singleton

问题 So let's say I have a singleton class instance that I register in the DI like this: services.AddSingleton<IFoo, Foo>(); And let's say the Foo class has a number of other dependencies (mostly repository classes that allow it to load data). With my current understanding, the Foo instance is not created until it's first used (asked). Is there a way to initialize this class other than the constructor? Like right after ConfigureServices() completes? Or should the initialization code (loading data

问题 My question is quite similar to this one: Use Singleton In Interface Builder? The only difference is that I use ARC. So, if simplified, my singleton looks like that: Manager.m @implementation Manager + (instancetype)sharedManager { __strong static id sharedInstance = nil; static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ sharedInstance = [[self alloc] init]; }); return sharedInstance; } @end So the question is if it's possible to adopt it for Interface Builder still being with

问题 I'm learning Python and i've been trying to implement a Singleton-type class as a test. The code i have is as follows: _Singleton__instance = None class Singleton: def __init__(self): global __instance if __instance == None: self.name = "The one" __instance = self else: self = __instance This works in part but the self = __instance part seems to be failing. I've included some output from the interpretor to demonstrate (the code above is saved in singleton.py): >>> import singleton >>> x =

问题 I am converting my project to use DLLs and am trying to break apart my Singleton class to avoid using templates. My class, LudoMemory , originally inherited from Singleton . I am trying to give it the functions to destroy and create itself now and have my main engine not rely on the Singleton . I have written a simple destroy method like such: LudoMemory *memory_Singleton = NULL; void LudoMemory::Destroy() { LUDO_SAFE_DELETE(m_Singleton) } and upon running the program (no compiler errors) I

问题 I am converting my project to use DLLs and am trying to break apart my Singleton class to avoid using templates. My class, LudoMemory , originally inherited from Singleton . I am trying to give it the functions to destroy and create itself now and have my main engine not rely on the Singleton . I have written a simple destroy method like such: LudoMemory *memory_Singleton = NULL; void LudoMemory::Destroy() { LUDO_SAFE_DELETE(m_Singleton) } and upon running the program (no compiler errors) I

问题 Not during instantiation, but once instantiation of singleton object is done, what will happen if two or more threads are trying to access the same singleton object? Especially in the case where the singleton object takes lot of time to process the request (say 1 min)... In this case, if for ex., 5 threads try to access the same singleton object, what will the result be? Additional question: normally when should we go for the singleton pattern and when should we avoid it? 回答1: Unless

问题 In my endeavours as a python-apprentice i got recently stuck at some odd (from my point of view) behaviour if i tried to work with class attributes. I'm not complaining, but would appreciate some helpful comments to shed some light on this issue. To reduce a complex matter into a more concise question i would formulate it like this: What is the "pythonic" way to ensure that a class-attribute behaves more like a static variable in an inheritance tree? It seems to me like a class-attribute

问题 I am following up image cashing tutorial using Volley on Android developers, I am having problem with requesting an image request and caching it, I guess because of the singelton that I created (copied from the tutorial). My Eclipse is giving error in the getInstance(this) because this is context and I am requesting an image I guess. ImageRequest request = new ImageRequest( url, new Response.Listener<Bitmap>() { @Override public void onResponse(Bitmap bitmap) { mNetworkImageView =

问题 I have 5 fragments in ViewPager used to fill business object with several fields step by step, in each step some of those fields will be set. I've read many articles about communication between fragments but I'm not feeling comfortable the way others preferred, so after thinking about HOW should I do this in my case, finally I start thinking to use singleton model object which all fragments can easily access to its fields and fill them in specific steps. As I'm new to android I want to hear

问题 I read at many places that singletons can use interfaces. Some how I am unable to comprehend this. 回答1: Every class can implement an interface, and a Singleton is just a "normal" class that makes sure that only one instance of it exists at any point in time apart from the other business logic it may implement. This also means that a Singleton has at least 2 responsibities and this is not good OO design as classes should only have 1 responsibility and make sure they are good at that