[RESOLVED] [2005] Losing values

Okay im making a class for my MP3 to read ID3 Tags,

VB Code:

Public Class MP3
    Private Structure ID3
        Dim SONGNAME As String
        Dim ALBUM As String
        Dim ARTIST As String
        Dim YEAR As String
        Dim COMMENT As String
        Dim GENRE As String
    End Structure
    Dim _FILENAME As String
 
    Private mID3 As ID3
    Public Sub New(ByVal fileName As String)
        _FILENAME = fileName
        readFile()
    End Sub
 
    Private Sub readFile()
        Dim fs As New IO.FileStream(_FILENAME, IO.FileMode.Open, IO.FileAccess.Read)
        Dim br As New IO.BinaryReader(fs)
        br.BaseStream.Seek(-128, IO.SeekOrigin.End)
        If br.ReadChars(3) = "TAG" Then
            With mID3
                .SONGNAME = br.ReadChars(30)
                .ARTIST = br.ReadChars(30)
                .ALBUM = br.ReadChars(30)
                .YEAR = br.ReadChars(4)
                .COMMENT = br.ReadChars(30)
                .GENRE = br.ReadChars(1)
            End With
        Else
            fs.Close()
            br.Close()
        End If
    End Sub
 
    Public Function getSongName() As String
        Return mID3.SONGNAME
    End Function
 
    Public Function getAlbum() As String
        Return mID3.ALBUM
    End Function
 
    Public Function getArtist() As String
        Return mID3.ARTIST
    End Function
 
    Public Function getYear() As String
        Return mID3.YEAR
    End Function
 
    Public Function getComment() As String
        Return mID3.COMMENT
    End Function
 
    Public Function getGenre() As String
        Return mID3.GENRE
    End Function
 
End Class

VB Code:

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim myMP3 As New MP3("C:\Documents and Settings\Jason\My Documents\My Music\iTunes\iTunes Music\Trapt\Unknown Album\01 Headstrong.mp3")
        With myMP3
            Debug.Print(.getAlbum)
            Debug.Print(.getArtist)
            Debug.Print(.getComment)
            Debug.Print(.getSongName)
            Debug.Print(.getYear)
            Debug.Print(.getGenre)
        End With
    End Sub

It all works great, the values get filled. But as soon as I try and acess the values through .getArtist etc the mID3.ARTIST becomes Null..Why is the value being reset?

There is a free DLL that does all of the MP3 tag ID stuff for you. It is called
UltraIDLib. Here is the URL http://home.fuse.net/honnert/hundred/?UltraID3Lib

Of course it is more fun to roll your own.

In your readFile method you are creating an ID3 object but only in a local variable. You never assign it to the mID3 member variable. You should do away with the local variable altogether because it doesn't serve a useful purpose. Local variables that hide member variables with the same name are generally a bad idea for this very reason: they make it easier to make this kind of mistake.

Got it to work.

Change the values from a structure to fields in the class itself. Each time it's accessed, it creates that structure and erases all previous data. If you make them private fields, it works fine (which means remove the mID3 object).

Quote:

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Originally Posted by warrenayen

Got it to work.

Change the values from a structure to fields in the class itself. Each time it's accessed, it creates that structure and erases all previous data. If you make them private fields, it works fine (which means remove the mID3 object).

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That's not true. Accessing a structure doesn't recreate it. The only time a new structure is created is in the readFile method and, as I said, that value is never assigned to the mID3 member variable. The reason it would have worked for you is because you removed the ID3 structure altogether, thus you also removed the local variable in the readFile method.

Note that this is also a good reason to always qualify your member variables with "Me." when using them. I've seen it written that that is bad practice but to me it increases clarity. Doing so may have prevented this error by highlighting the fact that it was a local variable being accessed and not a member variable of the same name.

Gee. Cant believe i missed that. Thanks JM

Wait I lied. Even though that last error was definately going to turn up an error, it still returns nothing in the later calls.

You're right. I thought that it was being recreated because that's what I changed - not realizing there was a local variable and that's why it wasn't working. Either way, I got it to work, anyway :)

And yes, using ME is a great idea. I always use ME at all times...

Any other ideas? I removed the definition in the ReadFile sub, still is nothing though. I cant understand this, never ran into this problem before in this manner.

Can you tell me how you got it to work? Because I cant

Have you debugged your readFile method? I just ran your code on a couple of MP3 files. The first one successfully read a song name, artist and genre only, and the genre was a non-ASCII character. All that information was successfully written to the Immediate window in one line. The second one entered the Else block so never read any information, hence all ID3 fields were Nothing.

Im sooo stupid. I changed the file to a file with no ID3 tags and thats why it wasnt working. Also that else block was definately not how i intended it so numerous things were going wrong. Ive been writing Java code for too long now I guess :S

Quote:

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Originally Posted by |2eM!x

Ive been writing Java code for too long now I guess :S

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I was thinking that all those getSomething functions looked like Java. The .NET way would be a to declare a ReadOnly property.