Why the OuterHTML feature leads to an Error

Question

0.00/5 (No votes)

See more:

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:

C#

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>");            
}

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.

Posted 26-Apr-13 21:52pm

pedramham

Updated 27-Apr-13 0:06am

Sandeep Mewara

v2

Add a Solution

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Sandeep Mewara · Accepted Answer · 2013-04-27T00:07:00

Solution 1

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.

Posted 27-Apr-13 0:07am

Sandeep Mewara

Comments

pedramham 27-Apr-13 6:38am

@Sandeep:Thank you but my problem is something else.
My code will work like this:
private void Form1_Load(object sender, EventArgs e)
{
GenerateHTMLClass gnh = new GenerateHTMLClass(@"D:\test2.xml", @"D:\test.htm");
htmlLoadWebbrowser1.LoadHTML(@"D:\test.htm");
MessageBox.Show("");
htmlLoadWebbrowser1.SetListboxHTML("D8876943-5861-4D62-9249-C5FEF88219FA", "<SELECT id=D8876943-5861-4D62-9249-C5FEF88219FA title=\"Type of property\" name=PropertyType type=\"select\" value=\"\" width=\"10\"><OPTION value=\"1\">item 1</OPTION><OPTION value=\"2\">item 2</OPTION><OPTION value=\"3\">item 3</OPTION></SELECT>");
}

I mean when I add messagebox.show() to my code it works.
What can I do to get it done without messagebox

Sandeep Mewara 27-Apr-13 6:50am

I don't see the information that 'it works' when you add messagebox shared before.

Now, if you say that it works with above code and not with code in question, then it must be some race condition. Try to put some delay/sleep and see.