NSURL 

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NSString *urlString = @"http://www.books.com:3321/lib/query;steve?key=job&sort=asc#chapter2";
NSURL *url = [NSURL URLWithString:urlString];
   
NSLog(@"url.absoluteString %@",url.absoluteString);
NSLog(@"url.absoluteURL %@",url.absoluteURL);
NSLog(@"url.baseURL %@",url.baseURL);
   
NSLog(@"url.scheme %@",url.scheme);
NSLog(@"url.host %@",url.host);
NSLog(@"url.port %@",url.port);
NSLog(@"url.query %@",url.query);
NSLog(@"url.fragment %@",url.fragment);
NSLog(@"url.parameterString %@",url.parameterString);
NSLog(@"url.pathExtension %@",url.pathExtension);
NSLog(@"url.path %@",url.path);
NSLog(@"url.pathComponents %@",url.pathComponents);
NSLog(@"url.lastPathComponent %@",url.lastPathComponent);
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url.absoluteString http://www.books.com:3321/lib/query;steve?key=job&sort=asc#chapter2
url.absoluteURL http://www.books.com:3321/lib/query;steve?key=job&sort=asc#chapter2
url.baseURL (null)
url.scheme http
url.host www.books.com
url.port 3321
url.query key=job&sort=asc
url.fragment chapter2
url.parameterString steve
url.pathExtension 
url.path /lib/query
url.pathComponents (
    "/",
    lib,
    query
)
url.lastPathComponent query

Size Class

iPhone4S,iPhone5/5s,iPhone6
竖屏：(w:Compact h:Regular)
横屏：(w:Compact h:Compact)
iPhone6 Plus
竖屏：(w:Compact h:Regular)
横屏：(w:Regular h:Compact)
iPad
竖屏：(w:Regular h:Regular)
横屏：(w:Regular h:Regular)

NSObject load 和 initialize 的调用时间和次数 

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@interface Animal : NSObject  @end
@interface Cat : Animal @end
@interface Dog : Animal @end

@implementation Animal
+ (void)load {
    NSLog(@"in Animal load %@",NSStringFromClass([self class]));
}
+(void) initialize{
    NSLog(@"in Animal initialize with %@",NSStringFromClass([self class]));
}
@end

@implementation Cat @end
@implementation Dog @end

@implementation AppDelegate
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    NSLog(@">1");
    Cat *cat0 = [[Cat alloc] init];
    NSLog(@">2");
    Dog *dog0 = [[Dog alloc] init];
    NSLog(@">3");
    Cat *cat1 = [[Cat alloc] init];
    NSLog(@">4");
    Dog *dog1 = [[Dog alloc] init];
    return YES;
}
@end

####console output

Animal initialize with Animal
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in Animal load Animal
>1
in Animal initialize with Cat
>2
in Animal initialize with Dog
>3
>4

KVO 几个options 

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NSKeyValueObservingOptions.New   新值
NSKeyValueObservingOptions.Old    旧值
NSKeyValueObservingOptions.Initial 注册监听的时候会立即发送
NSKeyValueObservingOptions.Prior  更改之前会额外发送一次
 
只有 NSKeyValueObservingOptions.New 
和 NSKeyValueObservingOptions.Old   
会存在于 observeValueForKeyPath 方法的change dictionary中

swift 通过 string 创建 object 

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class IndexViewController: UIViewController{}
 
let className = "IndexViewController"
 
let bundlePath = NSBundle.mainBundle().bundlePath
let bundleFullName = bundlePath.componentsSeparatedByString("/").last
let bundleName = bundleFullName?.componentsSeparatedByString(".").first
let clazz = NSClassFromString(bundleName! + "." + className)! as! UIViewController.Type
 
let object = clazz.init()
// let object1 = Index() 普通方法

cocoa 查看无线是否打开 可链接的wifi列表 

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CWInterface *wifi = [CWWiFiClient sharedWiFiClient].interface;
 
NSLog(@"interfaceName: %@", wifi.interfaceName);
NSLog(@"ssid: %@", wifi.ssid);
NSLog(@"powerOn: %@", @(wifi.powerOn));
 
NSSet<CWNetwork *> *result = [wifi scanForNetworksWithName:nil error:nil];
NSLog(@"可连接的wifi列表");
for (CWNetwork *each in result) {
    NSLog(@"--->%@",each.ssid);
}

cocoa播放音频 系统声效 

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NSString *resourcePath = [[NSBundle mainBundle] pathForResource:@"alert" ofType:@"wav"];
_sound = [[NSSound alloc] initWithContentsOfFile:resourcePath byReference:YES];

播放系统声效

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int soundIndex = 0;
- (void) tryLoopPlaySound{
    NSArray *directoryContents = [[NSFileManager defaultManager] contentsOfDirectoryAtPath:@"/System/Library/Sounds"
                                                                                     error:nil];
    NSUInteger arrayCount = [directoryContents count];
    if (soundIndex < arrayCount-1) {
        soundIndex++;
    }
    else {
        soundIndex = 0;
    }
    [self playSystemSound:soundIndex];
}

-(void) playSystemSound:(int) index{
    NSArray *directoryContents = [[NSFileManager defaultManager] contentsOfDirectoryAtPath:@"/System/Library/Sounds"
                                                                                     error:nil];
    NSUInteger arrayCount = [directoryContents count];
    if(index >= arrayCount) {
        return;
    }
    NSString *soundName = [directoryContents objectAtIndex:
                           index];
    soundName = [soundName stringByDeletingPathExtension];
    NSSound *systemSound = [NSSound soundNamed:soundName];
    NSLog(@"soundName %@ %d",soundName, index);
    [systemSound play];
}