MultiSelectDropDown:用户控件:对象引用问题 [英] MultiSelectDropDown :user control : object reference problem

问题描述

我正在使用用户控件进行多个下拉选择

Hi,

I am using the user control for multiple dropdown selection

protected void Page_Load(object sender, EventArgs e)
    {

 MultiSelectDropDown1.Clear(); //Error
MultiSelectDropDown1.List.Items.Add(new System.Web.UI.WebControls.ListItem(new System.Web.UI.WebControls.ListItem("Apple", "1"));
MultiSelectDropDown1.List.Items.Add(new System.Web.UI.WebControls.ListItem("Grapes", "2"));

}

But getting exception at the first line itself.
Error:- Object reference not set to an instance of an object.

Please provide me the solution for this problem.

Thanks in advance.

推荐答案

问题很明显，如果您不这样做的话"不知道它是什么，您不应该编写代码.尝试阅读入门书籍，学习使用调试器，然后从那里开始工作. MultiSelectDropDown1不仅被愚蠢地命名，而且它为null，因此显然没有为其分配值，这使我想知道它的来源，显然不是aspx.

Your problem is so obvious, if you don''t know what it is, you should not be writing code. Try reading a beginner book, learn to use the debugger, and then work from there. MultiSelectDropDown1 is not only stupidly named, it is null, so it''s obviously not been assigned a value, which makes me wonder where it comes from, obviously not the aspx.

用户控件注册为:-


]]>

========================
并用作:-

< asp:content id ="Content2" contentplaceholderid ="ContentPlaceHolder1" runat ="Server" xmlns:asp =#unknown">
< cc2:multiselectdropdown id ="MultiSelectDropDown1" runat ="server" xmlns:cc2 =#unknown">

User control is Registered as :-


]]>

==========================
And used as :-

<asp:content id="Content2" contentplaceholderid="ContentPlaceHolder1" runat="Server" xmlns:asp="#unknown">
<cc2:multiselectdropdown id="MultiSelectDropDown1" runat="server" xmlns:cc2="#unknown">

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