如何使用 sortedArrayUsingDescriptors 对 NSMutableArray 进行排序？

Question

我有一个关于排序NSMutableArray 的问题。我可以使用sortedArrayUsingDescriptors: 方法对包含对象的数组进行排序。

例如，我有一个NSMutableArray 的places，其中我有一个属性frequency（int 值），我想按frequency 降序排序，但我不知道如何正确使用它。

我在initWithKey 中输入什么作为键？

我的对象place 包含：

NSString * name;
NSString * address;
NSString * frequency;
NSString * type;

---

NSMutableArray * places;

... populate array with objects ...

NSSortDescriptor * sortByFrequency =
   [[[NSSortDescriptor alloc] initWithKey:@"????????" ascending:NO] autorelease];

NSArray * descriptors = [NSArray arrayWithObject:sortByFrequency];
NSArray * sorted = [x sortedArrayUsingDescriptors:descriptors];

Answer 1

要对对象数组进行排序：

1. setup NSSortDescriptor - 使用变量名称作为键来设置用于排序的描述符以及要在这些键上执行的选择器
2. 使用您设置的NSSortDescriptor 获取描述符数组
3. 根据这些描述符对数组进行排序

这里有两个示例，一个使用NSDictionary 和NSString/NSNumber 值对NSNumber 进行排序，另一个使用自定义类对两个NSString 字段进行排序。

在 Cocoa 编程主题中关注 Sorting and Filtering NSArray Objects 以查看更多示例和说明。

示例：

这是在 GNUStep 上完成的，它在 Cocoa 上的工作方式应该相同 - 代码完全相同 - 我会在我坐在 Mac 前尝试：

第一个示例使用 NSString 和 NSNumber 值并对 NSNumber 值进行排序：

NSString * NAME      = @"name";
NSString * ADDRESS   = @"address";
NSString * FREQUENCY = @"frequency";
NSString * TYPE      = @"type";

NSMutableArray * array = [NSMutableArray array];

NSDictionary * dict;

dict = [NSDictionary dictionaryWithObjectsAndKeys:
            @"Alehandro", NAME, @"Sydney", ADDRESS,
            [NSNumber numberWithInt:100], FREQUENCY,
            @"T", TYPE, nil];
[array addObject:dict];

dict = [NSDictionary dictionaryWithObjectsAndKeys:
            @"Xentro", NAME, @"Melbourne", ADDRESS,
            [NSNumber numberWithInt:50], FREQUENCY,
            @"X", TYPE, nil];
[array addObject:dict];

dict = [NSDictionary dictionaryWithObjectsAndKeys:
            @"John", NAME, @"Perth", ADDRESS,
            [NSNumber numberWithInt:75],
            FREQUENCY, @"A", TYPE, nil];
[array addObject:dict];

dict = [NSDictionary dictionaryWithObjectsAndKeys:
            @"Fjord", NAME, @"Brisbane", ADDRESS,
            [NSNumber numberWithInt:20], FREQUENCY,
            @"B", TYPE, nil];
[array addObject:dict];

---

使用频率字段为NSNumber的描述符对部分进行排序：

NSSortDescriptor * frequencyDescriptor =
    [[[NSSortDescriptor alloc] initWithKey:FREQUENCY
                                 ascending:YES] autorelease];

id obj;
NSEnumerator * enumerator = [array objectEnumerator];
while ((obj = [enumerator nextObject])) NSLog(@"%@", obj);

NSArray * descriptors =
    [NSArray arrayWithObjects:frequencyDescriptor, nil];
NSArray * sortedArray =
    [array sortedArrayUsingDescriptors:descriptors];

NSLog(@"\nSorted ...");

enumerator = [sortedArray objectEnumerator];
while ((obj = [enumerator nextObject])) NSLog(@"%@", obj);

---

输出 - 按频率字段排序：

2009-12-04 x[1] {address = Sydney; frequency = 100; name = Alehandro; type = T; }
2009-12-04 x[1] {address = Melbourne; frequency = 50; name = Xentro; type = X; }
2009-12-04 x[1] {address = Perth; frequency = 75; name = John; type = A; }
2009-12-04 x[1] {address = Brisbane; frequency = 20; name = Fjord; type = B; }
2009-12-04 x[1]
Sorted ...
2009-12-04 x[1] {address = Brisbane; frequency = 20; name = Fjord; type = B; }
2009-12-04 x[1] {address = Melbourne; frequency = 50; name = Xentro; type = X; }
2009-12-04 x[1] {address = Perth; frequency = 75; name = John; type = A; }
2009-12-04 x[1] {address = Sydney; frequency = 100; name = Alehandro; type = T; }

---

---

第二个示例，自定义类并按两个 NSString 变量排序。

要排序的数组（参见底部的A 类）：

NSMutableArray * array = [NSMutableArray array];
[array addObject:[[A alloc] initWithFirstName:@"Alehandro"
                                     lastName:@"Xentro"
                                          age:[NSNumber numberWithInt:40]]];
[array addObject:[[A alloc] initWithFirstName:@"John"
                                     lastName:@"Smith"
                                          age:[NSNumber numberWithInt:30]]];
[array addObject:[[A alloc] initWithFirstName:@"John"
                                     lastName:@"Smyth"
                                          age:[NSNumber numberWithInt:25]]];
[array addObject:[[A alloc] initWithFirstName:@"Torro"
                                     lastName:@"Ola"
                                          age:[NSNumber numberWithInt:45]]];
[array addObject:[[A alloc] initWithFirstName:@"Alehandro"
                                     lastName:@"Bento"
                                          age:[NSNumber numberWithInt:41]]];
[array addObject:[[A alloc] initWithFirstName:@"Alehandro"
                                     lastName:@"Axel"
                                          age:[NSNumber numberWithInt:41]]];

---

排序部分，先按姓氏排序，再按名字排序：

NSString * LASTNAME = @"lastName";
NSString * FIRSTNAME = @"firstName";

NSSortDescriptor *lastDescriptor =
    [[[NSSortDescriptor alloc]
        initWithKey:LASTNAME
          ascending:YES
           selector:@selector(localizedCaseInsensitiveCompare:)] autorelease];

NSSortDescriptor *firstDescriptor =
    [[[NSSortDescriptor alloc]
        initWithKey:FIRSTNAME
          ascending:YES
           selector:@selector(localizedCaseInsensitiveCompare:)] autorelease];

NSArray * descriptors =
   [NSArray arrayWithObjects:lastDescriptor, firstDescriptor, nil];
NSArray * sortedArray =
   [array sortedArrayUsingDescriptors:descriptors];

---

打印结果：

NSLog(@"\nSorted ...");

enumerator = [sortedArray objectEnumerator];
while ((obj = [enumerator nextObject])) NSLog(@"%@", obj);

---

结果（排序前后）：

2009-12-04 00:52:16.637 x[11375] Alehandro, Xentro, age:40
2009-12-04 00:52:16.644 x[11375] John, Smith, age:30
2009-12-04 00:52:16.644 x[11375] John, Smyth, age:25
2009-12-04 00:52:16.644 x[11375] Torro, Ola, age:45
2009-12-04 00:52:16.645 x[11375] Alehandro, Bento, age:41
2009-12-04 00:52:16.645 x[11375] Alehandro, Axel, age:41
2009-12-04 00:52:16.645 x[11375]
Sorted ...
2009-12-04 00:52:16.645 x[11375] Alehandro, Axel, age:41
2009-12-04 00:52:16.645 x[11375] Alehandro, Bento, age:41
2009-12-04 00:52:16.645 x[11375] Torro, Ola, age:45
2009-12-04 00:52:16.645 x[11375] John, Smith, age:30
2009-12-04 00:52:16.645 x[11375] John, Smyth, age:25
2009-12-04 00:52:16.645 x[11375] Alehandro, Xentro, age:40

A 类扩展 NSObject - 这里没什么特别的：

#import <Foundation/Foundation.h>

@interface A : NSObject
{
    NSString * firstName;
    NSString * lastName;
    NSNumber * age;
}

- (id)initWithFirstName:(NSString*)aFirstName
               lastName:(NSString*)aLastName
                    age:(NSNumber*)anAge;

-(NSString* )description;
+(NSString*)action;

@end

实施：

#import <Foundation/Foundation.h>
#import "A.h"

@implementation A

- (id)init
{
    return [self initWithFirstName:@"N/A"
                          lastName:@"N/A"
                               age:0];
}

- (id)initWithFirstName:(NSString*)aFirstName
               lastName:(NSString*)aLastName
                    age:(NSNumber*)anAge
{
    self = [super init];
    if (!self) return nil;

    firstName = [aFirstName copy];
    lastName = [aLastName copy];
    age = [anAge copy];

    return self;
}

- (void)dealloc
{
    [firstName release];
    [lastName release];
    [age release];
    [super release];
}

---

- (NSString *) description
{
    return [NSString stringWithFormat: @"%@, %@, age:%@",
                                       firstName, lastName, age];
}
@end

Answer 2

“键”是您的对象（数组“x”的元素）的一种方法，它返回您想要排序的东西。所以在这种情况下，你说你想按“频率”排序。那么你所要做的就是使用返回频率的方法名作为key。

Answer 3

下面是如何对 NSMutableArray 进行排序：

NSMutableArray *numberSort =[[NSMutableArray alloc] init];

    while ((key = [enumerator nextObject])) {
        //(NSNumber *)integer = [key integerValue];
        [numberSort  addObject:[NSNumber numberWithInt:[key intValue]]];
        // code that uses the returned key 
    }


    NSArray *stringSort = [numberSort sortedArrayUsingSelector:@selector(compare:)];
    enumerator = [stringSort objectEnumerator];
    NSNumber  *intKey;

    NSMutableArray *backToString =[[NSMutableArray alloc] init];

    while ((intKey = [enumerator nextObject])) {
        //(NSNumber *)integer = [key integerValue];
        [backToString  addObject:[intKey stringValue]];
        // code that uses the returned key