧的样式值 */
        }

         .result_success {
            width: 60%;
            margin: auto;
        }

        .result_faile{
            width: 60%;
            margin: auto;
        }

        .add_banner{
            width: 60%;
            margin: auto;
        }

        .add_banner input{
            width: 80%;
            height: 50px;
            box-shadow: 3px 5px grey, 1px 1px #333;
        }

        .add_banner button{
            width: 18%;
            height: 50px;
            margin-left: 6px;
            box-shadow: 3px 5px grey, 1px 1px #333;
        }

        #search_banner{
            font-size: 40px;
            border-bottom: 1px solid black;
        }

        p{
            text-indent:2em;
            font-size: 20px;
        }

        .hide{
            display: none;
        }

        .contenner{
            background: url("img/bg.jpg");
            height: 900px;
        }

        .author{
            text-align: right;
        }
        .author p{
            display: inline-block;
            font-size: 14px;
        }
    </style>
</head>

<body>
    <div class="contenner">
        <div class="logo">
            <div class="name">SUPER DICTIONARY</div>
            <div class="img logo_rotate">
                <img src="img/logo.png" alt="">
            </div>
        </div>
        <div class="noExtension hide" id="noExtension">
            NOTE: Please install <a target="_blank" href="https://github.com/ChengOrangeJu/WebExtensionWallet">WebExtensionWallet</a>  to use SUPER DICTIONARY
        </div>
        <div class="search">
            <input id="search_value" type="text">
            <button id=search>search</button>
        </div>

        <div class="result_success hide">
            <div id=search_banner></div>
            <p id=search_result> wait for content </p>
            <div class="author">
                <i><p> Author:</p> <p id=search_result_author> dasdajkajksdhjasdkjahdkjad</p></i>
            </div>
        </div>

        <div class="result_faile hide">
            Failed to find related information. Do you want to <button id="add">add</button> infromation for "<i id="result_faile_add">asd</i>"?
        </div>

        <div class="add_banner hide">
            <input type="text" id="add_value" placeholder="input contents for your keyword">
            <button id="push">submit</button>
            </div>
    </div>
    <script src=lib/jquery-3.3.1.min.js></script>
    <script src=lib/nebPay.js></script>
    <script src=lib/bootstrap-4.0.0-dist/js/bootstrap.min.js></script>
    <script>
        var NebPay = require("nebpay");     //https://github.com/nebulasio/nebPay
        var nebPay = new NebPay();

        $("#search_value").attr("disabled",true)
        $("#search").attr("disabled",true)


        //to check if the extension is installed
        //if the extension is installed, var "webExtensionWallet" will be injected in to web page
        if(typeof(webExtensionWallet) === "undefined"){
            //alert ("Extension wallet is not installed, please install it first.")
            $("#noExtension").removeClass("hide")
        }else{
            $("#search_value").attr("disabled",false)
            $("#search").attr("disabled",false)
        }

        var dappAddress = "n1yQtfkR2EnayXEW71T7kP4wyaU4eC6adik";

        // 搜索功能: 查找Super-Dictionary 中有没有该词条
    $("#search").click(function(){
        // $("#search_value").val() 搜索框内的值

        var to = dappAddress;
        var value = "0";
        var callFunction = "get";
        var callArgs = "[\"" + $("#search_value").val() + "\"]"; //in the form of ["args"]
        nebPay.simulateCall(to, value, callFunction, callArgs, {    //使用nebpay的simulateCall接口去执行get查询, 模拟执行.不发送交易,不上链
            listener: cbSearch      //指定回调函数
        });
    })

    //return of search,
    function cbSearch(resp) {
        var result = resp.result
        console.log("return of rpc call: " + JSON.stringify(result))

        if (result === 'null'){
            $(".add_banner").addClass("hide");
            $(".result_success").addClass("hide");

            $("#result_faile_add").text($("#search_value").val())

            $(".result_faile").removeClass("hide");
        } else{
            //if result is not null, then it should be "return value" or "error message"
            try{
                result = JSON.parse(result)
            }catch (err){
                //result is the error message
            }

            if (!!result.key){      //"return value"
                $(".add_banner").addClass("hide");
                $(".result_faile").addClass("hide");

                $("#search_banner").text($("#search_value").val())
                $("#search_result").text(result.value)
                $("#search_result_author").text(result.author)

                $(".result_success").removeClass("hide");
            } else {        //"error message"
                $(".add_banner").addClass("hide");
                $(".result_faile").addClass("hide");

                $("#search_banner").text($("#search_value").val())
                $("#search_result").text(result)
                $("#search_result_author").text("")

                $(".result_success").removeClass("hide");
            }

        }

    }

    // 添加信息功能: 像super-dictionary 中添加词条
    $("#add").click(function() {
        $(".result_faile").addClass("hide");
        $(".add_banner").removeClass("hide");

        $("#add_value").val("")
    })

    $("#push").click(function() {

        var to = dappAddress;
        var value = "0";
        var callFunction = "save"
        var callArgs = "[\"" + $("#search_value").val() + "\",\"" + $("#add_value").val() + "\"]"

        nebPay.call(to, value, callFunction, callArgs, {    //使用nebpay的call接口去调用合约,
            listener: cbPush
        });
    });

    function cbPush(resp) {
        console.log("response of push: " + resp)
    }


</script>
</body>

</html>