singleton

问题 I've read several post regarding singleton class destruction or singleton pattern is bad in android like this and this But I am not able to understand how to declare a singleton class properly or use sharedpreference for persistance can anyone provide any example on how to maintain global objects across application or how to achieve this in proper way any help is appreciated. 回答1: I think this link you mentioned is quite good.As my personal experience the best way to maintain global objects

问题 Wrote the following code to display a chessboard using Tkinter in Python: import tkinter as tk class Gui(tk.Tk): _instance = None def __new__(cls, *args, **kwargs): if not cls._instance: cls._instance = super().__new__(cls, *args, **kwargs) cls._instance.__initialized = False return cls._instance def __init__(self): if self.__initialized: return self.__initialized = True super().__init__() class Color(object): white =(0xff,0xff,0xff) black =(0x00,0x00,0x00) class Tile(tk.PhotoImage):

问题 I have the following service defined: @Injectable() export class UserService { private _users: User[] = [] private _currentUser:User; ///Creates an instance of the Angular2 Http Service constructor(private _http: Http) {console.log("in the constructor"; } This is called from the login component: @Component({ selector: 'app-login', templateUrl: './login.component.html', styleUrls: ['./login.component.css'] }) export class LoginComponent implements OnInit { returnUrl: string; constructor

问题 I searched for 2-3 days a solution to my problem, but i haven't found anyone who had a similar problem. Basically, my app is the "mobile version" of a web site, so I have to store temporally different account's informations, so I used a signleton class, call it "user". Yet while navigationg through certain 2 activities (in one I have an expandable list and in the the other a listview , like you have a cart (1st activity) to substitute its empty spaces with elements from the "shop" (2nd

问题 I have Singleton enterprise bean, which starts immediately after deploy. I packed EJB into jar and want to distribute it. I set several fields of Singleton like private final String initParam = "value"; . How can I expose those init parameters to administrator who will be deploy my jar onto his own GlassFish server? 回答1: You can use Environment Entries, these should fit your needs. Such parameters must be described in ejb-jar.xml: <enterprise-beans> <session> <ejb-name>YourBean</ejb-name>

问题 I'm trying to create an instance of a class to be used throughout the application. I have two forms: form1 and form2 and I have a class called Singleton1. I created an instance of Singleton1 in form1 called obTest: Singeton1 obTest = Singleton1.Instance; From here I need to access the variable "obTest" from form2. Is it possible to do this? How I can access that variable without creating a new Singleton1 variable? Thanks in advance. 回答1: If your Instance method is written correctly, then you

问题 I am trying to use a singleton class to choose custom content to display based on the selection made by the user. It goes like this: a list is displayed, users select one of the rows in the list, and the app goes into another ViewController view. The ViewController used is the same for all the list options, however the content is different. Currently I managed to do this for only 1 option, and am trying to use a singleton class to tell the app which content to choose from. This is what

问题 My question is about threads being queued. For my example I have one Spring context. I have a method named CalculateTax in a stateless class. A request comes in, a thread is created (tA) and it eventually enters the CalculateTax method. Within the same "time frame" another request comes in and another thread is created (tB). Now, here is what I want to understand. AFAIK tB cannot execute CalculateTax until tA has exited the method. Is this true? 回答1: As long as CalculateTax only uses local

问题 I want to know what is use of making Instance variable as volatile in double null check implementation of Singleton. Because as per my understanding synchronize block provide happens before implicitly. No two threads can access that synchronized block concurrently and while exiting from synchronized block, thread write all its local cached data to main memory. I search a lot but still i have doubts in this implementation. Please explain correct use. private volatile Singleton INSTANCE; public

问题 Im trying to store a particular columns data in a method and call that method in another classes String [] where a spinner will access that array to display the columns rows for the user to select which will then get stored in another database. Im getting nulpointerexception and when I try and open() the database the database gets locked. Sorry for sounding like a complete amateur, relatively new to android. Thank you in advance for any help. Here is my code when I call getInstance() and