simple question about ref with object?? PLEASE HELP

[giddy]

ok i have a datagridview in my app and i have a function defined like
so:
public void FillColumns(ref DataGridView theDGV)
when i call it ... like this :
FillColumns(ref dataGridView2);

i get : Object reference not set to an instance of an object.

i dont get it , is'nt my datagridview defined in form.designer.c s????
-private System.Windows. Forms.DataGridV iew dataGridView2;

PLEASE HELP ME OUT.. i need this in a hurry!

Thanks
Gideon

[Jon Skeet [C# MVP]]

Kevin Spencer <sp**@uce.govwr ote:

Now, don't put words in my mouth. I pointed out that it wasn't necessary to
pass the object by reference because I don't know much else about the
problem, but one important aspect to problem-solving is to simplify the
problem. In this case, passing by reference was unnecessary, and, depending
on other factors, *may* have contributed to the problem in some indirect
way. By eliminating that one step, the problem is at least simplified.

But we don't know whether passing by reference was unnecessary or not -
we've only seen the call, not what the method actually did. If the OP
had posted the code to FillColumns, we might well have seen that it was
unnecessary, but as he hasn't, we can't tell.

If you will re-read my post, you will see that the remark about not needing
to pass the DataGridView by reference was the only remark I made.

Indeed, and we don't know whether it was accurate or not - but I
believe it gave an inaccurate impression.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
If replying to the group, please do not mail me too

[Jon Skeet [C# MVP]]

giddy <gi*******@gmai l.comwrote:

Firstly , i need to use ref because i have a 2 datagrid views that have
to be filled more or less the same way , and i could have a 3rd one
soon. Whatever is common between the dgvs goes into one function and
then obviously has to change the datagridview passed to it.

That in itself doesn't mean you have to pass by reference.

It's very important that you understand reference types and passing by
reference. See
http://www.pobox.com/~skeet/csharp/parameters.html

I just tried the whole thing without the ref keyword both in the
function and when i call it. and i GET THE SAME EXCEPTION.

the exception occurs inside the function on the first line :
public void FillColumns(ref DataGridView theDGV)
{
theDGV.ColumnCo unt =
dataSet.Tables["customers"].Columns.Count; //THIS IS THE LINE.

Okay - in that case, either theDGV is null, or dataSet is null, or
dataSet.Tables["customers"] is null, or
dataSet.Tables["customers"].Columns is null.

You should be able to tell that in the debugger.

In Form1.Designer. cs :
the dgv is declared like this : private
System.Windows. Forms.DataGridV iew dataGridView2;

and its properties are set like this :
this.dataGridVi ew2.ColumnHeade rsHeightSizeMod e =
System.Windows. Forms.DataGridV iewColumnHeader sHeightSizeMode .AutoSize;
this.dataGridVi ew2.Location = new System.Drawing. Point(5, 50);
this.dataGridVi ew2.Name = "dataGridView2" ;

so why is it null!

Well, we don't know for sure that it's that that's null - see above for the options.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
If replying to the group, please do not mail me too

[Kevin Spencer]

Hi Jon,

But we don't know whether passing by reference was unnecessary or not -
we've only seen the call, not what the method actually did. If the OP
had posted the code to FillColumns, we might well have seen that it was
unnecessary, but as he hasn't, we can't tell.

I'll have to admit, I made an educated guess. It was highly unlikely (IMHO),
but as I said, I made an educated guess that there was no need in this case.

Indeed, and we don't know whether it was accurate or not - but I
believe it gave an inaccurate impression.

Well, impressions are subjective, but I will certainly grant you that it at
least gave *you* an inaccurate impression, for whatever reason. Furthermore,
if it gave you an inaccurate impression, it might have given others an
inaccurate impression. :)

I have a tendancy to be concise. I often forget that human perception
involves a great deal of interpretation! While I may mean no more and no
less than what I say, I do find that I am sometimes misunderstood, simply
because I didn't clarify my remarks more. If only I had more time!

--
Best Wishes,

Kevin Spencer
Microsoft MVP
Ministry of Software Development
http://unclechutney.blogspot.com

Never trust a dunderhead with a blunderbuss.
"Jon Skeet [C# MVP]" <sk***@pobox.co mwrote in message
news:MP******** *************** *@msnews.micros oft.com...

Kevin Spencer <sp**@uce.govwr ote:

>Now, don't put words in my mouth. I pointed out that it wasn't necessary
to

<snip>

Indeed, and we don't know whether it was accurate or not - but I
believe it gave an inaccurate impression.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
If replying to the group, please do not mail me too

[Kevin Spencer]

Congratulations ! We've all been there before. I am embarassed on a daily
basis by things that only I know I did!

--

Kevin Spencer
Microsoft MVP
Ministry of Software Development
http://unclechutney.blogspot.com

Never trust a dunderhead with a blunderbuss.
"giddy" <gi*******@gmai l.comwrote in message
news:11******** **************@ b28g2000cwb.goo glegroups.com.. .

>
hi ,

i'm really embarrased about this ,

theDGV.ColumnCo unt =
dataSet.Tables["customers"].Columns.Count; //THIS IS THE LINE.

after a 2 more hours of debugging i found out that ......
the DataSet was null not the dgv! =S , and this itself was a cause of
two silly mistakes

I'm really sorry to have wasted your time.

Thank you for your concern!

Gideon

On Nov 23, 9:09 am, "giddy" <gidisr...@gmai l.comwrote:

>ok im sorry if i did'nt give enough detail and i'm really sorry if i'm
being rude by saying its urgent , i do have to to finish this project
by the end of this month! and a few more setbacks like this could
jeopardize a lot more than my job , also i cannnot! afford paid
support!
i have good programming background but i started C# just a while ago.
I made quite a few fuctions with ref, and naturally started to panic
when one of them did'nt work!

Firstly , i need to use ref because i have a 2 datagrid views that have
to be filled more or less the same way , and i could have a 3rd one
soon. Whatever is common between the dgvs goes into one function and
then obviously has to change the datagridview passed to it.

I just tried the whole thing without the ref keyword both in the
function and when i call it. and i GET THE SAME EXCEPTION.

the exception occurs inside the function on the first line :
public void FillColumns(ref DataGridView theDGV)
{
theDGV.ColumnCo unt =
dataSet.Tabl es["customers"].Columns.Count; //THIS IS THE LINE.

VS says :

NullRefrenceEx ception was not handled
Object reference not set to an instance of an object.]
Troubleshootin g tips :
use the 'new' keyword to create an object of the instance (????
check to determine if the object is null before calling the method

i have Form1 , the datagridview is ON Form1 and FillColumns() is in
Form1.cs

In Form1.Designer. cs :
the dgv is declared like this : private
System.Windows .Forms.DataGrid View dataGridView2;

and its properties are set like this :
this.dataGridV iew2.ColumnHead ersHeightSizeMo de =
System.Windows .Forms.DataGrid ViewColumnHeade rsHeightSizeMod e.AutoSize;
this.dataGridV iew2.Location = new System.Drawing. Point(5, 50);
this.dataGridV iew2.Name = "dataGridView2" ;

so why is it null!

thanks

Gideon

On Nov 23, 5:18 am, "Kevin Spencer" <[e-mail] >
wrote:----------------------------------------

Kevin Spencer <[e-mail] ote:
A DataGridView is a reference type. There is no need to pass it by
ref.

Now, often people *do* use ref when they don't need to, but without
seeing the OP's method, we can't tell whether that's the case or not.

--------------------------------------

>>Peter Duniho wrote:
What line of code does thedebugger say has the null reference? What
variable in that line of

code is
the one that is null? And why is it that you expect that variable to
NOT be
null? --------------------------------------

>>cbmeeks wrote :is the dataGridView2 in the same scope as the function?

In other words, are you calling that function from a class that doesn't
know where the dgv is?

[Jon Skeet [C# MVP]]

Kevin Spencer <sp**@uce.govwr ote:

Congratulations ! We've all been there before. I am embarassed on a daily
basis by things that only I know I did!

That's one of the interesting things about having open source projects
available on the web - *anyone* can see how awful your code is. Having
recently found some clangers in my miscutil library, I'm very red in
the face.

Still, so long as we learn lessons from it... in this case, it's a
retrospective lesson that unit tests make a huge difference :)

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
If replying to the group, please do not mail me too