singleton

问题 In this link i found the singleton instantiation as below: public static Singleton getInstanceDC() { if (_instance == null) { // Single Checked (1) synchronized (Singleton.class) { if (_instance == null) { // Double checked _instance = new Singleton(); } } } return _instance; } I am not getting the point of single check ie (1) . Whats its use here any way the single thread will be checking the instance inside synchronized block , so what is point of using the first check? 回答1: Consider that

问题 I'm implementing singleton pattern in Swift. I came to a point I need to inherit the singleton class. I found a hint using this: [[[self class] alloc] init] How to translate that in Swift? I want to create something: class var sharedInstance : MyClass //instanceType { struct Static { // something like this static let instance: MyClass = [[[self class] alloc] init] } return Static.instance } Thanks. 回答1: No need to use [[[self class] alloc] init] . You can do like this: MyClass.swift import

问题 I'm a beginner of Unity. I had a question while studying. I refer to the document below. using UnityEngine; public class Singleton<T> : MonoBehaviour where T : MonoBehaviour { private static T _instance; private static object _lock = new object(); public static T Instance { get { if (applicationIsQuitting) { Debug.LogWarning("[Singleton] Instance '"+ typeof(T) + "' already destroyed on application quit." + " Won't create again - returning null."); return null; } lock(_lock) { if (_instance ==

问题 I have read many blogs about how singleton are vulnerable in android.so my question is how to maintain such global objects or list in application.i know shared preference is one way but is there any way to maintain such objects or list efficiently.any help will be more helpful. 回答1: You can use a file or SQLite database to save data in android app. You can check below links to learn more about saving data in a file or SQLite database: Saving data to a file is ideal to store long sequences of

问题 I have a Broadcast receiver in a singleton class that's not receiving Broadcast intents. The singleton is initialized with a context (i.e. getInstance(context)). I call getContext().sendBroadcast(intent); but the BroadcastReceiver doesn't get anything. I've confirmed the intent filters are matching. The way I register the receiver is in my singleton constructor like so private class Singleton(Context context) { context.registerReceiver(mReceiver, INTENT_FILTER); .... private onDestroy(Context

问题 I have a singleton 'util' class. This class is doing a lot of operation with UI elements (with some custom button, edittext etc.), so it's quite uncomfortable to pass all of the ui object's reference every time I use the util class. So I created a 'setup' method, like public void setStatusButtons (Button button1, Button button2, etc... ) { this.mButton1 = button1; this.mButton2 = button2; etc... } Then if I want to use them just use the mButton1, mButton2 ... fields. But there is a problem

问题 I need some guidance here on the Azure paradigm. I am building a multi-user data model. I want the core data model available as one set of services (e.g. a contract) on one URL, I want another set of services for managing the cache, statistics, start, stop, etc. on another URL (e.g. another contract for operator-type functions) and a third site for developer extensions (e.g. non-trivial, user-defined transactions). All three of these services need to share the common data model. I get the

问题 In the code snippet below when I originally designed it, the "next number" needed to send the next incremented value throughout the execution of the application. So I made the class a singleton. However, with some recent change in requirements I needed to do a reset on the "next number". I just added a reset method to do that. However, it definitely violates the Singleton pattern and also I know it is not a good idea to initialize a static member this way. What do you think I should do

问题 class MyManager { private static var __once: () = { Static.instance = MyManager() }() class var sharedInstance: MyManager { struct Static { static var onceToken: Int = 0 static var instance: MyManager? = nil } _ = MyManager.__once return Static.instance! } fileprivate init() { print("MyManager init"); } ....... etc calling it aManager = MyManager.sharedInstance results in MyManager init fatal error: unexpectedly found nil while unwrapping an Optional value 回答1: _ = MyManager.__once isn't

问题 I was trying to understand singleton design pattern and created a simplest one: #include <iostream> class mySingleton{ private: static mySingleton *ptr; mySingleton(){ } public: static mySingleton* getInstance(){ if(!ptr){ ptr = new mySingleton(); return ptr; } else return ptr; } void msg(){ std::cout << " Hello World!! " << std::endl; } }; int main(){ mySingleton* obj = mySingleton::getInstance(); mySingleton* obj2 = mySingleton::getInstance(); return 0; } When I try to compile I get :