Re: [Banshee-List] New INotify plugin - question re LibraryTrackRemovedArgs

[Mike Urbanski <urbanskm msoe edu>]

Jacob,

Hi.

> 1) I am probably missing something...?

No, you're right on from what I can remember.  If a single track was
removed 'LibraryTrackRemovedArgs.Track' will be non-null, if multiple
tracks were removed 'LibraryTrackRemovedArgs.Tracks' will be non-null.

Looking at the class def...

<snip>
    public class LibraryTrackRemovedArgs : EventArgs
    {
        public LibraryTrackInfo Track;
        public ICollection Tracks;
    }
</snip>

It is possible that both 'Track' and 'Tracks' could be null.  A
modification to prevent this case could look something like the attached
file...  Which is only an example, one that I haven't tested or even
compiled.  Just an example.

> 2) Why are there two fields LibraryTrackRemovedArgs.Track and
> LibraryTrackRemovedArgs.Tracks, anyway?

It's an efficiency thing.  Instead of raising an event for each track
removed, the 'Tracks' field groups all tracks that were removed as the
result of the same operation.  So in the case of say a UI or DB app, you
wouldn't have to update the display or write to the DB n-times.
Instead, you can handle the removal of all of the tracks at once and
then commit to the db / update the display only as many times as
absolutely necessary.

~Mike


/***************************************************************************
 *  LibraryTrackRemovedArgs.cs
 *
 *  Copyright (C) 2007 Michael C. Urbanski
 *  Written by Mike Urbanski <michael c urbanski gmail com>
 ****************************************************************************/

/*  THIS FILE IS LICENSED UNDER THE MIT LICENSE AS OUTLINED IMMEDIATELY BELOW: 
 *
 *  Permission is hereby granted, free of charge, to any person obtaining a
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using System;
using System.Collections;
using System.Collections.Generics;

namespace Banshee.Base
{
    public class LibraryTrackRemovedArgs : EventArgs
    {
        private readonly LibraryTrackInfo track;
        private readonly ICollection<LibraryTrackInfo> tracks;
        
        public LibraryTrackInfo Track {
            get { return track; }
            protected internal set {
                TestCombination (value, tracks);
                track = value;
            }            
        }
        
        public ICollection<LibraryTrackInfo> Tracks {
            get { return tracks; }   
            protected internal set {
                TestCombination (track, value);
                tracks = value;
            }
        }
        
        public LibraryTrackRemovedArgs (LibraryTrackInfo track)
            : this (track, null) {}        
 
        public LibraryTrackRemovedArgs (ICollection<LibraryTrackInfo> tracks)
            : this (null, tracks) {}
 
        protected internal LibraryTrackRemovedArgs () {}   
        protected internal LibraryTrackRemovedArgs (LibraryTrackInfo track, 
                                                    ICollection<LibraryTrackInfo> tracks)
        {
            TestCombination (track, tracks);
            
            this.track = track;
            this.tracks = tracks;
        }
        
        private void TestCombination (LibraryTrackInfo track, 
                                      ICollection<LibraryTrackInfo> tracks)
        {
            if (track != null && tracks != null) {
                throw new ArgumentException (
                    "Either Track or Tracks must be non-null"
                );
            } else if (track == null && tracks == null) { 
                // Possibly an 'ArgumentNullException' in the case of 
                // the constructor.
                throw new InvalidOperationException (
                    "Both Track and Tracks may not be null"
                );
            }
        }    
    }
}