再從數據庫中獲得數據，更改選擇選項

Question

當我有一個選擇下拉菜單是這樣的：

<select name="city" id="order_form_select"> 
    <option value="" disabled selected>Ort ↓</option> 
    <option>Option 1</option> 
    <option>Option 2</option> 
    <option>Option 3</option> 
    <option>Option 4</option> 
</select> 

而且我得到一些像這樣的單選按鈕：

<?php 
$statement = $pdo->prepare('SELECT some_column FROM my_table WHERE some_value = "abc" AND city = :city'); 
$statement->execute(array('city' => $city)); 
$row = $statement->rowCount(); 
if ($row == 0) { 
    echo "<input type=\"radio\" name=\"something\" value=\"option1\">Option 1</p>"; 
} 

$statement = $pdo->prepare('SELECT some_column FROM my_table WHERE some_value = "xyz" AND city = :city'); 
$statement->execute(array('city' => $city)); 
$row = $statement->rowCount(); 
if ($row == 0) { 
    echo "<input type=\"radio\" name=\"something\" value=\"option2\">Option 2</p>"; 
} 
?> 

正如你所看到的，這些單選按鈕取決於選擇選項。這意味着，只要用戶更改選項選項，PHP代碼就必須刷新，但選擇框的選擇必須保持登錄狀態。

什麼是正確/常用的方法？

Answer 1

Supossing你想每次刷新頁面，你選擇一個值：

1. 創建這個JavaScript

   <script type="text/javascript"> 
   window.onload = function() { 
       var citySelector = document.getElementById('order_form_select'); 
       citySelector.addEventListener('change', function() { 
        if (this.value) { 
         window.location = 'yourphp.php?city=' + this.value 
        } 
       }, false); 
   } 
   </script> 
   

2. 在你的HTML代碼，增值到您的選擇：

<select name="city" id="order_form_select"> 
    <option value="" disabled selected>Ort ↓</option> 
    <option value="City1">Option 1</option> 
    <option value="City2">Option 2</option> 
    <option value="City3">Option 3</option> 
    <option value="City4">Option 4</option> 
</select> 

爲了保持刷新後的值：

<select name="city" id="order_form_select"> 
    <option value="" disabled <?php echo !isset($_GET['city']) ? 'selected' : ''; ?>>Ort ↓</option> 
    <option value="City1" <?php echo isset($_GET['city']) && $_GET['city'] == 'City1' ? 'selected' : ''; ?>>Option 1</option> 
    <option value="City2" <?php echo isset($_GET['city']) && $_GET['city'] == 'City2' ? 'selected' : ''; ?>>Option 2</option> 
    <option value="City3" <?php echo isset($_GET['city']) && $_GET['city'] == 'City3' ? 'selected' : ''; ?>>Option 3</option> 
    <option value="City4" <?php echo isset($_GET['city']) && $_GET['city'] == 'City4' ? 'selected' : ''; ?>>Option 4</option> 
</select> 

編輯後的版本：

如果你想避免使用JavaScript來做到這一點任務，你可以改變你的方式：

<form action="yourphpfile.php" method="GET"> 
    <select name="city" id="order_form_select"> 
    <option value="" disabled <?php echo !isset($_GET['city']) ? 'selected' : ''; ?>>Ort ↓</option> 
    <option value="City1" <?php echo isset($_GET['city']) && $_GET['city'] == 'City1' ? 'selected' : ''; ?>>Option 1</option> 
    <option value="City2" <?php echo isset($_GET['city']) && $_GET['city'] == 'City2' ? 'selected' : ''; ?>>Option 2</option> 
    <option value="City3" <?php echo isset($_GET['city']) && $_GET['city'] == 'City3' ? 'selected' : ''; ?>>Option 3</option> 
    <option value="City4" <?php echo isset($_GET['city']) && $_GET['city'] == 'City4' ? 'selected' : ''; ?>>Option 4</option> 
    </select> 
<input type="submit" value="search by city"> 
</form> 

希望這可以幫到你