“返回的值不是可轉換的字元串”（web3js & React 前端）

編輯：要清楚， getMessage() 函式在混音中工作正常。它似乎不適用於我的前端。

我正在嘗試為我的契約設置前端，但是在嘗試呼叫返回字元串的某個函式時，我在 Web 控制台中收到以下錯誤：

Error: ERROR: The returned value is not a convertible string: formatters.js:261

當我在getMessage這裡呼叫函式時（在 App.js 中），似乎發生了錯誤：

async componentDidMount() {
const host = await chatroom.methods.host().call();
const members = await chatroom.methods.getMembers().call();
const chatLoglength = await chatroom.methods.getMessagesLength().call();
const chatLog = [];

for (let i = 0; i < chatLoglength; i++) {
 const newMessage = await chatroom.methods.getMessage(i+1).call();
 chatLog.push(newMessage);
}

this.setState({ host, members, chatLog });
}

我正在使用 web3 版本 1.0.0-beta.35。我已經確認我使用正確的字節碼和 ABI 實例化了合約。我不確定為什麼我能夠從其他函式返回字元串，但不能從這個函式返回。任何幫助將不勝感激。程式碼如下。

契約：

pragma solidity ^0.4.25;

contract Chatroom {
address public host;
string private password;

address[] public members;
Message[] public chatLog;

mapping(uint => Message) msgIDPair;
mapping(address => bool) isMember;

struct Message {
   address author;
   string content;
}

// @notice Creates the chat-room. Host role is given to the address of the sender
// @dev The password could be inferred from the constructor argument, not strong security
// @param _password The password the host wishes to set for the chat-room
constructor(string _password) public {
   host = msg.sender;
   addMember(host); // adds host address to members array

   password = _password;
}

// @notice Send a message `(_message)` to the chat-room (must be a member)
// @param _message The content of the message to be sent
function sendMessage(string _message) external mustBeMember {
   uint msgID = chatLog.length + 1;

   msgIDPair[msgID] = Message(msg.sender, _message); // pairs message ID with Message struct object
   chatLog.push(msgIDPair[msgID]); // adds Message object to chatLog array
}

// @notice Retrieve a message via ID `(_ID)`
// @dev Returns struct of Message, use front-end to get specific properties
// @param _ID The ID assigned to the desired message
// @return The target message
function getMessage(uint _ID) public view mustBeMember returns(string) {
   return(msgIDPair[_ID].content);
}

// @notice Check if an address is a member
// @param _target The address to be checked
// @return true if the target address is a member, false otherwise
function checkMember(address _target) public view returns(bool) {
   if (isMember[_target] == true) { // returns true if address has a "true" value assigned in isMember mapping table
       return(true);
   }
   else { // returns false if address does not have a "true" value assigned in isMember mapping table
       return(false);
   }
}

modifier mustBeMember() {
   require(checkMember(msg.sender) == true);
   _;
}


// @notice Become a member the chat-room (requires `(password)`)
// @param _password The password to evaluate
function joinChat(string _password) public requirePassword(_password) {
   addMember(msg.sender);
}

// @notice Leave the chat-room (must be a member)
function leaveChat() public mustBeMember {
   require(msg.sender != host); // host cannot leave, must transfer role first

   for (uint i = 0; i < members.length; i++) { // loops through entire members array, deletes matching address
       if (members[i] == msg.sender) {
           swapReduceIndex(members, i);
       }
   }

   isMember[msg.sender] = false;
}

// @notice Add a new member address that is not already a member
// @dev This is a helper function
// @param _newMember The address to be granted membership
function addMember(address _newMember) private {
   if (isMember[_newMember] == true) { // does nothing if address is already a member
       return();
   }
   else { // adds address to isMember mapping table and pushes the address to the members array
       isMember[_newMember] = true;
       members.push(msg.sender);
   }
}

// @notice Retrieve a list of all members
// @return A list of all member addresses
function getMembers() public view returns(address[]) {
   return(members);
}

modifier requirePassword(string _password) {
   require(keccak256(password) == keccak256(_password));
   _;
}

modifier onlyHost {
   require(msg.sender == host);
   _;
}

// @notice Remove a member (requires 'host' status)
// @param _member Address of the member to be removed
function kickMember(address _member) external onlyHost {
   require(msg.sender != _member); // host cannot kick himself

   for (uint i = 0; i < members.length; i++) { // loops through entire members array, deletes matching address
       if (members[i] == _member) {
           swapReduceIndex(members, i);
       }
   }

   isMember[_member] = false;
}

// @notice Transfer 'Host' role to another member (requires 'host' status)
// @param newHost The address of the member to be granted the 'host' role.
function switchHost(address newHost) external onlyHost {
   require(checkMember(newHost));

   host = newHost;
}

// @notice Delete index of array, swap last index with deleted, remove last index
// @dev Only works with address arrays, inteded to be used as a helper function with removing member addresses
// @param array The array in which to modify
// @param _blankIndex The number of the index to be deleted
function swapReduceIndex(address[] storage array, uint _blankIndex) internal {
   delete array[_blankIndex];
   uint lastIndex = array.length-1;
   array[_blankIndex] = array[lastIndex];
   array.length--;
}

// @notice Get length of chatLog array
// @dev Useful for displaying messages on front-end
function getMessagesLength() external view returns (uint) {
 return(chatLog.length);
}

}

App.js（格式問題，不得不使用github連結）： https ://github.com/PresidentPorpoise/chatroom-react/blob/master/src/App.js

上的mustBeMember修飾符getMessage()會與此有關嗎？

我發現基於權限的修飾符與視圖函式一起使用的方式可能有點奇怪。正如你不會看到拋出但你會得到一些其他數據。

在這種情況下……合約可能期望返回一個字元串，因為它是一個視圖函式，而實際上它由於不滿足修飾符權限要求而正在拋出……這意味著它將返回一個拋出而不是細繩。

引用自：https://ethereum.stackexchange.com/questions/60905