>我有一个下拉列表，当所选值等于"关闭"时。我希望启用必填字段。我试过这个
<asp:DropDownList ID="DropDownList9" runat="server"
DataSourceID="SqlDataCaseStatus" DataTextField="CaseStatus"
DataValueField="CaseStatus" Text='<%# Bind("Case_Status") %>' AutoPostBack="False" onchange="if(this.options[this.selectedIndex].text='Closed')ValidatorEnable('RequiredFieldValidatorDateOfWriteOff', true);else ValidatorEnable('RequiredFieldValidatorDateOfWriteOff', false); " >
</asp:DropDownList>
<asp:RequiredFieldValidator ID="RequiredFieldValidatorDateOfWriteOff" runat="server"
ControlToValidate="TextBox13"
ErrorMessage="Date Of Write Off is a Required Field">*</asp:RequiredFieldValidator>
但是当我更改下拉列表时，出现错误：
Microsoft JScript runtime error: Unable to set value of the property 'visibility': object is null or undefined.
任何帮助将不胜感激
首先，在将文本与"已关闭"进行比较时，尝试将 = 更改为 ==。
您需要
使用 Enabled 属性。试一试，代码非常粗糙，仅供参考。我将行为提取到一种方法中，只是为了便于演示。
<body>
<form id="form1" runat="server">
<script type="text/javascript">
function EnableValidator() {
var dropdown1 = document.getElementById('DropDownList1');
var a = dropdown1.options[dropdown1.selectedIndex];
if (a.text == "ValidateYes1") {
document.getElementById("RequiredFieldValidator1").enabled = true;
} else {
document.getElementById("RequiredFieldValidator1").enabled = false;
}
};
</script>
<div>
</div>
<asp:DropDownList ID="DropDownList1" runat="server" onchange="EnableValidator();">
<asp:ListItem>ValidateYes1</asp:ListItem>
<asp:ListItem>ValidateNo2</asp:ListItem>
</asp:DropDownList>
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
<asp:RequiredFieldValidator
ID="RequiredFieldValidator1" runat="server" ControlToValidate="TextBox1" ErrorMessage="RequiredFieldValidator"></asp:RequiredFieldValidator><asp:Button
ID="Button1" runat="server" Text="Button" />
</form>
</body>
ValidatorEnable 需要控制，而您正在传递控制权的 ID
ValidatorEnable('RequiredFieldValidatorDateOfWriteOff', true)
这就是您收到对象空错误的原因。
请将其更改为
ValidatorEnable(document.getElementById('<%= RequiredFieldValidatorDateOfWriteOff.ClientID %>'), true);
<asp:DropDownList ID="DropDownList9" runat="server"
DataSourceID="SqlDataCaseStatus" DataTextField="CaseStatus"
DataValueField="CaseStatus" Text='<%# Bind("Case_Status") %>' AutoPostBack="False" onchange="validateSelection(this);" >
</asp:DropDownList>
<script language="javascript" type="text/javascript">
function validateSelection(drp) {
var vc = document.getElementById('<% = RequiredFieldValidatorDateOfWriteOff.ClientID %>');
if (drp.text == 'Closed') {
ValidatorEnable(vc, true);
}
else {
ValidatorEnable(vc, false);
}
}
</script>