NSArray，NSSet等集合类的使用

NSArray与NSSet

NSArray：有序的集合，存储的元素在一个整块的内存中并按序排列；
NSSet：无序的集合，散列存储。
读developer.apple关于NSSet的解释：You can use sets as an alternative to arrays when the order of elements isn’t important and performance in testing whether an object is contained in the set is a consideration—while arrays are ordered, testing for membership is slower than with sets.
就是说，如果搜索一个元素，NSSet的效率会比NSArray高。为什么呢？道理比较简单：hash！NSSet中元素的存储和访问都是一个hash的过程。比如你要存储元素A，一个hash算法直接就能直接找到A应该存储的位置；同样，当你要访问A时，一个hash过程就能找到A存储的位置。而对于NSArray，若想知道A到底在不在数组中，则需要一个一个元素比较，显然效率没了。

循环使用整个NSArray内的对象

循环使用整个NSArray内的对象是非常常用的了，而且最近我在研究究竟怎么能方便的把NSArray存入Core Data，所以这更是必要了，看看如下的方法吧：

1，Objective-C 2.0法，最应该使用的

NSArray *aArray; //我们的Array，假设他已经初始化有内容了
 
for(id innerObj in aArray) //id可以由其他对象类型替代
{
//也就是说, 在循环中的参数innerObj就是aArray中的对象
//由于NSArray中只能储存对象，所以我们使用id作为内涵对象的类型，其实就是个指针了
//而且如果NSArray中的内容不一致，id更不会出现冲突
}

2，C的老方法，不推荐，低性能

NSArray *aArray; //我们的Array，假设他已经初始化有内容了
 
for(int i=0;i<[aArray count]; i++)
{
[[aArray objectAtIndex:i] 然后作你想作的事情]; //做爱 作的事情...
}

3, 用NSEnumerator（不知道怎么翻译阿….）

 NSEnumerator* myIterator = [myArray reverseObjectEnumerator];
 id anObject;
 
 while( anObject = [myIterator nextObject]) //每次读取“逐读器”的下一个对象
 {
     //anObject和刚才的innerObj是一个意思，但是看看多了这么多行
 }

三种集合类来收集cocoa对象（NSObject对象）：
NSArray 用于对象有序集合（相当于是数组）
NSSet 用于对象无序集合
NSDictionary用于键值映射
以上三种集合类是不可变的（一旦初始化后，就不能改变）

以下是对应的三种可变集合类(这三种可变集合类是对应上面三种集合类的子类)：
NSMutableArray
NSMutableSet
NSMutableDictionary

注：这些集合类只能收集cocoa对象（NSOjbect对象），如果想保存一些原始的C数据（例如，int, float, double, BOOL等），则需要将这些原始的C数据封装成NSNumber类型的，NSNumber对象是cocoa对象，可以被保存在集合类中。

NSArray
Ordered collection of objects. Immutable. You cannot add or remove objects to it once it’s created.
Important methods:
+ (id)arrayWithObjects:(id)firstObject, ...;     // nil terminated 
- (int)count;
- (id)objectAtIndex:(int)index;                     //  NSString *s1=[[myarray objectAtIndex: 0];
- (void)makeObjectsPerformSelector:(SEL)aSelector;
- (NSArray *)sortedArrayUsingSelector:(SEL)aSelector;
- (id)lastObject; // returns nil if there are no objects in the array (convenient)
注：
类方法arrayWithObjects 可以创建an autoreleased NSArray of the items.例如
@implementation MyObject
- (NSArray *)coolCats {
return [NSArray arrayWithObjects:@“Steve”, @“Ankush”, @“Sean”, nil];
}
@end
Other convenient create with methods (all return autoreleased objects):
[NSString stringWithFormat:@“Meaning of %@ is %d”, @“life”, 42];
[NSDictionary dictionaryWithObjectsAndKeys:ankush, @“TA”, janestudent, @“Student”, nil];
[NSArray arrayWithContentsOfFile:(NSString *)path];
-----创建数组 -----
    //NSArray *array = [[NSArray alloc] initWithObjects:
    @"One",@"Two",@"Three",@"Four",nil];

    self.dataArray = array;
    [array release];

    //- (unsigned) Count;数组所包含对象个数；
    NSLog(@"self.dataArray cound:%d",[self.dataArray count]);

    //- (id) objectAtIndex: (unsigned int) index;获取指定索引处的对象;
    NSLog(@"self.dataArray cound 2:%@",[self.dataArray objectAtIndex:2]);

------ 从一个数组拷贝数据到另一数组(可变数级) -------   

    //arrayWithArray:
    //NSArray *array1 = [[NSArray alloc] init];
    NSMutableArray *MutableArray = [[NSMutableArray alloc] init];
    NSArray *array = [NSArray arrayWithObjects:
                      @"a",@"b",@"c",nil];
    NSLog(@"array:%@",array);
    MutableArray = [NSMutableArray arrayWithArray:array];
    NSLog(@"MutableArray:%@",MutableArray);

    array1 = [NSArray arrayWithArray:array];
    NSLog(@"array1:%@",array1);

    //Copy

    //id obj;
    NSMutableArray *newArray = [[NSMutableArray alloc] init];
    NSArray *oldArray = [NSArray arrayWithObjects:
                         @"a",@"b",@"c",@"d",@"e",@"f",@"g",@"h",nil];

    NSLog(@"oldArray:%@",oldArray);
    for(int i = 0; i < [oldArray count]; i++)
    {        
        obj = [[oldArray objectAtIndex:i] copy];
        [newArray addObject: obj];
    }
    //     
    NSLog(@"newArray:%@", newArray);
    [newArray release];

//快速枚举
    //NSMutableArray *newArray = [[NSMutableArray alloc] init];
    NSArray *oldArray = [NSArray arrayWithObjects:
                         @"a",@"b",@"c",@"d",@"e",@"f",@"g",@"h",nil];   
    NSLog(@"oldArray:%@",oldArray);

    for(id obj in oldArray)
    {
        [newArray addObject: obj];
    }
    //     
    NSLog(@"newArray:%@", newArray);
    [newArray release];   

    //Deep copy

    //NSMutableArray *newArray = [[NSMutableArray alloc] init];
    NSArray *oldArray = [NSArray arrayWithObjects:
                         @"a",@"b",@"c",@"d",@"e",@"f",@"g",@"h",nil];   
    NSLog(@"oldArray:%@",oldArray);   
    newArray = (NSMutableArray*)CFPropertyListCreateDeepCopy(kCFAllocatorDefault, (CFPropertyListRef)oldArray, kCFPropertyListMutableContainers);
    NSLog(@"newArray:%@", newArray);
    [newArray release];   

    //Copy and sort

    //NSMutableArray *newArray = [[NSMutableArray alloc] init];
    NSArray *oldArray = [NSArray arrayWithObjects:

NSMutableArray
Mutable version of NSArray.
- (void)addObject:(id)anObject;
- (void)insertObject:(id)anObject atIndex:(int)index;
- (void)removeObjectAtIndex:(int)index;
- (void)removeAllObjects;

-----给数组分配容量-----
    //NSArray *array;
    array = [NSMutableArray arrayWithCapacity:20];

-----在数组末尾添加对象-----
    //- (void) addObject: (id) anObject;
    //NSMutableArray *array = [NSMutableArray arrayWithObjects:@"One",@"Two",@"Three",nil];
    [array addObject:@"Four"];
    NSLog(@"array:%@",array);

-----删除数组中指定索引处对象-----   
    //-(void) removeObjectAtIndex: (unsigned) index;   
    //NSMutableArray *array = [NSMutableArray arrayWithObjects:@"One",@"Two",@"Three",nil];
    [array removeObjectAtIndex:1];
    NSLog(@"array:%@",array);

 ----- 数组枚举-----  
//1、- (NSEnumerator *)objectEnumerator;  //从前向后
    //NSMutableArray *array = [NSMutableArray arrayWithObjects:@"One",@"Two",@"Three",nil];
    NSEnumerator *enumerator;
    enumerator = [array objectEnumerator];

    id thingie;
    while (thingie = [enumerator nextObject]) {
        NSLog(@"thingie:%@",thingie);
    }
//2、- (NSEnumerator *)reverseObjectEnumerator;  //从后向前
    //NSMutableArray *array = [NSMutableArray arrayWithObjects:
    @"One",@"Two",@"Three",nil];
    NSEnumerator *enumerator;
    enumerator = [array reverseObjectEnumerator];

    id object;
    while (object = [enumerator nextObject]) {
        NSLog(@"object:%@",object);
    }
//3、快速枚举
    //NSMutableArray *array = [NSMutableArray arrayWithObjects:
    @"One",@"Two",@"Three",nil];
    for(NSString *string in array)
    {
        NSLog(@"string:%@",string);
    }

----- NSValue（对任何对象进行包装）-----
//将NSRect放入NSArray中
    NSMutableArray *array = [[NSMutableArray alloc] init];
    NSValue *value;
    CGRect rect = CGRectMake(0, 0, 320, 480);   
    value = [NSValue valueWithBytes:&rect objCType:@encode(CGRect)];
    [array addObject:value];
    NSLog(@"array:%@",array);
//从Array中 提取
    value = [array objectAtIndex:0];
    [value getValue:&rect];
    NSLog(@"value:%@",value);

----★使用NSMutableArray要防止内存泄露★------
NSObject* p1 = [[NSObject alloc] init];
NSObject* p2 = [[NSObject alloc] init];
NSMutableArray* objectsArray = [[NSMutableArray alloc] init];

[objectsArray addObject:p1];
NSLog(@"p1 count:%d", [p1 retainCount]);//输出 2，也就是执行追加对象后，对象的计数器也被加1
//[p1 release];
//NSLog(@"p1 count:%d", [p1 retainCount]);

//同样做数组替换时
[objectsArray replaceObjectAtIndex:0 withObject:p2];
NSLog(@"p2 count:%d", [p2 retainCount]);//输出 2，同样也是2
NSLog(@"p1 count:%d", [p1 retainCount]);//输出 1，对象p1仍然存在
//[p2 release];
//NSLog(@"p2 count:%d", [p2 retainCount]);

//执行清空数组
[objectsArray removeAllObjects];
NSLog(@"p2 count:%d", [p2 retainCount]);//输出 1，对象p2仍然存在
//[p2 release];

由此可知，每次执行上面的数组操作后，要执行对象release，如上面注释中的语句，才能保证内存不泄露。

NSSet
Unordered collection of objects.
Immutable. You cannot add or remove objects to it once it’s created.
Important methods:
+ setWithObjects:(id)firstObj, ...;  // nil terminated

- (int)count;
- (BOOL)containsObject:(id)anObject;
- (id)anyObject;
- (void)makeObjectsPerformSelector:(SEL)aSelector;
- (id)member:(id)anObject; // uses isEqual: and returns a matching object (if any)

NSMutableSet
Mutable version of NSSet.
+ (NSMutableSet *)set;

- (void)addObject:(id)anObject;
- (void)removeObject:(id)anObject;

- (void)removeAllObjects;
- (void)unionSet:(NSSet *)otherSet;
- (void)minusSet:(NSSet *)otherSet;
- (void)intersectSet:(NSSet *)otherSet;

NSDictionary
key-value, key-value, ..... 一系列键值对。

key（键）在整个dictionary是唯一的，通过key可以查询其对应的一个或多个value（值）。

Hash table. Look up objects using a key to get a value.
Immutable. You cannot add or remove objects to it once it’s created.
Keys are objects which must implement.  Keys are usually NSString objects.
- (NSUInteger)hash & - (BOOL)isEqual:(NSObject *)obj
Important methods:
+ dictionaryWithObjectsAndKeys: (id)firstObject, ...;

- (int)count;
- (id)objectForKey:(id)key;
- (NSArray *)allKeys;
- (NSArray *)allValues;

 -----创建字典 -----
    //- (id) initWithObjectsAndKeys;

    //NSDictionary *dictionary = [[NSDictionary alloc] initWithObjectsAndKeys:@"One",@"1",@"Two",@"2",@"Three",@"3",nil];
    NSString *string = [dictionary objectForKey:@"One"];
    NSLog(@"string:%@",string);
    NSLog(@"dictionary:%@",dictionary);
    [dictionary release];

NSMutableDictionary
Mutable version of NSDictionary.
+ (NSMutableDictionary *)dictionary;

- (void)setObject:(id)anObject forKey:(id)key;
- (void)removeObjectForKey:(id)key;

- (void)removeAllObjects;
- (void)addEntriesFromDictionary:(NSDictionary *)otherDictionary;

 -----创建可变字典 -----   
//创建
    NSMutableDictionary *dictionary = [NSMutableDictionary dictionary]; 
//添加字典
    [dictionary setObject:@"One" forKey:@"1"];
    [dictionary setObject:@"Two" forKey:@"2"];
    [dictionary setObject:@"Three" forKey:@"3"];
    [dictionary setObject:@"Four" forKey:@"4"];
    NSLog(@"dictionary:%@",dictionary);
//删除指定的字典
    [dictionary removeObjectForKey:@"3"];
    NSLog(@"dictionary:%@",dictionary);