using Explicit Interface Implementation

Question

I am trying to change the property type in interface implementation class using explicit interface implementation.

interface ISample
{    
   object Value { get; set; }     
} 

class SampleA : ISample
{    
   SomeClass1 Value { get; set; } 

   object ISample.Value
    {    
        get { return this.Value; }
        set { this.Value = (SomeClass1)value; }
    }    
}


class SampleB : ISample
{

   SomeClass2 Value { get; set; } 

   object ISample.Value
    {    
        get { return this.Value; }
        set { this.Value = (SomeClass2)value; }    
    }    
}

class SomeClass1
{    
   string s1;    
   string s2;    
}

But when I need to pass in interface obj in a function, I cant access the objects of SomeClass1 or SomeClass2.

For eg:

public void MethodA(ISample sample)    
{    
  string str = sample.Value.s1;//doesnt work.How can I access s1 using ISample??    
}

I don't know if this is understandable, but I cant seem to get an easier way to explain this. Is there a way to access the properties of SomeClass1 using interface ISample?

Thanks

payo · Accepted Answer · 2012-03-28 22:47:02Z

1

That is because you've received the object as the interface, so it doesn't know about the class's new property type. You would need to:

public void MethodA(ISample sample)
{
  if (sample is SampleA)
  {
    string str = ((SampleA)sample).Value.s1;
  }     
}

A better solution might be to use the visitor pattern - which would have implementations for handling the different ISample's.

edited Mar 28, 2012 at 22:47

answered Mar 28, 2012 at 22:31

payo

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4 Comments

ntziolis Over a year ago

the second example does not work since SomeClass1 is the type of the property not the type of ISample and the first will throw an exception if ISample is of SampleA

payo Over a year ago

then use constraints :) and I'm assuming things are public, his code shows it not-public.

payo Over a year ago

I added some type checks for ntziolis - I wasn't showing the safe route, I was showing how to cast the objects. Clearly, some design should be added to make the code more reliable.

payo Over a year ago

@user1299340 - do I get the answer accepted?!?! [always going for more SO points]

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