Checking if an object is null in C#

Question

I would like to prevent further processing on an object if it is null.

In the following code I check if the object is null by either:

if (!data.Equal         


        

Answer 1

The problem in this case is not that data is null. It is that dataList itself is null.

In the place where you declare dataList you should create a new List object and assign it to the variable.

List<object> dataList = new List<object>();

Answer 2

in C# > 7.0 use

if (obj is null) ...

This will ignore any == or != defined by the object (unless of course you want to use them ...)

For not null use if (obj is object) and from C# 9 you can also use if (obj is not null)

Answer 3

I did more simple (positive way) and it seems to work well.

Since any kind of "object" is at least an object

    if (MyObj is Object)
    {
            //Do something .... for example:  
            if (MyObj is Button)
                MyObj.Enabled = true;
    }

Answer 4

As of C# 8 you can use the 'empty' property pattern (with pattern matching) to ensure an object is not null:

if (obj is { })
{
    // 'obj' is not null here
}

This approach means "if the object references an instance of something" (i.e. it's not null).

You can think of this as the opposite of: if (obj is null).... which will return true when the object does not reference an instance of something.

For more info on patterns in C# 8.0 read here.

Answer 5

C# 6 has monadic null checking :)

before:

if (points != null) {
    var next = points.FirstOrDefault();
    if (next != null && next.X != null) return next.X;
}   
return -1;

after:

var bestValue = points?.FirstOrDefault()?.X ?? -1;

Answer 6

As of C# 9 you can do

if (obj is null) { ... }

For not null use

if (obj is not null) { ... }

If you need to override this behaviour use == and != accordingly.