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I'm trying to detect if a list which is in a model contains any objects, if it does then it will execute code in the razor view, if it doesn't it should skip the code. I am witnessing some unusual behaviour that i cant get to the bottom of. The null check is ignored and the code inside the if statement is being validated even though the if statement is false when debugging.

Model contains a list of details pertaining to a user. The model also has other attributes e.g 

Public List<UserDetails> User {get;set;}
Public List<CompanyDetails> Companies {get;set;}

Controller does not pass anything into this list (list is not initialised) to the view, so just an instance of the model. On the view I try to use an if statement to toggle html depending on if this list isn't null, in this case toggling the display of the users details:

if(Model.User != null){
 //do something with the list of objects in html
}

The if statement returns "false" therefore it should not execute the code inside the if statement. However i am getting a Null Reference Exception and the compiler throws an error from inside the if statement (when putting a break-point in the razor view).

I have tried different approaches for example making an instance of the object e.g an empty list on the controller

var Model = new UserLocatorModel();
Model.User=new List<UserDetails>();

and change the code to:

if(Model.User.Count() != 0){
 //do something with the list of objects in html
}

But this introduces the System.ArgumentOutOfRangeException

Lastly, if i add an empty class object to the new list, i introduce more issues as now i need to enter the list and check an item in the object to see if it exists.

Code example

//model UserLocatorModel

public class UserModel(){
public List<Detail> User {get;set;}
Public List<CompanyDetails> Companies {get;set;}
}

//view
@Model Project.Models.UserLocatorModel
@if(Model.User != null){
  //do something
}

I want to be able to detect the null list and skip the code inside the if statement which sounds basic enough. Thanks in advance

::Edit. This is not a duplicate question, I am trying to identify why i get a null reference exception whilst using an if statement to rule out the null object. If i have an "if" statement which handles the null why am i still evaluating the code inside?

QuickQuestion
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  • Why there're parenthesis in declaring `List`? It should be `public List User { get; set; }` – Ammar Jul 05 '19 at 23:39
  • Could you please update your question and show some code which actually compiles? `Model-> Public List
    User();` this is not C# syntax... `Model.User=new List
    ()};` this has typo... `if(Model.User != null){ //do something with the list of objects in html }` this does not execute in a view...
     – Hooman Bahreini Jul 05 '19 at 23:45
  • @Ammar thanks for the response, i mocked up the code roughly off the top of my head to imitate the scenario – QuickQuestion Jul 06 '19 at 09:24
  • Model-> was intended to show this is a model in a different class file. The model has a list object. – QuickQuestion Jul 06 '19 at 09:33
  • if(Model?.User!=null && Model?.User?.Any()!=null){//code to execute}; for anyone who stumbles on a similar issue :) – QuickQuestion Jul 06 '19 at 13:53

1 Answers1

0

You need to check that Model is not null:

if (Model != null && Model.User != null && Model.User.Count() > 0)
{
    //do something with the list of objects in html
}
tim
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  • thanks for the response, unfortunately this doesn't prevent the error from being thrown, it seems to be ignoring the null checks – QuickQuestion Jul 06 '19 at 09:10
  • okay, so this was not the exact answer but exploring these variations allowed me to get close enough to the answer, not sure why the additional checks are required but on the view if i do: if(Model?.User!=null && Model?.User?.Any()!=null){//code to execute}; This works – QuickQuestion Jul 06 '19 at 13:49