Re: Exception handling - C# Discussion Boards

Hi all,

I am getting null exception in try block.
what i want to do is:
not breaking the normal execution and run the next line of code.

dont know what to do?

please help me.

thanks in advance
Preetpal Kaur Parhar

The easiest way is usually to check for null before trying to use the reference.

I don't think that it's useful to be more specific than that without seeing any actual code.

Despite everything, the person most likely to be fooling you next is yourself.

thanks a lot...
but i have thought of this way before.
and the thing is i have around 20 of fields n i cannot put the check before everything.

so need to do something which applies to all.

can u please guide me little more?

You have no other choice but to fix your code. You cannot jump back into a try block, your other option is to put a try block around each attempt to assign, and it sounds in general like you're overusing try blocks to allow you to write bad code.

One thing you can do, is write a helper method that takes two values and does the null check and only assigns if it's not null, and call this method 20 times.

Christian Graus

Driven to the arms of OSX by Vista.

If you apply something to all the code, it can't apply to each of the fields. To handle an exception separately for each field, you would need a try...catch for each of them, which would be a lot more code than checking for a null reference if it's done correctly.

Despite everything, the person most likely to be fooling you next is yourself.

preetpal wrote:
i cannot put the check before everything.

Why not??

There might be another way, depending on your concrete situation. But if it appears that sth. can be null, you simply have to check for it. No escape, no excuse. Everything else is just incorrect code!

Regards
Thomas

www.thomas-weller.de

Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning.
Programmer - an organism that turns coffee into software.

Provide the code that is causing the problem and someone may be able to help you better.

"The clue train passed his station without stopping." - John Simmons / outlaw programmer

"Real programmers just throw a bunch of 1s and 0s at the computer to see what sticks" - Pete O'Hanlon

"Not only do you continue to babble nonsense, you can't even correctly remember the nonsense you babbled just minutes ago." - Rob Graham

preetpal wrote:
not breaking the normal execution and run the next line of code.

It is generally no good idea to ignore an exception. If you don't care in a certain situation if sth. is null, then you should check that before with an if-statement.

What you are describing sounds like a flaw in your control flow...

Regards
Thomas

www.thomas-weller.de

Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning.
Programmer - an organism that turns coffee into software.

thx

my code which is causing error is below
XmlNodeList rows = iElement.SelectNodes("./TBODY/TR");
_callerFirstName = rows[2].ChildNodes[0].InnerText.Trim();
_callerLastName = rows[2].ChildNodes[1].InnerText.Trim();
_callerPhone = rows[4].ChildNodes[0].InnerText.Trim();
_callerDept = rows[4].ChildNodes[1].InnerText.Trim();
_callerUserID = rows[6].FirstChild.InnerText.Trim();//error
_callerEMail = rows[8].FirstChild.InnerText.Trim();

user id id null in the html page so i am getting error Frown | :(

its like i can get anything as blank in html page as of now userid is blank

I'm afraid I don't really get your problem. You are trying to dereference sth. that is null, so you get an exception. This is absolutely correct. I'd be very afraid if I'd see sth. other than that. As I said: Check for null at the appropriate places! Don't try to save typings in the first place.

Remember:
Programming is not about writing the shortest possible code, but about writing code as correct, robust, and readable as possible.

Regards
Thomas

www.thomas-weller.de

Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning.
Programmer - an organism that turns coffee into software.

preetpal wrote:
user id id null in the html page so i am getting erro

So, this is an ASP.NET question ?

This code just plain sucks. You should not be accessing child nodes by index, but by name. Your code is illegible and hard to maintain.

Christian Graus

Driven to the arms of OSX by Vista.

string getVal(XmlNode node) {
    return (node == null ? null : node.InnerText.Trim);
}

// in your code: _callerFirstName = getVal(rows[2].ChildNodes[0]);

My LinkedIn Profile

Hello ,
I want to thank you for your great Facebook articles.
I have a question on FaceBook API , is it possible to know if a friend is connected to facebook with a c# code ? I watched all methods , i don't find solution.

Thanks

Si tu aimes ce que tu fais , tu finis par réussir !
(french proverb of David Zenou)

I haven't written any facebook articles. If you want to speak to someone who wrote an article, use the forum provided under the article itself.

Christian Graus

Driven to the arms of OSX by Vista.

Christian Graus wrote:
any facebook articles

Are there any submitted here on CP? Never really noticed it if there has been.

"The clue train passed his station without stopping." - John Simmons / outlaw programmer

"Real programmers just throw a bunch of 1s and 0s at the computer to see what sticks" - Pete O'Hanlon

"Not only do you continue to babble nonsense, you can't even correctly remember the nonsense you babbled just minutes ago." - Rob Graham

He said ' I love your facebook articles' so I just assumed another guy who thinks CP is a sweatshop where the same people write the articles and work the forums.

Christian Graus

Driven to the arms of OSX by Vista.

Hmmm, just did a search on facebook api and 5 articles did pop up. The simple WPF facebook application one looks kind of interesting.

"The clue train passed his station without stopping." - John Simmons / outlaw programmer

"Real programmers just throw a bunch of 1s and 0s at the computer to see what sticks" - Pete O'Hanlon

"Not only do you continue to babble nonsense, you can't even correctly remember the nonsense you babbled just minutes ago." - Rob Graham

here's my sample program in my addProducts..
if i click my save button.. when i run it, i prompts an error message that reader is closed.. can anyone help me?

private void btnSaveChangesObject_Click(object sender, EventArgs e)
{
try
{
clsPublic.objConn.Open();
OdbcCommand com = new OdbcCommand("Select Name from Products", clsPublic.objConn);

OdbcDataReader read;
read = com.ExecuteReader();

while (read.Read())
{
if (read[0].ToString() == txtprodname.Text)
{
MessageBox.Show("Error!");

}

else

try
{
String strSQL;

if (clsPublic.BoolUpdateProductsRec == true)
{

strSQL = "Update products Set Id = '" + txtprodId.Text +
"', Name = '" + txtprodname.Text +
"', Description = '" + txtdesc.Text +
"', Type = '" + txttype.Text +
"', Price = '" + txtprice.Text +
"', Brand = '" + txtbrand.Text +
"' where Id = '" + txtprodId.Text + "'";
}

else
{

strSQL = "Insert Into products Values('" + txtprodId.Text +
"', '" + txtprodname.Text +
"', '" + txtdesc.Text +
"', '" + txttype.Text +
"', '" + txtprice.Text +
"', '" + txtbrand.Text + "')";
}

SaveObjectRecord(strSQL);
btnCloseSaveChangesObject.PerformClick();

}

catch (NullReferenceException NRE)
{
MessageBox.Show("Error:" + NRE.Message, "ARTM", MessageBoxButtons.OK, MessageBoxIcon.Error);
}

}

}
catch (NullReferenceException NRE)
{
MessageBox.Show("Error:" + NRE.Message, "ARTM", MessageBoxButtons.OK, MessageBoxIcon.Error);
}
}

Looks messy. When do you get the error ? Which catch block is it in ?

Christian Graus

Driven to the arms of OSX by Vista.

Christian Graus wrote:
Looks messy.

Yes, it does. Not to mention the sql injection attack vulnerability Eek! | :eek:

"The clue train passed his station without stopping." - John Simmons / outlaw programmer

"Real programmers just throw a bunch of 1s and 0s at the computer to see what sticks" - Pete O'Hanlon

"Not only do you continue to babble nonsense, you can't even correctly remember the nonsense you babbled just minutes ago." - Rob Graham

I've given up on pointing that out. People who hire teams who have no idea how to write secure code, deserve what they get.

Christian Graus

Driven to the arms of OSX by Vista.

Christian Graus wrote:
given up on pointing that out

Same here. Used to point people towards Colin's article and some were grateful and others, well, they didn't really care ( at least until someone tosses a

'; drop database master; --

or some crap like that into the query string ).

"The clue train passed his station without stopping." - John Simmons / outlaw programmer

"Real programmers just throw a bunch of 1s and 0s at the computer to see what sticks" - Pete O'Hanlon

"Not only do you continue to babble nonsense, you can't even correctly remember the nonsense you babbled just minutes ago." - Rob Graham

I suppose that the SaveObjectRecord method closes the connection? Then you will get the error after saving a record when you try to continue to read the rest of the records.

Do you really indend to update/insert the same record over and over again, once for each record in the Products table? Or did you accidentally put the code that saves the record inside the loop instead of after the loop?

Despite everything, the person most likely to be fooling you next is yourself.

Don't build query string on the fly, use parametrized queries: Parametrized Queries VS String Concatenation[^]

Giorgi Dalakishvili

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Asynchronous Registry Notification Using Strongly-typed WMI Classes in .NET [^]

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Hi guys,
I'm starting out with C# and since I dont like messing with simple things ( Big Grin | :-D

) I'm already "playing" with threads and delegates. In my program I create a net socket, connect to a server and start to receive data async with BeginReceive.
When a message is received, the program(secondary thread of BeginReceive) pass it to RlsInsert(message) that split it with a regular expression and populate a listview. It seems to work perfectly but randomly VS pops up with an exception about NullReferenceException and tells me to use the "new" keyword, but as you can see I'm already using it:

//Add item to the list view
public delegate void RlsInsertCallback(string text);

public void RlsInsert(string text)
{
if (this.InvokeRequired)
this.Invoke(new RlsInsertCallback(this.RlsInsert),new object[] { text }); <--- expection on this line pointin to object[]
else
{
**more code that check text with regular expression, split text and populate subitems etc
lvRelease.Items.Add(aItem);

}
}

Can anybody tell me what I am doing wrong? Because I cant figure it out. It works and then It crashes after a while.
Sorry if this has already been asked, I did used search but I could not find anything that really match my problem.
Thank you in advance.
Matteo