I am looking for this Java code's equivalent in C#
public class MainClass {
public MainClass() {
OtherClass o = new OtherClass(this); //I am looking for "this" keyword to send the instance
}
public void someMethod() {
}
}
public class OtherClass {
public OtherClass(MainClass m) { //and this receiver method
m.someMethod();
}
}
I think there should be a way in C# to sent the current class as a parameter so that I can call the someMethod() in MainClass from OtherClass ?
How can I do that in C#?
Thanks for help..
I am looking for this Java code's equivalent in C#
Well, no equivalency needed. Your code is already a valid C# code without any modification. Here is a demo.
Note: I would be very worried about the circular reference in your code, but I'm sure it was just a simple sample and you wouldn't actually implement code like that.
Important Note: Just to be clear, you are not sending the "class". That's just not possible. You are sending an instance of the class. Maybe that's what you meant, but just so nobody reads it and get confused.
Related
I was searching for a common question but couldn't find any solution even after googling. Maybe I am searching wrong?
Is it possible to know from which class the object has been created?
For Example: In Visual Basic Code:
I have a class,
Public Class dummyA
End Class
I have another class,
Public Class dummyMain
Dim dmmA As New dummyA
End Class
Can I check in dummyA, if the object has been created from dummyMain?
Answer with c# or VB.Net would be great. Thanks.
Easiest way is to have an overloaded constructor and pass the owner into it.
public class DummyA
{
public DummyA(object owner)
{
var createdByDummyMain = owner is DummyMain;
}
}
and then do
public class DummyMain
{
public DummyMain()
{
var dmmA = new DummyA(this);
}
}
There is also this but it won't give you exactly what you want. There are other proposals too that deal with StackFrame but it isn't reliable due to JIT optimizations.
I have a simple interface called IEvent and it just contains this one method:
void Execute();
I have several derived classes from this interface and one of them needs access to an object that the caller of the method owns. The object is used in this fashion:
using (MyObject object = new MyObject(this.MessageService)
{
foreach (IEvent myEvent in eventList)
{
myEvent.Execute(); // <--- I need to pass object without adding argument here if possible?
}
}
I would add the object as a field in the derived class that needs access to it, but by the time I get to this part of the code, the IEvent objects are already constructed and running on a background thread. Currently, the only way I can think of is to add a setter in the IEvent interface for this object, but then I am exposing a field that most derived classes won't care about and doesn't seem like a clean solution.
I would add it as an argument to Execute(), but the problem is that the object belongs to an assembly that the assembly that contains IEvent doesn't know about (and don't want it to know about) and again 99% of the events don't care about this object anyway. Is there a better way to accomplish what I am trying to do here?
"If a class that implements IEvent does not/can not implement all the methods specified by IEvent the same way as they are declared in IEvent, that class should not implement IEvent in the first place." - Sweeper
So there's probably something wrong with your design of the whole program. I think you better revise your design a little bit and change some relationships between the classes and interfaces.
If you don't want to do that, there is another (not recommended) way to solve this problem.
Suppose your method caller is of type MethodCaller. You just change the declaration of Execute in the interface to this:
void Execute(MethodCaller obj = null);
And all the classes that implement IEvent can ignore the parameter except the class you mentioned in your question.
I'm going to piggyback on Jon Skeet's amazing knowledge of C#, .NET, CLR, IL and everything that surrounds any of those topics. You can't get to the instance of the calling object and especially the local varaible in the calling method. You can get its type, you can get the calling method through StackTrace, for example (StackTrace.GetFrames()), but none of those are going to do you any good in this situation. What you're trying to accomplish would require some heavy dive into the debugging API. As far as walking the stack, here's a quick sample I created to try see if I can figure something out for you (I made assumptions in regards to how your program is structured... obviously it's not a one to one sample):
using System;
using System.Collections.Generic;
using System.Diagnostics;
namespace SampleApp
{
class Program
{
static void Main(string[] args)
{
var eventList = new List<IEvent> { new SomeClass() };
using (MyObject obj = new MyObject(new MessageService()))
{
foreach (IEvent myEvent in eventList)
{
myEvent.Execute();
}
}
}
}
public interface IEvent
{
void Execute();
}
public class SomeClass : IEvent
{
public void Execute()
{
var stackTrace = new StackTrace();
var stackFrames = stackTrace.GetFrames();
var callingMethod = stackFrames[1].GetMethod();
var callingType = callingMethod.DeclaringType;
}
}
public class MyObject : IDisposable
{
public MessageService Service { get; }
public MyObject(MessageService service)
{
Service = service;
}
public void Dispose()
{
Service.Stop();
}
}
public class MessageService
{
public void Start() { }
public void Stop() { }
}
}
I like your question, because it presents an interesting and an unusual situation, but I'm afraid that you won't be able to accomplish your task without going outside of conventional routines that C# has in its arsenal. You may be able to pull something off with unmanaged code, but that's a different topic altogether.
However, aside from it being an interesting question... look at what you're trying to do. You have MyObject, which obviously implements IDisposable and will call Dispose() at the end of that using statement, and you're trying to grab its reference from a different assembly. I don't think this is a good idea.
I suggest revisiting your design and make use of things such as an optional parameter. May not be the "perfect" solution for your situation, as you'll pass it to every Execute in that foreach loop, but it's better than jumping through a thousand fiery hoops of debug API's.
In my project, I have many DLL assemblies referenced. One of those DLL's contains the bool method that I want to change. I do not have the original source for the DLL and using a Reflector to decompile a project seems impractical. All I want to do is intercept or override this method or method call so that I can change it's return value to match my own method outside of said DLL.
Any such way to do this? Thanks!
Edit:
Here is an example:
public virtual bool isOwner()
{
return false;
}
Essentially, I just want to change getOwner to return true;
If the class is public and the method is marked as virtual, then you can simply override it with this syntax:
public MyClass : TheClass
{
public override ReturnType MethodName(Arguments)
{
//class the base class implementation if needed
//base.MethodName(Arguments)
//do your own stuff and return whatever is needed
}
}
Hope this helps
EDIT: A word of caution though, this won't replace the calling code within the DLL. It will only work if you instantiate the derived class yourself and call it from your code.
Is there a general way to do what you want, built into .NET?
Yes, and no.
If you want every usage of class X' method Y to be replaced by some other code, then no, there is nothing built into .NET class system or compiler that will do this.
If you can inherit from class X, overriding method Y, and then ensure that all places where class X is used, your new class is used instead, then yes, that is the proper way to do this.
This is easily done:
public class YourFixedClass : TheProblematicClass
{
public override string YourProblematicMethod()
{
// probably call the problematic method through base.
// and fix the return value, or fix the parameters
// or don't call it at all, re-doing whatever it does
}
}
Or, if you can make a new class that implements all the same interfaces, wrapping (delegating) all the methods and properties of the original (problematic) class, then that might be doable, but this requires all actual usage of the class to go through the interfaces.
As this:
public class Wrapper : IInterface1, IInterface2
{
private readonly YourProblematicClass _C;
public Wrapper(YourProblematicClass c)
{
_C = c;
}
public string YourProblematicMetho()
{
// probably call the problematic method through _C.
// and fix the return value, or fix the parameters
// or don't call it at all, re-doing whatever it does
}
}
If, on the other hand, you don't have control of where all the code is that calls the class/method, then no, you can't do any of this.
So what else is there? Well, there is always the debugger interfaces. You can make a program that is somehow the debugger of itself, patching in the right code upon demand, but this is likely to be extraordinary difficult to get right.
In short, no, there is no way to do what you want. You need to find a different way to accomplish this.
Have you thought about changing the original assembly in the first place? I understand that you don't have the source code for it, but is that because:
You lost it
You didn't make it
In point 1, I would really work towards recreating the source code, either through a decompiler or similar, and get a new project going to fix that.
In point 2, have you thought about contacting the people that made it and asking them for help?
Uhm Ok you can do something like this:
public class MyNameClass : MyDllname.MyClassName
{
public bool isOwner()
{
return !base.isOwner();
}
}
Then you have override the method and you can use all the other methods in the DLL simply using an istance(if there aren't static) of the MyNameClass
You can use "new" modifier.
See example on http://msdn.microsoft.com/en-us/library/435f1dw2.aspx
Or this:
class Program
{
static void Main(string[] args)
{
Console.WriteLine(new ClassA().IsEvenDayToday()); // Result: true
Console.WriteLine(new ClassB().IsEvenDayToday()); // Result: false
Console.ReadKey();
}
}
public class ClassA : ClassB
{
public new bool IsEvenDayToday()
{
return DateTime.Now.Day % 2 == 0;
}
}
public class ClassB
{
public bool IsEvenDayToday()
{
return DateTime.Now.Day % 2 != 0;
}
}
I am a Java programmer trying to transition to C# and I'm hoping there's a way to do something in C# that I'm accustomed to in Java: overriding a method in the declaration of an abstract object like so:
//This is the way I do it in Java and want to do in C#
Keyword k = new Keyword("quit"){
public abstract void do(String context){
//TODO Do stuff
}
};
This is for some text game stuff I've been doing for a while in Java. I've looked into abstract and virtual and anonymous classes but none of them do exactly this. Abstract and virtual want me to create a whole new subclass, but this would be time consuming and unfeasible on a large scale. Anonymous classes don't (as far as I can tell) enable me to override methods, just fields and don't provide any stabilization for me to rely on.
If there is a way to do this or something similar please explain. Thanks for your time.
That doesn't work in C#. You'll have to create a new class that inherits from Keyword.
public class MyKeyword : Keyword
{
public MyKeyword(string s) : base(s)
{ }
public override void do(string context)
{
// TODO: Do stuff.
}
}
Anonymous Types in C# aren't classes that you can provide any public methods for. They only have properties, and are intended to be a quick, intra-method way of pasing complex data from one line to the next.
To be honest, I didn't know you could do what you show in Java. That is, if I'm understanding it as kind of an in-line class derivation.
Brian Rasmussen mentions using a delegate. That would look something like this:
public delegate void DoSomething(string context);
public class Keyword
{
public DoSomething Do;
private void CallsDo()
{
if (Do != null) Do("some string");
}
}
Then you can assign to it:
Keyword k = new Keyword();
k.Do = (ctx) => { /* Do something with ctx string */ };
Delegates are probably what you are after.
You can utilize a delegate for this approach: Note the example
public class Keyword
{
public delegate void Do();
}
//Area of Execution
{
//...
Keyword k = new Keyword();
k.Do = delegate()
{
Console.Writeln("Anonymous Inner function assigned to a callback function i.e a Delegate!");
};
}
These are much like function pointers in C/C++ but that may mean nothing to you depending on your background.
A delegate is, in the simplest terms, a type-safe object that encapsulates a method/function. What this means is that it maintains a reference to the method or methods and can invoke them later through the delegate object rather than explicitly on the method(s) themselves. You can assign an anonymous function to the right hand side much the same as you can to a method in Java as you described.
hope this helps. Read more here for delegates in-depth
Delegates
In C# is it possible to create a function that can only be called from within another function?
e.g., can you do something like this?
private void a()
{
b();
c();
...do something else
private void b()
{
..do something but can only be called from a()
}
private void c()
{
..do something but can only be called from a()
}
}
The reason I want to do this is that function b() and c() split some implentation details of a() and they are just cleaner and easier to read in their own scope. However, these functions are of no use to the class as a() does some handling after they are called which must take place.
Use an anonymous nested function maybe?
I wouldn't worry about taking explicit steps to ensure b() and c() are only called by a().
It makes sense to worry about the public methods you expose on a class, since you're providing an interface to the outside world, potentially to people who don't have access to the source code of your class (or at the very least don't want to worry about the implementation details of your class).
Inside your class, though, you should feel free to have whatever private methods you want for whatever reasons you want. Code re-use is one reason to create a new private method, but creating multiple smaller, single-use methods to break up a larger one is also a perfectly valid (and common) reason.
Beyond that, for future maintainers of your code a simple comment like:
//this method should only be called by a()
private void b()
{
...
}
is going to be far more understandable than most of the other solutions presented here.
Using a delegate you can do:
public voidMyFunction()
{
Func<string> myFunction=(s)=>Console.WriteLine(s);
foreach(string str in myStringList)
{
myFunction(str);
}
}
The short answer is no; however, you can create an anonymous delegate or lambda expression as your internal b() method.
You could use the StackFrame class to check at runtime who's the caller of the function:
public class MyClass
{
public static void A()
{
B();
}
public static void B()
{
var stackTrace = new StackTrace();
if (stackTrace.FrameCount < 1 || stackTrace.GetFrame(1).GetMethod() != typeof(MyClass).GetMethod("A"))
throw new InvalidOperationException("Not called from A()");
}
}
But that is
1) Only at runtime
2) Slow
3) A really dirty hack
Well you could use reflection and just get the calling method name and throw an exception if it were anything other than A.
http://www.csharp-examples.net/reflection-calling-method-name/
But if b and c are private they can only be called from within that class anyway, and if you're the only one that is writing the class, then i fail to see the problem. So it seems to me its not a coding problem but rather one of policy.
I'd just document the intent in the method headers/comments.
Similar Question Here - Note the comments on the answer
Not exactly but you could implement both within their own class. Mark b() as private.
To gain the effect of only a() calling b(), either do as Andrew noted already, by putting a() and b() in a class and marking b() appropriately. If you're working inside of an assembly that you control totally, you could use internal instead of private if a() and b() will be in different classes, but in the same assembly. Then user code cannot call it (from outside of your assembly, that is, from their application program) and you can control via policy the writing of your assembly.
You can also create something like this:
internal abstract class SecretFunctionWrapper
{
private void MySecretFunction()
{
...
}
protected void FunctionWhichCalls()
{
...
MySecretFunction();
}
}
public MyRealClass : SecretFunctionWrapper
{
...
}
This will work only for one function. You can also try nested private class like this:
public class A
{
private static class Wrapped
{
private static void A()
{
secred code
}
public static void B()
{
A();
}
}
public void UsingA()
{
Wrapped.B();
}
}
i dont know but maybe Code by Contracts may help but this is not supported natively
Maybe easier to use #region in this case
You could use the internal keyword and put both those functions inside the same class, while leaving other other functions in a different class:
http://msdn.microsoft.com/en-us/library/7c5ka91b.aspx