两个html下拉列表事件

小编典典

两个html下拉列表事件

jsp

我有两个html下拉列表，它们的值是使用jsp从数据库中检索的。

<%
  String query =" SELECT question_text,question_id FROM questions WHERE id = ?";
   PreparedStatement stmt = conn.prepareStatement(query);
   stmt.setString(1,request.getParameter("QID"));
   ResultSet rs = stmt.executeQuery();
    if(!rs.next()) {} else {%>
   <form action="#" method="post">
   <p> First Question </p>
   <select name="currentQuestion">
<%do{%> 
<option value="<%=rs.getString("question_id")%>"><%=rs.getString("question_text")%>  </option>
<%}while(rs.next());}%>
</select>

<%                  
  String query =" SELECT question_text,question_id FROM questions WHERE id = ? AND question id != ? ";
  PreparedStatement stmt = conn.prepareStatement(query);
  stmt.setString(1,request.getParameter("QID"));
  stmt.setString(2,CHOOSEN QUESTION);
  ResultSet rs = stmt.executeQuery();
  if(!rs.next()) {} else {%>
  <p> Next Question </p>
 <select name="currentQuestion">
 <%do{%>    
  <option value="<%=rs.getString("question_id")%>"><%=rs.getString("question_text")%></option>
 <%}while(rs.next());}%>
  </select>
  </form>

现在，当用户从第一个下拉列表中选择特定问题时，第二个下拉列表的值不包含该问题怎么办？有谁知道该怎么做？

阅读 256

2020-06-10

共1个答案

小编典典

您无需CHOOSEN QUESTION在代码中的任何位置进行设置。
您忘记了他id和元素中的name标签option。
CHOOSEN QUESTION 是变量的非法名称，因为它包含空格。
您无法以尝试的方式进行操作，因为此代码在用户选择选项之前先在服务器端运行。您可能想做的是加载所有选项（如果它们没有太多），并创建一个JS / jQuery，它将onChange在第一个保管箱发生事件时刷新第二个保管箱（在用户选择一个选项之前-您可能要禁用第二个保管箱）
您可能想要做的另一件事是创建一个form，它将最终将用户的选择提交到JSP（服务器端）。
您还可以使用AJAX来实现相同的行为，您可以在此处找到如何执行此操作的示例。

UPDATE（使用JS更改选项的示例代码）：

<html>
<head>
<script type="text/javascript" >
<!-- hide

function update(x){
    if (x != "null") {
        if (x == "1") {
            var jumpmenu2 = document.getElementById("jumpmenu2");
            var newOption1 = document.createElement('option');
            newOption1.text = "a"; //HERE You'll use newOption1.text = "<?php echo $db_option_text;?>"; 
            newOption1.value = "1"; //HERE You'll use newOption1.text = "<?php echo $db_option_value;?>"; 
            var newOption2 = document.createElement('option');
            newOption2.text = "b"; // same like above
            newOption2.value = "2"; // same like above
            var newOption3 = document.createElement('option');
            newOption3.text = "c"; // same like above
            newOption3.value = "3"; // same like above
            jumpmenu2.remove(jumpmenu2.length-1);
            jumpmenu2.remove(jumpmenu2.length-1);
            jumpmenu2.remove(jumpmenu2.length-1);
            try {
                // For standard browsers
                jumpmenu2.add(newOption1,null);
                jumpmenu2.add(newOption2,null);
                jumpmenu2.add(newOption3,null);
            }
            catch (ex) {
                // For Microsoft Internet Explorer and other non-standard browsers.
                jumpmenu2.add(newOption1);
                jumpmenu2.add(newOption2);
                jumpmenu2.add(newOption3);
            }
        }
        else if (x == "2"){
            var jumpmenu2 = document.getElementById("jumpmenu2");
            var newOption1 = document.createElement('option');
            newOption1.text = "d";
            newOption1.value = "1";
            var newOption2 = document.createElement('option');
            newOption2.text = "e";
            newOption2.value = "2";
            var newOption3 = document.createElement('option');
            newOption3.text = "f";
            newOption3.value = "3";
            jumpmenu2.remove(jumpmenu2.length-1);
            jumpmenu2.remove(jumpmenu2.length-1);
            jumpmenu2.remove(jumpmenu2.length-1);
            try {
                // For standard browsers
                jumpmenu2.add(newOption1,null);
                jumpmenu2.add(newOption2,null);
                jumpmenu2.add(newOption3,null);
            }
            catch (ex) {
                // For Microsoft Internet Explorer and other non-standard browsers.
                jumpmenu2.add(newOption1);
                jumpmenu2.add(newOption2);
                jumpmenu2.add(newOption3);
            }
        }
    }
}

// end hide -->
</script>
</head>
<body>
<form name="form1" id="form1">
<select name="jumpmenu" name="jumpmenu" onChange="update(document.form1.jumpmenu.options[document.form1.jumpmenu.options.selectedIndex].value)">
<option value=1>1</option>
<option value=2>2</option>
</select>
</form>
<select name="jumpmenu2" id="jumpmenu2">
<option value=a id=1>a</option>
<option value=b id=2>b</option>
<option value=c id=3>c</option>
</select>
</body>
</html>

2020-06-10