Re: abstarct class basic question - C# Discussion Boards

Mirko19801-Jun-11 3:24

Mirko1980

1-Jun-11 3:24

I said that at the end of my post.
I agree you are losing many advatages of polymorphism, but, at least, you can reuse the Create login in multple classes.

Re: abstarct class basic question

BobJanova1-Jun-11 1:34

BobJanova

1-Jun-11 1:34

There's a very simple way, if you know you want a D1: call new D1() not myD1Instance.Create().

I'm guessing this is a simplified example, because it simply doesn't make sense to do things this way in most cases. What is your actual problem?

Accepting for the moment that you need a Create method at all: If you know that an instance of b is actually a D1 (for example within the D1 class itself) then you can cast the result of Create safely. Casting is not necessarily bad (it's safer than the use of dynamic, I would say). For example, in some similar code to what I have at the moment for cloning objects in an inheritance tree:

class b {
 private int someField;

 public b Copy() {
  b newB = Create();
  CopyTo(newB);
  return newB;
 }
 
 protected virtual void CopyTo(b newB){
  // copy properties into the target
  newB.someField = someField;
 }

class D1 : b {
 private double derivedField;

 protected override void CopyTo(b newD1){
  // This method will only be called if we are a D1,
  // and therefore the result of Create is also a D1,
  // and therefore the parameter is also a D1
  D1 target = (D1)newD1; // ... so this must succeed
  target.derivedField = derivedField; // ... and we can access D1's members
 }
}

Outside the class tree, it's unlikely that you know for sure at compile time which of the classes you have an instance of (otherwise you wouldn't need the abstract base class at all), so you can normally only cast the result inside the class, or using if(my is D1) type tests. And if you find yourself writing those you probably just found somewhere that an abstract method should be provided on the base class.

Re: abstarct class basic question

Luc Pattyn1-Jun-11 0:46

Luc Pattyn

1-Jun-11 0:46

Actually, you don't need Visual Studio at all. What you are meaning to say is "this requires .NET 4.0"

Smile | :)

Luc Pattyn [My Articles] Nil Volentibus Arduum

The quality and detail of your question reflects on the effectiveness of the help you are likely to get.
Please use <PRE> tags for code snippets, they improve readability.
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Re: abstarct class basic question

PIEBALDconsult1-Jun-11 2:57

PIEBALDconsult

1-Jun-11 2:57

Re: abstarct class basic question [modified]

Steven.Pinto20001-Jun-11 0:28

Steven.Pinto2000

1-Jun-11 0:28

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace general
{

class Program
{
static void Main(string[] args)
{
D1 myClass = new D1();
D1 newClass = myClass.Create();

//this is what I would like
b myClassAb = new D1();
b newClassAb = myClassAb.Create<D1>();
newClass.KM = 1.23;

}
}

abstract class b
{
//work in this way !!!
public T Create<T>() where T:new() { return new T(); }

}

class D1 : b
{
public double KM;
public D1() { KM = 1.0; }
// public D1 Create() { return new D1(); }
}
class D2 : b
{
public double KM;
public D2() { KM = 2.0; }
// public D2 Create() { return new D2(); }
}

}

here is one solution using generics

modified on Wednesday, June 1, 2011 9:53 AM

Re: abstarct class basic question [modified]

PozzaVecia1-Jun-11 1:03

PozzaVecia

1-Jun-11 1:03

Sorry probably I did not explain very well the problem. I need to have avaiable methods in newClassAb
//this is what I would like
b myClassAb = new D1();
b newClassAb = myClassAb.Create<D1>();
//This is what I need to see K from newClassAb
Console.WriteLine(newClassAb.K)>//but I can't see .K avaiable

Thanks for your time

modified on Wednesday, June 1, 2011 7:32 AM

Re: abstarct class basic question

Steven.Pinto20001-Jun-11 3:52

Steven.Pinto2000

1-Jun-11 3:52

what is K is it KM well i can see KM
try it once more because there was some error in my code

Re: abstarct class basic question

PozzaVecia1-Jun-11 4:03

PozzaVecia

1-Jun-11 4:03

b myClassAb = new D1();
          b newClassAb = myClassAb.Create<D1>();
          newClassAb.KM = 1.23;

apparently return this error" Error 1 'general.b' does not contain a definition for 'KM' and no extension method 'KM' accepting a first argument of type 'general.b' could be found (are you missing a using directive or an assembly reference?)"

The working solution example, thanks to BobJanova is:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
 
namespace general
{
 
class Program
{
static void Main(string[] args)
{

 
//this is what I would like
b myClassAb = new D1();
b newClassAb = myClassAb.Create();
Console.WriteLine(newClassAb.KM);
}
}


abstract class b
{
    public double KM { get; protected set; }  // C# 2.0 automatic property syntax
    public b Create() { return (b)Activator.CreateInstance(GetType()); }
}

class D1 : b
{
    public D1() { KM = 1.0; }
}
class D2 : b
{
    public D2() { KM = 2.0; }
}
}

Re: abstarct class basic question

BobJanova1-Jun-11 1:40

BobJanova

1-Jun-11 1:40

In response to your modification: KM should clearly be defined on the base class. It should probably also be a property.

abstract class b
{
    public double KM { get; protected set; }  // C# 2.0 automatic property syntax
    public b Create() { return Activator.CreateInstance(GetType()); }
}

class D1:b
{
    public D1() { KM = 1.0; }
}
class D2 : b
{
    public D2() { KM = 2.0; }
}

Re: abstarct class basic question

PozzaVecia1-Jun-11 1:52

PozzaVecia

1-Jun-11 1:52

Console.WriteLine(b.//<big>b.KM is still not avaiable!!</big>}

namespace general
{
 
class Program
{
static void Main(string[] args)
{

 
//this is what I would like
b myClassAb = new D1();
b newClassAb = myClassAb.Create();
    Console.WriteLine(b.//K is still not avaiable!!}
}


abstract class b
{
    public double KM { get; protected set; }  // C# 2.0 automatic property syntax
    public b Create() { return (b)Activator.CreateInstance(GetType()); }
}

class D1 : b
{
    public D1() { KM = 1.0; }
}
class D2 : b
{
    public D2() { KM = 2.0; }
}

Re: abstarct class basic question

BobJanova1-Jun-11 1:53

BobJanova

1-Jun-11 1:53

You should be able to use newClassAb.KM.

Re: abstarct class basic question

PozzaVecia1-Jun-11 2:09

PozzaVecia

1-Jun-11 2:09

Great!!!! It works...Thanks a lot Cool | :cool:

Re: abstarct class basic question

_Erik_1-Jun-11 4:10

_Erik_

1-Jun-11 4:10

I am sorry but, what is the point in creating an instance of a class to just create another instance of the same class? I mean, since Create method is not static it would just work as a constructor so, why don't you just use a constructor?

For example, what you want to do is this:

D1 obj = new D1();
D1 obj2 = D1.Create();

And what I am saying is... why not?

D1 obj = new D1();
D1 obj2 = new D1();

I guess you want a static Create method in your base class, don't you? In this case you will have to make your Create method static and use generics:

abstract class BaseClass
{
    public static T Create<T>() where T : BaseClass, new()
    {
        return new T();
    }
}

class DerivedClass : BaseClass { }

This way you could use it like this:

DerivedClass obj = BaseClass.Create<DerivedClass>();

Re: abstarct class basic question

PozzaVecia1-Jun-11 5:24

PozzaVecia

1-Jun-11 5:24

I was looking for a way to avoid to write the same piece of code in each derived class since they basically do the same thing. I Would like to create a method in the base class. But this should allow you to use methods of derived class Is it?

class D1:b
  {
      ..
      public D1 Create() { return new D1(); }
  }
  class D2 : b
  {
      ..
      public D2 Create() { return new D2(); }
  }

So my goal is not to do

D1 obj = new D1();
D1 obj2 = D1.Create();

but to do

b myClassAb = new D1();
b newClassAb = myClassAb.Create();
Console.WriteLine(newClassAb.KM); //i.e. I need to access to proprieties, methods, etc of class

Re: abstarct class basic question

_Erik_2-Jun-11 2:00

_Erik_

2-Jun-11 2:00

Member 4282287 wrote:
I need to access to proprieties, methods, etc of class

That does not depend on how you create the objects, I mean, your Create method will not help you to achieve what you want. If you can access KM property of a D1 object which you have declared as its base class type (b in this case), you can becouse KM property is definied within the "b" class interface, but not becouse you have made such a strange Create method. So in your sample:

b myClassAb = new D1();
b newClassAb = myClassAb.Create();
Console.WriteLine(newClassAb.KM)

You don't need the Create method at all. Just use the constructor and one instance of the object:

b myClassAb = new D1();
Console.WriteLine(myClassAb.KM)

Re: abstarct class basic question

PozzaVecia2-Jun-11 2:11

PozzaVecia

2-Jun-11 2:11

ok thanks understood.
Really the starting example was a bit different ... i.e. I needed a method avaiable only in derived class.
During the forum this method ... become a proprierties..
Apparently I understood. You are right of course.
Thanks for your time

C# COM Interop

Vijjuuu.31-May-11 19:15

Vijjuuu.

31-May-11 19:15

Hi All,

i googled how we can added events in C# class for COM Interop that can be called in VB6.0 but not able to find out any article that help me.

if any one tried it before then pls guide me.

here is my code.

public interface ICalculator
{
// I guess we need to add a event here but i am not sure .
int Add(int Number1, int Number2);
}

public class ManagedClass:ICalculator
{
public int Add(int Number1,int Number2)
{
// I want to raise an event here so that this event should be consumed in VB
return Number1+Number2;
}
}

i done all the step to make the dll to be used in VB.

Re: C# COM Interop

BobJanova31-May-11 23:05

BobJanova

31-May-11 23:05

COM interop is supposed to work with normal .Net events (i.e. event EventHandler<MyEventArgs> Calculate), isn't it? The problem here might be VB6 ...

Re: C# COM Interop

Mirko19801-Jun-11 0:12

Mirko1980

1-Jun-11 0:12

You have to play a bit with interfaces.
Look here for a sample.

Re: C# COM Interop

Eddy Vluggen1-Jun-11 0:57

Eddy Vluggen

1-Jun-11 0:57

You'd need to declare the object WithEvents in VB6, otherwise VB6 won't hook those up. Microsoft made a toolkit[^] to make interop between VB6 and .NET a lot easier. I suggest you download it and have a look. There's also a CodeProject article[^] on the subject.

Bastard Programmer from Hell Suspicious | :suss:

Re: C# COM Interop

DaveyM691-Jun-11 0:59

DaveyM69

1-Jun-11 0:59

I'm not sure about COM interop stuff as I've never needed it - but events are quite straight forward to add:

public interface ICalculator
{
    event EventHandler CalculationPerformed;
    event EventHandler<int> CalculatedResult;

    int Add(int Number1, int Number2);
}

public class ManagedClass : ICalculator
{
    public event EventHandler CalculationPerformed;
    public event EventHandler<int> CalculatedResult;

    public int Add(int number1, int number2)
    {
        int result = number1 + number2;
        OnCalculationPerformed(EventArgs.Empty);
        OnCalculatedResult(new EventArgs<int>(result));
        return result;
    }
    protected virtual void OnCalculationPerformed(EventArgs e)
    {
        EventHandler eh = CalculationPerformed;
        if (eh != null)
            eh(this, e);
    }
    protected virtual void OnCalculatedResult(EventArgs<int> e)
    {
        EventHandler<int> eh = CalculatedResult;
        if (eh != null)
            eh(this, e);
    }
}

public delegate void EventHandler<T>(object sender, EventArgs<T> e);
public class EventArgs<T> : EventArgs
{
    private T value;

    public EventArgs(T value)
    {
        this.value = value;
    }

    public T Value
    {
        get { return value; }
    }
}

Dave

Binging is like googling, it just feels dirtier.
Please take your VB.NET out of our nice case sensitive forum.
Astonish us. Be exceptional. (Pete O'Hanlon)

BTW, in software, hope and pray is not a viable strategy. (Luc Pattyn)

Bitmap.SelectActiveFrame

H@is@here31-May-11 12:53

H@is@here

31-May-11 12:53

Hi everyone,

I would like to know if someone have experienced slow issues with Bitmap.SelectActiveFrame in a 64 bit system,
or why is the method so much slower in a 64 bit system than in a 32 bit?

Here is a sample code that I have used to test:

Bitmap m_bmp = new Bitmap("C:\\01.tif");
           String m_Start = DateTime.Now.ToString("hh:mm:ss");
           System.Diagnostics.Debug.WriteLine("Started at: " + m_Start);
           for (Int32 a = 0; a < 22; a++)
           { m_bmp.SelectActiveFrame(FrameDimension.Page, a); }
           String m_Finish = DateTime.Now.ToString("hh:mm:ss");
           System.Diagnostics.Debug.WriteLine("Finished at: " + m_Finish.ToString());

The 01.tif file is a black & white image with 1bpp and 23 pages with 300dpi.
Test made with Windows7 VS2010 .NetFramework 4.0 32 bit: Less than 1 second.
Test made with Windows7 VS2010 .NetFramework 4.0 64 bit: 6 seconds.
This is really a lot.
Can someone be kind to help me ?

Thank you. Best regards.

Load image that really are 2 images into imagelist

manchukuo31-May-11 9:20

manchukuo

31-May-11 9:20

Hello

i want to load an image that is 50x25, which are really 2 images of 25x25 into imagelist an use the index to refer them, i can't make it work

Thanks Smile | :)

Re: Load image that really are 2 images into imagelist

Mark Salsbery31-May-11 11:19

Mark Salsbery

31-May-11 11:19

ImageList has an Images property which has an AddStrip() method[^]

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

Re: Load image that really are 2 images into imagelist

manchukuo31-May-11 11:28

manchukuo

31-May-11 11:28

Thank you that was the one

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