This presentation contains new ideas in the field of mobile software development, discussed at NSConference 6 – one of the most popular mobile conferences in Europe. Presentation by Yuriy Berdnikov, leading engineer, GlobalLogic. Mobile TechTalk, Lviv, 2014. More details - www.globallogic.com.ua/press-releases/mobile-techtalk-lviv/

1. CONFIDENTIAL©2013 GlobalLogic Inc.
Interesting talks from
NSConference 6
by Yuriy Berdnikov

2. ©2013 GlobalLogic Inc. CONFIDENTIAL

3. CONFIDENTIAL
Key Value Observing (KVO)
Core Data Sync with Ensembles
“Don’t reinvent the wheel”. Why ?

4. CONFIDENTIAL
 Yearly event since 2009
 More then 300 people attended this year
 Speakers - lead developers, book writers, etc. Some of
them was performed on Apple WWDC.
 Balance between technical and UX material
NSConference

5. CONFIDENTIAL
Key Value Observing

6. CONFIDENTIAL
What is KVO ?
It provides a way for objects to get notified when the properties of other
objects are changed. One object observes a key of another object. When
the observed object changes the value of that key, the observer gets
notified.

7. CONFIDENTIAL
Subscribing

8. CONFIDENTIAL
Responding

9. CONFIDENTIAL
So how does that work, not needing any
code in the observed object?

10. CONFIDENTIAL
isa-swizzling
• It creates a brand new class at runtime that
subclasses your class
• It overrides the set methods for any observed
keys
• It switches out the isa pointer of your object

11. CONFIDENTIAL
Sample

12. CONFIDENTIAL
@interface TestClass : NSObject
{
int x;
int y;
int z;
}
@property int x;
@property int y;
@property int z;
@end

13. CONFIDENTIAL
static NSArray *ClassMethodNames(Class c)
{
NSMutableArray *array = [NSMutableArray array];
unsigned int methodCount = 0;
Method *methodList = class_copyMethodList(c, &methodCount);
for (unsigned int i = 0; i < methodCount; i++)
[array addObject:
NSStringFromSelector(method_getName(methodList[i]))];
free(methodList);
return array;
}

14. CONFIDENTIAL
static void PrintDescription(NSString *name, id obj)
{
NSString *str = [NSString stringWithFormat:
@"%@: %@nt NSObject class %snt”
“libobjc class %snt implements methods <%@>",
name,
obj,
class_getName([obj class]),
class_getName(obj->isa),
[ClassMethodNames(obj->isa) componentsJoinedByString:@", “]];
printf("%sn", [str UTF8String]);
}

15. CONFIDENTIAL
int main(int argc, char **argv)
{
[NSAutoreleasePool new];
TestClass *x = [[TestClass alloc] init];
TestClass *y = [[TestClass alloc] init];
TestClass *xy = [[TestClass alloc] init];
TestClass *control = [[TestClass alloc] init];
[x addObserver:x forKeyPath:@"x" options:0 context:NULL];
[xy addObserver:xy forKeyPath:@"x" options:0 context:NULL];
[y addObserver:y forKeyPath:@"y" options:0 context:NULL];
[xy addObserver:xy forKeyPath:@"y" options:0 context:NULL];
PrintDescription(@"control", control);
PrintDescription(@"x", x);
PrintDescription(@"y", y);
PrintDescription(@"xy", xy);
return 0;
}

16. CONFIDENTIAL
Running the Code
control: <TestClass: 0x104b20>
NSObject class TestClass
libobjc class TestClass
implements methods <setX:, x, setY:, y, setZ:, z>
x: <TestClass: 0x103280>
NSObject class TestClass
libobjc class NSKVONotifying_TestClass
implements methods <setY:, setX:, class, dealloc, _isKVOA>
y: <TestClass: 0x104b00>
NSObject class TestClass
libobjc class NSKVONotifying_TestClass
implements methods <setY:, setX:, class, dealloc, _isKVOA>
xy: <TestClass: 0x104b10>
NSObject class TestClass
libobjc class NSKVONotifying_TestClass
implements methods <setY:, setX:, class, dealloc, _isKVOA>

17. CONFIDENTIAL
Core Data Sync with Ensembles

18. CONFIDENTIAL
Elements of Sync
• Identifying corresponding objects across stores
• Determining what has changed since the last sync
• Resolving conflicts due to concurrent changes

19. CONFIDENTIAL
Ensembles
• Requires minimal changes to existing code
• Backend agnostic
• Eventual consistency of data across client devices
• Conflict resolution

20. CONFIDENTIAL
• github.com/drewmccormack/ensembles
• ensembles.io

21. CONFIDENTIAL
“Don’t reinvent the wheel”

22. CONFIDENTIAL
Why ?
• Old code sucks
• 1000 solutions for 1000 problems, but you only
need 1
• Maintenance

23. CONFIDENTIAL

24. CONFIDENTIAL
• There is a good code!
• Manage risks
• Learn technologies that 3rd party code uses
• Write own frameworks

25. CONFIDENTIAL©2013 GlobalLogic Inc.
Q&A

26. CONFIDENTIAL©2013 GlobalLogic Inc.
Thank you