優化慢代碼 - 枚舉字典

Question

我有下面的代碼，將JSON字符串解碼爲一個對象數組，然後可以在UITableView中使用。

起初我以爲JSON解碼是慢的部分，但它似乎並不像「字典完成」幾乎立即出現。

有關如何讓代碼更快一點的任何想法？

-(void)parseJSON:(NSString *)jsonData{ 

    NSLog(@"Start parsing"); 
    NSDictionary *deserializedData = [jsonData objectFromJSONString]; 
    NSLog(@"Dictionary Done"); 

    NSArray *flights = [deserializedData valueForKeyPath:@"flights.flight"]; 
    NSMutableArray *localArray = [[NSMutableArray alloc] init ]; 
    NSString *lastFlightno =@""; 

    for (NSDictionary *flight in flights){ 

     ArchiveFlight *aFlight = [[ArchiveFlight alloc] initWithFlightno:[flight objectForKey:@"flightno"] route:[flight objectForKey:@"route"]]; 
     aFlight.flightID = [flight objectForKey:@"primary_key"]; 
     aFlight.timeStamp = [aFlight niceDate:[flight objectForKey:@"timestamp"]]; 

     if (![lastFlightno isEqualToString:aFlight.flightno]) { 
      [localArray addObject:aFlight]; 
     } 

     lastFlightno =aFlight.flightno; 
     [aFlight release]; 
    } 
    NSLog(@"End Parsing"); 
    [self loadupTable:localArray]; 
    self.flightArray = localArray; 
    [localArray release]; 

} 

編輯：添加時間戳

時間戳如下NSLogs的...

2011-04-26 13:22:36.104 App[1778:707] Finished request 
2011-04-26 13:22:36.109 App[1778:707] Start parsing 
2011-04-26 13:22:36.128 App[1778:707] Dictionary Done 
2011-04-26 13:22:37.713 App[1778:707] End Parsing 

樣品的JSON的...

{"flights":[{"flight":{"flightno":"RYR54WP","timestamp":"2011-04-26 12:13:04","route":"EGNX-LEAL","primary_key":"836453"}},{"flight":{"flightno":"RYR24LU","timestamp":"2011-04-26 09:14:03","route":"EVRA-EGNX","primary_key":"831318"}},{"flight":{"flightno":"RYR39WH","timestamp":"2011-04-26 05:33:03","route":"EGNX-EVRA","primary_key":"825492"}},{"flight":{"flightno":"RYR7PX","timestamp":"2011-04-25 20:07:03","route":"LELC-EGNX","primary_key":"816703"}},{"flight":{"flightno":"RYR2VB","timestamp":"2011-04-25 16:57:06","route":"EGNX-LELC","primary_key":"810900"}},{"flight":{"flightno":"RYR3JN","timestamp":"2011-04-25 12:36:04","route":"GCTS-EGNX","primary_key":"802631"}},{"flight":{"flightno":"RYR8GV","timestamp":"2011-04-25 06:07:03","route":"EGNX-GCTS","primary_key":"792945"}},{"flight":{"flightno":"RYR82QR","timestamp":"2011-04-24 19:42:04","route":"EPKK-EGNX","primary_key":"783306"}},{"flight":{"flightno":"RYR51PV","timestamp":"2011-04-24 16:31:05","route":"EGNX-EPKK","primary_key":"777835"}},{"flight":{"flightno":"RYR53AQ","timestamp":"2011-04-24 14:09:05","route":"LIME-EGNX","primary_key":"773572"}},{"flight":{"flightno":"RYR1CX","timestamp":"2011-04-24 11:02:05","route":"EGNX-LIME","primary_key":"768285"}},{"flight":{"flightno":"RYR9ZW","timestamp":"2011-04-24 08:21:04","route":"LEGE-EGNX","primary_key":"764624"}},{"flight":{"flightno":"RYR63BC","timestamp":"2011-04-24 05:48:02","route":"EGNX-LEGE","primary_key":"761726"}},{"flight":{"flightno":"RYR7PX","timestamp":"2011-04-23 19:39:03" 

格式化樣本：

{ 
    "flights":[ 
     { 
     "flight":{ 
      "flightno":"RYR54WP", 
      "timestamp":"2011-04-26 12:13:04", 
      "route":"EGNX-LEAL", 
      "primary_key":"836453" 
     } 
     }, 
     { 
     "flight":{ 
      "flightno":"RYR24LU", 
      "timestamp":"2011-04-26 09:14:03", 
      "route":"EVRA-EGNX", 
      "primary_key":"831318" 
     } 
     } 
    ] 
} 

編輯2：

因此，這裏是 「niceDate」，是造成減速！

-(NSString *)niceDate:(NSString *)oldDate{ 
    NSDateFormatter *formatter = [[[NSDateFormatter alloc] init]autorelease]; 
    [formatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"]; 
    NSDate *sourceDate = [formatter dateFromString:oldDate]; 
    NSDateFormatter *dateFormatter = [[[NSDateFormatter alloc] init] autorelease]; 
    [dateFormatter setDateStyle:NSDateFormatterFullStyle]; 
    [dateFormatter setTimeStyle:NSDateFormatterLongStyle]; 
    NSString *timeString = [dateFormatter stringFromDate:sourceDate]; 
    return [NSString stringWithFormat:@"%@",timeString]; 
} 

Answer 1

浮現在腦海中有些事情：

NSArray *flights = [deserializedData valueForKeyPath:@"flights.flight"]; 

你需要使用KVC？你的JSON數據的結構是什麼？

ArchiveFlight *aFlight = [[ArchiveFlight alloc] initWithFlightno:[flight objectForKey:@"flightno"] route:[flight objectForKey:@"route"]]; 
aFlight.flightID = [flight objectForKey:@"primary_key"]; 
aFlight.timeStamp = [aFlight niceDate:[flight objectForKey:@"timestamp"]]; 

你總是創建ArchiveFlight實例和解析時間戳...

if (![lastFlightno isEqualToString:aFlight.flightno]) { 
     [localArray addObject:aFlight]; 
    } 

...即使你沒有這樣做，所有的時間。取決於你有多少重複的flightnos，這可能會引起顯着的差異。

爲什麼不讀[flight objectForKey:@"flightno"]，將它與lastFlightno進行比較，當且僅當它們不同時，創建一個實例，將其添加到數組中並釋放它？

---

編輯：請嘗試以下KVC-免費代碼：

NSArray *flights = [deserializedData objectForKey:@"flights"]; 
NSMutableArray *localArray = [[NSMutableArray alloc] init ]; 
NSString *lastFlightno =@""; 

for (NSDictionary *flightWrapper in flights) { 
    NSDictionary *flight = [flightWrapper objectForKey:@"flight"]; 
    NSString *flightno = [flight objectForKey:@"flightno"]; 

    if (! [flightno isEqual:lastFlightno]) { 
     // create instance, add it to the array, release the instance 
    } 
} 

---

編輯：你創建和（自動）發佈這個方法裏面NSDateFormatter兩個實例。一般情況下，這樣可以，但是由於執行次數大於1K，因此需要考慮兩個因素：a）創建/使用/釋放這兩個實例的次數大於1K次，實際上，如果沒有兩次，則會出現b ）你應該在你的循環中使用一個autorelease池。

您應該使此方法成爲類方法（或函數），因爲它不依賴於該類的實例的狀態。您的格式化程序將是類（靜態）變量。例如：

@implementation ArchiveFlight 

static NSDateFormatter *formatter1; // choose better names! 
static NSDateFormatter *formatter2; 

+ (void)initialize { 
    if (self == [ArchiveFlight class]) { 
     formatter1 = [[NSDateFormatter alloc] init]; 
     [formatter1 setDateFormat:@"yyyy-MM-dd HH:mm:ss"]; 

     formatter2 = [[NSDateFormatter alloc] init]; 
     [formatter2 setDateStyle:NSDateFormatterFullStyle]; 
     [formatter2 setTimeStyle:NSDateFormatterLongStyle]; 
    } 
} 

+ (NSString *)niceDate:(NSString *)oldDate { 
    NSDate *sourceDate = [formatter1 dateFromString:oldDate]; 
    NSString *timeString = [formatter2 stringFromDate:sourceDate]; 
    return timeString; 
    // why +stringWithFormat:? It’s not necessary! 
    // return [NSString stringWithFormat:@"%@",timeString]; 
} 

這修復項），但你因爲你使用回報Cocoa方法自動釋放對象真正應該使用自動釋放池的循環內。通過爲循環的每次迭代使用自動釋放池，可以減少代碼的內存佔用量 - 儘管如此，也可能會降低性能。我建議你嘗試使用和不使用內部自動釋放池。

for (NSDictionary *flightWrapper in flights) { 
    NSAutoreleasePool *pool = [NSAutoreleasePool new]; 

    … 

    [pool drain]; 
}