iphone中NSDateFormatter模擬器可以正常顯示，但在真機(jī)上不行，轉(zhuǎn)換后的NSString為NULL，部分代碼如下：

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
    
    NSString *dateStr = @"Dec 29, 2016 11:19:39 PM";
    NSDate *date = [self dateFromString:dateStr];
    NSLog(@"%@",date);  //模擬器上正常，真機(jī)打出來為Null
    NSLog(@"%@",[self stringFromDate:date]);

}

//NSDate轉(zhuǎn)NSString
-(NSString *)stringFromDate:(NSDate *)date
{
    NSLocale *locale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US"];
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setLocale:locale];
    //設(shè)置格式：zzz表示時(shí)區(qū)
    [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
    //NSDate轉(zhuǎn)NSString
    NSString *currentDateString = [dateFormatter stringFromDate:date];
    //輸出currentDateString
    NSLog(@"%@",currentDateString);
    return currentDateString;
}

//NSString轉(zhuǎn)NSDate
-(NSDate *)dateFromString:(NSString *)string
{
    NSLocale *locale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US"];
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init] ;
    [formatter setLocale:locale];
    [formatter setDateFormat:@"MMM dd, yyyy K:mm:ss aa"];
    //NSString轉(zhuǎn)NSDate
    NSDate *date=[formatter dateFromString:string];
    return date;
}

找了半天，終于找到原因：
在真機(jī)運(yùn)行需要設(shè)置Local，添加下面一段代碼就OK：

NSLocale *locale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US"];
[formatter setLocale:locale];