IOS 开发之 NSMutableArray与NSArray 的区别

Z时代
2024-01-10
分类：综合

首先,来看下2者的区别:


NSArray and its subclass NSMutableArray manage collections of objects called arrays.
 NSArray creates static arrays, and NSMutableArray creates dynamic arrays.

NSMutableArray是NSArray的子类,NSArray建立静态数组,而NSMutableArray则是动态数组.换句话说,NSArray建立之后不可修改,而NSMutableArray则可以修改.

由于在ObjC中,简单的看下函数addObject,会发现数组的元素是id类型,也就是说是指针.


-
 (void)addObject:(id)anObject

如此一来数组里就不能压入NSUInteger,BOOL之类的非指针型数据了,要命吧..

那要压入这些内容怎么办呢?对,类型转换,ObjC提供了NSNumber来给大家转换用,NSNumber本身是个指针类型变量.

Inherits from NSValue : NSObject

来个简单的转换例子:


NSUInteger
 count = 1;
NSNumber
 *j = [NSNumber numberWithInt:count];
[ary
 addObject:j];

还算明了吧,就是用到这个值的时候又要转换一次,...

昨天刚好又用到数组的乱序,在网上找了个Sample修改了下,代码如下:


#pragma
 mark -
#pragma
 mark (NSMutableArray *)randArray:(NSMutableArray *)ary
-
 (NSMutableArray *)randArray:(NSMutableArray *)ary{
  NSMutableArray
 *tmpAry = [NSMutableArray arrayWithArray:ary];
  NSUInteger
 count = [ary count];
  for
(NSUInteger i = 0; i < count; ++i) {
    int
nElements = count - i;
    //
 Seed the random number generator
    srandom(time(NULL));
    int
n = (random() % nElements) + i;
    [tmpAry
 exchangeObjectAtIndex:i withObjectAtIndex:n];
  }
  return
tmpAry;
}