singleton

问题 I am working on C# winforms . I have function Validate() which is present in the CS file. When I call function Validate() it opens ErrorForm using ErrorForm ew = new ErrorForm(Errors); // Errors is list<string> ew.Show(); But when I call it again, a new window opens and my previous window is open too. I have to close that window manually. Is there any method available such that if I call validate() again, it will close the current ErrorForm and will open new ErrorForm . 回答1: try this one: var

问题 I am working on C# winforms . I have function Validate() which is present in the CS file. When I call function Validate() it opens ErrorForm using ErrorForm ew = new ErrorForm(Errors); // Errors is list<string> ew.Show(); But when I call it again, a new window opens and my previous window is open too. I have to close that window manually. Is there any method available such that if I call validate() again, it will close the current ErrorForm and will open new ErrorForm . 回答1: try this one: var

问题 I'm familiar with the concept of Singleton and this mechanism is pretty handy but.. What happens in case I want one, shared instance of some third-party class e.g. AFHTTPRequestOperation or maybe some Magical Record? What should I do when I'm using one object from external class in many controllers? Or maybe it is a good practice to instantiate a new object in each controller? 回答1: I'm not familiar with Magical Record but for AFNewtorking it definitely makes sense to make a singleton in many

问题 This question already has answers here : Undefined reference to static class member (7 answers) Closed 3 years ago . I'am trying to implement a method that returns me an instance of the class, but it's is crashing when it tries to create the instance at the first time. I don't know how to implement the singleton in C++/QT Main #include <QCoreApplication> #include "carro.h" int main(int argc, char *argv[]) { QCoreApplication a(argc, argv); Carta* nueva; nueva->getInstance(); nueva->setColor(

问题 I am working on a project in which I need to use Cassandra Database . I have a sample program that will populate data into Cassandra database . I am using Pelops client for that. So now I am thinking of making a Singleton class for Cassandra database that will make a connection to Cassandra database and then I be using that instance from Singelton class into my CassandraDAO to insert into Cassandra database and retrieve the data from Cassandra database as well. Below is my Singleton class

问题 I have a UIViewController in a tab bar application. I've added the controller from the MainWindow.nib file (i.e. not programatically). My question is how can I make my view controller a singleton? (To resolve the Facebook delegate issue). 回答1: You probably want to make your "Facebook connection code" a singleton (or part of the app delegate), but not the view controller itself. Then just wire up the FB thing with any view controller that needs it. 回答2: If you really want to create singletons

问题 We are in the process of deprecating ACE libraries in our project which consists of around 120 binaries and in many of binaries we have used ACE_Singleton.Since after deprecating we will not have this class so we are thinking of writing our own generic singleton in our shared library that is common across all these binaries and one of the goals that we want to achieve is if somebody inherit from this class (using CRTP) say Logger and even when Logger constructor is public then also we cannot

问题 Here's the scenario: public class A { public A {} void doSomething() { // do something here... } } Right now, the class is setup where you can create multiple instances. But I also see a need where I might want to restrict the class to only one instance, i.e. Singleton class. The problem is I'm not sure how to go about the design of accomplishing both goals: Multiple instances and one instance. It doesn't sound possible to do in just one class. I imagine I'll need to use a derived class, an

问题 There's a discusson here about testing and singletons... but that is about Java patterns. My question is specifically about the Groovy @Singleton (annotation) way of implementing this pattern. This seems like another bit of Groovy Goodness. But I have a bit of a problem when testing (with Spock) using a class which has this annotation. If any of the state of this instance changes during a test (from the pristine, just-constructed state), as far as my experiments indicate this will then carry

问题 I am writing a library of utility classes, many of which are singletons. I have implemented them as such using inheritance: template <class T> class Singleton { public: T& getInstance() { if(m_instance == 0) { m_instance = new T; } return m_instance; } private: static T* m_instance; }; class SomeClass : public Singleton<SomeClass> { public: SomeClass() {} virtual ~SomeClass() {} void doSomething() {;} }; Obviously this is a simple example, not an actual class. Anyways, I am finding that using