singleton

问题 I have a main class with the singleton function instance() and the associated variable $instance . Now I create several subclasses and let the main class inherit. I do not re-define the singleton function and variable, because of the useful inheritance. Unfortunately, each instance points to the 1st subclass. Only when in the subclasses the $instance variable is initialized to null it works, but why? With the keywords static and not self , the scope should remain in the subclass. Here is the

问题 I have a main class with the singleton function instance() and the associated variable $instance . Now I create several subclasses and let the main class inherit. I do not re-define the singleton function and variable, because of the useful inheritance. Unfortunately, each instance points to the 1st subclass. Only when in the subclasses the $instance variable is initialized to null it works, but why? With the keywords static and not self , the scope should remain in the subclass. Here is the

问题 If a class implements a singleton pattern, should all the variables be declared static? Is there any reason they shouldn't be declared static? Does it make a difference? 回答1: No. The singleton pattern just means that a single instance is the only instance -- it does not mean "make everything statically accessible". The singleton pattern gives you all the benefits of a "single instance", without sacrificing the ability to test and refactor your code. Edit: The point I'm trying to make is that

问题 If a class implements a singleton pattern, should all the variables be declared static? Is there any reason they shouldn't be declared static? Does it make a difference? 回答1: No. The singleton pattern just means that a single instance is the only instance -- it does not mean "make everything statically accessible". The singleton pattern gives you all the benefits of a "single instance", without sacrificing the ability to test and refactor your code. Edit: The point I'm trying to make is that

问题 I have written a program in C#. Now I finished all the functionality and it works. But only running with one thread. I'm doing a lot of calculation and sometimes loading about 300 MB or more of measurement files into the application. I now want to make the program multithreaded because the user experiance is really bad in times of intense processing or i/o operations. What is the best way to refactor the program, so that it can be made multithreaded without too much affort? I know this is

问题 I'm trying to use a Singleton Class (its a program-wide debug logger called 'PrisLog') across my Qt Application. The program also has plugins. I want to make my singleton class available to those plugins, but this doesn't work. From what I can tell, trying to use the class in the plugin results in another instance being created. -The singleton class is just a *.cpp and *.h file, nothing else. I've linked both my main application and the plugin to these files individually... is this the right

问题 i'm building a web application with asp.net c# and i have a class that i want to use in multiple pages witouth instantiate it every time. I need to load the data in it and never lose them during the user session time. I thought about the singleton-pattern but it shared the instance of the class beetween browsers. How can i solve the problem? 回答1: Singleton is not the answer. Look at Session State, ViewState and Cookies. 回答2: UserData data = new UserData(somedata); Session["UserData"] = data;

问题 In essence, what is the difference between these two classes: @ApplicationScoped @Singleton class A {} @Dependent @Singleton class B {} Contextual EJB instances I prefer not to use @Inject when looking for EJB:s, unless the EJB is a @Stateful and I want the CDI container to manage the stateful's life-cycle which could be very convenient. Otherwise, using @Inject to retrieve a contextual EJB instance is a bit dangerous. For example, a @Remote client-view cannot be retrieved using CDI unless we

问题 This is my code : class SomeAudioManager: NSObject { class var sharedInstance: SomeAudioManager{ struct Static { static var onceToken: dispatch_once_t = 0 static var instance: SomeAudioManager? = nil } dispatch_once(&Static.onceToken) { Static.instance = SomeAudioManager() } return Static.instance! } func audioView(songname: NSString,format: NSString) { let audioPlayer:ava audioPlayer=try AVAudioPlayer(contentsOfURL: NSURL(fileURLWithPath: NSBundle.mainBundle().pathForResource(songname,

问题 This is my code : class SomeAudioManager: NSObject { class var sharedInstance: SomeAudioManager{ struct Static { static var onceToken: dispatch_once_t = 0 static var instance: SomeAudioManager? = nil } dispatch_once(&Static.onceToken) { Static.instance = SomeAudioManager() } return Static.instance! } func audioView(songname: NSString,format: NSString) { let audioPlayer:ava audioPlayer=try AVAudioPlayer(contentsOfURL: NSURL(fileURLWithPath: NSBundle.mainBundle().pathForResource(songname,