How to define a null reference in C #?

Question

How to determine if an object reference is null in C # without throwing an exception if it is null?

i.e. If I have a reference to the class and I don't know if it is null or not.

Answer 1

What Robert said, but in this particular case, I would like to express it with a security proposal like this, instead of embedding the entire method block in an if block:

void DoSomething( MyClass value ) { if ( value == null ) return; // I might throw an ArgumentNullException here, instead value.Method(); } 

Answer 2

testing against null will never * throw an exception

 void DoSomething( MyClass value ) { if( value != null ) { value.Method(); } } 

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* never, never, never. As @Ilya Ryzhenkov points out, an incorrect statement implementation! = For MyClass may raise an exception. Fortunately, Greg Buck has a good blog post about implementing object equality in .NET .

Answer 3

Please note that the presence of the operator! = defined on MyClass will likely result in a different check result and a NullReferenceException later. To be absolutely sure, use object.ReferenceEquals (value, null)

Answer 4

 if(p != null) { DoWork(p); } 

In addition, the “how” keyword is useful if you want to determine if a class has the correct type and use it all at once.

 IExample e = p as IExample; if(e != null) DoWork(e); 

In the above example, if you selected e like (IExample) e, it will throw an exception if e does not implement IExapmle. If you use 'as' and e does not implement IExample, e will just be null.

Answer 5

If you look at most of the .NET Framework source codes, you will see that they put checks like this at the top of their functions.

 public void DoSomething(Object myParam) { if (myParam == null) throw new ArgumentNullException("myParam"); // Carry on } 

Answer 6

With C # 6.0, this is much more elegant; you can do it in one line :-)

 value?.Method(); 

If "value" is null, nothing will happen - and there will be no exceptions.

Answer 7

This is nothing, but I always code them as ...

 if (null == obj) { obj = new Obj(); } 

instead

 if (obj == null) { obj = new Obj(); } 

to avoid accidental recording

 if (obj = null) { obj = new Obj(); } 

because

 if (null = obj) { obj = new Obj(); } 

will give you a compiler error

Answer 8

 (YourObject != Null) 

can you compare with null?

If it is null instead of throwing an exception, you can initialize your object. You can use the null pattern.

Answer 9

Or, if you use value types, you can read about types with NULL capability: http://www.c-sharpcorner.com/UploadFile/mosessaur/nullabletypes08222006164135PM/nullabletypes.aspx

Answer 10

I have a definition of a xaml.cs derivative application in my application:

 private SortedList myList; 

And I want to be able to reuse my constructors. Therefore I need:

 if ( myList == null) myList = new SortedList(); 

Thanks Robert!