singleton

问题 I know we can create singleton classes using the factory in Dart. But i happen to recall reading somewhere, classes registered using type(MyController) or type(MyServiceClass) happen to be singleton on their own. Is that true? If so, does it apply to just classes registered with type(MyController) or does it use the annotation @NgController, etc. How does that impact the service and factory classes we write. Also, where can i find a doc or link explaining the same. 回答1: Short answer: No,

问题 I am working on a java based desktop application. One requirement is that if application is running and user try to start the application again it should do something like show some alert etc. I used file for this, when user run the app it add some text into a file and save it somewhere on the local system and when user try to run the app again i check the file and handle the situation accordingly, but there are some issue with this, like if application is abnormally terminated i am not able

问题 I have a class which, by design, must follow the singleton pattern. So I went ahead and implemented it using a metaclass . Everything worked nicely until a bug was reported which, in summary, said that deepcopy -ied instances of my singleton class were not the same instances. I can get around this bug by inheriting from a base singleton -type class, but I'd rather not, for reasons pointed out in this question. A working example of this issue is presented below: class SingletonMeta(type): def

问题 I have a Singelton in Java (in an OSGi Service) and want to maintain some state in it (a counter). Should this variable be static? or synchronized? or both? Or should i wrap the actions in a syncronized method? (would this be any different than just making the var syncronized?) I want consumers of the service actions to increment this counter. public MyServiceImpl implements MyService { private int count = 0; // static? syncronized? public String helloWorld() { count++; return "Hello World";

问题 I'm using a singleton called CSAppData to store data for my iPhone app. I'm storing an object called CSInbox in the singleton. When I logout of my app, I want to clear the data for that object. Here is my singleton code, including the method for clearing the data: - (id)init { self = [super init]; if (self) { self.inbox = [[CSInbox alloc] init]; } return self; } + (CSAppData *)appData { static CSAppData * appDataInstance; @synchronized(self) { if(!appDataInstance) { appDataInstance = [

问题 I have a Visual C# 2010 application, and it has one main form called MainWnd with other tool windows and dialogs. I want the other tool windows to be able to 'talk' to the main form, and call its methods. But that requires an instance of MainWnd , and since there will only be one of these forms created at any given time there is no reason while I should enumerate through all instances of MainWnd or look for the first one. So I want my main application form MainWnd to be a singleton so other

问题 I'm working on implementing a Factory class along the lines of what is proposed in this response to a previous question: Factory method implementation - C++ It's a Factory that stores a map from strings to object creation functions so I can request different types of objects from the factory by a string identifier. All the classes this factory produces will inherit from an abstract class (Connection) providing a common interface for connections over different protocols (HTTPConnection,

问题 There are many questions related to the use of the Singleton pattern in python, and although this question might repeat many of the aspects already discussed, I have not found the answer to the following specific question. Let's assume I have a class MyClass which I want to instantiate only exactly once. In python I can do this as follows in the code myclass.py : class MyClass(object): def foo(self): .... instance = MyClass() Then in any other program I can refer to the instance simply with

问题 I have a singleton class similar to this public class Singleton { private static Singleton m_instance; private Timer m_timer; private static List<CustomObject> m_cacheObjects; private Singleton() { m_cacheObjects = new List<CustomObject>(); m_timer= new Timer(MyTimerCallBack, null, TimeSpan.FromSeconds(60), TimeSpan.FromSeconds(60)); } public static Singleton Instance { get { if (m_instance == null) { m_instance = new Singleton(); } return m_instance; } } private void MyTimerCallBack(object

问题 After reading this tutorial I need some assistance in understanding what the most efficient way to do the following. When my app is opened, it needs to load a Profile object. Since there should only be one of these in the lifetime of the app I set it up to be a singleton. Realm seemed to be a great way to save and retrieve data. Upon further viewing it seems I need to have a data model in order to use Realms. After a failed attempt of integrating Object into the Profile.swift shown below I