Nullreferenceexception rust как исправить

ullReferenceException: Object reference not set to an instance of an object.
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Rust.Workshop.WorkshopSkin+<SkinQueueCoroutine>d__32.MoveNext () (at <00000000000000000000000000000000>:0)
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00000000000000000000000000000000>:0)
Rust.Workshop.WorkshopSkin.LoadOrUnloadSkinAssets (System.UInt64 workshopId) (at <00000000000000000000000000000000>:0)
Rust.Workshop.WorkshopSkin.LoadFromWorkshop (System.UInt64 workshopId) (at <00000000000000000000000000000000>:0)
Rust.Workshop.WorkshopSkin.Apply (System.UInt64 workshopId, System.Action callback) (at <00000000000000000000000000000000>:0)

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BaseNetworkable.ClientSpawn (ProtoBuf.Entity info) (at <00000000000000000000000000000000>:0)
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Client.OnEntities (Network.Message packet) (at <00000000000000000000000000000000>:0)
Client.OnNetworkMessage (Network.Message packet) (at <00000000000000000000000000000000>:0)
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Rust.Workshop.<LoadSkin>d__34:MoveNext()
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Rust.Workshop.<SkinQueueCoroutine>d__32:MoveNext()
UnityEngine.SetupCoroutine:InvokeMoveNext(IEnumerator, IntPtr)
Rust.Workshop.<LoadItem>d__33:MoveNext()
UnityEngine.SetupCoroutine:InvokeMoveNext(IEnumerator, IntPtr)
Rust.Workshop.<ItemQueueCoroutine>d__31:MoveNext()
UnityEngine.SetupCoroutine:InvokeMoveNext(IEnumerator, IntPtr)
Rust.Workshop.WorkshopSkin:LoadOrUnloadSkinAssets(UInt64)
Rust.Workshop.WorkshopSkin:LoadFromWorkshop(UInt64)
Rust.Workshop.WorkshopSkin:Apply(UInt64, Action)
Rust.Workshop.WorkshopSkin:Apply(GameObject, UInt64, Action)
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Client:Update()

While working on custom maps, some questions and issues will pop up eventually. Most of them are happening only to beginners, so if you have just joined the map making scene then this article may be helpful for you.

Errors

Why do I get this error when connecting? (World Mismatch, World File Outdated)

If attempting to load the map results in errors World cache version mismatch: 8 != ########## or World File Outdated: ###### then you should rename your map to something unique that you have never used before.

Whenever you make changes to your map you should give it a new unique name when hosting it in-game. Add V2.0 to the name. If you do not then your original first map will still be within your local game files, when connecting to the server it will respond with the .map name and if your client detects the same name it will attempt to load the already downloaded old version of the file. Resulting in you attempting to load a different version than the server, causing file mismatch error. Alternatively you can delete the .map file within your Rust install directory. This is unlikely to be possible for all players who play your server.

Server freezes while loading a map

Usually this happens when your custom map does not have an access to the ocean, which means there is no area that can be used for generating ocean paths for the Cargo Ship. Can also happen if your map is all Water as well. You can fix this by adding some area for ocean surrounding your custom map. Alternatively you can just disable Cargo Ship event using these two server startup parameters: baseboat.generate_paths false and cargoship.event_enabled false.

Errors while trying to download the map

This means that the server could not download your custom map using the provided URL. Make sure that it is a direct download link, there is no spelling mistakes in the link and the website that hosts your map is up and can be accessed by everyone.

Example of a valid download link: https://blahblah.net/thats/a/valid.map

Example of a bad download link: mymap.map, or any Discord message link or Dropbox link without dl=1 in the end.

Example of local link (If local testing) C:Usersmymap.map would work only if the server is running on your local computer. But would not work for anyone else not on your computer.

Couldn’t Download Level when connecting to a Rust server

Sometimes there’s an issue when player cannot download the map, although it worked fine server-side. There is no uniform solution to this error, but when troubleshooting, but you can try downloading the map directly. Open your F1 console, and find the line that starts with «Download map file <…>». Copy the URL and paste it in your browser. If download succeeds, take this map and put it in <root Rust folder>maps, after that you can try joining the server again.

If mentioned solution does not work, you can try troubleshooting by checking following factors:

LoadPrefab — should start with assets/

One of the provided prefab IDs on your custom map cannot be found in Rust’s assets, which means it was probably removed from the game. Since June 2018, some relatively popular prefabs were removed from Rust, so this error appears pretty often on old custom maps. Some map editors will automatically remove all missing prefabs on load, so you only have to load and re-save the map to fix.

[Server-side] NullReferenceException: Object reference not set to an instance of an object (any)

This means that your custom map has a broken prefab that breaks the server. If you are sure it is not a file corruption, then open your map in the editor and remove the broken prefab. Keep in mind that server console only notifies about the NRE – detailed error can be found in the full server log. It is not always possible to identify the problematic prefab, so sometimes debugging can be a very annoying process. Pay attention to a full NRE log, since sometimes function calls might be helpful to understand the context.

[Client-side] NullReferenceException: Object reference not set to an instance of an object — MaterialConfig.GetMaterialPropertyBlock <…>

This is a client-side NRE that shows up as soon as player connects to the server. This is usually related to a small set of «splash effect» prefabs that got broken sometime in early 2022, so it also affects mostly old maps. You have to open the map in any editor and make sure that scene does not have following prefabs:

Why is my custom map getting stuck while attempting to generate the ocean path?

This can happen if your custom map has little, or no ocean. The server will attempt to generate the ocean patrol path, but will struggle to do so.

To fix this issue, you can either change your map to have a larger ocean around the island, or add the following commands to your startup parameters :
cargoship.event_enabled false
baseboat.generate_paths false
ai.ocean_patrol_path_iterations 0

These commands will remove the cargo event, and disable ocean pathing. This will allow your server to startup without getting stuck on generating ocean path. Keep in mind that if you spawn the cargo ship on this map, it will result into ship being static and moving anywhere, since there’s no generated cargo path on the map.

Tips

How do I make changes to my map mid-wipe without wiping the server?

Making changes mid-wipe is not practical, in severe circumstances such as bugs or exploits, you can make changes to the map by doing the following.

Original Map:
MapVersion1.map
Original generated sav:
MapVersion1.182.sav

Shut down server completely.

Change server.url to download new map:
MapVersion2.map

Rename existing sav file from first map to second map:
MapVersion2.182.sav

Do not rename the existing MapVersion1.map file. This will result in clients receiving a World File Mismatch or World cache checksum mismatch error. The Rust server does not re-download a custom map on every start if the map is already present. If you did this, you’ll need to delete both Mapversion1.map and Mapversion2.map files before restarting the server.

Information gathered provided by the Rust Map Making community.

Null reference exception rust

— open your rust console by pressing [f1]
— Type: effects.showoutlines 0
— press [enter]

NOTE: When rust has the update for MAC, it can be that you need to do this again and turn the 0 into 1 to enable the outlines again!

i didnt play since the update but is this a thing that pops up in red text and freezes the game? It happened to me 3 times last week.

This is a fix for everybody that got kicked out of the server and shows the «nullreferenceexception» message. It is mostly on Mac, and after this last update.

Do you mean the red text on the left-top corner sometimes?
I also seeing this sometimes almost over a month now and think it’s another problem.
Because I was not able to take screenshot or read fast enough I was not able to post this issue.

THANK YOU ILL LET YOU KNOW IF IT WORKS

it works.. this guy is smarter than facepunch studios

I got the same problem here, but what do you mean by «open rust console by pressing f1»? sorry i don’t it bro. Mac user as well here

Press the «F1» key which opens the console. Or if you’ve adjusted settings at all for keyboard bindings, press the «fn» and «F1» keys together. Once open, input the text as written above, then press enter.

Confirmed this worked. Thanks for the bandaid!

i didnt play since the update but is this a thing that pops up in red text and freezes the game? It happened to me 3 times last week.

This is a fix for everybody that got kicked out of the server and shows the «nullreferenceexception» message. It is mostly on Mac, and after this last update.

Do you mean the red text on the left-top corner sometimes?
I also seeing this sometimes almost over a month now and think it’s another problem.
Because I was not able to take screenshot or read fast enough I was not able to post this issue.

Источник

Null reference exception rust

My friend gets this error when connecting to most servers. It persists through restarting the server. I see this error posted all over the place but no one has anything near a reasonable explanation.

Most people say it’s related to DDOS attacks which it’s obviously not.

Garry please help, this error is all over the place.

It means the devs of whatever managed code module ‘forgot’ to trap the exception. Basically a reference was made to an object that had not yet been instantiated. The dev’s should have wrapped a try <> catch () around it at least at the main entry point of the application or module. They didn’t so when the codeing error occured during runtime it bubbled up past main and exposed itself in your runtime instance. The user should technically never see this in Beta or beyond. However in Alpha it is usefull so the devs/QA can track down where it occured and fix the problem. However in a ‘public’ Alpha I still feel it should never be seen but ratter logged in a text file and sent back to the error server. I doubt Facepunch has an error server so they should then trap it and tell you how to send the error dump to them so they can fix it. As I recall most of the managed code in this game is in C#.

I can be forgiving of this in Alpha. If I saw it in mid or late Beta I’d worry. So look around your install folder and see if you can find an error.txt or something like that. I should contain that message with a long list of the call stack. Until we have that information it means it’s a coding bug anywhere in the program. I know they do create a crash dump folder and maybe if you’re lucky it will have the call stack information in it. If it got created before .Net took over and shut things down.

Tried to keep that in as simple terms as I could.

Источник

Nullreferenceexception rust как исправить

I have some code and when it executes, it throws a NullReferenceException , saying:

Object reference not set to an instance of an object.

What does this mean, and what can I do to fix this error?

Dear future visitors, the answers to this question equally apply to an ArgumentNullException. If your question has been closed as a duplicate of this one, and you are experiencing an ANE, please follow the directions in the answers to debug and fix your problem. @will ANE should only happen if a null is passed as a parameter. Can you give an example if an ANE question closed as a duplicate of this one? Comments disabled on deleted / locked posts / reviews |

Более подробно

Если среда выполнения выбрасывает исключение NullReferenceException , то это всегда означает одно: вы пытаетесь воспользоваться ссылкой. И эта ссылка не инициализирована (или была инициализирована, но уже не инициализирована).

Это означает, что ссылка равна null , а вы не сможете вызвать методы через ссылку, равную null . В простейшем случае:

Этот код выбросит исключение NullReferenceException на второй строке, потому что вы не можете вызвать метод ToUpper() у ссылки на string , равной null .

What is the cause?

Debugging

How do you find the source of a NullReferenceException ? Apart from looking at the exception itself, which will be thrown exactly at the location where it occurs, the general rules of debugging in Visual Studio apply: place strategic breakpoints and inspect your variables, either by hovering the mouse over their names, opening a (Quick)Watch window or using the various debugging panels like Locals and Autos.

If you want to find out where the reference is or isn’t set, right-click its name and select «Find All References». You can then place a breakpoint at every found location and run your program with the debugger attached. Every time the debugger breaks on such a breakpoint, you need to determine whether you expect the reference to be non-null, inspect the variable, and verify that it points to an instance when you expect it to.

By following the program flow this way, you can find the location where the instance should not be null, and why it isn’t properly set.

More Specifically

The runtime throwing a NullReferenceException always means the same thing: you are trying to use a reference, and the reference is not initialized (or it was once initialized, but is no longer initialized).

This means the reference is null , and you cannot access members (such as methods) through a null reference. The simplest case:

This will throw a NullReferenceException at the second line because you can’t call the instance method ToUpper() on a string reference pointing to null .

Examples

Some common scenarios where the exception can be thrown:

Generic

If ref1 or ref2 or ref3 is null, then you’ll get a NullReferenceException . If you want to solve the problem, then find out which one is null by rewriting the expression to its simpler equivalent:

Indirect

If you want to avoid the child (Person) null reference, you could initialize it in the parent (Book) object’s constructor.

Nested Object Initializers

The same applies to nested object initializers:

This translates to:

While the new keyword is used, it only creates a new instance of Book , but not a new instance of Person , so the Author the property is still null .

Nested Collection Initializers

The nested collection Initializers behave the same:

This translates to:

The new Person only creates an instance of Person , but the Books collection is still null . The collection Initializer syntax does not create a collection for p1.Books , it only translates to the p1.Books.Add(. ) statements.

Array

Array Elements

Jagged Arrays

Collection/List/Dictionary

Range Variable (Indirect/Deferred)

Bad Naming Conventions:

If you named fields differently from locals, you might have realized that you never initialized the field.

WPF Control Creation Order and Events

WPF controls are created during the call to InitializeComponent in the order they appear in the visual tree. A NullReferenceException will be raised in the case of early-created controls with event handlers, etc., that fire during InitializeComponent which reference late-created controls.

Here comboBox1 is created before label1 . If comboBox1_SelectionChanged attempts to reference `label1, it will not yet have been created.

Changing the order of the declarations in the XAML (i.e., listing label1 before comboBox1 , ignoring issues of design philosophy) would at least resolve the NullReferenceException here.

Cast with as

This doesn’t throw an InvalidCastException but returns a null when the cast fails (and when someObject is itself null). So be aware of that.

LINQ FirstOrDefault() and SingleOrDefault()

The plain versions First() and Single() throw exceptions when there is nothing. The «OrDefault» versions return null in that case. So be aware of that.

foreach

foreach throws when you try to iterate on a null collection. Usually caused by unexpected null result from methods that return collections.

More realistic example — select nodes from XML document. Will throw if nodes are not found but initial debugging shows that all properties valid:

Ways to Avoid

Explicitly check for null and ignore null values.

If you expect the reference sometimes to be null , you can check for it being null before accessing instance members:

Explicitly check for null and provide a default value.

Methods you call expecting an instance can return null , for example when the object being sought cannot be found. You can choose to return a default value when this is the case:

Explicitly check for null from method calls and throw a custom exception.

You can also throw a custom exception, only to catch it in the calling code:

Use Debug.Assert if a value should never be null , to catch the problem earlier than the exception occurs.

When you know during development that a method could, but never should return null , you can use Debug.Assert() to break as soon as possible when it does occur:

Though this check will not end up in your release build, causing it to throw the NullReferenceException again when book == null at runtime in release mode.

Use GetValueOrDefault() for nullable value types to provide a default value when they are null .

The shorthand to providing a default value when a null is encountered:

This is also sometimes called the safe navigation or Elvis (after its shape) operator. If the expression on the left side of the operator is null, then the right side will not be evaluated, and null is returned instead. That means cases like this:

If the person does not have a title, this will throw an exception because it is trying to call ToUpper on a property with a null value.

This will result in the title variable being null , and the call to ToUpper is not made if person.Title is null .

Of course, you still have to check title for null or use the null condition operator together with the null coalescing operator ( ?? ) to supply a default value:

Likewise, for arrays you can use ?[i] as follows:

This will do the following: If myIntArray is null , the expression returns null and you can safely check it. If it contains an array, it will do the same as: elem = myIntArray[i]; and returns the i th element.

A nullable reference type is noted using the same syntax as nullable value types: a ? is appended to the type of the variable.

Special techniques for debugging and fixing null derefs in iterators

If whatever results in null then MakeFrob will throw. Now, you might think that the right thing to do is this:

Why is this wrong? Because the iterator block does not actually run until the foreach ! The call to GetFrobs simply returns an object which when iterated will run the iterator block.

By writing a null check like this you prevent the NullReferenceException , but you move the NullArgumentException to the point of the iteration, not to the point of the call, and that is very confusing to debug.

The correct fix is:

That is, make a private helper method that has the iterator block logic and a public surface method that does the null check and returns the iterator. Now when GetFrobs is called, the null check happens immediately, and then GetFrobsForReal executes when the sequence is iterated.

If you examine the reference source for LINQ to Objects you will see that this technique is used throughout. It is slightly more clunky to write, but it makes debugging nullity errors much easier. Optimize your code for the convenience of the caller, not the convenience of the author.

A note on null dereferences in unsafe code

In unsafe mode, you should be aware of two important facts:

• dereferencing a null pointer produces the same exception as dereferencing a null reference
• dereferencing an invalid non-null pointer can produce that exception in some circumstances

Memory is virtualized in Windows ; each process gets a virtual memory space of many «pages» of memory that are tracked by the operating system. Each page of memory has flags set on it that determine how it may be used: read from, written to, executed, and so on. The lowest page is marked as «produce an error if ever used in any way».

That’s why dereferencing both a null pointer and a null reference produces the same exception.

What about the second point? Dereferencing any invalid pointer that falls in the lowest page of virtual memory causes the same operating system error, and thereby the same exception.

Why does this make sense? Well, suppose we have a struct containing two ints, and an unmanaged pointer equal to null. If we attempt to dereference the second int in the struct, the CLR will not attempt to access the storage at location zero; it will access the storage at location four. But logically this is a null dereference because we are getting to that address via the null.

If you are working with unsafe code and you get a NullReferenceException , just be aware that the offending pointer need not be null. It can be any location in the lowest page, and this exception will be produced.

30 ноя. 2017 в 17:47

— open your rust console by pressing [f1]
— Type: effects.showoutlines 0
— press [enter]

NOTE: When rust has the update for MAC, it can be that you need to do this again and turn the 0 into 1 to enable the outlines again!

30 ноя. 2017 в 18:24 please comment bellow if this works, so everybody can see this 😉 30 ноя. 2017 в 18:34 i didnt play since the update but is this a thing that pops up in red text and freezes the game? It happened to me 3 times last week. 30 ноя. 2017 в 18:42 i didnt play since the update but is this a thing that pops up in red text and freezes the game? It happened to me 3 times last week.

This is a fix for everybody that got kicked out of the server and shows the «nullreferenceexception» message. It is mostly on Mac, and after this last update.

Do you mean the red text on the left-top corner sometimes?
I also seeing this sometimes almost over a month now and think it’s another problem.
Because I was not able to take screenshot or read fast enough I was not able to post this issue.

30 ноя. 2017 в 19:28 30 ноя. 2017 в 19:35 30 ноя. 2017 в 19:42

THANK YOU ILL LET YOU KNOW IF IT WORKS

30 ноя. 2017 в 19:47

it works.. this guy is smarter than facepunch studios

30 ноя. 2017 в 22:00 30 ноя. 2017 в 22:09 I got the same problem here, but what do you mean by «open rust console by pressing f1»? sorry i don’t it bro. Mac user as well here

Press the «F1» key which opens the console. Or if you’ve adjusted settings at all for keyboard bindings, press the «fn» and «F1» keys together. Once open, input the text as written above, then press enter.

Confirmed this worked. Thanks for the bandaid!

1 дек. 2017 в 5:13 I’m not smarter than Facepunch studios, I just know my things.
Don’t say stupid things please :p 22 сен. 2018 в 4:57 13 окт. 2018 в 7:28 Maybe because this was about an issue half a year ago lol 18 янв. 2019 в 5:15 i didnt play since the update but is this a thing that pops up in red text and freezes the game? It happened to me 3 times last week.

This is a fix for everybody that got kicked out of the server and shows the «nullreferenceexception» message. It is mostly on Mac, and after this last update.

Do you mean the red text on the left-top corner sometimes?
I also seeing this sometimes almost over a month now and think it’s another problem.
Because I was not able to take screenshot or read fast enough I was not able to post this issue.
Sending to you a screenshot in the Discord. I’m having this issue with no luck.

Object reference not set to an instance of an object.

В экземпляре объекта не задана ссылка на объект.

55.2k 7 7 золотых знаков 62 62 серебряных знака 134 134 бронзовых знака

30.5k 18 18 золотых знаков 75 75 серебряных знаков 98 98 бронзовых знаков Добавил важный каноничный ответ с английского SO What is a NullReferenceException and how do I fix it?. Теперь можно закрывать большинство вопросов про NRE как дубль, а не ковыряться с каждым отдельным случаем. Всё равно почти всегда одно и то же.

Bottom Line

Like anything else, null gets passed around. If it is null in method «A», it could be that method «B» passed a null to method «A».

null can have different meanings:

The rest of this article goes into more detail and shows mistakes that many programmers often make which can lead to a NullReferenceException .

Причина

Отладка

Как определить источник ошибки? Кроме изучения, собственно, исключения, которое будет выброшено именно там, где оно произошло, вы можете воспользоваться общими рекомендациями по отладке в Visual Studio: поставьте точки останова в ключевых точках, изучите значения переменных, либо расположив курсор мыши над переменной, либо открыв панели для отладки: Watch, Locals, Autos.

Если вы хотите определить место, где значение ссылки устанавливается или не устанавливается, нажмите правой кнопкой на её имени и выберите «Find All References». Затем вы можете поставить точки останова на каждой найденной строке и запустить приложение в режиме отладки. Каждый раз, когда отладчик остановится на точке останова, вы можете удостовериться, что значение верное.

Следя за ходом выполнения программы, вы придёте к месту, где значение ссылки не должно быть null , и определите, почему не присвоено верное значение.

Примеры

Несколько общих примеров, в которых возникает исключение.

Цепочка

Если ref1 , ref2 или ref3 равно null , вы получите NullReferenceException . Для решения проблемы и определения, что именно равно null , вы можете переписать выражение более простым способом:

Неявно

То же верно для вложенных инициализаторов:

Несмотря на использование ключевого слова new , создаётся только экземпляр класса Book , но экземпляр Person не создаётся, поэтому свойство Author остаётся null .

Массив

Элементы массива

Массив массивов

Collection/List/Dictionary

События

Неудачное именование переменных

Если бы в коде ниже у локальных переменных и полей были разные имена, вы бы обнаружили, что поле не было инициализировано:

Можно избежать проблемы, если использовать префикс для полей:

Если вы возвращаете пустую модель (или свойство модели) в контроллере, то вью бросит исключение при попытке доступа к ней:

Способы избежать

Явно проверять на null , пропускать код

Если вы ожидаете, что ссылка в некоторых случаях будет равна null , вы можете явно проверить на это значение перед доступом к членам экземпляра:

Явно проверять на null , использовать значение по умолчанию

Методы могут возвращать null , например, если не найден требуемый экземпляр. В этом случае вы можете вернуть значение по умолчанию:

Явно проверять на null , выбрасывать своё исключение

Вы также можете бросать своё исключение, чтобы позже его поймать:

Использовать Debug.Assert для проверки на null для обнаружения ошибки до бросания исключения

Если во время разработки вы знаете, что метод может, но вообще-то не должен возвращать null , вы можете воспользоваться Debug.Assert для быстрого обнаружения ошибки:

Однако эта проверка не будет работать в релизной сборке, и вы снова получите NullReferenceException , если book == null .

Использовать GetValueOrDefault() для Nullable типов

Краткая запись для задания значения по умолчанию:

Это оператор безопасного доступа к членам, также известный как оператор Элвиса за специфическую форму. Если выражение слева от оператора равно null , то правая часть игнорируется, и результатом считается null . Например:

Разумеется, если переменная person может быть равна null , то надо проверять и её. Также можно использовать операторы ?. и ?? вместе, чтобы предоставить значение по умолчанию:

Если любой член в цепочке может быть null , то можно полностью обезопасить себя (хотя, конечно, архитектуру стоит поставить под сомнение):

30.5k 18 18 золотых знаков 75 75 серебряных знаков 98 98 бронзовых знаков @VladD Есть слишком много случаев, когда null — допустимое значение: ленивая инициализация, отсутствие значения «не задано» у типа и т. п. Не везде получается избавиться от null. Так что рекомендация сводится к «старайтесь не использовать null, если это возможно». Это да, есть случаи, когда null валиден. Тогда, вероятно, первым вопросом должно быть: валиден ли null в этой точке? Если да, нужна проверка на null и адекватная реакция. Если нет, то код верен, а проблема где-то раньше (скорее всего в инициализации).

В дополнение к ответу @Discord @Squidward @Athari @Kyubey, давайте рассмотрим вопрос с другой стороны.

Если у вас в процессе выполнения программы случился NullReferenceException при доступе по какой-то ссылке, вы должны прежде всего задать себе важный вопрос:

а имеет ли право эта ссылка иметь значение null ?

Во многих случаях правильным ответом будет «нет», и значит, исправлять придётся истинную причину ошибки, которая находится в другом месте, и произошла раньше.

Пример: если у вас есть такой класс:

Так вот, мотор у машины быть обязан в любом случае, всегда. А вот водитель может в принципе и не сидеть в машине.

Поэтому если вы видите, что обращение к engine.HorsePower падает с NullReferenceException , реальная проблема состоит в том, что вы забыли инициализировать engine в конструкторе. Поэтому и исправлять ошибку нужно не в точке, где падает, а в том месте, которое реально должно бы обеспечить ненулевое значение engine .

А вот если вылетает обращение driver.Age , то здесь уже проблема прямо в точке обращения, вам необходимо сначала проверить, что driver != null , а потом уж обращаться.

Если же ссылка имеет право быть null -ом, то в этом случае нужно корректно обработать и этот случай.

Важное замечание: Если вашу функцию вызывает «внешний мир», вы не должны рассчитывать, что вашей функции передадут хорошие, правильные аргументы. Даже если вы требуете, чтобы объект, который вам передан, не был null -ом, всё равно вам могут передать неправильный объект. Поэтому для функций, доступных внешним модулям, необходимо проверять аргументы на null сразу же в начале кода, и бросать нужное исключение:

Где именно проводить границу между «внутренним» и «внешним» миром, вопрос достаточно нетривиальный. Обычно эта граница есть граница модуля (сборки), или даже той её логической части, которая находится в вашей ответственности. Слишком мелкое дробление ведёт к повторению бессмысленного кода (одна часть программы не доверяет другой и постоянно перепроверяет её). Слишком крупное дробление ведёт к необходимости держать в голове миллионы зависимостей («могу я тут передавать null или нет?»). Пользуйтесь здравым смыслом и личным опытом.

В этом случае сам компилятор сможет проконтролировать, что вы забыли проинициализировать значение поля engine , и выдать вам предупреждение.

Вкратце

Как и любое другое значение, null может передаваться от объекта к объекту, от метода к методу. Если нечто равно null в методе «А», вполне может быть, что метод «В» передал это значение в метод «А».

Остальная часть статьи описывает происходящее в деталях и перечисляет распространённые ошибки, которые могут привести к исключению NullReferenceException .

Ошибка NullReferenceException: Object reference not set to an instance of an object [дубликат]

указывающую на строку

Не понимаю сути ошибки.

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Суть ошибки NullReferenceException — вы пытаетесь что-то сделать со ссылочной переменной, которая имеет значение null. т.е. mContr на момент вашего обращения к ней ничего не назначено и эта переменная указывает в пустоту. Как следствие вызов метода у пустоты выдаёт ошибку.

А раз там пусто, значит нижеприведённая строчка кода ничего не находит. Не стоит делать такие длинные цепочки вызовов, когда вы не уверены, что всё и везде назначено. Как вариант, хотя бы, ставьте проверку, чтобы знать сразу, что всё плохо. Например, так:

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