Both have most of the same attributes, both support different kind of animations, both represent different data.
What are the differences between a UIView and a CALayer?
Ios – What are the differences between a UIView and a CALayer
calayeriosuikituiview
Related Solutions
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.
You will only need a
ScrollView
if the contents you have now do not fit in the iPhone screen. (If you are adding theScrollView
as the superview of the components just to make theTextField
scroll up when keyboard comes up, then it's not needed.)The standard way to prevent the
TextField
s from being covered by the keyboard is to move the view up/down whenever the keyboard is shown.
Here is some sample code:
#define kOFFSET_FOR_KEYBOARD 80.0
-(void)keyboardWillShow {
// Animate the current view out of the way
if (self.view.frame.origin.y >= 0)
{
[self setViewMovedUp:YES];
}
else if (self.view.frame.origin.y < 0)
{
[self setViewMovedUp:NO];
}
}
-(void)keyboardWillHide {
if (self.view.frame.origin.y >= 0)
{
[self setViewMovedUp:YES];
}
else if (self.view.frame.origin.y < 0)
{
[self setViewMovedUp:NO];
}
}
-(void)textFieldDidBeginEditing:(UITextField *)sender
{
if ([sender isEqual:mailTf])
{
//move the main view, so that the keyboard does not hide it.
if (self.view.frame.origin.y >= 0)
{
[self setViewMovedUp:YES];
}
}
}
//method to move the view up/down whenever the keyboard is shown/dismissed
-(void)setViewMovedUp:(BOOL)movedUp
{
[UIView beginAnimations:nil context:NULL];
[UIView setAnimationDuration:0.3]; // if you want to slide up the view
CGRect rect = self.view.frame;
if (movedUp)
{
// 1. move the view's origin up so that the text field that will be hidden come above the keyboard
// 2. increase the size of the view so that the area behind the keyboard is covered up.
rect.origin.y -= kOFFSET_FOR_KEYBOARD;
rect.size.height += kOFFSET_FOR_KEYBOARD;
}
else
{
// revert back to the normal state.
rect.origin.y += kOFFSET_FOR_KEYBOARD;
rect.size.height -= kOFFSET_FOR_KEYBOARD;
}
self.view.frame = rect;
[UIView commitAnimations];
}
- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
// register for keyboard notifications
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(keyboardWillShow)
name:UIKeyboardWillShowNotification
object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(keyboardWillHide)
name:UIKeyboardWillHideNotification
object:nil];
}
- (void)viewWillDisappear:(BOOL)animated
{
[super viewWillDisappear:animated];
// unregister for keyboard notifications while not visible.
[[NSNotificationCenter defaultCenter] removeObserver:self
name:UIKeyboardWillShowNotification
object:nil];
[[NSNotificationCenter defaultCenter] removeObserver:self
name:UIKeyboardWillHideNotification
object:nil];
}
Best Answer
On iOS, every UIView is backed by a Core Animation CALayer, so you are dealing with CALayers when using a UIView, even though you may not realize it. Unlike NSViews on the Mac, which evolved before Core Animation existed, UIViews are intended to be lightweight wrappers around these CALayers.
As I describe in the similar question "When to use CALayer on the Mac/iPhone?", working directly with CALayers doesn't give you significant performance advantages over UIViews. One of the reasons you might want to build a user interface element with CALayers instead of UIViews is that it can be very easily ported to the Mac. UIViews are very different from NSViews, but CALayers are almost identical on the two platforms. This is why the Core Plot framework lays out its graphs using CALayers instead of other UI elements.
One thing UIViews provide over CALayers is built-in support for user interaction. They handle hit-testing on touches and other related actions that you would need to build yourself if managing a hierarchy of CALayers. It's not that hard to implement this yourself, but it is extra code you'd need to write when building a CALayer-only interface.
You will often need to access the underlying layers for a UIView when performing more complex animations than the base UIView class allows. UIView's animation capabilities have grown as the iOS SDK has matured, but there are still a few things that are best done by interacting with the underlying CALayer.