Myujth

I'm passing a list to a method that operates on the list. However first I want to iterate over the list and check whether or not there are any null values within the list before any further processing takes place.

Initally I thought using the IEnumerable.All() method would help with this, however this method actually checks that all elements of the list satisfy a condition, I'd like to check each element in turn and if any are null then handle this.

This is the (non-working) code that I have already. I'm not sure how I would adapt this for use within an if statement condition.

if (questions == null || questions.Any() == false || questions.All(q => q == null))

 throw new ArgumentException("Exception raised.");

Essentially I want to check:

1. Questions isn't null.


2. Questions isn't empty.


3. Any elements held within questions aren't null values.

The first two have been done, it's just the third.

You can use this more concise version that uses Any and the ?-operator:

bool valid = questions?.Any(q => q != null) == true;
if (!valid)
 throw new ArgumentException("Exception raised.");

The comparison with true is necessary to convert the bool? to bool. It also might be more efficient because it doesn't need to execute it multiple times(in case questions is a query). It also handles the case that questions is empty, then Any returns false.

I think you want to

if (questions != null && questions.Any() && questions.All(q => q != null))

I suggest spliting in two tests - for questions itself (it must not be null) and for items within questions (there must be at least one not null item); your current code changed:

if (null == questions)
 throw new ArgumentNullException(nameof(questions));
else if (questions.All(q => q == null))
 throw new ArgumentException("At least one not null question expected.",
 nameof(questions)); 

Or even into three: when implementing a contract, in your case it is

1. 
   questions isn't null.


2. 
   questions isn't empty.


3. Any elements held within questions aren't null values.

try throw separate exception for each violation:

 if (null == questions)
 throw new ArgumentNullException(nameof(questions));
 else if (!questions.Any())
 throw new ArgumentException("Questions must not be empty.",
 nameof(questions)); 
 else if (questions.Any(item => null == item))
 throw new ArgumentException("Null questions are not allowed.",
 nameof(questions)); 

Such kind implementation may appear wordy but it saves time when you are debugging ("Exception raised." provides no info when meaning of "Questions must not be empty." is evident).