Either you'll get the same error (in which case there's probably no DI involved), or you'll get your ArgumentNullException - in which case there is and it's badly configured. An easy way, and good practise, is to check for a null LoginModel being passed in that constructor and throw an exception (typically ArgumentNullException the use of Code Contracts as mentioned by another answer here is a good plan) and then run the site again. If there's a DI framework creating the controller - then check that it can resolve an instance of LoginModel. I'm going to take a guess that you've inherited this Controller from someone else and that they have written unit tests for it - hence the additional constructor unless, as Jon has mentioned, there is some DI framework active on the site (in which case it's misconfigured). NullReferenceException can be avoided by writing code that checks for null before accessing an object, or uses try/catch blocks.Surely it's because the loginModel is supposed to be set in the constructor but MVC will not fire the constructor that sets it it'll be firing the default constructor - so by that point it's null hence the NullReferenceException.The error message that appears tells you a great deal about where in the code the problem happens.NullReferenceException happens when your script code tries to use a variable which isn’t set (referencing) and object.The catch block displays a message which might be more helpful to artists and game designers, and reminds them to set the light in the inspector. Attempting to change the color of the light in the try block causes a NullReferenceException which is picked up by the catch block. If this variable is not set, then it will default to null. In this code example, the variable called myLight is a Light which should be set in the Inspector window. Public Light myLight // set in the inspectorĭebug.Log("myLight was not set in the inspector") For example, this code: using UnityEngine A different way to deal with NullReferenceException is to use try/catch block. If you forget to do this, then the variable will be null. Try/Catch BlocksĪnother cause for NullReferenceException is to use a variable that should be initialised in the Inspector A Unity window that displays information about the currently selected GameObject, asset or project settings, allowing you to inspect and edit the values. If it is null, then we display a message. Now, before we try and do anything with the go variable, we check to see that it is not null. GameObject go = GameObject.Find("wibble") ĭebug.Log("No game object called wibble found") The solution in this simple example is to change the code like this: using UnityEngine Because we are accessing a game object that doesn’t exist the run-time gives us a NullReferenceException Null ChecksĪlthough it can be frustrating when this happens it just means the script needs to be more careful. On the next line (line 9) we use the go variable and try and print out the name of the game object it references. In this example there is no game object with that name, so the Find() function returns null. The code simply looks for a game object called “wibble”. (class-GameObject.html)See in (Glossary.html#GameObject) go = GameObject.Find("wibble") A GameObject's functionality is defined by the Components attached to it. _GameObject_ The fundamental object in Unity scenes, which can represent characters, props, scenery, cameras, waypoints, and more. In this example, the code is: //c# example This makes the Null Reference Exception easy to find and fix. Also, the message says that the exception happened inside the Start() function. This error message says that a NullReferenceException happened on line 10 of the script file Example.cs. The error message will look something like: NullReferenceException: Object reference not set to an instance of an objectĪt Example.Start () in /Unity/projects/nre/Assets/Example.cs:10 When you get a NullReferenceException in your code it means that you have forgotten to set a variable before using it. Hence, if you try and access the object that is being referenced and there isn’t one, you will get a NullReferenceException. Reference types default to null to indicate that they are not referencing any object. Reference variables in c# and JavaScript are similar in concept to pointers in C and C++. The run-time will tell you that you are trying to access an object, when the variable is null by issuing a NullReferenceException. If a reference variable isn’t referencing an object, then it’ll be treated as null. A NullReferenceException happens when you try to access a reference variable that isn’t referencing any object.
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