关于EnumerateObjectsUsingBlock和for-in之间的较量

原文：http://www.jianshu.com/p/ef3f1731a353

若是咱们要遍历一个数组, 上过编程课程的童鞋都会想到For语句去循环.
Objective C 提供一个Block的遍历方法, 那么用它仍是用For好呢？

遍历一个数组看谁快

参赛选手 ForLoop, For - in, enumerateObjectsUsingBlock这个三个方法:

NSMutableArray *test = [NSMutableArray array]; for (int i = 0; i < 1000000; i ++) { [test addObject:@(i)]; } __block int sum = 0; double date_s = CFAbsoluteTimeGetCurrent(); for (int i = 0; i < test.count; i ++) { sum += [test[i] integerValue]; } double date_current = CFAbsoluteTimeGetCurrent() - date_s; NSLog(@"Sum : %d ForLoop Time: %f ms",sum,date_current * 1000); sum = 0; date_s = CFAbsoluteTimeGetCurrent(); for (NSNumber *num in test) { sum += [num integerValue]; } date_current = CFAbsoluteTimeGetCurrent() - date_s; NSLog(@"Sum : %d For-in Time: %f ms",sum,date_current * 1000); sum = 0; date_s = CFAbsoluteTimeGetCurrent(); [test enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) { sum += [obj integerValue]; }]; date_current = CFAbsoluteTimeGetCurrent() - date_s; NSLog(@"Sum : %d enumrateBlock Time: %f ms",sum,date_current * 1000);

最后输出以下:

 

• For-in方法最快速

  结论:

  当只是遍历一个数组的时候使用For-in会比较快速, 推荐使用For-in遍历数组.

经过Value查找Index看谁快

假如如今咱们要查找一个Value, 这个Value 值是100001, 找出它的index (数组的序列号).

那么如今咱们来比较一下
参赛选手 For - in, enumerateObjectsUsingBlock, enumerateObjectsWithOptions 这个三个方法: (ForLoop已经再也不继续讨论了）

NSMutableArray *test = [NSMutableArray array]; for (int i = 0; i < 10000000; i ++) { [test addObject:@(i + 10)]; } //For-in __block NSInteger index = 0; double date_s = CFAbsoluteTimeGetCurrent(); for (NSNumber *num in test) { if ([num integerValue] == 9999999) { index = [test indexOfObject:num]; break; } } double date_current = CFAbsoluteTimeGetCurrent() - date_s; NSLog(@"index : %ld For-in Time: %f ms",(long)index,date_current * 1000); //enumerateObjectsUsingBlock index = 0; date_s = CFAbsoluteTimeGetCurrent(); [test enumerateObjectsUsingBlock:^(id num, NSUInteger idx, BOOL *stop) { if ([num integerValue] == 9999999) { index = idx; *stop = YES; } }]; date_current = CFAbsoluteTimeGetCurrent() - date_s; NSLog(@"index : %ld enumerateBlock Time: %f ms",(long)index,date_current * 1000); //enumerateObjectsWithOptions index = 0; date_s = CFAbsoluteTimeGetCurrent(); [test enumerateObjectsWithOptions:NSEnumerationConcurrent usingBlock:^(id num, NSUInteger idx, BOOL *stop) { if ([num integerValue] == 9999999) { index = idx; *stop = YES; } }]; date_current = CFAbsoluteTimeGetCurrent() - date_s; NSLog(@"index : %ld enumerateObjectsWithOptions Time: %f ms",(long)index,date_current * 1000);

最后输出以下图:

 

• enumerateObjectsWithOptions方法最快速

  结论:

  经过Value查询index的时候, 面对大量的数组推荐使用 enumerateObjectsWithOptions的并行方法.
  For-in和enumerateObjectsWithOptions方法这里我比较喜欢第二种写法简洁直观.

如今我们要遍历字典

这里咱们比较一下使用 For-in 和 enumerateKeysAndObjectsUsingBlock 这个两个方法:

NSDictionary *testDictionary = @{ @"Auther" : @"糖醋排骨", @"blog" : @"http://www.cnblogs.com/tate-zwt/", @"name" : @"zwt"}; 

//For - in NSMutableArray *forInArry = [NSMutableArray array]; double date_s = CFAbsoluteTimeGetCurrent(); NSArray *keys = [testDictionary allKeys]; for (NSString *key in keys) { NSString *Value = testDictionary[key]; [forInArry addObject:Value]; } double date_current = CFAbsoluteTimeGetCurrent() - date_s; NSLog(@"index : %ld For-in Time: %f ms",(long)index,date_current * 1000); //enumerateKeysAndObjectsUsingBlock date_s = CFAbsoluteTimeGetCurrent(); NSMutableArray *enumArry = [NSMutableArray array]; [testDictionary enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) { [enumArry addObject:obj]; }]; date_current = CFAbsoluteTimeGetCurrent() - date_s; NSLog(@"index : %ldenumerateKeysAndObjectsUsingBlockTime: %f ms",(long)index,date_current * 1000); NSLog(@"ForInArr: %@",forInArry); NSLog(@"enumArry: %@",enumArry);

最后输出以下图:

 

• enumerateKeysAndObjectsUsingBlock胜出

  结论:

  当咱们想遍历字典类型的时候, 推荐使用enumerateKeysAndObjectsUsingBlock不单单是由于速度快, 更是由于代码更优雅和直观.