仅当 PHP 变量具有值时才生成图表

Question

我正在使用 php 和 Charts.js 生成基于 html <select> 的数据图表我的问题是即使没有从 html <select> 页面底部显示空白图表，而不是在我的 else {} 块中显示 echo 语句。

如果从 html <select>

<body>
    <form method="POST">
    <p>Select Sales Name:
            <select name="Name">
                <option value="">Select A Name...</option>
                <option value="Joe">Joe</option>
                <option value="Jack">Jack</option>
                <option value="Jerry">Jerry</option>
                <option value="Jimmy">Jimmy</option></select></p>
        <input type="submit" name="submit" value="Show Me">
    </form>
</body>
<?php
if (isset($_POST['submit'])) {
    $whatsalesprsn = $_POST['Name'];
    if ($whatsalesprsn == "Joe") { $region = "East"; }
    if ($whatsalesprsn == "Jack") { $region = "West"; }
    if ($whatsalesprsn == "Jerry") { $region = "North"; }
    if ($whatsalesprsn == "Jimmy") { $region = "South"; }
    if (isset($region)) {
        $query = "Select * from salesdata where salesregion = '$region'";
        $db->setQuery($query);
        $rows = $db->loadColumn();
        $output = array();
        for ($i = 0; $i <= 3; $i++) {
        $column = $db->loadColumn($i);
        array_push($output, $column);
    }
    $data = json_encode($output[0]);
    } else { echo "PLease select a sales person to display data for."; }
}
?>

<html>
    <head>
        <script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.6.0/Chart.min.js"></script>
    </head>
    <body>
        <div id="container" style="width: 75%;">
            <canvas id="canvas"></canvas>
        </div><script>
            //JavaScript to generate chart
        </script>
    </body>
</html>

Answer 1

您一定是在某个地方打电话 new Chart(...)。如果您在没有传递有效数据的情况下这样做，那么 Chart.js 将创建一个空图表（因为这是您告诉它要做的）。

如果您没有获得有效数据（即 <select> 元素中未选择任何内容），请不要实例化 Chart.js。类似于：

if (data.length) {
    new Chart(...);
}

Answer 2

您需要添加 if statement 和 empty() function. SO if if statement will check $whatsalesprsn variable if is empty or not by using empty() 功能

if(!empty($whatsalesprsn)){
 $whatsalesprsn = $_POST['Name'];
    if ($whatsalesprsn == "Joe") { $region = "East"; }
    if ($whatsalesprsn == "Jack") { $region = "West"; }
    if ($whatsalesprsn == "Jerry") { $region = "North"; }
    if ($whatsalesprsn == "Jimmy") { $region = "South"; }
    if (isset($region)) {
        $query = "Select * from salesdata where salesregion = '$region'";
        $db->setQuery($query);
        $rows = $db->loadColumn();
        $output = array();
        for ($i = 0; $i <= 3; $i++) {
        $column = $db->loadColumn($i);
        array_push($output, $column);
    }
    $data = json_encode($output[0]);
}

仅当 PHP 变量具有值时才生成图表

Only Generate Chart If PHP Variable Has Value

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