How to override List.Add method?

问题

Currently I have a error logging class like so:

public class Log
{
    public enum LogTypes
    {
        Info = 1,
        Error = 2,
        Warning = 3
    }


    public string Message { get; set; }
    public LogTypes LogType { get; set; }


    public Log(string Message, LogTypes LogType)
    {
        this.Message = Message;
        this.LogType = LogType;
    }

I have this initialiser for a new list:

List<Log> LogList = new List<Log>();

How can I use LogList.Add(Message, LogType) instead of LogList.Add(new Log(Message, LogType));?

I know it is a minor change but I am still learning C# and am curious. Thanks!

回答1:

Firstly, I wouldn't do this. It's not what anyone using a List<Log> would expect. Rather than exposing a plain List<Log>, consider creating a Logger class or something similar which contains a List<Log> and exposes a Log(string message, LogType type) method, but doesn't actually expose the List<Log>.

If you really want to be able to call Add(message, type) directly on the list, there are two options:

Create a new class derived from List<Log>:
```
public LogList : List<Log>
{
    public void Add(string message, LogType type)
    {
        Add(new Log(message, type));
    }
}
```
Note that this is overloading (adding a new method signature but with the same name, Add), not overriding (providing new behaviour for an existing signature method for a virtual method) - and you'll need to create an instance of LogList rather than List<Log>:
```
LogList list = new LogList();
list.Add(message, type);
```

Add an extension method to List<Log>, which will effectively add that method to all List<Log> instances.

public static LogListExtensions
{
    public static void Add(this Log<List> list, string message, LogType type)
    {
        list.Add(new Log(message, type));
    }
}

As an aside, I'd probably also remove the setters from your Log type - why would you need to be able to change the message or type after construction?

回答2:

You can create your own class derived from List and define new Add method for your needs, e.g.:

public class MyListClass : List<Log>
{
    public void Add(string message, Log.LogTypes logType)
    {
        this.Add(new Log(message, logType));
    }
}

回答3:

It is not going make any difference apart from saving a second or two of typing. Having said that you can always implement your own list class and use that. Or you could make use of extension methods.

来源：https://stackoverflow.com/questions/22165015/how-to-override-list-add-method

标签

.net

c#-4.0

overriding