刷新页面后，下拉菜单不会通过php保持选中状态

Question

The following script would let the user to chose between on and off. The problem is that the selected value does not stay selected after refreshing the page. Any idea how to fix this?

<form action="Conf.php" name="Calculation" method="post">      
    <?php
        if (isset($_POST['Submit1'])) 
        {
            $Wave = $_POST['WaveHMap'];
        }
    ?>

    <?php 
        $attr = 'selected="selected"'; 
    ?>

    Wave Height Maps: &nbsp;
    <select selected="selected" name="WaveHMap" VALUE="<?PHP print $Wave ; ?>">
        <?php $attr= 'selected="selected"'; ?>
        <option VALUE="On"<?php echo  $Wave == 'On' ? $attr : '';  ?>>On</option>
        <option VALUE="Off"<?php echo  $Wave== 'Off' ? $attr : ''; ?>>off</option> 
    </select>
    <Input Type="Submit" Name="Submit1" Value="Save Parameters">
</form>

Answer 1

Try this

<select  name="WaveHMap" >
        <option VALUE="On" <?php echo $Wave == 'On' ? 'selected' : '';  ?>>On</option>
        <option VALUE="Off" <?php echo $Wave== 'Off' ? 'selected': ''; ?>>off</option> 
    </select>