Question

我终于使用了AJAX，但问题是，每当我在phpMyAdmin中更改一些数据时都不是实时的，我需要在网站上刷新它。

这是我的代码： ajax.js

$(document).ready(function() {
    $.ajax({
        url: "http://localhost/projectZeus/private/data.php",
        method: "GET",
        async: true,
        success: function(data) {
            var energy = [];

            for(var i in data) {
                energy.push(data[i].energyPercent);
            }   

            var chartdata = {
                labels: ["Jan", "Feb", "Mar", "Apr", "May"],
                datasets: [{
                    label: "Harvested",
                    lineTension: 0.3,
                    backgroundColor: "rgba(2,117,216,0.2)",
                    borderColor: "rgba(2,117,216,1)",
                    pointRadius: 6,
                    pointBackgroundColor: "rgba(2,117,216,1)",
                    pointBorderColor: "rgba(255,255,255,0.8)",
                    pointHoverRadius: 8,
                    pointHoverBackgroundColor: "rgba(2,117,216,1)",
                    pointHitRadius: 20,
                    pointBorderWidth: 2,
                    data: energy
                }]
            };

            var ctx = $("#AreaChart");

            var lineChart = new Chart(ctx, {
                type: 'line',
                data: chartdata
            });
        },
        error: function(data) {

        }
    });
});

这是我在 data.php

中的代码

<?php
require_once('initialize.php');

header('Content-Type: application/json');
global $db;

$sql = "SELECT energyPercent FROM energy";
$result = mysqli_query($db, $sql);

$data = array();
foreach($result as $row) {
    $data[] = $row;
}
mysqli_free_result($result);

echo json_encode($data);

＆GT？;

如何在不刷新页面的情况下实时显示？请帮助，谢谢！

Answer 1

您可以使用服务器发送事件代替轮询，这不会对服务器造成太大压力，因为只有在发生新事件（例如新行）时才会发送数据。在这里可以找到更多关于它们的信息：https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events

这是一个例子，因为链接中的那个不太好。

结果将如下所示：

<强> chart.html

<html>

<head>
    <meta charset="UTF-8">
    <title>Server-sent events demo</title>
    <script type="text/javascript" src="https://www.gstatic.com/charts/loader.js"></script>
</head>

<body>

    <div id="chart_div"></div>

    <button>Close the connection</button>

    <script>
        // google chart function
        function chart(chart_data) {
            google.charts.load('current', { packages: ['corechart', 'line'] });
            google.charts.setOnLoadCallback(drawBasic);

            function drawBasic() {

                var data = new google.visualization.DataTable();
                data.addColumn('number', 'X');
                data.addColumn('number', 'Dogs');

                data.addRows(chart_data);

                var options = {
                    hAxis: {
                        title: 'Time'
                    },
                    vAxis: {
                        title: 'Popularity'
                    }
                };

                var chart = new google.visualization.LineChart(document.getElementById('chart_div'));

                chart.draw(data, options);
            }
        }

        // stop button
        var button = document.querySelector('button');

        // the rest is the EventSource, simplez.. 
        var evtSource = new EventSource('sse.php', { withCredentials: true });

        evtSource.onopen = function() {
            chart([])
        }

        evtSource.onmessage = function(e) {
            chart(JSON.parse(e.data))
        }

        evtSource.onerror = function() {
            console.log("EventSource failed.");
        }

        button.onclick = function() {
            console.log('Connection closed');
            evtSource.close();
        }

        /**
        * or you could use addEventListener's to listen to specific events, like event: chartdata (or incase you wanted to send multiple events in the same stream)
        */
        //   evtSource.addEventListener("ping", function(e) {
        //      // do somthing with JSON.parse(e.data)
        //   }, false);      

        //   evtSource.addEventListener("message", function(e) {
        //      // do somthing with JSON.parse(e.data)
        //   }, false);
    </script>
</body>

</html>

然后是事件循环，请注意这不是一个无限循环，也不需要维护它，一旦客户端连接就会创建它，并在客户端断开连接后退出。

<强> sse.php

<?php
// no normal requests
if ($_SERVER['HTTP_ACCEPT'] !== 'text/event-stream') {
    exit();
}

// make session read-only
session_start();
session_write_close();

// disable default disconnect checks
ignore_user_abort(true);

// set headers for stream
header("Content-Type: text/event-stream");
header("Cache-Control: no-cache");
header("Access-Control-Allow-Origin: *");

// a new stream or an existing one
$lastEventId = intval(isset($_SERVER["HTTP_LAST_EVENT_ID"]) ? $_SERVER["HTTP_LAST_EVENT_ID"] : 0);

if ($lastEventId === 0) {
    // resume from a previous event
    $lastEventId = intval(isset($_GET["lastEventId"]) ? $_GET["lastEventId"] : 0);
}

echo ":".str_repeat(" ", 2048)."\n"; // Padding for IE
echo "retry: 2000\n";

// query initial data, or select by event id
$data = [
    [0, 0],
    [1, 5],
    [2, 15],
    [3, 45],
    [4, 34],
    [5, 21],
];

// mock we at event 6
$lastEventId = 6;

// start stream
while (true) {

    // user disconnected, kill process
    if (connection_aborted()) {
        exit();
    } else {

    // force an update, normally you would assign ids to your events/data
    $latestEventId = $lastEventId+1;

    //
    if ($lastEventId < $latestEventId) {

        // generate some data, use array_shift() before to limit array leght whilst rolling
        $data[] = [$latestEventId, rand(0, 100)];

        echo "id: " . $latestEventId . "\n";
        echo "event: message\n";
        echo "data: ".json_encode($data)."\n\n";

        $lastEventId = $latestEventId;
    } else {
        echo "event: ping\n";
    }
  }

  // flush buffer
  ob_flush();
  flush();

  // 2 second sleep
  sleep(2);
}

希望它有所帮助，避免轮询其2018年！

Answer 2

你可以做的是设置一个计时器，然后每n秒/分钟执行一次ajax调用，但如果你的数据太大/太大，这是很昂贵的。我建议使用网络套接字，因为这只会一次打开从服务器端到客户端的网桥连接，然后只花费最少的资源来传输数据。

参考php web socket：http://socketo.me/

或者只是用你的javascript做计时器：

setInterval(function() {
   //call your ajax function here
}, 5 * 1000) //1000 millisecond = 1 second, so multiply by 5 for 5 seconds

Answer 3

有两种方法可以做到这一点（还有更多，我知道）。首先是你创建一个不时执行这个请求的javascript函数（这将花费处理成本）。

function functionAjax () {
    console.log ('Running');
}
var interval = setInterval (Ajax function, 3000);

另一个是你学习时尚的东西，RXJS，一个javascript技术，你需要一个学习的好时机。如果仅用于学习，我建议FireBase (google technology) in which it provides this database in real time

RxJs documentation

使用RxJS进行简单的Ajax实现

总是记得在发布任何内容之前进行搜索，也许你找到了你正在寻找的答案，好学习=）

如何将其置于实时状态？我已经把（async：True）但它不起作用

3 个答案: