singleton

问题 I like the simplicity of the eager singleton in java, and most articles about it call its creation thread safe. class Singleton { public static final Singleton instance = new Singleton (); private Singleton (){}; public static Singleton getInstance(){ return instance; } } However I have heard some claims that its creation might not be thread safe after all. For example one source claimed that it is not safe if more than 1 class loader or App domain is used. Is the creation of the Eager

问题 I am trying out to create a singleton in SWIFT and this is what I have done so far class Global { class var sharedInstance:Global { struct singleton { static let instance:Global = Global() } return singleton.instance } } var a = Global.sharedInstance var b = Global() if a === b { println("Pointing to Same Instance") } else { println("Pointing to different instance") } I have used computed type property to create a singleton (learnt that from another stackoverflow question).As of now the

问题 This question already has answers here : What does @synchronized() do as a singleton method in objective C? (6 answers) Closed 7 months ago . After reading the responses to a question about singletons in Objective C it appears that each solution makes some tradeoff in regards to threading in the instance accessor. i.e. @synchronized(self) { if (sharedInstance == nil) sharedInstance = [[MySingleton alloc] init]; } return sharedInstance; This essentially single-threads access to the singleton,

问题 I want to use the singleton UIApplication to access the managedObjectContext of the AppDelegate. But when I write [[[UIApplication sharedApplication] delegate] managedObjectContext] or [[[UIApplication sharedApplication] delegate] __managedObjectContext] it doesn't work. But this line works fine : NSLog(@"Seeking for the AppDelegate : %@", [[[UIApplication sharedApplication] delegate] class]); Do you have a solution ? Niels 回答1: Try casting it to your actual app delegate implementation, like

问题 I have a very common situation here. And for years I haven't found if what i am doing is RIGHT by industry standards.Consider an application which connects to the database, but where the connection string instead of being stored in some file/setting is being passed as a command line parameter at startup OR the database is browsed to at the time the application starts up. Well it becomes necessary to save that connection string somewhere within the scope of the app. Most common way I have seen

问题 I've been reading a bit about Singleton pattern usage in Android and its disadvantages regarding to keeping the Context. In fact, when I implement the following code: private static HttpManager sSingleton; private Context mContext; private HttpManager(Context context) { mContext = context; } public static synchronized HttpManager getInstance(Context context) { if (sSingleton == null) { sSingleton = new HttpManager(context); } return sSingleton; } Android Studio shows me the following warning:

问题 I have a singleton that contains reference to statistics object. When I run couple of unit test on the program that uses that singleton - the values sustained between the tests. I though that when I'm doing Program.Main() it all starts over between unit tests, but somehow it remembers the results from last test. How can I write unit tests that will be isolated from each other (I don't want clean() functions - I want it to start over with new "everything"), 回答1: Short version: do not write

问题 Would the following code facilitate lazy initialization ? Or would the singletonInstance be created as soon as somebody includes the header (or even at program startup time)? class SingletonClass { private: SingletonClass(); ~SingletonClass(); public: static const SingletonClass& Instance() { static SingletonClass singletonInstance; return singletonInstance; } }; 回答1: This is known as the Meyers singleton and they are lazy instantiated. There are some considerations: the singletons will be

问题 I'm very new to iOS programming and swift. I am trying to create a singleton class to store my global data. My global data are a struct and an array of this struct. I want to have only one instance of this class, thus a singleton class. Global data should be accessible and editable to all ViewControllers. I have been searching around and I almost have it figured out except one last part. Here is the singleton class: import Foundations class Global { struct Info { var firstname:String! var

问题 I have a lot of Singleton implementation in asp.net application and want to move my application to IIS Web Garden environment for some performance reasons. CMIIW, moving to IIS Web Garden with n worker process, there will be one singleton object created in each worker process, which make it not a single object anymore because n > 1. can I make all those singleton objects, singleton again in IIS Web Garden? 回答1: I don't believe you can ( unless you can get those IIS workers to use objects in