Method call if not null in C#

From C# 6 onwards, you can just use:

MyEvent?.Invoke();

or:

obj?.SomeMethod();

The ?. is the null-propagating operator, and will cause the .Invoke() to be short-circuited when the operand is null. The operand is only accessed once, so there is no risk of the "value changes between check and invoke" problem.

===

Prior to C# 6, no: there is no null-safe magic, with one exception; extension methods - for example:

public static void SafeInvoke(this Action action) {
    if(action != null) action();
}

now this is valid:

Action act = null;
act.SafeInvoke(); // does nothing
act = delegate {Console.WriteLine("hi");}
act.SafeInvoke(); // writes "hi"

In the case of events, this has the advantage of also removing the race-condition, i.e. you don't need a temporary variable. So normally you'd need:

var handler = SomeEvent;
if(handler != null) handler(this, EventArgs.Empty);

but with:

public static void SafeInvoke(this EventHandler handler, object sender) {
    if(handler != null) handler(sender, EventArgs.Empty);
}

we can use simply:

SomeEvent.SafeInvoke(this); // no race condition, no null risk

What you're looking for is the Null-Conditional (not "coalescing") operator: ?.. It's available as of C# 6.

Your example would be obj?.SomeMethod();. If obj is null, nothing happens. When the method has arguments, e.g. obj?.SomeMethod(new Foo(), GetBar()); the arguments are not evaluated if obj is null, which matters if evaluating the arguments would have side effects.

And chaining is possible: myObject?.Items?[0]?.DoSomething()

A quick extension method:

    public static void IfNotNull<T>(this T obj, Action<T> action, Action actionIfNull = null) where T : class {
        if(obj != null) {
            action(obj);
        } else if ( actionIfNull != null ) {
            actionIfNull();
        }
    }

example:

  string str = null;
  str.IfNotNull(s => Console.Write(s.Length));
  str.IfNotNull(s => Console.Write(s.Length), () => Console.Write("null"));

or alternatively:

    public static TR IfNotNull<T, TR>(this T obj, Func<T, TR> func, Func<TR> ifNull = null) where T : class {
        return obj != null ? func(obj) : (ifNull != null ? ifNull() : default(TR));
    }

example:

    string str = null;
    Console.Write(str.IfNotNull(s => s.Length.ToString());
    Console.Write(str.IfNotNull(s => s.Length.ToString(), () =>  "null"));