The last two are identical; "atomic" is the default behavior (note that it is not actually a keyword; it is specified only by the absence of nonatomic
-- atomic
was added as a keyword in recent versions of llvm/clang).
Assuming that you are @synthesizing the method implementations, atomic vs. non-atomic changes the generated code. If you are writing your own setter/getters, atomic/nonatomic/retain/assign/copy are merely advisory. (Note: @synthesize is now the default behavior in recent versions of LLVM. There is also no need to declare instance variables; they will be synthesized automatically, too, and will have an _
prepended to their name to prevent accidental direct access).
With "atomic", the synthesized setter/getter will ensure that a whole value is always returned from the getter or set by the setter, regardless of setter activity on any other thread. That is, if thread A is in the middle of the getter while thread B calls the setter, an actual viable value -- an autoreleased object, most likely -- will be returned to the caller in A.
In nonatomic
, no such guarantees are made. Thus, nonatomic
is considerably faster than "atomic".
What "atomic" does not do is make any guarantees about thread safety. If thread A is calling the getter simultaneously with thread B and C calling the setter with different values, thread A may get any one of the three values returned -- the one prior to any setters being called or either of the values passed into the setters in B and C. Likewise, the object may end up with the value from B or C, no way to tell.
Ensuring data integrity -- one of the primary challenges of multi-threaded programming -- is achieved by other means.
Adding to this:
atomicity
of a single property also cannot guarantee thread safety when multiple dependent properties are in play.
Consider:
@property(atomic, copy) NSString *firstName;
@property(atomic, copy) NSString *lastName;
@property(readonly, atomic, copy) NSString *fullName;
In this case, thread A could be renaming the object by calling setFirstName:
and then calling setLastName:
. In the meantime, thread B may call fullName
in between thread A's two calls and will receive the new first name coupled with the old last name.
To address this, you need a transactional model. I.e. some other kind of synchronization and/or exclusion that allows one to exclude access to fullName
while the dependent properties are being updated.
Best Answer
Related:
Larger version of this article can also be found HERE, to be transparent it is my personal blog.
Hybrid vs Native apps
Hybrid apps:
Pro:
Cons:
Native apps:
Pro:
Cons:
In your case, if you have a good web development/design skills and/or have a good designer you should choose a hybrid app. Go native only if this app is going to be a complex one. Everything you want can be done with a hybrid app. And you will find a great and supporting community.
Hybrid apps
What I didn't previously mentioned you need to be specially careful here. Even if you are seasoned developer you will find a lot of problems you can't solve. Hybrid development should not be mistaken for a basic web development.
Every mobile platform has its own set of problems, not to mention that mobile phones behave differently depending on a device. If possible always create a app that works on a slower devices because native app will successfully work on almost any device.
There's one last thing, when creating hybrid apps, app development will take you about 30%-50% of your time, rest goes to specific platform debugging and learning. Believe me, even after several years of mobile development sometimes I am facing problems I can't solve alone or fast enough.
So be careful when choosing mobile framework, pick 2-3 and spend several days reading about them.
Links
Here are few links to help you decide:
PhoneGap + jQuery Mobile 1.4 tutorial - This is a step by step tutorial for PhoneGap and last version of jQuery Mobile
PhoneGap + jQuery Mobile 1.4 tutorial - MacOS version - This is a step by step tutorial for PhoneGap deployment on MacOS. jQuery Mobile part is covered in a previous article, no point in repeating things.
jQuery Mobile vs Sencha Touch - jQuery Mobile Sencha Touch comparison
jQuery Mobile vs Kendo UI - jQuery Mobile Kendo UI comparison
7 best known HTML5 mobile frameworks - Name tells everything
7 less known HTML5 mobile frameworks - Name tells everything