盡量不要用#define來定義key的文字

應該要改用const NSString以避免可能發生文字覆蓋的錯誤

例如：

.h檔

#import <Foundation/Foundation.h>

extern NSString *SelectionSort;

extern NSString *InsertionSort;

extern NSString *BubbleSort;

@interface Algorithm : NSObject

@end

.m檔

#import "Algorithm.h"

@implementation Algorithm

const NSString *SelectionSort = @"SelectionSort";

const NSString *InsertionSort = @"InsertionSort";

const NSString *BubbleSort    = @"BubbleSort";

@end

以NSString形式寫入NSData

我要寫入Ble時，會先用文字格式給出命令，再轉為NSData寫入device

-(void) setGSensorParameter:(NSString*)parameter completion:(WriteValueResponse)completion{

    if (![_bleManager isConnected]) {

        return;

    }

    NSUInteger len = parameter.length;

    NSString* dataString = [[NSString alloc]initWithString:parameter];

    

    NSMutableData* data = [[NSMutableData alloc]init];

    if (dataString.length % 2 != 0) {

        dataString = [NSString stringWithFormat:@"0%@",dataString];

    }

    //逐字轉成Bytes
    for (int i = 0; i < len; i = i + 2)
    {
        NSRange range = NSMakeRange(i, 1);
        NSString *firstString = [dataString substringWithRange:range];
        range = NSMakeRange(i + 1, 1);
        NSString *secondString = [dataString substringWithRange:range];
        NSNumber* firstDigit = [NSNumber numberWithInt:[[DataManager unitDigitFromHexString:firstString] intValue] * 16];
        NSNumber* secondDigit = [DataManager unitDigitFromHexString:secondString];
        NSNumber* number = [NSNumber numberWithInt:[firstDigit intValue] + [secondDigit intValue]];

        

        unsigned char charNumber = [number charValue];
        [data appendBytes:&charNumber length:1];

        

    }
    //NSLog(@"data:%@",data);

    [_bleManager writeValueWithWithData:data

                         forServiceUUID:@"XXXX"

                     characteristicUUID:@"YYYY"

                           withResponse:completion];

}

+ (NSNumber *) unitDigitFromHexString:(NSString *)unitDigit{

    int number = 0;

    if ([unitDigit isEqualToString:@"a"] || [unitDigit isEqualToString:@"A"]) {

        number = 10;

    }

    else if ([unitDigit isEqualToString:@"b"] || [unitDigit isEqualToString:@"B"]) {

        number = 11;

    }

    else if ([unitDigit isEqualToString:@"c"] || [unitDigit isEqualToString:@"C"]) {

        number = 12;

    }

    else if ([unitDigit isEqualToString:@"d"] || [unitDigit isEqualToString:@"D"]) {

        number = 13;

    }

    else if ([unitDigit isEqualToString:@"e"] || [unitDigit isEqualToString:@"E"]) {

        number = 14;

    }

    else if ([unitDigit isEqualToString:@"f"] || [unitDigit isEqualToString:@"F"]) {

        number = 15;

    }

    else if (0 <= [unitDigit intValue] < 10)

    {

        NSNumber *result = [NSNumber numberWithInt:[unitDigit intValue]];

        return result;

    }

    else

    {

        return nil;

    }

    

    NSNumber *result = [NSNumber numberWithInt:number];

    return result;

}

iOS7 的main thread只是UI預設的執行緒，不是code的

為了要檢查get main queue的順序與值的對應關係，我寫了下列程式碼

__block int i = 1;

    NSLog(@"1. normal 1  i=%i",i);

    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{

        NSLog(@"2. after two seconds  i=%i",i);

        i = 2;

    });

    dispatch_async(dispatch_get_main_queue(), ^{

        NSLog(@"3. main thread 1  i=%i",i);

        i = 3;

    });

    NSLog(@"4. normal 2  i=%i",i);

    i = 4;

    dispatch_async(dispatch_get_main_queue(), ^{

        NSLog(@"5. main thread 2  i=%i",i);

        i = 5;

    });

    NSLog(@"i =%i",i);

得到的結果如下，

2014-05-20 16:45:00.513 ConceptComfirm[25891:60b] viewDidLoad

2014-05-20 16:45:00.513 ConceptComfirm[25891:60b] class : Concepts

2014-05-20 16:45:00.514 ConceptComfirm[25891:60b] 1. normal 1  i=1

2014-05-20 16:45:00.514 ConceptComfirm[25891:60b] 4. normal 2  i=1

2014-05-20 16:45:00.514 ConceptComfirm[25891:60b] i =4

2014-05-20 16:45:00.515 ConceptComfirm[25891:60b] viewWillAppear

2014-05-20 16:45:00.652 ConceptComfirm[25891:60b] viewDidAppear

2014-05-20 16:45:00.652 ConceptComfirm[25891:60b] 3. main thread 1  i=4

2014-05-20 16:45:00.653 ConceptComfirm[25891:60b] 5. main thread 2  i=3

2014-05-20 16:45:02.516 ConceptComfirm[25891:60b] 2. after two seconds  i=5

結論是，iOS7已經不再將code預設執行的main thread

而是把UI用main thread去跑，你想要跑在main thread的code要自行宣告使用。

Note.
//創造一個新的執行緒

dispatch_queue_t _newQueue   = dispatch_queue_create("forCentralManagerOnly", DISPATCH_QUEUE_SERIAL);

在runtime決定你要用的class

Class concept = NSClassFromString(@"Concept");

    NSLog(@"class : %@", concept);

//如果找到了，會回傳class name；如果沒有，則回傳null

NSBundle的-classNamed:也是類似相同的功能。

如果只有開始跟結束的小時，要如何判斷是今日或昨日

NSCalendar *cal = [NSCalendar currentCalendar];

            NSDateComponents *sleepComps = [cal components:NSHourCalendarUnit | NSMinuteCalendarUnit fromDate:se.sleepDate];

            NSDateComponents *wakeUpComps = [cal components:NSHourCalendarUnit | NSMinuteCalendarUnit fromDate:se.wakeUpDate];

            date = [_displayDate startDayDate];

            if (sleepComps.hour > wakeUpComps.hour)

                date = [date dateByAddingTimeInterval:-86400];

在OS X Mavericks中打開FTP Server

//打開FTP

sudo -s launchctl load -w /System/Library/LaunchDaemons/ftp.plist

//關閉FTP

sudo -s launchctl unload -w /System/Library/LaunchDaemons/ftp.plist

簡述雜湊hash

把你的key經過hash function運算之後，會得到一個長度固定的數值，存入該數值編號的桶(bucket)中，如果有二個key以上的運算到相同的雜湊值，那就叫碰撞(collision)，這時的解決方式就是存放在桶中另一個槽(slot)，如果桶中的槽都滿時，又遇到碰撞，就叫溢位(over flow)