Chrome 扩展程序 sendResponse 回调值未发送

Question

我正在编写一个与 gmail api 交互的 chrome 扩展程序（chrome 45 是我的版本），我在将消息从 background.js 发送到我的内容脚本时遇到问题。异步方面是问题所在。回调后如何获取要发送的消息？

//---------in content script---------
chrome.runtime.sendMessage({ messageId: _id }, function (response) {    
    console.log('the respose.messagePayload is: ' + response.messagePayload); 
});

//---------in background script---------
chrome.runtime.onMessage.addListener(function (request, sender, sendResponse) {
    getMessage('me', request.messageId, function (payload) {
        //i want to send my response here
        //this executes and grabs the payload of data from the api, but isn't sending back the message to the content-script
        sendResponse({ messagePayload: payload }); 
    });
    //this synchronous call sends a message to the content-script
    //sendResponse({ messagePayload: "payload" });
    return true;
});

function getMessage(userId, messageId,callback) {
    var request = gapi.client.gmail.users.messages.get({
        'userId': userId,
        'id': messageId
    });
    request.execute(callback);
}

Chrome Extension Message passing: response not sent

Answer 1

您应该在回调中发送sendResponse 函数。

getMessage('me', request.messageId, sendResponse);

然后在您的getMessage 调用完成时执行此操作。

function getMessage(userId, messageId, sendResponse) {
    var request = gapi.client.gmail.users.messages.get({
        'userId': userId,
        'id': messageId
    });

    request.execute(function(response) {
        sendResponse({messagePayload: response.payload});
    });
}

另一种可能的解决方案：

1. 从sender 对象中获取tab id。
2. 只需将选项卡 ID 发送到您的 getMessage 函数，而不是回调函数。
3. 现在，getMessage 函数中的回调函数会将有效负载发送回您的内容脚本。
4. 在您的内容脚本中添加一个类似的 onMessage 侦听器，该侦听器将接收您的负载，然后对负载执行您想要执行的操作。

您的代码如下：

//---------in background script---------
chrome.runtime.onMessage.addListener(function (request, sender,sendResponse) {
    getMessage('me', request.messageId, sender.tab.id);
});

function getMessage(userId, messageId, tabId) {
    var request = gapi.client.gmail.users.messages.get({
        'userId': userId,
        'id': messageId
    });
    request.execute(function(response) {
        // Whatever response you want to sent
        // Below URL explains your response object
        // https://developers.google.com/gmail/api/v1/reference/users/messages#resource
        // Assuming you want to send payload
        chrome.tabs.sendMessage(tab.id, {messagePayload: response.payload});
    });
}

//---------in content script---------
chrome.runtime.sendMessage({ messageId: _id });

chrome.runtime.onMessage.addListener(function (request, sender,sendResponse) {
    // Just to verify that the request is from the getMessage callback
    // Because this will listen to all request from your extension
    if (request.messagePayload) {
        console.log('the respose.messagePayload is: ' + request.messagePayload);
    }
});

我希望这会有所帮助。