Null 检查是否在 C#

Question

I am checking two conditions which is following in C#:

 if (result.Data.Count > 0)
 {
     if(result.Data[0].AdditionalData != null)
      {
         // To Do
      }
  } 

My confusion is there is any better way to check these in a single if condition?

I am trying to use Null-Condition operator, but did not work it. Null-Conditional operator in MSDN

Answer 1

You can create extension method on IEnumerable and use it

    public static bool HasValue<T>(this IEnumerable<T> source, int index)
    {
        if (source == null)
            return false;

        return source.Count() > index && source.ElementAt(index) != null;
    }

// usage
if(result.Data.HasValue(0))
{
}

Answer 2

One liner using System.Linq .

if (result.Data.FirstOrDefault()?.AdditionalDate != null)
{
 
} 

Answer 3

You forgot to check the value is empty or not. Empty or null is differences value.

Answer 4

Like written also by @Hans Killian try to use the extensions already there for IEnumerables In your case I think .ElementAtOrDefault(0) (or if you always want to use index 0 just use .FirstOrDefault() ) is the best fit for you here.

if (result?.Data != null && result.Data.Any())
{
    /// Expecting 'AdditionalData' is `string`
    if (!string.IsNullOrEmpty(result.Data.ElementAtOrDefault(0)?.AdditionalData))
    {
        Console.WriteLine("Null check working...");
    }
    else
    {
        Console.WriteLine("AdditionalData is null or empty!");
    }
}
else
{
    Console.WriteLine("No data!");
}

Full working example can be found here

Answer 5

I think the best way to have clean and good code is to use FluentValidation. Please note the following code snippet:

  public class RegisterValidator : AbstractValidator<RegisterDTO>
{
    public RegisterValidator()
    {
        RuleFor(a => a.PhoneNumber).NotNull().WithMessage(Utility.GetEnumTitlePersian(enmErrorMessage.InValidMobileNumber));
        RuleFor(a => a.PhoneNumber).NotEmpty().WithMessage(Utility.GetEnumTitlePersian(enmErrorMessage.InValidMobileNumber));
        RuleFor(a => a.PhoneNumber).MinimumLength(11).WithMessage(Utility.GetEnumTitlePersian(enmErrorMessage.InValidMobileNumber));
        RuleFor(a => a.PhoneNumber).MaximumLength(11).WithMessage(Utility.GetEnumTitlePersian(enmErrorMessage.InValidMobileNumber));
    }

}

The above code is an example of validating a model to check null, empty and etc. and this code must check validation in business logic:

var validator = new RegisterValidator();
var validatorResult = await validator.ValidateAsync(register);

if (!validatorResult.IsValid)
    return BadRequest("", validatorResult.Errors[0].ToString());

It is very simple to use and very clean. You can even perform multiple checks and get results through the error list This link is the site address of FluentValidation

Answer 6

Null conditional can work along with Any , and short-circuiting the next check

if (result?.Data?.Any() && result.Data[0]?.AdditionalData != null)
{
    // to do
}