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？
下面我们去实践一下:
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:

打印输出

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:

打印输出

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" :
@"南望青天",
@"Game" :
@"Dota",
@"App" :
@"麦刀塔",
@"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);
打印输出:

打印输出

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.