關於EnumerateObjectsUsingBlock和for-in之間的較量

如果我們要遍歷一個數組, 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, 那麼用它還是用For好呢？

下面我們去實踐一下:

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);

最後輸出如下:

打印輸出

• 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.

通過Value查找Index看誰快

假如現在我們要查找一個Value, 這個Value 值是100001, 找出它的index (數組的序列號).

那麼現在我們來比較一下
參賽選手 For - in, enumerateObjectsUsingBlock, enumerateObjectsWithOptions 這個三個方法: (ForLoop已經不再繼續討論了）

    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);

最後輸出如下圖:

打印輸出

• enumerateObjectsWithOptions方法最快速

  結論:

  通過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.

現在咱們要遍歷字典

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

    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);

打印輸出:

打印輸出

• enumerateKeysAndObjectsUsingBlock勝出

  結論:

  當我們想遍歷字典類型的時候, 推薦使用enumerateKeysAndObjectsUsingBlock
  不僅僅是因爲速度快, 更是因爲代碼更優雅和直觀.