I was trying how Interfaces are working but I couldn't do it. My goal is write "n" for WriteNorM() in writeN class and write "m" for WriteNorM() in writeM class. But when I try it it's saying that "you are trying to convert void into bool!" please help.(btw don't mind class names it's only a test program)
class xd
{
interface Ixd
{
void WriteNorM();
}
class writeN : Ixd
{
public void WriteNorM()
{
Console.WriteLine("n");
}
}
class writeM: Ixd
{
public void WriteNorM()
{
Console.WriteLine("m");
}
}
static void Main()
{
Ixd D = new writeN();
Ixd D1 = new writeM();
Console.WriteLine(D.WriteNorM());
Console.WriteLine(D1.WriteNorM());
}
}
Console.WriteLine expects an argument, but WriteNorM is defined as
void WriteNorM();
so it doesn't return anything, and you can't pass void to a method.
Conceptually a void method doesn't return anything, so there's no return value to pass into another method like you're trying to do:
Console.WriteLine(D.WriteNorM()); // is the same as Console.WriteLine(void)
^^^^^^^^^^^^^
void
Changing your code to
static void Main()
{
Ixd D = new writeN();
Ixd D1 = new writeM();
D.WriteNorM();
D1.WriteNorM();
}
will produce the output you want:
n
m
Alternatively, you could change your interface to have
string GetNorM();
instead (i.e. GetNorM now returns a string that you can then pass into Console.WriteLine, instead of void):
class xd
{
interface Ixd
{
string GetNorM();
}
class writeN : Ixd
{
public string GetNorM()
{
return "n";
}
}
class writeM: Ixd
{
public string GetNorM()
{
return "m";
}
}
static void Main()
{
Ixd D = new writeN();
Ixd D1 = new writeM();
Console.WriteLine(D.GetNorM());
Console.WriteLine(D1.GetNorM());
}
}
Related
I want to call many tests like this.
var test8001 = new Test8001();
test8001.Execute(drv);
var test8002 = new Test8002();
test8002.Execute(drv);
var test8007 = new Test8007();
test8007.Execute(drv);
How can I automatically instantiate all test function with a int list of all test numbers?
List<int> classNameNumbers = new List<int>() { 8001, 8002, 8007 };
I need a for-loop where Execute() is called on every instance.
Edit:
The name of the type e.g. 'Test8001' should be retrieved from my integer list.
Try out the following
namespace Stackoverflow46529447
{
class Program
{
static void Main(string[] args)
{
var drv = new Drv();
var numbers = new[] {8001, 8002, 8003};
var executables = numbers.Select(x => Activator.CreateInstance(Type.GetType($"Stackoverflow46529447.Test{x:0000}")))
.OfType<IExecutable>()
.ToArray();
foreach (var executable in executables)
{
executable.Execute(drv);
}
}
}
public class Test8001 : IExecutable
{
public void Execute(Drv drv)
{
Console.WriteLine("Hello from Test 8001");
}
}
public class Test8002 : IExecutable
{
public void Execute(Drv drv)
{
Console.WriteLine("Hello from Test 8002");
}
}
public class Test8003 : IExecutable
{
public void Execute(Drv drv)
{
Console.WriteLine("Hello from Test 8003");
}
}
public interface IExecutable
{
void Execute(Drv drv);
}
public class Drv
{
}
}
This uses reflection to create instance types.
Consider the following code :
class Program
{
static void Main(string[] args)
{
var a = new A();
var b = new B();
Print(a);
Print(b);
Console.WriteLine(b.Hello);
Console.ReadLine();
}
static void Print<T>(T t) where T : A
{
Console.WriteLine(typeof(T));
Console.WriteLine(t.GetType());
Console.WriteLine(t.Hello);
}
}
public class A
{
public string Hello { get { return "HelloA"; } }
}
public class B : A
{
public new string Hello { get { return "HelloB"; } }
}
The output I got (.NET FW 4.5)
//Print(a)
A
A
HelloA
//Print(b)
B
B
HelloA
//Explicit Writeline
HelloB
Can anyone explain how I got the 2nd HelloA, as I was expecting HelloB ?
public new string Hello { get { return "HelloB"; } }
The new keyword creates a new function which just happens to have the same name as the old one. Thus, B now has two methods: Hello (A), which is executed when invoked through a variable of compile-time type A, and Hello (B), which is executed when invoked through a variable of compile-time type B (or a subtype thereof).
Since your generic parameter is T : A, the compiler compiles t.Hello as a call to Hello (A).
B shadows (or hides) method Hello rather than overriding it.
What you probably wanted to write was:
public class A
{
public virtual string Hello { get { return "HelloA"; } }
}
public class B : A
{
public override string Hello { get { return "HelloB"; } }
}
Note that the base method is declared as virtual, and the subclass method as override.
I was making a test case for some code on binary search tree my professor gave
public static void Main(string [] args)
{
//on my prof's code, public class BinSearchTree<T>
BinSearchTree<int> myTree = new BinSearchTree<int>();
myTree.Insert(10);
myTree.Insert(15);
myTree.Insert(5);
myTree.Insert(2);
myTree.Insert(1);
Console.WriteLine(myTree.ToString());
Console.ReadKey();
}
It compiles, but it displays
BinSearchTree`1[System.Int32]
Can somebody tell me why it displays that?
my prof's code:
public class BinSearchTree<T> where T : IComparable<T>
{
private class OurTreeNode<T>
{
public T Data { get; set; }
public OurTreeNode<T> Left;
public OurTreeNode<T> Right;
public OurTreeNode(T d = default(T), OurTreeNode<T> leftnode = null, OurTreeNode<T> rightnode = null)
{
Data = d;
Left = leftnode;
Right = rightnode;
}
public override string ToString()
{
return Data.ToString();
}
}
//...other methods
//prof's Insert method
public void Insert(T newItem)
{
mRoot = Insert(newItem, mRoot);
}
private OurTreeNode<T> Insert(T newItem, OurTreeNode<T> pTmp)
{
if (pTmp == null)
return new OurTreeNode<T>(newItem, null, null);
else if (newItem.CompareTo(pTmp.Data) < 0)
pTmp.Left = Insert(newItem, pTmp.Left);
else if (newItem.CompareTo(pTmp.Data) > 0)
pTmp.Right = Insert(newItem, pTmp.Right);
else
throw new ApplicationException("...");
return pTmp;
}
}
I tried adding a ToString() method after the Insert method but it gives me an error when I used foreach. Is there a way of displaying it without making too much extra methods?
The class is using the default (Object's) ToString() implementation. You have 2 options:
walk though the elements of the tree and print it yourself
ask the author to implement/override the ToString() method
Can somebody tell me why it displays that?
It displays that because ToString() prints the type definition.
Default implementations of the Object.ToString method return the fully qualified name of the object's type. (from the docs)
For instance, the following short program prints System.Collections.Generic.List`1[System.Int32], which is the type of List<int>.
using System;
using System.Collections.Generic;
public class Program
{
public static void Main(string[] args)
{
List<int> myTree = new List<int>();
myTree.Add(10);
Console.WriteLine(myTree.ToString());
}
}
Here are the rudiments of how to override the ToString() method to produce some meaningful output.
using System;
using System.Collections.Generic;
public class Program
{
public static void Main(string[] args)
{
BinSearchTree<int> myTree = new BinSearchTree<int>();
myTree.Insert(10);
myTree.Insert(15);
Console.WriteLine(myTree.ToString());
}
}
public class BinSearchTree<T> where T : IComparable<T>
{
private List<T> values = new List<T>();
// rest of class omitted for clarity
public void Insert(T val) {
values.Add(val);
}
public override string ToString() {
var result = string.Empty;
foreach(var v in values)
{
result += v + ", ";
}
return result;
}
}
Output
10, 15,
As you have created the object of BinaryTree Class and have not overridden the ToString() method inside BinaryTree Class. You have not created object of OurTreeNode class and not calling ToString() method overriden inside it. Hence it is giving you the default ToString() method output of BinaryTree Class.
BinSearchTree<int> myTree = new BinSearchTree<int>();
You are calling
Console.WriteLine(myTree.ToString());
Suppose I have a class A:
class A
{
void b() {...}
}
and a class B:
class B
{
A m;
}
This way, if I write B x, I can call x.m.b().
What I need is to dynamically create a method b() inside the B class, so I could use it as x.b() (of course, the results from calls x.m.b() and x.b() should be the same).
How can I do it?
There is one generic solution (where you won't have to f.e create delegates for every method from A you want). Unfortunately, It won't be a strongly-typed one. If you want so, please see other answers.
class A
{
public int B()
{
return 1;
}
}
class B : DynamicObject
{
private readonly A m = new A();
private static readonly Lazy<IEnumerable<MethodInfo>> AMethods =
new Lazy<IEnumerable<MethodInfo>>(() =>
{
var type = typeof (A);
return type.GetMethods(
BindingFlags.Instance |
BindingFlags.Public);
});
public override bool TryInvokeMember(
InvokeMemberBinder binder,
object[] args,
out object result)
{
if (base.TryInvokeMember(binder, args, out result))
{
return true;
}
var methods = AMethods.Value;
var method = methods.SingleOrDefault(mth => mth.Name == binder.Name);
// TODO: additional match (arguments type to handle overloads)
if (method == null)
{
result = null;
return false;
}
result = method.Invoke(this.m, args);
return true;
}
public int OtherBMethods()
{
return 2;
}
}
Usage:
var b = new B();
int result = ((dynamic)b).B();
int other = b.OtherBMethods();
or
dynamic b = new B();
int result = b.B();
int other = b.OtherBMethods();
You could do this with delegates, in modern C# this could look like this
public class A
{
public void b() {...}
}
public class B
{
private A m = new A();
public Action b = ()=>m.b();
}
public void Main()
{
new B().b(); // This now invokes your delegates that invokes the b method on it's internal m object
}
Could also just do it with classical methods and simply expose a b method that does the exact same thing, don't see anything special / hard here? If you're trying to accomplish something else you need to clarify your question, like if you want to automate this there are easy compile time (T4 text templates) or at runtime (generating dynamic proxies).
What you are going to do is implement Decorator pattern in C#.
GoF defines Decorator pattern as "Attach additional responsibilities
to an object dynamically. Decorators provide a flexible alternative to
subclassing for extending functionality.
I would like to recommend look throught this article "Understanding and Implementing Decorator Pattern in C#".
I have created a simple example of the Decorator pattern implementation when you decorate Concrete with A and B functionality.
interface IDecorator
{
void Print();
}
class Concrete : IDecorator
{
public void Print()
{
Console.WriteLine("-> Concrete");
}
}
class A : IDecorator
{
IDecorator decorator;
public A(IDecorator decorator)
{
this.decorator = decorator;
}
public void Print()
{
decorator.Print();
Console.WriteLine("-> A");
}
}
class B : IDecorator
{
IDecorator decorator;
public B(IDecorator decorator)
{
this.decorator = decorator;
}
public void Print()
{
decorator.Print();
Console.WriteLine("-> B");
}
}
class Program
{
static void Main(string[] args)
{
Console.WriteLine("concrete object that should be decorated");
var concrete = new Concrete();
concrete.Print();
Console.WriteLine("let's decorate this object with A decorator");
var decoratedWithA = new A(concrete);
decoratedWithA.Print();
Console.WriteLine("let's decorate this object with B decorator");
var decoratedWithB = new B(concrete);
decoratedWithB.Print();
Console.WriteLine("let's decorate concrete with A and B");
var decoratedWithAB = new B(new A(concrete));
decoratedWithAB.Print();
}
}
I have an abstract A class and classes A1 : A, A2 : A, A3 : A. Then i
also have a method named c(). I want to create classes
A1_with_c_method, A2_with_c_method, A3_with_c_methos while leaving A1,
A2 and A3 unharmed. What is the best way to do this? – h8red
You could do something like this:
abstract class A
{
}
class A1 : A
{
}
class A2 : A
{
}
class A3 : A
{
}
#region Not a good idea, because too many classes
class A1_with_c : A1
{
public void c() { }
}
class A2_with_c : A2
{
public void c() { }
}
class A3_with_c : A3
{
public void c() { }
}
#endregion
// Decorate A with the c() method
class BaseDecorator
{
public A Instance { get; private set; }
public BaseDecorator(A instance)
{
Instance = instance;
}
public virtual void c()
{
// do something with instance
}
}
class Decorator : BaseDecorator
{
BaseDecorator decorator;
public Decorator(BaseDecorator decorator)
: base(decorator.Instance)
{
this.decorator = decorator;
}
public override void c()
{
Console.WriteLine("Ok");
}
}
class Program
{
static void Main(string[] args)
{
// not good
new A1_with_c().c();
new A2_with_c().c();
new A3_with_c().c();
// better
var a_with_c = new BaseDecorator(new A1());
a_with_c.c();
// Let's decorate with something interesting
new Decorator(a_with_c).c();
}
}
I agree with the comments that this really seems odd and I'm wondering why you would ever want to do this but here is a possibility for you.
interface IHasMethodb
{
void b();
}
class A : IHasMethodb
{
public void b() { ... }
}
class B : IHasMethodb
{
A m;
public void b() { return m.b(); }
}
Is this what you're trying to do?
It seems like you either want the concept of wrapping a method, which in your example is as simple as:
class A {
public void b() { ... }
}
class B {
A m;
public void b() { m.b(); }
}
Allowing you to:
B x = new B();
x.b();
If you want to be able to "dynamically create" the method then this might be more applicable, using an Action<T> to allow you to do whatever you like with the A instance, without actually exposing it:
class A {
public void b() {...}
}
class B {
A m;
public Action<A> doSomethingWithA;
public void b() {
if (doSomethingWithA != null)
doSomethingWithA(m);
}
}
Then you can:
B x = new B();
x.doSomethingWithA = a => a.b();
x.b();
This is what I want to do in C# (within class Helper - without generic arguments),
List<AbstractClass<dynamic>> data;
public void Add<T>(AbstractClass<T> thing)
{
this.data.Add((AbstractClass<dynamic>) thing);
}
This helper class would take and work with AbstractClass<> objects and give back AbstractClass<> of specific generic type. AbstractClass<T> contains many functions which return T / take in T like public T Invoke().
For Helper class T cannot be known beforehand. The Add<T>(.. thing) function is not in a class of type T.
To be used like this in Helper class's functions,
foreach(var c in data.Where(x => ...))
{
// public T Invoke() { ... } function within AbstractClass<T>
var b = c.Invoke();
// logic
}
This also fails,
List<AbstractClass<object>> data;
public void Add<T>(AbstractClass<T> thing)
{
this.data.Add((AbstractClass<object>) thing);
}
Now I think I can have,
List<dynamic> data; // or List<object> data;
public void Add<T>(AbstractClass<T> thing)
{
this.data.Add(thing);
}
but I want the constraint that List named data has only elements of type like
ConcreteClass : AbstractClass<OtherClass>
So we would know that there is an public T Invoke() function but we do not know what it returns. This is helpful to avoid mistakes of say misspelling Invocke and only knowing at run-time.
I want to avoid casting to dynamic every time to invoke functions that give back generic type T
To do what you want to do you are going to need to use a Contravariant interface
public class Program
{
static void Main()
{
var m = new Helper();
m.Add(new ConcreteClass());
m.Process();
}
class Helper
{
List<IAbstractClass<OtherClassBase>> data = new List<IAbstractClass<OtherClassBase>>();
public void Add(IAbstractClass<OtherClassBase> thing)
{
this.data.Add(thing);
}
public void Process()
{
foreach(var c in data.Where(x => x.ShouldBeProcessed()))
{
var b = c.Invoke();
Console.WriteLine(b.Question);
var castData = b as OtherClass;
if (castData != null)
Console.WriteLine(castData.Answer);
}
}
}
public interface IAbstractClass<out T>
{
bool ShouldBeProcessed();
T Invoke();
}
abstract class AbstractClass<T> : IAbstractClass<T>
{
public bool ShouldBeProcessed()
{
return true;
}
public abstract T Invoke();
}
class ConcreteClass : AbstractClass<OtherClass>
{
public override OtherClass Invoke()
{
return new OtherClass();
}
}
class OtherClassBase
{
public string Question { get { return "What is the answer to life, universe, and everything?"; } }
}
class OtherClass : OtherClassBase
{
public int Answer { get { return 42; } }
}
}
You do not need to tell Add what kind of class you are passing it, all that matters is it derives from the type specified. You could do public void Add(IAbstractClass<object> thing) and every class would work, but Invoke() would only return objects inside the foreach loop.
You need to figure out what is the most derived class you want Invoke() to return and that is what you set as the type in the list.
Maybe this will work for you:
public class Program
{
static void Main()
{
var m1 = new Helper<OtherClass>();
m1.Add(new ConcreteClass());
var m2 = new Helper<int>();
m2.Add(new ConcreteClass2());
}
class Helper<T>
{
List<AbstractClass<T>> data = new List<AbstractClass<T>>();
public void Add<T1>(T1 thing) where T1 : AbstractClass<T>
{
this.data.Add(thing);
}
}
class AbstractClass<T> { }
class OtherClass { }
class ConcreteClass : AbstractClass<OtherClass> { }
class ConcreteClass2 : AbstractClass<int> { }
}