NSSortDescriptor

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本文介绍了如何使用NSSortDescriptor对包含自定义类实例的NSArray进行排序。通过多个示例展示了按年龄、入职日期及姓名等属性进行排序的方法，并解释了如何实现自定义比较逻辑。

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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

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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