Question

I just came across this weird behavior today:

interface IFooBar
{
    void Foo();
    void Bar();
}

class FooBar : IFooBar
{
    void IFooBar.Foo()
    {
    }

    void IFooBar.Bar()
    {
        this.Foo();
    }
}

The line this.Foo(); raises the compiler error

‘MyProject.FooBar’ does not contain a
definition for ‘Foo’ and no extension
method ‘Foo’ accepting a first
argument of type ‘MyProject.FooBar’
could be found (are you missing a
using directive or an assembly
reference?)

If I choose public methods instead of the interface.method declaration style, the code compiles:

class FooBarOk : IFooBar
{
    public void Foo()
    {
    }

    public void Bar()
    {
        this.Foo();
    }
}

I’d like to understand why this error is raised, and how it can be worked around using the interface.method notation

Answer 1

To work around it, you can write:

((IFooBar)this).Foo();

Take a look at the Explicit Interface Implementation Tutorial for answer why this.Foo() doesn’t work.