PHP生成HTML多选下拉框问题：缺失multiple属性求助

Let's break down what's going wrong here and walk through how to fix it:

First, looking at your generated HTML, there are two clear red flags:

1. The id you set as property_feature got incorrectly changed to property_feature[] — this is a bug in the select_form method's parameter handling, where it's incorrectly syncing the name attribute's suffix to the id.
2. Your multiple => true parameter isn't appearing in the final <select> tag at all, meaning the method isn't properly processing boolean-type attributes.

Step 1: Fix the missing multiple attribute #

Many custom form-building functions struggle with boolean attributes like multiple. Instead of passing a boolean true, try passing the attribute as a string value (since HTML boolean attributes only need to exist to take effect):

$select_features = New_Options::select_form( 
    Property_A::get_property_features( 'id' ), 
    array( 
        'id' => 'property_feature', 
        'name' => 'property_feature[]', 
        'multiple' => 'multiple', // Swap boolean true for string value
        'default' => esc_html__( 'Select', 'name-estate-agent' ), 
        'echo' => false, 
    ) 
);

This is a common fix for form generators that expect explicit string values for attributes instead of boolean flags.

Step 2: Fix the corrupted id attribute #

This issue lives directly in the New_Options::select_form method's code. You'll need to access that class file and inspect how it handles the id parameter:

• It's almost certainly taking the name value (which includes []) and incorrectly applying that suffix to the id — this is invalid HTML, as id attributes shouldn't contain square brackets.
• Look for logic that auto-modifies the id based on the name attribute, and remove or adjust that code to preserve your original id value.

Bonus: Example of proper multiple handling if you control the select_form method #

If you can edit the select_form function, add this logic to ensure boolean attributes like multiple are rendered correctly:

function select_form($options, $args) {
    $attr_string = '';

    // Handle ID
    if (!empty($args['id'])) {
        $attr_string .= ' id="' . esc_attr($args['id']) . '"';
    }

    // Handle Name
    if (!empty($args['name'])) {
        $attr_string .= ' name="' . esc_attr($args['name']) . '"';
    }

    // Handle Multiple (supports both boolean true and string 'multiple')
    if (!empty($args['multiple']) && $args['multiple'] !== false) {
        $attr_string .= ' multiple'; // HTML5 shorthand, or use ' multiple="multiple"' for older standards
    }

    // Add other attribute handling here...

    // Build and return the full select element
    $select = '<select' . $attr_string . '>';
    // Add options logic here...
    $select .= '</select>';
    return $select;
}

内容的提问来源于stack exchange，提问作者Marc Hughes