關於EnumerateObjectsUsingBlock和for-in之間的較量

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

若是咱們要遍歷一個數組, 上過編程課程的童鞋都會想到For語句去循環.
Objective C 提供一個Block的遍歷方法, 那麼用它仍是用For好呢？

遍歷一個數組看誰快

參賽選手 ForLoop, For - in, enumerateObjectsUsingBlock這個三個方法:

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);

最後輸出以下:

 

• For-in方法最快速

  結論:

  當只是遍歷一個數組的時候使用For-in會比較快速, 推薦使用For-in遍歷數組.

經過Value查找Index看誰快

假如如今咱們要查找一個Value, 這個Value 值是100001, 找出它的index (數組的序列號).

那麼如今咱們來比較一下
參賽選手 For - in, enumerateObjectsUsingBlock, enumerateObjectsWithOptions 這個三個方法: (ForLoop已經再也不繼續討論了）

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);

最後輸出以下圖:

 

• enumerateObjectsWithOptions方法最快速

  結論:

  經過Value查詢index的時候, 面對大量的數組推薦使用 enumerateObjectsWithOptions的並行方法.
  For-in和enumerateObjectsWithOptions方法這裏我比較喜歡第二種寫法簡潔直觀.

如今我們要遍歷字典

這裏咱們比較一下使用 For-in 和 enumerateKeysAndObjectsUsingBlock 這個兩個方法:

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);

最後輸出以下圖:

 

• enumerateKeysAndObjectsUsingBlock勝出

  結論:

  當咱們想遍歷字典類型的時候, 推薦使用enumerateKeysAndObjectsUsingBlock不單單是由於速度快, 更是由於代碼更優雅和直觀.