javascript 错误：无法读取 null 的属性“选项”
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javascript error: Cannot read property 'options' of null
提问by user123456789
I have a GridView that has a column with a textbox where the user can enter a value and a column with a dropdownlist. If the user enter a values that is not equal to 1 in the textbox, they must select a value from the dropdownlist. The default value in the DDL is "Select" which is just an empty value that was coded in: ddlReasons.Items.Insert(0, new ListItem("Select"));. The DDL is created dynamically but select will always be the default value.
我有一个 GridView，它有一列带有一个文本框，用户可以在其中输入一个值和一个带有下拉列表的列。如果用户在文本框中输入一个不等于 1 的值，他们必须从下拉列表中选择一个值。DDL 中的默认值是“Select”，它只是一个编码为的空值：ddlReasons.Items.Insert(0, new ListItem("Select"));。DDL 是动态创建的，但 select 将始终是默认值。
function UpdateSerialQtyRcvd(SerNoID, QtyRcvd) {
if (QtyRcvd != 1) {
var ddl = document.getElementById("ddlReasons");
var selectedValue = ddl.options[ddl.selectedIndex].value;
if (selectedValue == "Select") {
alert("Must select reason");
}
}
else {
PageMethods.UpdateSerialQtyRcvdUserControl(SerNoID, QtyRcvd, OnUpdateSuccess, OnUpdateFail);
}
}
If the user enters a value that is not 1 then I need to check what value is in the DDL. If "Select" is the value I need the user to select something else in the DDL but I am getting this error on the line var selectedValue = ddl.options[ddl.selectedIndex].value;
如果用户输入的值不是 1，那么我需要检查 DDL 中的值。如果“选择”是我需要用户在 DDL 中选择其他内容的值，但我在线上收到此错误var selectedValue = ddl.options[ddl.selectedIndex].value;
Uncaught TypeError: Cannot read property 'options' of null
未捕获的类型错误：无法读取 null 的属性“选项”
Code for dropdownlist:
下拉列表的代码：
<asp:TemplateField HeaderText="Reason">
<ItemTemplate>
<asp:DropDownList ID="ddlReasons" runat="server" class="ReasonDDL" ></asp:DropDownList>
</ItemTemplate>
</asp:TemplateField>
采纳答案by christiandev
You'll need to get the ClientId...
您需要获取ClientId...
Javascript:
Javascript:
var ddl = document.getElementById("<%=ddlReasons.ClientID%>");
JQuery:
查询：
var ddl = $('#<%=ddlReasons.ClientID%>');
Check out the MSDN documentationon how to access the Client ID and the different settings.
查看MSDN documentation有关如何访问客户端 ID 和不同设置的信息。
回答by Parthipan Natkunam
One more way to do it using JQuery:
使用JQuery 的另一种方法：
var ddlReason = $("[id*=ddlReasons]");
var selectedValue = ddlReason.val();
