如何将扩展方法放在库中？

Question

I wanted to have the removeAll method to remove items in a observableCollection. The code is:

public static class ExtensionMethods
{
    public static int Remove<T>(
        this ObservableCollection<T> coll, Func<T, bool> condition)
    {
        var itemsToRemove = coll.Where(condition).ToList();

        foreach (var itemToRemove in itemsToRemove)
        {
            coll.Remove(itemToRemove);
        }

        return itemsToRemove.Count;
    }
}

I have my main project and I created a new DLL project with utilities related with collections, so I created in this second project a class that has this code.

However, I don't have the RemoveAll method in available to the observableCollection, I mean that:

ObservableCollection<MyType> o = new ObservableCollection<MyType>();
o.RemoveAll ??

Is not available. I add a new reference in my main project to the second project and I include the using of the library.

If in my main project I create a class then the method is available. But I would like to have a library with this extension methods to have this methods to another project and not to add a new class in each project.

Answer 1

The problem is that you did not implement a RemoveAll method, but a Remove<T> method.

public static int Remove<T>(this ObservableCollection<T> coll, Func<T, bool> condition)

Maybe if you declare it like this...?

public static int RemoveAll<T>(this ObservableCollection<T> coll, Func<T, bool> condition)

Also, of course you have to reference the DLL in your original project and include the namespace.

What strikes me funny is that you say it works when you change the class name from ExtensionMethods to ObservableCollection . Could it be that you accidentially created a class named ObservableCollection that now conflicts with System.Collections.Generic.ObservableCollection ?

Answer 2

You must include the namespace with "using" keyword. For example:

using System.Collections.Generic;
using System.Linq;