flip image horizontally 左右翻轉圖片

UIImage *flippedImage = [UIImage imageWithCGImage: yourImage.CGImage
                                                scale:trimmedImage.scale
                                          orientation:UIImageOrientationUpMirrored];

orientation 螢幕方向

// 這個是裝置的實際方向
[UIDevice currentDevice].orientation

// 這個是螢幕的方向（如果你鎖住一些方向，他就不會顯示那些方向）
[UIApplication sharedApplication].statusBarOrientation


// 旋轉螢幕時的callback
 override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        NotificationCenter.default.addObserver(self, selector: #selector(deviceRotated), name: NSNotification.Name.UIDeviceOrientationDidChange, object: nil)
    }

    override func viewWillDisappear(_ animated: Bool) {
        NotificationCenter.default.removeObserver(self, name: NSNotification.Name.UIDeviceOrientationDidChange, object: nil)
    }

    func deviceRotated(){
        if UIDeviceOrientationIsLandscape(UIDevice.current.orientation) {
            print("Landscape")
            // Resize other things
        }
        if UIDeviceOrientationIsPortrait(UIDevice.current.orientation) {
            print("Portrait")
            // Resize other things
        }
    }

nested preprocessor ifdef

#ifdef PRODUCTION
    [buildInfoLabel setText:@""];
#else
#ifdef App_Sentry_Environment
    [buildInfoLabel setText:App_Sentry_Environment];
#endif
#endif

Compiler Warning messages

no rule to process file of type net.daringfireball.markdown for architecture x86_64

1. Select Project Navigator
2. Select your project
3. Select your target
4. Select Build Phases
5. Move files (in this case, CHANGLELOG.md) that you don't want the compiler to process from Compile Sources to Copy Bundle Resources
 

Property access result unused - getters should not be used for side effects

1. self.lables.removeLastObject; 方法不要用. 要用[]，不然compiler會認為是getter
2. [self.lables removeLastObject];

Implicit conversion from enumeration type 'SO_LOG_LEVEL' to different enumeration type 'DDLogFlag' (aka 'enum DDLogFlag')

1.  LOG_MAYBE(LOG_ASYNC_ENABLED, LOG_LEVEL_DEF, level, 0, nil, __PRETTY_FUNCTION__, message); 要先轉好型再放進去
2.  LOG_MAYBE(LOG_ASYNC_ENABLED, LOG_LEVEL_DEF, (DDLogFlag)level, 0, nil, __PRETTY_FUNCTION__, message);

Format string is not a string literal (potentially insecure) 

1. LOG_MAYBE(LOG_ASYNC_ENABLED, LOG_LEVEL_DEF, (DDLogFlag)level, 0, nil, __PRETTY_FUNCTION__, message); 參數是是用Format String不是普通String
2. LOG_MAYBE(LOG_ASYNC_ENABLED, LOG_LEVEL_DEF, (DDLogFlag)level, 0, nil, __PRETTY_FUNCTION__, @"%@", message);

  

PerformSelector may cause a leak because its selector is unknown

1. 因為可能會找不到function所以使用selector可能會有leak，這裡我們直接忽略它 

   #pragma clang diagnostic push
   #pragma clang diagnostic ignored "-Warc-performSelector-leaks"
       [self performSelector: aSelector];
   #pragma clang diagnostic pop

    

warning: Consistency Error: Setting the No Action Delete Rule on EmployeeQueue.child may result in relationships to deleted objects

1. 

Fixed width constraints may cause clipping

1. 這是Localization Issue，Xcode9擔心我們的文字輸入框在固定寛度的情況下，文字過長時會被clip掉，你可以用它推薦的解法，把trailing或leading設為>=或<=現在的寬度，也可以移除這個constrains
2. 如果是textField你不會想在使用者輸入太長的時候延長它，你可以把width改成依container的寬度比例來work around.

版本號判斷

Starting Xcode 9, in Objective-C:

if (@available(iOS 11, *)) {
    // iOS 11 (or newer) ObjC code
} else {
    // iOS 10 or older code
}

Starting Xcode 7, in Swift:

if #available(iOS 11, *) {
    // iOS 11 (or newer) Swift code
} else {
    // iOS 10 or older code
}

#if __IPHONE_OS_VERSION_MAX_ALLOWED >= 110000 // iOS 11

#else

#endif 


如果你是用10.3的SDK，那你就會看到下面的設定 （在10.3SDK中的AvailabilityInternal.h）

/* make sure a default max version is set */
    #ifndef __IPHONE_OS_VERSION_MAX_ALLOWED
        #define __IPHONE_OS_VERSION_MAX_ALLOWED     __IPHONE_10_3
    #endif

#define __IPHONE_2_0      20000
#define __IPHONE_2_1      20100
#define __IPHONE_2_2      20200
#define __IPHONE_3_0      30000
#define __IPHONE_3_1      30100
#define __IPHONE_3_2      30200
#define __IPHONE_4_0      40000
#define __IPHONE_4_1      40100
#define __IPHONE_4_2      40200
#define __IPHONE_4_3      40300
#define __IPHONE_5_0      50000
#define __IPHONE_5_1      50100
#define __IPHONE_6_0      60000
#define __IPHONE_6_1      60100
#define __IPHONE_7_0      70000
#define __IPHONE_7_1      70100
#define __IPHONE_8_0      80000
#define __IPHONE_8_1      80100
#define __IPHONE_8_2      80200
#define __IPHONE_8_3      80300
#define __IPHONE_8_4      80400
#define __IPHONE_9_0      90000
#define __IPHONE_9_1      90100
#define __IPHONE_9_2      90200
#define __IPHONE_9_3      90300
#define __IPHONE_10_0    100000
#define __IPHONE_10_1    100100
#define __IPHONE_10_2    100200
#define __IPHONE_10_3    100300
/* __IPHONE_NA is not defined to a value but is uses as a token by macros to indicate that the API is unavailable */