做app的时候，总免不了要多次遍历数组或者字典。
究竟哪种遍历方式比较快呢？我做了如下测试：
首先定义测试用宏：
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#define
MULogTimeintervalBegin(INFO) NSTimeInterval start = [NSDate timeIntervalSinceReferenceDate];\
NSTimeInterval
duration = 0;\
NSLog(@"MULogTimeintervalBegin:%@",
INFO)
#define
MULogTimeintervalPauseAndLog(INFO) duration = [NSDate timeIntervalSinceReferenceDate] - start;\
start
+= duration;\
NSLog(@"%@:%f",
INFO, duration);\
duration
= 0
#define
TESTSCALE 100000
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接着编写测试代码：
NSarray：
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-
(void)testArray
{
NSMutableArray*
testArray = [NSMutableArray
arrayWithCapacity:TESTSCALE];
for
(NSInteger
i = 1; i <= TESTSCALE; ++i) {
[testArray
addObject:[NSString
stringWithFormat:@"%ld",
i]];
}
NSLog(@"init:%ld",
[testArray count]);
__block
NSMutableString*
sum = [NSMutableString
stringWithCapacity:TESTSCALE];
MULogTimeintervalBegin(@"ArrayTest");
NSUInteger
count = [testArray count];
for
(NSInteger
i = 0; i < count; ++i) {
[sum
appendString:[testArray objectAtIndex:i]];
}
[sum
setString:@""];
MULogTimeintervalPauseAndLog(@"for
statement");
for(NSString*
item in testArray) {
[sum
appendString:item];
}
[sum
setString:@""];
MULogTimeintervalPauseAndLog(@"for-in");
[testArray
enumerateObjectsUsingBlock:^(id
obj, NSUInteger
idx, BOOL
*stop) {
[sum
appendString:obj];
}];
[sum
setString:@""];
MULogTimeintervalPauseAndLog(@"enumerateBlock");
}
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NSDictionary：
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-
(void)testDictionary
{
NSMutableDictionary*
testDic = [NSMutableDictionary
dictionaryWithCapacity:TESTSCALE];
for
(NSInteger
i = 1; i <= TESTSCALE; ++i) {
[testDic
setObject:@"test"
forKey:[NSString
stringWithFormat:@"%ld",
i]];
}
NSLog(@"init:%ld",
[testDic count]);
__block
NSMutableString*
sum = [NSMutableString
stringWithCapacity:TESTSCALE];
MULogTimeintervalBegin(@"DictionaryTest");
for
(NSString*
object in [testDic allValues]) {
[sum
appendString:object];
}
[sum
setString:@""];
MULogTimeintervalPauseAndLog(@"for
statement allValues");
for
(id
akey in [testDic allKeys]) {
[sum
appendString:[testDic objectForKey:akey]];
}
[sum
setString:@""];
MULogTimeintervalPauseAndLog(@"for
statement allKeys");
[testDic
enumerateKeysAndObjectsUsingBlock:^(id
key, id
obj, BOOL
*stop) {
[sum
appendString:obj];
}
];
MULogTimeintervalPauseAndLog(@"enumeration");
}
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下面是测试结果：
Test Case ‘-[LoopTestTests testArray]‘ started.
2012-08-02 17:14:22.061 otest[388:303] init:100000
2012-08-02 17:14:22.062 otest[388:303] MULogTimeintervalBegin:ArrayTest
2012-08-02 17:14:22.075 otest[388:303]for statement:0.013108
2012-08-02 17:14:22.083 otest[388:303]for-in:0.008186
2012-08-02 17:14:22.095 otest[388:303] enumerateBlock:0.012290
Test Case ‘-[LoopTestTests testArray]‘ passed (0.165 seconds).
Test Case ‘-[LoopTestTests testDictionary]‘ started.
2012-08-02 17:14:22.273 otest[388:303] init:100000
2012-08-02 17:14:22.274 otest[388:303] MULogTimeintervalBegin:DictionaryTest
2012-08-02 17:14:22.284 otest[388:303] for statement allValues:0.010566
2012-08-02 17:14:22.307 otest[388:303] for statement allKeys:0.022377
2012-08-02 17:14:22.330 otest[388:303] enumeration:0.023914
Test Case ‘-[LoopTestTests testDictionary]‘ passed (0.217 seconds).
可以看出对于数组来说，for-in方式遍历速度是最快的，普通风格的for和block方式速度差不多。对于字典来说，allValues方式遍历最快，allKeys和block差不多。
那么，为什么会这样呢？
NSArray：
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for
(NSInteger
i = 0; i < count; ++i) {
[sum
appendString:[testArray objectAtIndex:i]];
}
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这里由于存在：[objectAtIndex:i]这样的取操作，所以速度会有所下降。
而
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for(NSString*
item in testArray) {
[sum
appendString:item];
}
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尽管也有取操作，但是绕开了oc的message机制，速度会快一点。也有可能是编译器为了for-in作了优化。
block为什么会慢一些这个有待研究。
NSDictionary：
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for
(id
akey in [testDic allKeys]) {
[sum
appendString:[testDic objectForKey:akey]];
}
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这个就很明显了，第二种方法多了一次objectForKey的操作。block的话有待研究。
google了一下，*上面有类似的讨论：点击打开链接
大意是：for-in语法会对容器里面的元素的内存地址建立一个缓冲，遍历的时候从缓冲直接取得元素的地址而不是通过调用方法来获取，所以效率比较高。另外，这也是不能在循环体中修改容器元素的原因之一。
oc/object-c/ios哪种遍历NSArray/NSDictionary方式快？测试报告,布布扣,bubuko.com