How to determine whether object reference is null?

问题

What is the best way to determine whether an object reference variable is null?

Is it the following?

MyObject myObjVar = null;
if (myObjVar == null)
{
    // do stuff
}

回答1:

Yes, you are right, the following snippet is the way to go if you want to execute arbitrary code:

MyObject myObjVar; 
if (myObjVar == null) 
{ 
    // do stuff 
} 

BTW: Your code wouldn't compile the way it is now, because myObjVar is accessed before it is being initialized.

回答2:

The way you are doing is the best way

if (myObjVar == null)
{
    // do stuff
}

but you can use null-coalescing operator ?? to check, as well as assign something

var obj  = myObjVar ?? new MyObject();

回答3:

You can use Object.ReferenceEquals

if (Object.ReferenceEquals(null, myObjVar)) 
{
   ....... 
} 

This would return true, if the myObjVar is null.

回答4:

you can:

MyObject myObjVar = MethodThatMayOrMayNotReturnNull();
if (if (Object.ReferenceEquals(null, myObjVar)) 
{
    // do stuff
}

来源：https://stackoverflow.com/questions/12000228/how-to-determine-whether-object-reference-is-null