页面刷新后保留下拉列表的选定值

Question

单击页面刷新后，我需要保留下拉列表的选定值。怎么了：从下拉列表中选择一个项目后，页面会自行重新加载，并且下拉列表的值会转到起始位置，尽管该值显示在 url 的末尾。这是我的代码：<script>function refreshPage(passValue){    window.location="index.php?cat_page=admin_post&sw_cat=sw_catn="+passValue;}</script><div class="form-group col-md-4">    <label for="inputState">Your health proplem</label>    <select name="illness_id_cat" class="form-control" onchange="refreshPage(this.value);" ><?php while(mysqli_stmt_fetch($stmt)){    echo "<option value='{$illness_id_cat}'>{$illness_name_cat}</option>";}?>    </select></div>此选项也不起作用：<script>var selectedItem = sessionStorage.getItem("SelectedItem");  $('#dropdown').val(selectedItem);$('#dropdown').change(function() {     var dropVal = $(this).val();    sessionStorage.setItem("SelectedItem", dropVal);});</script><div class="form-group col-md-4">    <label for="inputState">Your health proplem</label>    <select name="illness_id_cat" class="form-control" id="dropdown" ><?php while(mysqli_stmt_fetch($stmt)){    echo "<option value='{$illness_id_cat}'>{$illness_name_cat}</option>";}?>    </select></div>这个我不知道如何实现，什么是“itemname”：<script>var text = localStorage.getItem("itemname");if(text !== null) {    $("select option").filter(function() {        return this.text == text;    }).attr('selected', true);}</script>

Answer 1

一种更传统的方法是使用 PHP，并通过 window.location 命令获取您传递的查询字符串值：

<script>

function refreshPage(passValue){

    window.location="index.php?cat_page=admin_post&sw_cat="+passValue;

}

</script>

<div class="form-group col-md-4">

    <label for="inputState">Your health problem</label>

    <select name="illness_id_cat" class="form-control" onchange="refreshPage(this.value);" >

<?php 

while(mysqli_stmt_fetch($stmt)){

    echo "<option";

    //get the category value from the querystring and check it against the current category value in the loop. If it matches, pre-set the option as selected

    if (isset($_GET["sw_cat"])) {

      if ($_GET["sw_cat"] == $illness_id_cat) echo " selected";

    }

    echo " value='{$illness_id_cat}'>{$illness_name_cat}</option>";

}

?>

    </select>

</div>