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.
The nicest solution I have found is to do the following in the first view controller.
Objective-C
- (void)viewWillAppear:(BOOL)animated {
[self.navigationController setNavigationBarHidden:YES animated:animated];
[super viewWillAppear:animated];
}
- (void)viewWillDisappear:(BOOL)animated {
[self.navigationController setNavigationBarHidden:NO animated:animated];
[super viewWillDisappear:animated];
}
Swift
override func viewWillAppear(_ animated: Bool) {
self.navigationController?.setNavigationBarHidden(true, animated: animated)
super.viewWillAppear(animated)
}
override func viewWillDisappear(_ animated: Bool) {
self.navigationController?.setNavigationBarHidden(false, animated: animated)
super.viewWillDisappear(animated)
}
This will cause the navigation bar to animate in from the left (together with the next view) when you push the next UIViewController
on the stack, and animate away to the left (together with the old view), when you press the back button on the UINavigationBar
.
Please note also that these are not delegate methods, you are overriding UIViewController
's implementation of these methods, and according to the documentation you must call the super's implementation somewhere in your implementation.
Best Answer
Well if you are using storyboards , what you can do is set your uiviewcontrollers' storyboard id and use it for popping and pushing your views.
Lets say your Storyboards name is
MainStoryboard.storyboard
Above solution should work for you , but If I were you I would change the structure of my app , you say :
Since View1 is just logo and View 2 is also a view that you skip, you can remove them from navigation controller and make View3 your navigation controller's
root view controller
and when you need view1 and view2present them as Modal View Controllers
,when you are done with them lets say; user successfully loaded the app dismiss logo screen and
present Download Screen
if download successful then dismiss it.So your View3 Will be there as root view controller, lets say your at View(n) you want to go to home screen which is View3 all you need to do is call
When you are on
view(n)
and want to pop toview(n-1)
just usegood luck,