////  ObjectDetector.h//  ARCBlock////  Copyright (c) 2014年 Y.X. All rights reserved.//#import <Foundation/Foundation.h>@interface ObjectDetector : NSObject+ (void)startWatch;+ (void)addToWatch:(id)object;+ (NSArray *)allObjects;@end

////  ObjectDetector.m//  ARCBlock////  Copyright (c) 2014年 Y.X. All rights reserved.//#import "ObjectDetector.h"#ifndef GCDExecOnce#define GCDExecOnce(block) \{ static dispatch_once_t predicate = 0; dispatch_once(&predicate, block); }#endifstatic NSHashTable        *_table          = nil;static dispatch_source_t   _dispatchSource = nil;static dispatch_queue_t    _dispatchQueue  = nil;@implementation ObjectDetector+ (void)initialize{    if (self == [ObjectDetector class])    {        _table          = [NSHashTable weakObjectsHashTable];        _dispatchQueue  = dispatch_queue_create(nil, DISPATCH_QUEUE_CONCURRENT);        _dispatchSource = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, _dispatchQueue);                dispatch_source_set_timer(_dispatchSource,                                  dispatch_time(DISPATCH_TIME_NOW, 0),                                  NSEC_PER_SEC,                                  0);                dispatch_source_set_event_handler(_dispatchSource, ^{            NSLog(@"\n[==ObjectDetector LIST==]\n%@", _table);        });    }}+ (void)startWatch{    GCDExecOnce(^{        dispatch_resume(_dispatchSource);    });}+ (void)addToWatch:(id)object{    if (object == nil)    {        NSLog(@"object should not be nil.");        return;    }        if ([_table containsObject:object] == NO)    {        [_table addObject:object];    }}+ (NSArray *)allObjects{    return [_table allObjects];}@end

////  Prefix header////  The contents of this file are implicitly included at the beginning of every source file.//#import <Availability.h>#ifndef __IPHONE_3_0#warning "This project uses features only available in iOS SDK 3.0 and later."#endif#ifdef __OBJC__    #import <UIKit/UIKit.h>    #import <Foundation/Foundation.h>    #import "ObjectDetector.h"#endif

////  AppDelegate.m//  NSHashTable////  Copyright (c) 2014年 Y.X. All rights reserved.//#import "AppDelegate.h"#import "RootViewController.h"@implementation AppDelegate- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions{    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];    // Override point for customization after application launch.    UINavigationController *NC =         [[UINavigationController alloc] initWithRootViewController:[RootViewController new]];        self.window.rootViewController = NC;        // 开始检测    [ObjectDetector startWatch];        self.window.backgroundColor = [UIColor whiteColor];    [self.window makeKeyAndVisible];    return YES;}@end

////  RootViewController.m//  NSHashTable////  Copyright (c) 2014年 Y.X. All rights reserved.//#import "RootViewController.h"#import "SecondViewController.h"@interface RootViewController ()@end@implementation RootViewController- (void)viewDidLoad{    [super viewDidLoad];    self.title               = @"任重而道远";    UIButton *button         = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 120, 30)];    button.center            = self.view.center;    button.layer.borderWidth = 1.f;    button.titleLabel.font   = [UIFont fontWithName:@"HelveticaNeue-UltraLight"                                               size:20.f];    [button setTitle:@"YouXianMing" forState:UIControlStateNormal];    [button setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];    [button addTarget:self               action:@selector(buttonEvent:)     forControlEvents:UIControlEventTouchUpInside];    [self.view addSubview:button];}- (void)buttonEvent:(UIButton *)button{    [self.navigationController pushViewController:[SecondViewController new]                                         animated:YES];}@end

////  SecondViewController.m//  NSHashTable////  Copyright (c) 2014年 Y.X. All rights reserved.//#import "SecondViewController.h"@interface SecondViewController ()@end@implementation SecondViewController- (void)viewDidLoad{    [super viewDidLoad];        self.view.backgroundColor = [UIColor whiteColor];    self.title                = @"天道酬勤";        // 添加检测对象    [ObjectDetector addToWatch:self];}@end