flutter dart ..addAll

List<dynamic> test1=[];

List<dynamic> test2=[];

List<dynamic> test3=[];

List<dynamic> test4=[];

Code 1 and Code 2 are equivalent

• code 1

test4.addAll(test1);
test4.addAll(test2);
test4.addAll(test3);

• code 2

test4..addAll(test1)..addAll(test2)..addAll(test3);

Reference blog:
flutter dart syntax to merge multiple List arrays