Html 选择页面重置时字段重置

我编写了一个代码，用户可以在选择字段中选择一个选项。它有onchange=location=this.options[this.selectedIndex].value； 选择标记和每个选项标记都有自己的值

                    <?php

                    parse_str($_SERVER['QUERY_STRING']);

                    require ('../config.php');
                     /* connect and select db codes*/

                    $dbresult=mysqli_query($connection, "SELECT * FROM services");

                    while($row = mysqli_fetch_array($dbresult)){
                            $order_name = $row['name'];
                            $order_id = $row['id'];
                            echo "<option value=\"NewOrder.php?service=$order_id&quantity=1th\">$order_name</option>";
                    }
                    ?>

                            </select><br/>


  /* ...continue of my codes...*/

所以我的问题是：

                    <?php

                    parse_str($_SERVER['QUERY_STRING']);

                    require ('../config.php');
                     /* connect and select db codes*/

                    $dbresult=mysqli_query($connection, "SELECT * FROM services");

                    while($row = mysqli_fetch_array($dbresult)){
                            $order_name = $row['name'];
                            $order_id = $row['id'];
                            echo "<option value=\"NewOrder.php?service=$order_id&quantity=1th\">$order_name</option>";
                    }
                    ?>

                            </select><br/>


  /* ...continue of my codes...*/

当我从这个选择字段中选择一个选项时，它会将查询字符串发送到同一个页面，我希望我选择的选项保持选中状态，但当页面重置时，选择字段被重置。 事实并非如此，但我认为我在代码中做了一些改变，但我找不到，这就产生了问题

                    <?php

                    parse_str($_SERVER['QUERY_STRING']);

                    require ('../config.php');
                     /* connect and select db codes*/

                    $dbresult=mysqli_query($connection, "SELECT * FROM services");

                    while($row = mysqli_fetch_array($dbresult)){
                            $order_name = $row['name'];
                            $order_id = $row['id'];
                            echo "<option value=\"NewOrder.php?service=$order_id&quantity=1th\">$order_name</option>";
                    }
                    ?>

                            </select><br/>


  /* ...continue of my codes...*/

这是我的密码：

                    <?php

                    parse_str($_SERVER['QUERY_STRING']);

                    require ('../config.php');
                     /* connect and select db codes*/

                    $dbresult=mysqli_query($connection, "SELECT * FROM services");

                    while($row = mysqli_fetch_array($dbresult)){
                            $order_name = $row['name'];
                            $order_id = $row['id'];
                            echo "<option value=\"NewOrder.php?service=$order_id&quantity=1th\">$order_name</option>";
                    }
                    ?>

                            </select><br/>


  /* ...continue of my codes...*/

---

必须指定在属性中选择该选项。 因此，对于要选择的选项，需要添加selected=selected属性

                    <?php

                    parse_str($_SERVER['QUERY_STRING']);

                    require ('../config.php');
                     /* connect and select db codes*/

                    $dbresult=mysqli_query($connection, "SELECT * FROM services");

                    while($row = mysqli_fetch_array($dbresult)){
                            $order_name = $row['name'];
                            $order_id = $row['id'];
                            echo "<option value=\"NewOrder.php?service=$order_id&quantity=1th\">$order_name</option>";
                    }
                    ?>

                            </select><br/>


  /* ...continue of my codes...*/

在PHP中，这可以在echo语句之前使用类似的方法完成，如果订单id与查询字符串中指定的订单id相同，它将选择此选项

                    <?php

                    parse_str($_SERVER['QUERY_STRING']);

                    require ('../config.php');
                     /* connect and select db codes*/

                    $dbresult=mysqli_query($connection, "SELECT * FROM services");

                    while($row = mysqli_fetch_array($dbresult)){
                            $order_name = $row['name'];
                            $order_id = $row['id'];
                            echo "<option value=\"NewOrder.php?service=$order_id&quantity=1th\">$order_name</option>";
                    }
                    ?>

                            </select><br/>


  /* ...continue of my codes...*/

  if($service == $order_id){
     $selected = "selected";
  }
  else{
     $selected = "";
  }

在你的回音声明中

                    <?php

                    parse_str($_SERVER['QUERY_STRING']);

                    require ('../config.php');
                     /* connect and select db codes*/

                    $dbresult=mysqli_query($connection, "SELECT * FROM services");

                    while($row = mysqli_fetch_array($dbresult)){
                            $order_name = $row['name'];
                            $order_id = $row['id'];
                            echo "<option value=\"NewOrder.php?service=$order_id&quantity=1th\">$order_name</option>";
                    }
                    ?>

                            </select><br/>


  /* ...continue of my codes...*/

   echo "<option value=\"NewOrder.php?service=$order_id&quantity=1th\" ".$selected.">$order_name</option>";