几种循环遍历的方法

关于EnumerateObjectsUsingBlock和for-in之间的较量
如果我们要遍历一个数组, 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, 那么用它还是用For好呢？

1、遍历一个数组看谁快

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);

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.

2、通过Value查找Index看谁快

For - in
, enumerateObjectsUsingBlock
, enumerateObjectsWithOptions
这个三个方法: (ForLoop已经不再继续讨论了）

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);

enumerateObjectsWithOptions方法最快速
结论:
通过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.
3、遍历字典
这里我们比较一下使用For-in
和enumerateKeysAndObjectsUsingBlock
这个两个方法:

NSDictionary *testDictionary = @{ @"Auther" : @"yyyyy", @"Game" : @"Dota", @"App" : @"dddddd", @"Market" : @"AppStore" }; //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 : %ld For-in Time: %f ms",(long)index,date_current * 1000); NSLog(@"ForInArr: %@",forInArry); NSLog(@"enumArry: %@",enumArry);

enumerateKeysAndObjectsUsingBlock最快
结论:
当我们想遍历字典类型的时候, 推荐使用enumerateKeysAndObjectsUsingBlock
不仅仅是因为速度快, 更是因为代码更优雅和直观.