Here are some useful macros around NSLog I use a lot:
#ifdef DEBUG
# define DLog(fmt, ...) NSLog((@"%s [Line %d] " fmt), __PRETTY_FUNCTION__, __LINE__, ##__VA_ARGS__)
#else
# define DLog(...)
#endif
// ALog always displays output regardless of the DEBUG setting
#define ALog(fmt, ...) NSLog((@"%s [Line %d] " fmt), __PRETTY_FUNCTION__, __LINE__, ##__VA_ARGS__)
The DLog macro is used to only output when the DEBUG variable is set (-DDEBUG in the projects's C flags for the debug confirguration).
ALog will always output text (like the regular NSLog).
The output (e.g. ALog(@"Hello world") ) will look like this:
-[LibraryController awakeFromNib] [Line 364] Hello world
objectForKey:
is an NSDictionary
method. An NSDictionary
is a collection class similar to an NSArray
, except instead of using indexes, it uses keys to differentiate between items. A key is an arbitrary string you provide. No two objects can have the same key (just as no two objects in an NSArray
can have the same index).
valueForKey:
is a KVC method. It works with ANY class. valueForKey:
allows you to access a property using a string for its name. So for instance, if I have an Account
class with a property accountNumber
, I can do the following:
NSNumber *anAccountNumber = [NSNumber numberWithInt:12345];
Account *newAccount = [[Account alloc] init];
[newAccount setAccountNumber:anAccountNUmber];
NSNumber *anotherAccountNumber = [newAccount accountNumber];
Using KVC, I can access the property dynamically:
NSNumber *anAccountNumber = [NSNumber numberWithInt:12345];
Account *newAccount = [[Account alloc] init];
[newAccount setValue:anAccountNumber forKey:@"accountNumber"];
NSNumber *anotherAccountNumber = [newAccount valueForKey:@"accountNumber"];
Those are equivalent sets of statements.
I know you're thinking: wow, but sarcastically. KVC doesn't look all that useful. In fact, it looks "wordy". But when you want to change things at runtime, you can do lots of cool things that are much more difficult in other languages (but this is beyond the scope of your question).
If you want to learn more about KVC, there are many tutorials if you Google especially at Scott Stevenson's blog. You can also check out the NSKeyValueCoding Protocol Reference.
Hope that helps.
Best Answer
The bounds of an UIView is the rectangle, expressed as a location (x,y) and size (width,height) relative to its own coordinate system (0,0).
The frame of an UIView is the rectangle, expressed as a location (x,y) and size (width,height) relative to the superview it is contained within.
So, imagine a view that has a size of 100x100 (width x height) positioned at 25,25 (x,y) of its superview. The following code prints out this view's bounds and frame:
And the output of this code is:
So, we can see that in both cases, the width and the height of the view is the same regardless of whether we are looking at the bounds or frame. What is different is the x,y positioning of the view. In the case of the bounds, the x and y coordinates are at 0,0 as these coordinates are relative to the view itself. However, the frame x and y coordinates are relative to the position of the view within the parent view (which earlier we said was at 25,25).
There is also a great presentation that covers UIViews. See slides 1-20 which not only explain the difference between frames and bounds but also show visual examples.