在 C# 中创建通用列表类

Question

I am working on some university material and I Have the following question

Design and implement a collection class dedicated to storing all objects of company documents as per the class hierarchy, inheriting from any .NET suitable collection class (eg the ArrayList class, or generic List). The collection is to implement a single method Page 2 of 5 GetDataOfAll() returning a string that concatenates data of all objects with suitable separators. (The method will later be used to display data in a suitable output placeholder)

I wrote this:

class MainList : List<Document>
{
    public string GetDataFormAll()
    {
        string text = null;
        foreach (Document data in MainList)
        {
            text += data.GetData() + "\n";
        }
        return text;
    }
}

Is this the correct way to implement this?

foreach (Document data in MainList)

This is giving me an error it is telling me that MainList is not of the correct type. How am I to implement this, please.

Answer 1

You need to loop over the Document s in your own ( this ) collection. Since a List<T> is Enumerable<T> , you can simply write a foreach loop over the this :

public string GetDataFormAll() {
    string text = null;
    foreach (Document data in ) {
        text += data.GetData() + "\n";
    }
    return text;
}

(Yes, I code like an Egyptian )

Answer 2

Just another and shorter way, not necessarily better

public string GetDataFormAll()
{
    return string.Join("\n", this.Select(d => d.GetData());
}

And of course you can shorten it even more with .Select(GetData) syntax.

This will not add a \\n after the last element. Depends on what you want.