Question

Suppose I have a some fat interface, which cannot be changed. And also I have some client class which want to use only few methods from that fat interface. How can be implemented adapter pattern for this situation, to achieve Interface Segregation Principle?

Answer 1

You can do the following:

// Assuming this is your fat interface
interface IAmFat
{
    void Method1();
    void Method2();
    ...
    void MethodN();
}

// You create a new interface that copies part of the fat interface.
interface IAmSegregated
{
    void Method1();
}

// You create an adapter that implements IAmSegregated and forward
// calls to the wrapped IAmFat.
class FatAdapter : IAmSegregated
{
    private readonly IAmFat fat;

    public FatAdapter(IAmFat fat)
    {
        this.fat = fat;
    }

    void IAmSegregated.Method1()
    {
        this.fat.Method1();
    }
}