如何区分（）列出包含实现接口的类的列表？ C＃

Question

First of all, I have interfact ICommand :

public interface ICommand
{
}

and concrete classes ThreadSelectCommand , SearchCommand and so on:

public class ThreadSelectCommand : ICommand
{
    public int Value { get; set; }

    public ThreadSelectCommand()
    {
        Value = 1;
    }
}


public class SearchCommand : ICommand
{
    public string Value { get; set; }
    public SearchCommand()
    {
        Value = "";
    }
}

List<ICommand> resultCommands can contains a few of each command, and I need to Distinct() this list. How to do this? I know, that I should use comparator. But this classes are not the same.

Answer 1

The requirements you want (only one instance per concrete type) can be done by comparing the runtime types of the elements in the list.

public class  CommandTypeComparer : EqualityComparer<ICommand> 
{
    public override bool Equals(ICommand x, ICommand y)
    {
        return Type.Equals(x.GetType(), y.GetType());
    }

    public override int GetHashCode(ICommand x)
    {
        return x.GetType().GetHashCode()
    }
}

You would then use it like resultCommands.Distinct(new CommandTypeComparer());

Answer 2

Assume that you have a following list of object as your sample above

List<ICommand> resultCommands = new List<ICommand> {
    new ThreadSelectCommand(),
    new ThreadSelectCommand(),
    new ThreadSelectCommand(),
    new SearchCommand(),
    new SearchCommand(),
};  


var groups = resultCommands.GroupBy(x => x.GetType());

var distinctList = groups.Select(g => { 
    if(g.Key == typeof(ThreadSelectCommand))
    {
        return g.Select(x => (ThreadSelectCommand)x).GroupBy(x => new { x.Value }).Select(x => (ICommand)x.First()).First();
    }
    else if(g.Key == typeof(SearchCommand))
    {
        return g.Select(x => (SearchCommand)x).GroupBy(x => new { x.Value }).Select(x => (ICommand)x.First()).First();
    }
    else 
    {
        throw new NotSupportedException();
    }

    }).ToList();

The distinctList will contain 2 elements