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, 那么用它還是用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);

最后輸出如下:

屏幕快照 2017-08-10 下午5.28.27.png

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).
那么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);

最后輸出如下圖:

屏幕快照 2017-08-10 下午5.31.48.png

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的并行方法.
For-in和enumerateObjectsWithOptions方法這里我比較喜歡第二種寫法簡潔直觀.

現在咱們要遍歷字典,這里我們比較一下使用 For-in 和 enumerateKeysAndObjectsUsingBlock 這個兩個方法:

NSDictionary *testDictionary = @{
@"Auther" : @"Jane",
@"Game" : @"Dota",
@"App" : @"JJSHome",
@"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);

最后輸出如下圖:

屏幕快照 2017-08-10 下午5.34.08.png

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
不僅僅是因為速度快, 更是因為代碼更優雅和直觀.