ToList() - ArgumentNullException Handling

Question

Hi I have a class named Activity,

On a form I create its object array as,

 Activity[] _actList;

And then do this,

List<Activity> termsList = _actList.ToList<Activity>();

since _actiList is null its throwing the ArgumentNullException.

So my question is,

How can I handle this exception?
Or is there a work around to get the same functionality ?

Please Help!

do you mean without initializing? are you expecting an empty list? — Neville Nazerane, Sep 13 '17 at 04:32
without initializing `_actList` what are you expecting the machine to put in `termsList`? — bansi, Sep 13 '17 at 04:38

Titian Cernicova-Dragomir · Accepted Answer · 2017-09-13T05:21:43.243

11

You need to check for null before calling ToList

var termsList = _actList == null ? null : _actList.ToList();

If you are using the C# 6.0 or later you can write the same in a shorter way:

var termsList = _actList?.ToList();

You could also catch the exception, but I don't recommend that in this case especially if it is a common scenario for the array to be null

edited Sep 13 '17 at 05:21

answered Sep 13 '17 at 04:31

Titian Cernicova-Dragomir

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@Sunitha Glad to help :). FYI no need to specify type parameter for `ToList`, you can, but the compiler can figure it out so it's recommended to leave it out unless you have a good reason to put it there. – Titian Cernicova-Dragomir Sep 13 '17 at 04:43
Oh okay. Thanks again :) – Sunitha Sep 13 '17 at 04:47

score 0 · Answer 2 · answered Sep 13 '17 at 04:38

0

You could make sure that the array is never null with assigning an empty default array.

Activity[] _actList = new Activity[] { };

so, when the form is initialized the array also will be initialized with an empty array. If you are doing .ToList() now, you will get an empty list then instead of an exception.

answered Sep 13 '17 at 04:38

Armin Cheng

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instance of abstract class ? – bansi Sep 13 '17 at 04:43
@bansi It is not an instance of the `Activity` class. It is an instance of an array. – Neville Nazerane Sep 13 '17 at 04:44

score 0 · Answer 3 · answered Sep 13 '17 at 04:43

Using try catch which would work for any such issue:

try {
    List<Activity> termsList = _actList.ToList<Activity>();
}
catch(ArgumentNullException){

}

Or you can use set a default value if it is null using the ?? operator:

List<Activity> termsList = (_actList ?? new Employee[] { }).ToList<Activity>();

This would give you an empty list if your array is empty.

ToList() - ArgumentNullException Handling

3 Answers3