how i can check arraylist value?

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i make a array list with below code:

HTML

ArrayList aa = new ArrayList();

and fill this with this code:

HTML

aa.Add(fiststquery.getUserName(user, pass));

and now i want check value of arraylist with this code:

HTML

if(aa[0]).ToString()==null)

,but this dosn't work and send this error:
"Object reference not set to an instance of an object"

Posted 14-Apr-12 20:20pm

hanis29268

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2 solutions

Solution 2

Just to add a bit more to Abhinav's reply:

Before any checks, you can check the size of the array by using Count. In this way you will be pretty sure that the index is valid (i mean if count is more that 0, then aa will have at least one non-null object]

Posted 14-Apr-12 20:59pm

Lakamraju Raghuram

Comments

VJ Reddy 15-Apr-12 3:07am

Nice addition. 5!

Lakamraju Raghuram 15-Apr-12 3:10am

(:-

VJ Reddy 15-Apr-12 4:59am

Is my comment not appropriate, out of curiosity, as your expression is (:- which is a blank expression, as given here http://www.cool-smileys.com/text-emoticons.
Thank you.

Lakamraju Raghuram 15-Apr-12 11:35am

Oh is it?
Then I am very poor at these SMS type of symbols.
Thank you for your appreciation and I want to convey the same by that symbol. My bad if it is wrong.

VJ Reddy 16-Apr-12 0:26am

No problem.
Thank you for the response.

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Abhinav S · Accepted Answer · 2012-04-14T20:51:00

Solution 1

Try to debug through the getUserName method. Mae sure it is returning a value.
If fiststquery.getUserName(user, pass) is returning null, you are adding null to aa.

As a result, when you do aa[0].toString(), you are trying to convert a null to string - which throws an error.

An alternate way could be to use if (aa[0] == null) directly.
You don't need the ToString method at all.

Convert.ToString() can also be used. This will not throw an error when the sting to be converted is null.

Posted 14-Apr-12 20:51pm

Abhinav S

Comments

VJ Reddy 15-Apr-12 3:07am

Good answer. 5!

Abhinav S 15-Apr-12 3:17am

Thanks.

Mehdi Gholam 15-Apr-12 5:16am

My 5!

obj.ToString() is a source of many bugs when obj is null. I usually use (""+obj) which guarantees a string even if obj is null.

Abhinav S 15-Apr-12 11:09am

Thanks. Convert.ToString() could also be an option.