如果我收到 10 以太币的付款，我想自动发送一些文本如钥匙

如何解决如果我收到 10 以太币的付款，我想自动发送一些文本如钥匙

我有一个 Rinkeby Metamask 账户，我想让学生支付我 10 以太币，以表明他们已经理解以下原则作为挑战的一部分：

• 创建一个处理以太坊的在线钱包
• 能够获得足够的免费以太坊来完成支付
• 最后一次支付全款

付款完成后，我想给他们一个文本字符串“Well_Done_101”，以证明他们已完成挑战。

我知道可以使用智能合约，但我不确定这将如何工作，因为我希望文本字符串在付款完成之前不可见。

这是我之前尝试过的一些代码：

    // SPDX-License-Identifier: MIT
pragma solidity ^0.8.4;

contract payment_for_art {

    // default value is `false`,don't need to explicitly state it
    bool isPaid;
     
    
    function winner() public view returns (string memory) {
        return flag;
    }
    
    function hidden() private view returns (string memory) {
        string memory flag_true;
        flag_true = 'Well_done_101';
        return flag;
    }

    function invest() external payable {
        // to prevent multiple payments
        // reverts if the condition is not met
        require(isPaid == false);

        if(msg.value < 10 ether) {
            revert('Pay me the full amount');
        }
        
        if(isPaid = true) { // flag that the payment has been done
        //return ('Well_Done_101');
            return flag_true;
        }
    }

    function balance_of() external view returns(uint) {
        return address(this).balance;
    }
}

任何想法或意见将不胜感激。

解决方法

我认为您要搜索的内容是这样的。

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.4;

contract payment_for_art {

    // Mappings of studentNames to flag; Its like a key => value list data type.
    // Public storage variables can be accessed by anyone (solidity creates a getter implicitly),but can't be modified directly.
    mapping (string => string) public buyers;
    
    // Recieves the payment,and also the students name (your students must call this function with their name as a parameter).
    function invest(string memory studentName) external payable {
        
        // check if "studentname" isn't empty.
        require(bytes(studentName).length != 0,"You forgot to specify your student name.");
        
        // check if the payment is 10 eth.
        require(msg.value == 10 ether,"You are either paying too much,or too little.");
        
        // check if the student already bought,by checking if his flag is set in the mapping.
        require(bytes(buyers[studentName]).length == 0,"You already bought the art.");
        
        // set flag for student.
        // While regular string literals can only contain ASCII,// Unicode literals – prefixed with the keyword unicode – can contain any valid UTF-8 sequence (this allows you to use emogis and whatnot).
        // They also support the very same escape sequences as regular string literals. 
        buyers[studentName] = unicode"Well_Done_101 ?";
    }

    function balance_of() external view returns(uint) {
        return address(this).balance;
    }
}

要检查他们是否购买，只需调用映射并搜索您的学生姓名即可。

使用 web3 制作的示例：

 payment_for_artContract.methods.invest("Daniel Jackson")
        .send({ from: account,value: weiValue})
        .on('transactionHash',(hash) => {
          const studentsWhoBought = await payment_for_artContract.methods.buyers().call();
    // prints "Well_Done_101 ?";
    console.log(studentsWhoBought["Daniel Jackson"]);
    console.log(studentsWhoBought);
        })
        .on('error',(err) => {
          console.error(err);
        })

如果您想在它被调用时实际从中获取一个值，您需要使用事件（客户端可以订阅的触发器）并让 web3 订阅所述事件。

例如：

 // SPDX-License-Identifier: MIT
    pragma solidity ^0.8.4;
    
    contract payment_for_art {
    
        // Mappings of studentNames to flag; Its like a key => value list data type.
        // Public storage variables can be accessed by anyone (solidity creates a getter implicitly),but can't be modified directly.
        mapping (string => string) public buyers;
        
        // Event of buying.
        event Bought(string studentName,address studentAddress,string flag);
        
        // Recieves the payment,and also the students name (your students must call this function with their name as a parameter).
        function invest(string memory studentName) external payable {
            
            // check if "studentname" isn't empty.
            require(bytes(studentName).length != 0,"You forgot to specify your student name.");
            
            // check if the payment is 10 eth.
            require(msg.value == 10 ether,or too little.");
            
            // check if the student already bought,by checking if his flag is set in the mapping.
            require(bytes(buyers[studentName]).length == 0,"You already bought the art.");
            
            // set flag for student.
            // While regular string literals can only contain ASCII,// Unicode literals – prefixed with the keyword unicode – can contain any valid UTF-8 sequence (this allows you to use emogis and whatnot).
            // They also support the very same escape sequences as regular string literals. 
            buyers[studentName] = unicode"Well_Done_101 ?";
            
            emit Bought(studentName,msg.sender,unicode"Well_Done_101 ?");

        }
    
        function balance_of() external view returns(uint) {
            return address(this).balance;
        }
    }

然后在 web3 中：

    payment_for_artContract.methods.invest("Daniel Jackson")
                .send({ from: account,value: weiValue})
                .on('transactionHash',(hash) => {
                  console.log("transaction mined");
                })
                .on('error',(err) => {
                  console.error(err);
                });


    const options = {
        fromBlock: 0,// Number || "earliest" || "pending" || "latest"
        toBlock: 'latest'
    };
    
    payment_for_artContract.events.Bought(options)
// prints the student's name who bought,address of the student,and "Well_Done_101 ?";
    .on('data',event => console.log(event))
    .on('changed',changed => console.log(changed))
    .on('error',err => throw err)
    .on('connected',str => console.log(str));

我会坚持第一种方法，因为它更容易，但第二种方法应该如何正确完成。

尝试一下，如果这就是您要搜索的内容，请告诉我:)