Objective-C 关联引用的实例 （59）

#import <Foundation/NSArray.h> @interface NSArray (Random) - (id)anyOne; @end

#import "NSArray+Random.h" #import <objc/runtime.h> @implementation NSArray (Random) static char prevKey; //定义键使用的地址变了 static int random_value(void) { static unsigned long rnd = 201008; rnd = rnd * 1103515245UL + 12345; return (int)((rnd >> 16) & 0x7fff); } - (id)anyOne { id item; NSUInteger count = [self count]; if (count == 0) return nil; if (count == 1) item = [self lastObject]; else { id prev = objc_getAssociatedObject(self, &prevKey); NSUInteger index = random_value() % count; item = [self objectAtIndex:index]; if (item == prev) { if (++index >= count) index = 0; item = [self objectAtIndex:index]; } } objc_setAssociatedObject(self, &prevKey, item, OBJC_ASSOCIATION_RETAIN); return item; } @end

#import <Foundation/Foundation.h> #import "NSArray+Random.h" int main(void) { @autoreleasepool { id arr1 = [NSArray arrayWithObjects:@"A", @"B", @"C", @"D", @"E", @"F", @"G", @"H", nil]; id arr2 = [NSMutableArray arrayWithObjects:@"1", @"2", @"3", @"4", nil]; for (int i = 5; i < 20; i++) { @autoreleasepool { printf("%s %s\n",[[arr1 anyOne] UTF8String], [[arr2 anyOne] UTF8String]); } } } return 0; }