关于EnumerateObjectsUsingBlock和for-in之间的较量

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

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？

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);

最后输出如下:

 

• 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.

通过Value查找Index看谁快

假如现在我们要查找一个Value, 这个Value 值是100001, 找出它的index (数组的序列号).

那么现在我们来比较一下
参赛选手 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);

最后输出如下图:

 

• 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.

现在咱们要遍历字典

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

    NSDictionary *testDictionary = @{
                                     @"Auther" : @"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);

最后输出如下图:

 

• enumerateKeysAndObjectsUsingBlock胜出

  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.