CrowdFunding<\/em> – This is the\ncontract class.<\/p>\n\n\n\n FundingProject<\/em> \u2013 A custom type\nthat hold project details as part of the contract.<\/p>\n\n\n\n Funder<\/em> \u2013 A custom type\nthat holds funder details as part of the contract.<\/p>\n\n\n\n Let\u2019s walkthrough the code:<\/p>\n\n\n\n We first specify the Solidity version required to compile our\ncontract.<\/p>\n\n\n\n pragma solidity ^0.4.11;<\/p>\n\n\n\n We then create the CrowdFunding<\/em>\ncontract using the contract<\/em> keyword<\/p>\n\n\n\n contract CrowdFunding {<\/p>\n\n\n\n The CrowdFunding<\/em> contract contains the FundingProject<\/em> and Funder<\/em> custom types with required attributes. We then create instances of the custom types.<\/p>\n\n\n\n Next, we define methods\/operations that would be exposed by our\ncontract.<\/p>\n\n\n\n The CrowdFunding()<\/em> method shown below is the constructor of our contract which would initialize the project details. It expects parameters that are used to initialize the FundingProject<\/em> type. We will show you how to pass these parameters once we instantiate the contract through our wallet interface in the next section.<\/p>\n\n\n\n Next, we initialize the Funder<\/em>\ntype and assign it to the funders<\/em>\narray as part of the fundProject()<\/em>\nmethod. The attribute amountraised<\/em> of\nthe FundingProject<\/em> type will be\nupdated to reflect the funder\u2019s amount. It means the funder has provided\nfunding of that amount value. If the attribute amountraised<\/em> is greater than minimumfunds<\/em>\ni.e. if the project meets the funding target then the amount is sent to the\nbeneficiary account named ProjectAI<\/em>.\nThis is done using the send() <\/em>method\nof the FundingProject.owner<\/em>\nattribute. Following shows the code snippet \n–<\/p>\n\n\n\n fundingproject.owner.send(fundingproject.amountraised)<\/p>\n\n\n\n The important thing to note is that the amount reaches the ProjectAI\naccount only when minimum funding amount is raised. Until that duration, the\namount transferred from Funder\u2019s account is put on hold by the contract.<\/p>\n\n\n\n The below fundProject<\/em>() method uses the payable modifier to receive ethers from the application (i.e., from Funders account who is funding the project)<\/p>\n\n\n\n Next, we define the\nstopFundRaising() <\/em>method. The said method returns all the money to the\nrespective Funders (if the funding target is not met) by iterating through the\nfunders array and calling the send()<\/em>\nmethod of Funder.fundedBy<\/em> attribute for\neach funder object in the array. Following shows the code snippet –<\/p>\n\n\n\n funders[p].fundedby.send(funders[p].amount)<\/p>\n\n\n\n The stopFundRaising()<\/em> method\nuses the payable<\/em> modifier to send\nethers from the contract to respective funders account.<\/p>\n\n\n\n Next, we define the getProjectStatus()<\/em> constant method, that displays the status of the project at any interval.<\/p>\n\n\n\n We now have our CrowdFunding<\/em>\ncontract ready, the next step will be to deploy the same. You can copy the\ncontent of the CrowdSourceContract.sol file and navigate back to Ethereum\nWallet application. Click on Contracts<\/em> from the top menu. On contracts window, navigate to Deploy New Contract<\/em>. Select Main Account<\/em> as the From<\/em> option. <\/p>\n\n\n\n Paste the copied content inside the Solidity Contract Source code<\/em> window. The resulting contract will\nbe converted to bytecode once it is successfully compiled. If there were an\nerror in the contract, you would see a message \u201ccould not compile source code.\u201d<\/p>\n\n\n\n Once the contract is compiled successfully, select the contract Crowd Funding<\/em> from Select Contract to Deploy<\/em> dropbox as shown in the figure below and\nenter the following details:<\/p>\n\n\n\n On the Create contract<\/em>\nwindow, you would see the transaction fee and gas price for deploying the\ncontract as shown in the figure below. Enter the password of the Main Account<\/em> and click Send Transaction.<\/em> <\/p>\n\n\n\n If you go to Wallets<\/em> tab and scroll down to the Latest Transactions <\/em>section, you would see \u201cCrowdsourcing Contract\u201d being committed. Once all the confirmations are done, click on the transaction entry. You would see the transaction details and public address of the contract in the To<\/em> column as shown in the figure below. <\/p>\n\n\n\n Click on the Crowd Funding<\/em> public address link, and you would see the contract details. You can verify the contract details entered earlier. You will also see the status of the project as Funding Started<\/em> as shown in the figure below.<\/p>\n\n\n\n Now, in the Select function<\/em>\ndrop down, select Fund Project<\/em> method\nand enter name as \u201cFund from Funder 1\u201d. In the Execute from<\/em> option select Funder 1 and specify 700 as ether amount\nas shown in the figure below.<\/p>\n\n\n\n Click Execute. On the Execute Contract window, specify the password\nfor Funder1<\/em> and click Send Transaction<\/em>. You should see the\namount raised as 700000000000000000000 and status of the project changed as \u201cIn\nprogress.\u201d The 700000000000000000000 value is in wei units (1 Ether =\n1000000000000000000 wei), the Wallet displays currency in wei units. You can\nverify the transaction details in the Latest\nTransaction<\/em> view, and you should also see 700 ethers and transaction fee\ndeducted from the Funder1<\/em> balance. <\/p>\n\n\n\n Next, go back to the contract (either by clicking on contract link\nfrom the transaction view or by selecting Contracts<\/em>\nfrom the top menu and clicking on the specific contract address from the custom\ncontract list). <\/p>\n\n\n\n Now, select Fund Project<\/em> method from Select function<\/em> dropdown and this time, select Funder2<\/em> and transfer 350 ethers as shown below. <\/p>\n\n\n\n Click Execute<\/em> and send the transaction. Once the transaction is committed, you will see the status of the project changed to Funding Completed. You should also see 350 ethers and transaction fee deducted from the Funder2<\/em> balance. The ProjectAI<\/em> account would be credited with 1050 ether amount.<\/p>\n\n\n\n Next, we would execute the Stop Funding use case, where the amount funded by Funders would be transferred back to the Funders wallet if the funding target is not met.<\/p>\n\n\n\n For this use case, we would follow similar steps as described earlier\nwith the addition of executing the Stop Funding function. Let\u2019s call this as\nUse Case 2 (we would reference this later). To implement \u2018Stop Funding\u2019 use\ncase, carry out the following steps :<\/p>\n\n\n\n\/\/Funding project details\n struct FundingProject {\n \n string name;\n string email;\n string website;\n uint minimumfunds;\n uint amountraised;\n address owner;\n string status;\n \n }\n \n \/\/Funder who funds project.\n struct Funder {\n string name;\n address fundedby;\n uint amount;\n }\n\n\/\/Multiple funders can fund project\n Funder[] public funders;\n \n \/\/Instance\n FundingProject public fundingproject\n<\/code><\/pre>\n\n\n\nfunction CrowdFunding ( \n string _name,\n string _email,\n string _website,\n uint _minimumfunds,\n address _owner \n )\n {\n \t\n \/\/convert to ether\nuint minimumfunds = _minimumfunds * 1 ether;\nuint amountraised = 0;\nfundingproject = \nFundingProject(_name,_email,_website,\nminimumfunds,amountraised,_owner,\n\"Funding Started\");\n \n }\n<\/code><\/pre>\n\n\n\nfunction fundProject( string name) public payable {\n\nif (stringsEqual(fundingproject.status ,\"Funding Completed\")) revert();\n\tfunders.push(Funder({\n\t\t\t\tname: name,\n\t\t\t\tfundedby: msg.sender,\n\t\t\t\tamount: msg.value\n\t\t\t }) \n\t\t\t);\n\t fundingproject.amountraised =\t \n fundingproject.amountraised + msg.value ;\n\nif (fundingproject.amountraised >= \n fundingproject.minimumfunds) {\n\t\t\t\t \n if(!fundingproject.owner.send(fundingproject.amountraised )) revert();\t\t\t\t \n fundingproject.status = \"Funding Completed\";\n\t} \n\telse {\t\t \t\t\t\n fundingproject.status = \"In Progress\";\n\t}\n}\n<\/code><\/pre>\n\n\n\nfunction stopFundRaising() public payable {\n \t if (stringsEqual(fundingproject.status ,\"Funding Completed\")) revert();\n \t fundingproject.status = \"Funding Stopped\";\n \t \/\/return money to all funders\n \t for (uint p = 0; p < funders.length; p++) {\n \t \tif(!funders[p].fundedby.send(funders[p].amount)) throw;\n \t }\n \t fundingproject.amountraised = 0;\n }\n\n<\/code><\/pre>\n\n\n\nfunction getProjectStatus() public constant\treturns(string) {\n \t\treturn (fundingproject.status);\n}\n\n<\/code><\/pre>\n\n\n\n![\"\"](\"https:\/\/navveenbalani.dev\/wp-content\/uploads\/2019\/12\/image-54.png\")
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