NSSortDescriptor

Specifying Sorts Using NSSortDescriptor

 

 

Let’s assume, as an example, that we have an array (an instance of NSArray) containing instances of a custom class, Employee (that meets the requirements set out in “Requirements of Collection Objects”). The Employee class has attributes for an employee’s first and last name (instances of NSString), date of hire (an instance of NSDate), and age (an instance of NSNumber).

 

 

1：Sorting the array by the age key

ageDescriptor = [[[NSSortDescriptor alloc] initWithKey:@"age"
                                           ascending:YES] autorelease];
sortDescriptors = [NSArray arrayWithObject:ageDescriptor];
sortedArray = [employeesArray sortedArrayUsingDescriptors:sortDescriptors];

 

2：Sorting the array by the age and date of hire key

ageDescriptor = [[[NSSortDescriptor alloc] initWithKey:@"age"
                                                    ascending:YES] autorelease];
hireDateDescriptor = [[[NSSortDescriptor alloc] initWithKey:@"hireDate"
                                                     ascending:YES] autorelease];
sortDescriptors = [NSArray arrayWithObjects:ageDescriptor, hireDateDescriptor, nil];
sortedArray = [employeesArray sortedArrayUsingDescriptors:sortDescriptors];

 

 

Specifying Custom Comparisons

 

 

 Sorting the array using a localized case insensitive comparison

 

lastNameDescriptor = [[[NSSortDescriptor alloc]
              initWithKey:@"lastName"
              ascending:YES
              selector:@selector(localizedCaseInsensitiveCompare:)] autorelease];
 firstNameDescriptor = [[[NSSortDescriptor alloc]
              initWithKey:@"firstName"
              ascending:YES
              selector:@selector(localizedCaseInsensitiveCompare:)] autorelease];
 sortDescriptors = [NSArray arrayWithObjects:lastNameDescriptor,
              firstNameDescriptor, nil];
 sortedArray = [peopleArray sortedArrayUsingDescriptors:sortDescriptors];

 
The Foundation classes that have methods that can be used with sort descriptors are listed in Table 1.

 

Table 1  Common Foundation classes and comparison methods

 

 

 写道

Comparison Method Supporting Classes

compare: NSString, NSMutableString, NSDate, NSCalendarDate, NSValue (scalar types and unsigned char only), NSNumber
caseInsensitiveCompare: NSString, NSMutableString
localizedCompare: NSString, NSMutableString
localizedCaseInsensitiveCompare: NSString, NSMutableString