不可变数组和可变数组

Posted

tags:

篇首语:本文由小常识网(cha138.com)小编为大家整理,主要介绍了不可变数组和可变数组相关的知识,希望对你有一定的参考价值。

1.数组的特点:

      1)可以储存多个数据;

      2)储存的多个数据的类型要相同;

      3)储存在数组中的数据非常方便管理;

 

2.什么时候使用数组

        当我们有多个类型相同的数据,并且这些数据的意义是一样的,需要储存的时候,就可以使用数组;

 

=================== 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;                                                      // 得到array中的对象个数
- (id)objectAtIndex:(int)index;                       //  得到索引为i的对象

- (BOOL)containsObject:(id)anObject;      // 当anObject出现在array中,则返回yes(实际是通过isEqual:方法来判断)

- (unsigned)indexOfObject:(id)anObject; // 查找array中的anObject,并返回其最小索引值。没找到返回NSNotFound.

- (void)makeObjectsPerformSelector:(SEL)aSelector;

- (NSArray *)sortedArrayUsingSelector:(SEL)aSelector;
- (id)lastObject;                                         // 得到array中最后一个对象。如果array中没有任何对象存在,则返回nil
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];

    NSLog(@"self.dataArray count is:%d",[self.dataArray count]);

    NSLog(@"self.dataArray index 2 is:%@",[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];   

=================== NSMutableArray ====================
Mutable version of NSArray.
- (void)addObject:(id)anObject;                                              // 在array最后添加anObject, 添加nil是非法的.
- (void)addObjectsFromArray:(NSArray *)otherArray;         //在array最后把otherArray中的对象依次添加进去。

- (void)insertObject:(id)anObject atIndex:(int)index;          //在索引index处插入anObject, 若index被占用,会把之后的object向后移。

- (void)removeObjectAtIndex:(int)index;                               //删除index处的对象,后面的对象依次向前移。

- (void)removeObject:(id)anObject;                                      // 删除所有和anObject相等的对象,同样使用isEqual:作为相等比较方法.
- (void)removeAllObjects;

注:我们不能把nil加到array中。但有时候我们真想给array加一个空的对象,可以使用NSNull来做这件事。如:

[myArray addObject:[NSNull null]];

-----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。

以上是关于不可变数组和可变数组的主要内容,如果未能解决你的问题,请参考以下文章

Objective - C NSArray不可变数组和NSMutableArray可变数组

Scala学习(集合01)

Scala学习(集合01)

iOS 中 关于 NSUserDefault中存储可变数组的问题

Leetcode——区域和检索 - 数组不可变 / 二维区域和检索 - 矩阵不可变 (前缀和)

使用可变数组函数时,将变异方法发送到不可变对象错误