如何避免许多 null 在 foreach 循环之前检查关联/组合/聚合对象的层次结构？

Question

What is the best way to check for nulls in this situation?

foreach(var item in Vehicles.Car.CarModel)
{
   ...
   ...
}

Now the Car or CarModel can be Null and should be checked somehow. What is the best way?

Answer 1

You can write this to avoid some null checks in two lines before the loop:

TypeOfCarModel items = Vehicles?.Car?.CarModel ?? null;

if ( items != null )
  foreach ( var item in items )
  {
  }

This use Null-conditional and Null-coalescing operators.

In case of a list, for example, or any other thing like that, a variant may be:

List<CarModelItem> items = Vehicles?.Car?.CarModel ?? new List<CarModelItem>();

foreach ( var item in items )
{
}

It avoids the null check because the " IEnumerable " is empty, but it creates an instance...