如何在下拉選擇菜單上添加驗證？

Question

我如何添加驗證下拉選擇菜單我有代碼，我正在努力，但問題是，不工作沒有顯示錯誤消息。如果在點擊添加到購物車按鈕之前不應選擇下拉選擇值，我想顯示錯誤消息？

if(isset($_REQUEST['check'])){ 
if (isset($_POST['size']) && $_POST['size'] == '') { 
echo 'Error, select category'; 
exit; 
}} 

<form action="" id="size1" name="size1" method="post"> 
<select style="background-color:#CCC" 
name="size" id="size" onchange="this.form.submit();" > 
<option value="">Select</option> 
<option <?php if ($_POST['size'] == 'Small') 
print 'selected '; ?> value="Small">Small</option> 
<option <?php if ($_POST['size'] == 'Medium') 
print 'selected '; ?> value="Medium">Medium</option> 
<option <?php if ($_POST['size'] == 'Large') 
print 'selected '; ?> value="Large">Large</option> 
<option <?php if ($_POST['size'] == 'XL') 
print 'selected '; ?> value="XL">XL</option> 
</select> 

<input type="button" class="button1" name="check" 
value="Add To Cart" onclick="addtocart(<?php echo $row3['id'];?>);" /> 
</form 

Answer 1

請嘗試它的工作

它應該是這樣的

<?php 
    if($_POST['country']=="0") 
    { 
     echo 'Error, select category'; 
     //exit; 
    } 
?> 
<form action="" id="size1" name="size1" method="post"> 
<select style="background-color:#CCC" 
name="size" id="size" onchange="this.form.submit();" > 
    <option value="0">Select</option> 
    <option <?php if ($_POST['size'] == 'Small') 
print 'selected '; ?> value="Small">Small</option> 
    <option <?php if ($_POST['size'] == 'Medium') 
print 'selected '; ?> value="Medium">Medium</option> 
    <option <?php if ($_POST['size'] == 'Large') 
print 'selected '; ?> value="Large">Large</option> 
    <option <?php if ($_POST['size'] == 'XL') 
print 'selected '; ?> value="XL">XL</option> 
</select> 
<input type="button" class="button1" name="check" 
value="Add To Cart" onclick="addtocart(<?php echo $row3['id'];?>);" /> 
</form> 

Answer 2

如果我得到你的問題的權利，你希望得到的形式提交之前驗證？如果是這樣，那麼你需要使用客戶端驗證：在HTML

http://docs.jquery.com/Plugins/validation#Example

Answer 3

使U SMaL公司改變這裏

<option value="0">Select</option> 

和喜歡此功能檢查

function check_selected_or_not(){ 
var check_selected = jQuery('#size').val(); 
if (check_selected == 0){ 
    alert('Please select'); 
}else{ 
    alert('sucess'); 
} 

}