If you see this warning:
warning: receiver 'MyCoolClass' is a forward class and corresponding @interface may not exist
you need to #import
the file, but you can do that in your implementation file (.m), and use the @class
declaration in your header file.
@class
does not (usually) remove the need to #import
files, it just moves the requirement down closer to where the information is useful.
For Example
If you say @class MyCoolClass
, the compiler knows that it may see something like:
MyCoolClass *myObject;
It doesn't have to worry about anything other than MyCoolClass
is a valid class, and it should reserve room for a pointer to it (really, just a pointer). Thus, in your header, @class
suffices 90% of the time.
However, if you ever need to create or access myObject
's members, you'll need to let the compiler know what those methods are. At this point (presumably in your implementation file), you'll need to #import "MyCoolClass.h"
, to tell the compiler additional information beyond just "this is a class".
Compare method
Either you implement a compare-method for your object:
- (NSComparisonResult)compare:(Person *)otherObject {
return [self.birthDate compare:otherObject.birthDate];
}
NSArray *sortedArray = [drinkDetails sortedArrayUsingSelector:@selector(compare:)];
NSSortDescriptor (better)
or usually even better:
NSSortDescriptor *sortDescriptor;
sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"birthDate"
ascending:YES];
NSArray *sortedArray = [drinkDetails sortedArrayUsingDescriptors:@[sortDescriptor]];
You can easily sort by multiple keys by adding more than one to the array. Using custom comparator-methods is possible as well. Have a look at the documentation.
Blocks (shiny!)
There's also the possibility of sorting with a block since Mac OS X 10.6 and iOS 4:
NSArray *sortedArray;
sortedArray = [drinkDetails sortedArrayUsingComparator:^NSComparisonResult(Person *a, Person *b) {
return [a.birthDate compare:b.birthDate];
}];
Performance
The -compare:
and block-based methods will be quite a bit faster, in general, than using NSSortDescriptor
as the latter relies on KVC. The primary advantage of the NSSortDescriptor
method is that it provides a way to define your sort order using data, rather than code, which makes it easy to e.g. set things up so users can sort an NSTableView
by clicking on the header row.
Best Answer
In IB, you can hook up an
IBAction
to theValue Changed event
or in code add target/action forUIControlEventValueChanged
. For example:Note that if you want the value change events as the user is
sliding
, then be sure that theslider
'scontinuous property
is also set. On the other hand, if you don't want the event to fire as the user issliding
and only when they finish sliding, set continuous to NO (or uncheck in IB).