Say I have a class called LogHelper and it has a static method called GetLogger(string name).
Is there a way to add a static extension method that would just be GetLogger()?
I know that normally extension methods are static where they are declared, but is there a way to appear static on the class they are "Helping"?
You could use an extension method:
public static class StringExtensions
{
public static ILogger GetLogger(this string value)
{
...
}
}
And then you could use like this:
string foo = "bar";
ILogger logger = foo.GetLogger();
You can also use
public static ILogger GetLogger(string value)
{
...
}
public static ILogger GetLogger()
{
return GetLogger("Default Value");
}
This way when you called GetLogger() it would call GetLogger(string value) but with your default value.
It is not possible to extend static classes with extension methods, unfortunately...
(I'm assuming your LogHelper is static? At least that's what I understood so far.)
I'm not sure how efficient this is, but it should work. log4net has an overload that accepts a Type, and you often want to name the logger after the fully qualified type name.
void Main()
{
var foo = new Bar.Foo();
ILog logger = foo.GetLogger();
}
public static class LogHelper
{
public static ILog GetLogger(this object o)
{
return LogManager.GetLogger(o.GetType());
}
}
namespace Bar
{
public class Foo {}
}
// Faking log4net
public class ILog {}
public class LogManager
{
public static ILog GetLogger(Type type)
{
Console.WriteLine("Logger: " + type.ToString());
return null;
}
}
The above prints "Logger: Bar.Foo".
P.S. Use "this.GetLogger()" if you want a logger for the current class (assuming non-static method).
Since what you want is impossible, why not fake it?
After all, it doesn't really matter if your parameterless GetLogger() method is on LogHelper. Just write your own static class, called MyLogHelper or something, and define the method there. The code would look like this:
public static class MyLogHelper
{
public static ILog GetLogger()
{
return LogHelper.GetLogger("MyHardcodedValue");
}
}
I see only one solution is to use optional arguments, but unfortunately they appear only in C# 4.0:
public static class LogHelper
{
public static ILogger GetLogger(string name = "DefaultLoggerName")
{
...
}
}
Related
I have a generic class LoggerHelper<T>. There are properties in many different classes in the application, whose values are to be set to instances of LoggerHelper. In the constructors of these classes, this property will be set. For example:
public class Importer
{
ILogger _logger;
public Importer()
{
this._logger = new LoggerHelper<Importer>();
}
}
How can I avoid specifying the type each time? Is there are suitable pattern for this?
You could use a factory method, thus a type could be inferred by the compiler.
Static method
public static class LoggerHelperFactory
{
public static LoggerHelper<T> Create<T>(T instance)
{
return new LoggerHelper<T>();
}
}
Then you can call it as:
_logger = LoggerHelperFactory.Create(this);
Extension method
public static class LoggerHelperFactoryExtensions
{
public static LoggerHelper<T> CreateLogger<T>(this T instance)
{
return new LoggerHelper<T>();
}
}
Usage:
_logger = this.CreateLogger();
I have a program that needs to be able to interface with multiple platforms ie read/write files, read/write database or read/write web requests. The platform interface is selected from configuration and does not change while the application is running. I have a single read/write interface class which is inherited by the platform specific classes so that this is abstracted from the rest of the program.
My problem is that I have 10 classes in my framework that will need to use this interface. Instead of making multiple instances of this class, or passing a single reference to every class, I figured it would make sense to make the interface static. Unfortunately I have just learned that Interfaces cannot have static methods, static methods cannot call non-static methods and static methods cannot be abstract.
Can anyone show me another method of approaching this situation?
Edit:
Thanks for everyone's input, here is my solution based on the example given by Patrick Hofman (thank you!)
interface TheInterface
{
void read();
void write();
}
public class X : TheInterface
{
public void read() { //do something }
public void write() { //do something }
}
public class Y : TheInterface
{
public void read() { //do something }
public void write() { //do something }
}
public class FileAccessor
{
public static TheInterface accessor;
public static TheInterface Accessor
{
get
{
if(accessor) return accessor;
}
}
}
This can be called by any class as:
static void Main(string[] args)
{
switch (Config.interface)
{
case "X":
FileAccessor.accessor = new Lazy<X>();
case "Y":
FileAccessor.accessor = new Lazy<Y>();
default:
throw new Lazy<Exception>("Unknown interface: " + Config.interface);
}
FileAccessor.Accessor.read();
}
Indeed, interfaces, or abstract classes can't be static themselves, but the further implementation can. Also, you can use the singleton pattern to make your life easier, and allow inheritance, etc.
public class X : ISomeInterface
{
private X() { }
public static X instance;
public static X Instance
{
get
{
return instance ?? (instance = new X());
}
}
}
Or, using Lazy<T>:
public class X : ISomeInterface
{
private X() { }
public static Lazy<X> instanceLazy = new Lazy<X>(() => new X());
public static X Instance
{
get
{
return instance.Value;
}
}
}
Disclaimer: I am the author of the library described below.
I don't know if this helps you, but I have written a library (very early version yet) that allows you to define static interfaces, by defining normal interfaces and decorating their methods with an attribute named [Static], for example:
public interface IYourInterface
{
[Static]
void DoTheThing();
}
(Note that you don't explicitly add this interface to your implementations.)
Once you have defined the interface, you can instantiate it from within your code with any valid implementation you choose:
return typeof(YourImplementation).ToStaticContract<IYourInterface>();
If the methods can't be found in YourImplementation, this call fails at runtime with an exception.
If the methods are found and this call is successful, then the client code can polymorphically call your static methods like this:
IYourInterface proxy = GetAnImplementation();
proxy.DoTheThing();
You can make a Static Class which has Variable of your Interface.
public static class StaticClass
{
public static ISomeInterface Interface;
}
Now you can access the Instance from everywhere in your Framwork
static void Main(string[] args)
{
StaticClass.Interface = new SomeClass();
}
I've got a static log manager class that should return instances of a desired logger based on a parameter.
public static class LogManager {
private static ILoggerFactory Factory { ... }
public static ILogger GetLogger(string name) {
return Factory.Create(name);
}
}
Since the concrete implementation of ILoggerFactory must be set (initialization), I'm wondering if I should only keep a reference on the type of the implementation and return a new instance everytime the factory is requested - or if it's okay to keep a static reference of an instance of the implementation.
Version 1
private static Type _factoryType;
public static void SetFactory<TFactory>()
where TFactory : ILoggerFactory, new()
{
_factoryType = typeof(TFactory);
}
private static Factory {
get { return (ILoggerFactory)Activator.CreateInstance(_factoryType);
}
public static ILogger GetLogger(string name) {
return Factory.Create(name);
}
Version 2
private static ILoggerFactory _loggerFactory;
public static void SetFactory<TFactory>()
where TFactory : ILoggerFactory, new()
{
_loggerFactory = (ILoggerFactory)Activator.CreateInstance<TFactory();
}
public static ILogger GetLogger(string name) {
return _loggerFactory.Create(name);
}
Arguably, main difference appear to be in the lazy loading: v1 will create logger type when GetLogger is called, whereas v2 will create logger during SetFactory. There is not much of a difference otherwise. It is OK to keep a reference as a private static field to either the type of a logger or the factory itself.
However, if this is production code, I'd get rid of this log manager and factories altogether. Instead I'd use logging framework, like nlog or log4net directly. This simplifies code and makes it more maintainable. Building abstraction in this case is over-engineering.
Is there a work around on how to create a constructor for static class?
I need some data to be loaded when the class is initialized but I need one and only one object.
C# has a static constructor for this purpose.
static class YourClass
{
static YourClass()
{
// perform initialization here
}
}
From MSDN:
A static constructor is used to initialize any static data, or to
perform a particular action that needs to be performed once only. It
is called automatically before the first instance is created or any
static members are referenced
MSDN link
.
A static constructor looks like this
static class Foo
{
static Foo()
{
// Static initialization code here
}
}
It is executed only once when the type is first used. All classes can have static constructors, not just static classes.
Yes, a static class can have static constructor, and the use of this constructor is initialization of static member.
static class Employee1
{
static int EmpNo;
static Employee1()
{
EmpNo = 10;
// perform initialization here
}
public static void Add()
{
}
public static void Add1()
{
}
}
and static constructor get called only once when you have access any type member of static class with class name Class1
Suppose you are accessing the first EmployeeName field then constructor get called this time, after that it will not get called, even if you will access same type member.
Employee1.EmployeeName = "kumod";
Employee1.Add();
Employee1.Add();
Static constructor called only the first instance of the class created.
like this:
static class YourClass
{
static YourClass()
{
//initialization
}
}
We can create static constructor
static class StaticParent
{
StaticParent()
{
//write your initialization code here
}
}
and it is always parameter less.
static class StaticParent
{
static int i =5;
static StaticParent(int i) //Gives error
{
//write your initialization code here
}
}
and it doesn't have the access modifier
You can use static constructor to initialization static variable. Static constructor will be entry point for your class
public class MyClass
{
static MyClass()
{
//write your initialization code here
}
}
Static classes cannot have instance constructors (unlike the accepted answer). However, a class can have a static constructor. That is totally different.
public class BaseFoo
{
private string param;
public BaseFoo(string param)
{
this.param = param;
}
}
public sealed class SingletonFoo : BaseFoo
{
static readonly SingletonFoo instance = new SingletonFoo();
static SingletonFoo()
{
}
public static SingletonFoo Instance
{
get
{
return instance;
}
}
}
Is this kind of inheritance possible, where the base class requires a constructor with parameters? (The above code won't obviously compile because no parameter is passed to the base class.)
If yes, how is it accomplished?
You need to make an instance constructor, and then refer to it:
public sealed class SingletonFoo : BaseFoo
{
static readonly SingletonFoo instance = new SingletonFoo("Some Value");
static SingletonFoo()
{
}
private SingletonFoo(string value) : base(value)
{
}
// ...
This will let you declare the parameter in the inline constructor, and call it down the chain.
You use the 'base' keyword:
public SingletonFoo (string param) : base(param)
{
}
I'm pretty sure a 'singleton' deriving from a non-singleton base class completely invalidates the entire concept of the pattern, which is often used inappropriately to start with.
Static constructors do not take parameters, so the only way to pass them to the base class would be via constructor-chaining but I'm pretty sure you can't invoke an instance constructor from a static constructor...
What exactly are you trying to do here?