下拉列表ajax

Question

有人可以查看我的代码，看看是什么导致第二次下拉不填充？我不太清楚为什么。先感谢您。

查看：

    <div id="finder">
    <div class="form">
    <select id="brand" name="brand" onchange="myFunction()" >
        <option value="">&nbsp;&nbsp;- Printer Brand -&nbsp;&nbsp;</option>
        <?php foreach ($categories as $category_1) { ?>
        <?php if ($category_1['category_id'] == $category_id) { ?>
        <option value="<?php echo $category_1['category_id']; ?>" selected="selected"><?php echo $category_1['name']; ?></option>
        <?php } else { ?>
        <option value="<?php echo $category_1['category_id']; ?>"><?php echo $category_1['name']; ?></option>
        <?php } ?>
        <?php } ?>
    </select>
    </div>

    <br>

<div class="form">
    <select name="printerSeries" id="printerSeries">
    <option value="">&nbsp;&nbsp;- Printer Series -&nbsp;&nbsp;</option>

    </select>
  </div>
  <br>

Javascript ajax call

<script type="text/javascript">
function myFunction(){
var brand_id = document.getElementById("brand").value;
		$.ajax({
		url: 'index.php?route=common/home/getSeries&brand_id=' + brand_id, 
		type: 'post',
		dataType: 'json',
		success: function(json) {
			$('#printerSeries').append('<option value="<?php echo $json['category_id']; ?>"  Selected="selected"><?php echo $json['name']; ?></option>');
		
		}
		error: function(){
			alert('error');
		}		
	});

}
</script>

这是接收json请求的控制器函数

    public function getSeries($brand){
$brand_id = $_POST['brand_id'];
$json = array();
$categories_2 = $this->model_catalog_category->gettoner($brand_id);

    foreach ($categories_2 as $category_2) {

        $json = array(
            'category_id' => $category_2['category_id'],
            'name'        => $category_2['name'],
        );


}
    $this->response->addHeader('Content-Type: application/json');
    $this->response->setOutput(json_encode($json));


    }

Answer 1

此问题可能由以下功能引起：$ this-＆gt; model_catalog_category-＆gt; gettoner（$ brand_id）;

检查函数是否在每种情况下都返回一个值。如果没有，只需返回任何值。您的下拉菜单将会出现。