What does an question (?) mark and dot (.) in dart language?

Question

say I defined ...

final DocumentSnapshot doc;

variable doc might be null so I use a question mark and dot...

print(widget.doc); // null
print(widget.doc == null); // true
print(widget.doc?.data['name']);

why widget.doc?.data['name'] throw error Tried calling: []("name") instead returning null?

for my understanding ?. to check whether null and if it so will return null

Answer 1

To guard access to a property or method of an object that might be null, put a question mark (?) before the dot (.):

myObject?.someProperty

The preceding code is equivalent to the following:

(myObject != null) ? myObject.someProperty : null

You can chain multiple uses of ?. together in a single expression:

myObject?.someProperty?.someMethod()

The preceding code returns null (and never calls someMethod()) if either myObject or myObject.someProperty is null.

Code example Try using conditional property access to finish the code snippet below.

// This method should return the uppercase version of `str`
// or null if `str` is null.
String upperCaseIt(String str) {
  return str?.toUpperCase();
}