I know that we can call a parametered constructor from other constructor using constructor chaining.
But,
public class Program
{
public static void Main(string[] args)
{
Console.WriteLine("Hello, world!");
var t1 = new T1("t2");
}
}
public class T1
{
public T1()
{
Console.WriteLine("t1");
}
public T1(string s):base()
{
Console.WriteLine(s);
}
}
this doesn't seem to call the base constructor (without any parameters).
Any ideas ?
EDIT:
Current: t2 is printed. t1 is not on the console.
so, I have resorted to the following method:
public class Program
{
public static void Main(string[] args)
{
Console.WriteLine("Hello, world!");
var t1 = new T1("t2");
}
}
public class T1
{
private void privateMethod()
{
Console.WriteLine("common method");
}
public T1()
{
privateMethod();
}
public T1(string s):base()
{
Console.WriteLine(s);
privateMethod();
}
}
Is there any better ways of doing this ?
You are looking for this():
public class T1
{
public T1()
{
Console.WriteLine("t1");
}
public T1(string s) : this()
{
Console.WriteLine(s);
}
}
You're looking for the keyword this, base will call the parent class (as in the class you're extending).
You're actually calling Object() constructor when you use the base keyword. You want to use the this keyword
public class T1
{
public T1()
{
Console.WriteLine("t1");
}
public T1(string s) : this()
{
Console.WriteLine(s);
}
}
As mentioned in other answers, for calling the parameterless constructor you have to use :this() (base() calls the parameterless constructor of the base class)
However, I think this is a bad practice. The constructor with parameters is the one that defines better the initialization of the class, and thus, the parameterless constructor should call it rather than vice versa.
i.e:
public class T1
{
public T1():this(String.Empty) // <= calling constructor with parameter
{
Console.WriteLine("t1");
}
public T1(string s)
{
Console.WriteLine(s);
}
}
rather than:
public class T1
{
public T1()
{
Console.WriteLine("t1");
}
public T1(string s) : this() // <= calling parameterless constructor
{
Console.WriteLine(s);
}
}
BTW, it seems that the language is going towards encouraging using a primary constructor using, well - Primary constructors (it is was an experimental feature in C# 6 that was removed, not sure if for good...)
this called the current class instance while base the parent.
Related
I seem to have some trouble understanding generics in c#.
Basically i have a base class called ConfigWorker and a bunch of sub classes which should all use their own config class deriving from BaseConfig.
The ConfigWorker class i want to use should be determined dynamically during runtime given the name of the class as a parameter.
I can instantiate the sub class given it's name, but no matter what i try, i can't get the casting to a sensible base class to work.
Here's my code:
namespace DocumentHandler
{
public class BaseConfig
{
}
public class ConfigWorker<T> where T : BaseConfig
{
public virtual void Work(T options)
{
}
}
public class Worker1 : ConfigWorker<Worker1.Config>
{
public class Config : BaseConfig
{
public string test = "";
}
public override void Work(Config options)
{
//do something
}
}
public class Worker2 : ConfigWorker<Worker2.Config>
{
public class Config : BaseConfig
{
public string test = "";
}
public override void Work(Config options)
{
//do something else
}
}
public class Test
{
public static BaseConfig config;
public static void test()
{
(Activator
.CreateInstance(Type.GetType("DocumentHandler.Worker2"))
as ConfigWorker<BaseConfig>)
.Work(config);
}
}
}
The crucial line is
(Activator
.CreateInstance(Type.GetType("DocumentHandler.Worker2"))
as ConfigWorker<BaseConfig>)
.Work(config);
The casting to ConfigWorker<BaseConfig> returns null, as the cast can not be performed.
Trying to simply cast to ConfigWorker does not compile as the type parameter is missing.
Anything else i can try? CreateInstance obviously just returns an object and i need to cast that to be able to call the Work method
Any help is appreciated.
An instance of Worker2 is not a ConfigWorker<BaseConfig>! It's a ConfigWorker<Worker2.Config>. These are two totally different types. Generic classes are invariant. Only interfaces and delegates can be co- or contra-variant.
In your example, ConfigWorker is even contra-variant in T, meaning you use T as the type of an input parameter to a method. So what you try is actually dangerous.
Imagine your line would work: you get an variable of type ConfigWorker<BaseConfig>, so you could rely on this instance having a method Work() which takes a BaseConfig (or something derived from it) as argument. So nothing could stop you from calling it like
worker.Work(new Worker1.Config());
Compiles fine. But wait a moment! Didn't your line state that worker is a Worker2? Worker2 instances can only handle Worker2.Config arguments!
You completely loose type safety this way (well, you would if it was allowed).
There is a flaw in your class design.
This looks like a good problem that factory pattern has good good solution for.
Here is a simplified solution
namespace DocumentHandler
{
public interface IBaseConfig
{
}
public class ConfiManager : IBaseConfig
{
}
public abstract class WorkerFactory
{
private readonly IBaseConfig _config;
protected WorkerFactory(IBaseConfig config)
{
this._config = config;
}
public virtual void Work()
{
}
}
public class Worker1 : WorkerFactory
{
private readonly IBaseConfig _config;
public Worker1(IBaseConfig config):base(config)
{
_config = config;
}
public string test = "";
public override void Work()
{
//do something
}
}
public class Worker2 : WorkerFactory
{
private readonly IBaseConfig _config;
public string test = "";
public Worker2(IBaseConfig config):base(config)
{
this._config = config;
}
public override void Work()
{
Console.WriteLine("Hello world");
}
}
public class Test
{
public static IBaseConfig config = new ConfiManager();
public static void test()
{
WorkerFactory worker =
(Worker2) Activator.CreateInstance(Type.GetType("DocumentHandler.Worker2"), config);
worker.Work();
}
}
}
I wrote C# code as described below that inherits a class from a generic class with static methods. I want to call the child class for its static methods (inherited from the base class) without having to specify the type.
EDITED! More "real" code
public class Rec
{
public string Name { get; set; }
public override string ToString() { return this.Name; }
public virtual void Load() { /* HERE IT READS A TEXT FILE AND LOAD THE NAME */ }
}
public class BaseClass<T> : Rec
{
public T Argument { get; set; }
public override void Load() { /* NOW IT LOADS ALSO THE ARGUMENT */ }
public static H Method<H>() where H : Rec, new()
{
H iH = new H();
iH.Load();
iH.Name += " " + iH.Argument.ToString();
return iH;
}
}
public class Child : BaseClass<string> { }
public class SomeOtherClass
{
public void Test()
{
Child i = Child.Method();
//instead of Child.Method<Child>();
}
}
So, instead of having to call method<h>() i'd like to just call method(), so the code should assume that "h" is the caller type. Like in:
How can I do it?
Static methods are not inherited in C#
See this answer for an idea of a potential implementation: Stack Overflow whats-the-correct-alternative-to-static-method-inheritance
You could change method<h> to method and make it an instance method:
public class BaseClass<T> where T, new()
{
public T method() { /* RETURN SOMETHING */ }
}
And then call it as follows:
public class ABC : Child
{
public void Test()
{
var iABC = this.method();
}
}
Hey I have two classes
class Main
{
public exLog exLog;
public Main()
{
}
}
and
class exLog
{
public exLog()
{
}
public exLog(String where)
{
}
public exLog(String where, String message)
{
}
}
i tried to call exLog direct without giving exLog a parameter. So I can call any class with the Main Method.
How should I do that?
public String ReadFileString(String fileType, String fileSaveLocation)
{
try
{
return "";
}
catch (Exception)
{
newMain.exLog("", "");
return null;
}
}
I like to call them like a funtion in Main
You can call it as soon as you instantiate it.
public Main()
{
exLog = new exLog();
exLog.MethodInClass();
}
Also, if you are not in the same assembly you'll need to make exLog public.
Finally, this is C# and the style dictates that class names should be PascalCased. It's a good habit to form.
Methinks you want something like Adapter Pattern
class Main
{
private exLog exLog;
public Main()
{
}
public void ExLog()
{
exLog = new exLog();
}
public void ExLog(String where)
{
exLog = new exLog(where);
}
public void ExLog(String where, String message)
{
exLog = new exLog(where, message);
}
}
I think you're confused about classes, instances, constructors, and methods. This does not work:
newMain.exLog("", "");
because exLog in this case is a property, not a method. (It's confusing because you use the same name for the class and the property, which is why most conventions discourage that).
You can call a method on the instance:
newMain.exLog.Log("", "");
but then you'll need to change the names of the methods (and add a return type) in your exLog class so they don't get interpreted as constructors:
class exLog
{
public void Log()
{
}
public void Log(String where)
{
}
public void Log(String where, String message)
{
}
}
class Main
{
public exLog exLog;
public Main()
{
exLog = new exLog();
exLog.ReadFileString("", "");
}
}
I have the following base class:
public class Baseclass
{
public Baseclass(string anyparam)
{
}
}
I want to execute a lambda inside of the constructor of the child class:
public class Subclass : Baseclass
{
public Subclass() : base(delegate()
{
string returnstring;
// Do Something
return returnstring;
})
{
}
}
I don't want to waste any method on this, and I've not seen any example solving this without declaring the parameter type as func. How do I do this in C#?
You don't have to declare parameter as Func, you can create Func instance inline and call it:
public class Subclass : Baseclass
{
public Subclass()
: base((new Func<string>(() =>
{
const string returnstring = "a";
// Do Something
return returnstring;
})()))
{
}
}
It it looks very ugly, can produce problems and I don't recommend it to you.
I think the best you can do here is overload your base class constructor:
public class Baseclass
{
public Baseclass(string anyparam)
{
}
public Baseclass(Func<string> f):this(f())
{
}
}
public class Subclass : Baseclass
{
public Subclass()
: base(()=>
{
string returnstring="foo";
// Do Something
return returnstring;
})
{
}
}
How to avoid a pair of repetitive lines before and after invocations in sample below ?
Details: This is compileable mock of what is real larger code. Generally it is a layer of proxy classes containing service clients with variety of APIs. The repetitive part is pre- and post- invocation for every method of every client. Unfortunately there is no single signature for all possible methods, the pre- and post- parts need a pointer to client's channel and context.
Is it possible to apply something advanced like AOP, Generics, Delegates, Attributes etc. ? Thank you
using System;
namespace ConsoleApplication
{
class ClassServiceClient: IDisposable
{
public Object channel()
{
return "something";
}
public Object context()
{
return "something other";
}
}
class ClassA : ClassServiceClient
{
public Object methodA()
{
return "something other";
}
}
class ClassB : ClassServiceClient
{
public void methodB(string param)
{
return;
}
}
class ClassAProxy
{
public Object methodA()
{
using (ClassA client = new ClassA())
{
Program.preparation(client.channel()); //<---- repetitive part
Object result = client.methodA();
Program.postinvocation(client.context());//<---- repetitive part
return result;
}
}
}
class ClassBProxy
{
public void methodB(string param)
{
using (ClassB client = new ClassB())
{
Program.preparation(client.channel()); //<---- repetitive part
client.methodB(param);
Program.postinvocation(client.context());//<---- repetitive part
return;
}
}
}
class Program
{
public static void preparation(Object channel)
{
// Do something with channel
}
public static void postinvocation(Object context)
{
// Do something with context
}
static void Main(string[] args)
{
}
}
}
If you can use a common base class, you can easily use a public sealed method that does the invocation and a protected abstract method that does the logic, e.g.
class ProxyBase{
public void Method(params object[] args){
PreConditions();
Invoke(args);
PostConditions();
}
protected abstract void Invoke(object[] args);
}
class ClassAProxy{
protected override void Invoke(object[] args){
client.Method(args[0]);
}
}
You can achieve similar results functionally by declaring a InvocationHandler in your Program class that takes an action:
class Program{
public static void Invoke(object[] args, Action action){
PreConditions();
action();
PostConditions();
}
}
class ClassAProxy{
public void MethodA(int i){
Program.Invoke(() => client.Something(i));
}
}