Events and Delegates in c# : How to use Events & Delegates to Notify One class about changes in other class

Question

The question is below the proper way to use Events & Delegates to call method of class A:Show1() using event of class B which is raised in B:Show()

public class classA
{
    private classB _Thrower;

    public classA()
    {
        _Thrower = new classB();            
        _Thrower.ThrowEvent += (sender, args) => { show1(); };
    }

    public void show1()
    {
        Console.WriteLine("I am class 2");
    }
}

public class classB
{
    public delegate void EventHandler(object sender, EventArgs args);

    public event EventHandler ThrowEvent = delegate { };
    public classB()
    {
        this.ThrowEvent(this, new EventArgs());
    }
    public void show()
    {
        Console.WriteLine("I am class 1");            
    }
}

Sorry for any mistakes in question this is my first time of stackoverflow

Answer 1

Cant think of what you are trying to accomplish, but to answer your question this might do it. Unless I did not understand your question right.
Mind you that this violates a principle of OOP that states that each class should be independant of other classes.

public class classA
{
    public void show1()
    {
        Console.WriteLine("I am class A");
    }
}

public class classB
{
    public void show()
    {
        new classA().show1(); 
        Console.WriteLine("I am class B");            
    }
}

Answer 2

To get the result from your edited question you can use this code:

static void Main()
{
    classA obA = new classA();
    classB obB = new classB();
    obA.Shown += ( object sender, EventArgs e ) => { obB.ShowB(); };
    obA.ShowA();
}

public class classA
{
    public event EventHandler Shown;

    public classA()
    {
    }

    public void ShowA()
    {
        Console.WriteLine( "I am class A" );

        if( Shown != null )
            Shown( this, EventArgs.Empty );
    }
}

public class classB
{
    public event EventHandler Shown;

    public classB()
    {
    }

    public void ShowB()
    {
        Console.WriteLine( "I am class B" );

        if( Shown != null )
            Shown( this, EventArgs.Empty );
    }
}

In main() method you could do it vica versa as well:

obB.Shown += ( object sender, EventArgs e ) => { obA.ShowA(); };
obB.ShowB();

But you should not do both at the same time or you'll get an infinite loop ending up in a stackoverflow

Answer 3

I guess This is the answer @GuidoG @Kai Thoma

class A
{
    public A(B b)
    {
        b.ShowA += new methcall(this.showA);
    }
    public void showA()
    {
        Console.WriteLine("I am Class A");
    }
}
class B
{
    public event methcall ShowA;
    public void showB()
    {
        Console.WriteLine("I am Class B");
        if (ShowA != null)
            ShowA();
    }
}
class Program
{
    static void Main()
    {
        B b = new B();
        A a = new A(b);
        methcall m = new methcall(b.showB);
        m.Invoke();
        Console.ReadKey();
    }
}