为什么OuterHTML功能会导致错误 [英] Why the OuterHTML feature leads to an Error

问题描述

我一直在尝试在HTML代码中更改选择标记的HTML代码，但每当我这样做时，



对象引用未设置到一个对象的实例



错误发生。这是C＃代码：

I have been trying to change the HTML code of a select tag in an HTML code but whenever I do that the

"Object reference not set to an instance of an object"

error occurs.This is the C# code:

public void SetDefaultValue(string ControlID,string Value)
 {
HtmlDocument doc = webBrowser1.Document;
HtmlElement list = doc.GetElementById(ControlID);
list.OuterHTML+= Value;         
 }
private void Form1_Load(object sender, EventArgs e)
{            
    htmlLoadWebbrowser1.SetDefaultValue("D8876943-5861-4D62-9249-C5FEF88219FA", "<SELECT id=\"D8876943-5861-4D62-9249-C5FEF88219FA\" multiple size=\"4\" name=\"drop1\"> <OPTION value=\"3\">item 3</OPTION></SELECT>");            
}

该函数应该改变HTML页面中select标签的代码，它通过controlID接收控件的ID并生成内部代码由价值。我怀疑我需要在其他地方调用该函数，问题是我不知道在哪里。谢谢。

The function is supposed to change the code of an select tag in an HTML page,it receives the ID of the control by "controlID" and generates the inner code by "Value". I suspect that I need to call the function elsewhere,the problem is that I do not know where. Thank you.

推荐答案

对象引用未设置为对象的实例



当您尝试使用属性或调用null对象的方法时，会发生此错误。更多细节：此处 [ ^ ]



Visual Studio DEBUGGER的简单使用可以告诉你对象因为它正在发生。只需查看堆栈跟踪并将调试器放在该行上即可。检查该行的对象，看看是否有任何一个为null，并且您正在尝试使用该对象属性。处理相同。

Object reference not set to an instance of an object

This error happens when you try to use a property or call a method of an object that is null. More details: here[^]

A simple use of Visual studio DEBUGGER can tell you the object because of which it is happening. Just look at the stack trace and put a debugger on that line. Check the objects of that line and see if any one is null and you are trying to use that objects property. Handle the same.

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