在DropDownList中选择值 [英] Select Value in DropDownList

问题描述

我有一个名为master_litigants的主表
我将这些数据填充到一个下拉列表中
表格如下:-
Litigant_id Litigant_type Litignat_value
1 PETITIONER P
2响应R
3第三方T

ddlLitigantType.DataTextField ="Litigants_Type";
ddlLitigantType.DataValueField ="Litigants_value";
ddlLitigantType.DataBind();
我已将is(P，R，T)的值插入其他表中

为了更新，我从其他位置读取了数据，并希望显示在下拉列表中
为此，我正在使用代码
1)ddlLitigantType.SelectedValue = dr ["Litigant_type"].ToString();
和
2)ddlLitigantType.Items.FindByValue(dr ["Litigant_type"].ToString()).Selected = true;
两个代码都显示错误:

1)第一个代码的错误是:-ddlLitigantType的SelectedValue无效，因为它不存在于项目列表中.参数名称:值(但是ddlLitigant仅在页面加载中加载，因此存在该值)
2)第一个代码的错误是:-对象引用未设置为对象的实例.

我做错了吗r还有其他方法吗?
请帮助我

I have a master table called master_litigants
i m populating this data into a dropdown list
the table as follows:-
Litigant_id Litigant_type Litignat_value
1 PETITIONER P
2 RESPONDENT R
3 THIRD PARTY T

ddlLitigantType.DataTextField = "Litigants_Type";
ddlLitigantType.DataValueField = "Litigants_value";
ddlLitigantType.DataBind();
I have inserted Value that is(P,R,T) into other table

for updation i read the data from other and want to show in the dropdown list
for that i m using code
1)ddlLitigantType.SelectedValue = dr["Litigant_type"].ToString();
and
2)ddlLitigantType.Items.FindByValue(dr["Litigant_type"].ToString()).Selected = true;
both code showing Error:

Error for 1)st code is:-ddlLitigantType has a SelectedValue which is invalid because it does not exist in the list of items. Parameter name: value(But the ddlLitigant is loaded in the page load only so the value is present)
Error for 2)nd code is:-Object reference not set to an instance of an object.

m i doing it wrong r is there any other way of doing it.
plZ help me

推荐答案

此代码"ddlLitigantType.SelectedValue = dr ["Litigant_type"].ToString();如果您在绑定下拉列表项后将其写入，则可以使用.但是，它应该存在于下拉列表项中.

This code "ddlLitigantType.SelectedValue = dr["Litigant_type"].ToString();" works if u write it after binding dropdownlist items. However it should exist in the dropdownlist items.

您必须在Dropdownlist和数据库中都具有匹配的Item.并且在执行下面的行之前，应先绑定数据

You must have matching Items in both Dropdownlist and the database.and you should bind data before execute below lines

ddlLitigantType.DataTextField = "Litigants_Type";
ddlLitigantType.DataValueField = "Litigants_value";

但似乎您没有匹配的值.那就是为什么您遇到第二个错误

but it seems you don''t have matching values. thats why you are getting 2nd error

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