测试结果和源代码如下(您可以在应用程序中设置迭代次数)。时间以毫秒为单位，每个条目是运行测试5-10次的平均结果。我发现它通常精确到2-3位有效数字，之后它会随着每次运行而变化。这使得误差范围小于1%。测试在iPhone 3G上运行，因为这是我感兴趣的目标平台。

numberOfItems   NSArray (ms)    C Array (ms)    Ratio
100             0.39            0.0025          156
191             0.61            0.0028          218
3,256           12.5            0.026           481
4,789           16              0.037           432
6,794           21              0.050           420
10,919          36              0.081           444
19,731          64              0.15            427
22,030          75              0.162           463
32,758          109             0.24            454
77,969          258             0.57            453
100,000         390             0.73            534

The classes provided by Cocoa for handling data sets (NSDictionary, NSArray, NSSet etc.) provide a very nice interface for managing information, without having to worry about the bureaucracy of memory management, reallocation etc. Of course this does come at a cost though. I think it's pretty obvious that say using an NSArray of NSNumbers is going to be slower than a C Array of floats for simple iterations, so I decided to do some tests, and the results were pretty shocking! I wasn't expecting it to be this bad. Note: these tests are conducted on an iPhone 3G as that's the target platform I was interested in.

在这个测试中，我做了一个非常简单的随机访问性能比较C float*和NSNumbers的NSArray

我创建了一个简单的循环来总结每个数组的内容，并使用mach_absolute_time()计时。NSMutableArray平均需要400倍的时间!!(不是400%，只是400倍!长了40000% !)

标题:

/ / Array_Speed_TestViewController.h

//阵列速度测试

//由Mehmet Akten于05/02/2009创作。

//版权所有MSA视觉有限公司2009。版权所有。

#import <UIKit/UIKit.h>

@interface Array_Speed_TestViewController : UIViewController {

    int                     numberOfItems;          // number of items in array

    float                   *cArray;                // normal c array

    NSMutableArray          *nsArray;               // ns array

    double                  machTimerMillisMult;    // multiplier to convert mach_absolute_time() to milliseconds



    IBOutlet    UISlider    *sliderCount;

    IBOutlet    UILabel     *labelCount;


    IBOutlet    UILabel     *labelResults;

}


-(IBAction) doNSArray:(id)sender;

-(IBAction) doCArray:(id)sender;

-(IBAction) sliderChanged:(id)sender;


@end

实现:

/ / Array_Speed_TestViewController.m

//阵列速度测试

//由Mehmet Akten于05/02/2009创作。

//版权所有MSA视觉有限公司2009。版权所有。

    #import "Array_Speed_TestViewController.h"
    #include <mach/mach.h>
    #include <mach/mach_time.h>

 @implementation Array_Speed_TestViewController



 // Implement viewDidLoad to do additional setup after loading the view, typically from a nib.

- (void)viewDidLoad {

    NSLog(@"viewDidLoad");


    [super viewDidLoad];


    cArray      = NULL;

    nsArray     = NULL;


    // read initial slider value setup accordingly

    [self sliderChanged:sliderCount];


    // get mach timer unit size and calculater millisecond factor

    mach_timebase_info_data_t info;

    mach_timebase_info(&info);

    machTimerMillisMult = (double)info.numer / ((double)info.denom * 1000000.0);

    NSLog(@"machTimerMillisMult = %f", machTimerMillisMult);

}



// pass in results of mach_absolute_time()

// this converts to milliseconds and outputs to the label

-(void)displayResult:(uint64_t)duration {

    double millis = duration * machTimerMillisMult;


    NSLog(@"displayResult: %f milliseconds", millis);


    NSString *str = [[NSString alloc] initWithFormat:@"%f milliseconds", millis];

    [labelResults setText:str];

    [str release];

}




// process using NSArray

-(IBAction) doNSArray:(id)sender {

    NSLog(@"doNSArray: %@", sender);


    uint64_t startTime = mach_absolute_time();

    float total = 0;

    for(int i=0; i<numberOfItems; i++) {

        total += [[nsArray objectAtIndex:i] floatValue];

    }

    [self displayResult:mach_absolute_time() - startTime];

}




// process using C Array

-(IBAction) doCArray:(id)sender {

    NSLog(@"doCArray: %@", sender);


    uint64_t start = mach_absolute_time();

    float total = 0;

    for(int i=0; i<numberOfItems; i++) {

        total += cArray[i];

    }

    [self displayResult:mach_absolute_time() - start];

}



// allocate NSArray and C Array 

-(void) allocateArrays {

    NSLog(@"allocateArrays");


    // allocate c array

    if(cArray) delete cArray;

    cArray = new float[numberOfItems];


    // allocate NSArray

    [nsArray release];

    nsArray = [[NSMutableArray alloc] initWithCapacity:numberOfItems];



    // fill with random values

    for(int i=0; i<numberOfItems; i++) {

        // add number to c array

        cArray[i] = random() * 1.0f/(RAND_MAX+1);


        // add number to NSArray

        NSNumber *number = [[NSNumber alloc] initWithFloat:cArray[i]];

        [nsArray addObject:number];

        [number release];

    }


}



// callback for when slider is changed

-(IBAction) sliderChanged:(id)sender {

    numberOfItems = sliderCount.value;

    NSLog(@"sliderChanged: %@, %i", sender, numberOfItems);


    NSString *str = [[NSString alloc] initWithFormat:@"%i items", numberOfItems];

    [labelCount setText:str];

    [str release];


    [self allocateArrays];

}



//cleanup

- (void)dealloc {

    [nsArray release];

    if(cArray) delete cArray;


    [super dealloc];

}


@end

来自:memo.tv

////////////////////

自块引入以来一直可用，这允许迭代具有块的数组。它的语法不像快速枚举那样好，但有一个非常有趣的特性:并发枚举。如果枚举顺序不重要，并且作业可以并行完成而不需要锁定，那么这可以在多核系统上提供相当大的加速。在并发枚举一节中详细介绍。

[myArray enumerateObjectsUsingBlock:^(id object, NSUInteger index, BOOL *stop) {
    [self doSomethingWith:object];
}];
[myArray enumerateObjectsWithOptions:NSEnumerationConcurrent usingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
    [self doSomethingWith:object];
}];

/////////// NSFastEnumerator

快速枚举背后的思想是使用快速C数组访问来优化迭代。它不仅要比传统的NSEnumerator更快，而且Objective-C 2.0还提供了非常简洁的语法。

id object;
for (object in myArray) {
    [self doSomethingWith:object];
}

/////////////////

NSEnumerator

这是外部迭代的一种形式:[myArray objectEnumerator]返回一个对象。这个对象有一个方法nextObject，我们可以在循环中调用它，直到它返回nil

NSEnumerator *enumerator = [myArray objectEnumerator];
id object;
while (object = [enumerator nextObject]) {
    [self doSomethingWith:object];
}

/////////////////

, objectAtIndex:枚举

使用一个递增整数的for循环并使用[myArray objectAtIndex:index]查询对象是最基本的枚举形式。

NSUInteger count = [myArray count];
for (NSUInteger index = 0; index < count ; index++) {
    [self doSomethingWith:[myArray objectAtIndex:index]];
}

////////////// 来自:darkdust.net

为迅速

let arrayNumbers = [11, 12, 13, 14, 15, 16, 17, 18, 19, 20]

// 1
for (index, value) in arrayNumbers.enumerated() {
    print(index, value)
    //... do somthing with array value and index
}


//2
for value in arrayNumbers {
    print(value)
    //... do somthing with array value
}

将每个方法添加到NSArray类别中，你会非常需要它

来自ObjectiveSugar的代码

- (void)each:(void (^)(id object))block {
    [self enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
        block(obj);
    }];
}

适用于OS X 10.4。X和之前:

 int i;
 for (i = 0; i < [myArray count]; i++) {
   id myArrayElement = [myArray objectAtIndex:i];
   ...do something useful with myArrayElement
 }

适用于OS X 10.5。x(或iPhone)及其他版本:

for (id myArrayElement in myArray) {
   ...do something useful with myArrayElement
}

下面是如何声明一个字符串数组并遍历它们:

NSArray *langs = @[@"es", @"en", @"pt", @"it", @"fr"];

for (int i = 0; i < [langs count]; i++) {
  NSString *lang = (NSString*) [langs objectAtIndex:i];
  NSLog(@"%@, ",lang);
}

这样做:

for (id object in array) 
{
        // statement
}