singleton

问题 I'm currently working on a project where I'm using a singleton class to change the view for the user. This DisplayManager (the singleton) has methods like addView(View view) and replaceView(View view) . But it also has a method called displayRootView() which may only be called once (during init) and by only 1 class, i.e. the StartUp class that extends the Application class. Any idea as to how I can prevent other classes who use the singleton from calling the displayRootView() method? I

问题 package Test public class SingleObject { //create an object of SingleObject private static SingleObject instance = null; public String msg = "1"; //make the constructor private so that this class cannot be //instantiated private SingleObject(){} //Get the only object available public static SingleObject getInstance(){ if(instance!=null){ }else{ instance = new SingleObject(); } return instance; } package Test public class Main1 { public static void main(String[] args) { SingleObject object =

问题 So , I am working on an app which requires a local db connection and uses some web services to send and receive data back-forth as well. Whenever I need and database operation then I create an object of my DbConnection class (this is the name of class I am using to get my database) and perform operations on the same. Similarly for connecting with internet I use DefaultHttpClient and create a static object of the same, and whenever need to get connection and call a webservice I create

问题 Learning swift and just stuck with one issue. I'm trying to use delegates with singleton service. With delegate i want to update multiple views, but due to singleton implementation delegate keeps last UIView. So for example i have 3 UIViews with ids 1, 2, 3. When i'll do in init body self.myservice.delegate = self and will try to use specific delegate method ex. myServiceDidUpdate then in this delegate method accessing self.viewId always returning last id . I guess it's due to singleton

问题 I have an application that gets some data from the user when the application loads and is needed throughout the application, what is the best way to keep hold of the object that holds this data throughout the entire lifetime of the application? This data needs to be available to most other objects created during the lifetime of the application. I learnt the other day that Singletons are not necessarily a good idea. Especially in multi threaded environments, which my application is. I have

问题 My Question is what is the best way to maintain the single database connection in the entire application? Using Singleton Pattern? How? Conditions that are needed to be taken care of: In case of multiple requests, I should be using the same connection In case connection is closed, create a new connection If the connection has timed-out, on new request my code should create a new connection. The driver to my Database is not supported by the Django ORM. And due to same driver related issues, I

问题 I have war app that uses reasteasy to expose some services. I want to deploy the app in tomcat7. Inside this app I want to hold some information in a singleton and I want to initialize that singleton on app deploy. How can I do that? Thanks 回答1: I managed eventually to figure out how to do this First I created a custom ServletContextListener which implements two methods: contextInitialized and contextDestroyed. When contextInitialized is called I instanciate my singleton object. Then I

问题 In Python, assuming that obj has type objtype , are super(cls,obj) and super(cls,objtype) the same? Is it correct that super(cls,obj) converts obj to another object whose class is a superclass of objtype which is after cls in the MRO of objtype ? What does super(cls,objtype) mean then? For example, given an implementation of the Singleton design pattern: class Singleton(object): _singletons = {} def __new__(cls, *args, **kwds): if cls not in cls._singletons: cls._singletons[cls] = super

问题 As far as I can see there are two main principles how to deal with application-wide role player objects like a root model object (in MVC context): create the object and pass it through the object tree (e.g. in the constructor) provide it as a singleton or other global variable technique The first approach seems to be cleaner because the dependencies are better visible but there is a lot of additional work to do (parameters, class variables,...). What do you prefer? Edit: The first technique

问题 In this answer a singleton decorator is demonstrated as such def singleton(cls): instances = {} def getinstance(): print len(instances) if cls not in instances: instances[cls] = cls() return instances[cls] return getinstance but instances is 'local' to each class that is decorated, so I tried to be more efficient and use def BAD_singleton(cls): instances = None def getinstance(): if instances is None: instances = cls() return instances return getinstance @BAD_singleton class MyTest(object):