.net - Lambda 式を使用しようとする際の問題

Question

音楽ファイルのタグ フィールドを設定する汎用関数をコーディングしたいのですが、「TagLib Sharp 」ライブラリを使用しています。「 TagLib Sharp Helper Class」と名づけられるものをコーディングしようとしています。

プロシージャを呼び出すには、次のような構文を使用してフィールド「Album」を設定します。

 TagLibSharp.Set_Tag_And_Save( _
             "C:\Test.mp3", _
             Function() TagLib.File.Create("").Tag.Album, _
             "Test album name" _
 )

問題は、プロシージャ内のラムダ式をどうすればよいかわかりません...

すべてのコードは次のとおりです (問題がどこにあるかを説明するコメント行に注意してください)。

#Region " TagLib Sharp "

Public Class TagLibSharp

''' <summary>
''' Stores the Taglib object.
''' </summary>
Private Shared TagFile As TagLib.File = Nothing

''' <summary>
''' Sets a Tag field and saves the file changes.
''' </summary>
Public Shared Sub Set_Tag_And_Save(ByVal File As String, _
                                   ByVal Field As Linq.Expressions.Expression(Of Func(Of Object)), _
                                   ByVal Value As String)

    TagFile = TagLib.File.Create(File)

    Dim member As Linq.Expressions.MemberExpression = _
        If(TypeOf Field.Body Is Linq.Expressions.UnaryExpression, _
           DirectCast(DirectCast(Field.Body, Linq.Expressions.UnaryExpression).Operand, Linq.Expressions.MemberExpression), _
           DirectCast(Field.Body, Linq.Expressions.MemberExpression))

    MsgBox(member.Member.Name) ' Result: "Album"

    ' member.Member = Value ' Here is where I don't know what to do
    '
    ' This would be the ewuivalent:
    TagFile.Tag.Album = Value

    TagFile.Save()

End Sub

End Class

#End Region

アップデート

Ben Allred ソリューションの手順に従って問題を解決しようとすると、例外が発生します。

TagLibSharp.Set_Tag_And_Save("c:\1.mp3", Function() TagLib.File.Create("").Tag.Album = "Test album name")

変更されたサブ:

Public Shared Sub Set_Tag_And_Save(ByVal File As String, _
                                   ByVal FieldSetter As Action(Of TagLib.File))

    TagFile = TagLib.File.Create(File)
    FieldSetter(TagFile) ' Here throws an exception with this message: "taglib/"
    ' FieldSetter(TagLib.File.Create(File)) ' The same exception with this one.
    TagFile.Save()

End Sub

更新 2:

例外は発生しませんが、タグ フィールドが設定されていません。

TagLibSharp.Set_Tag_And_Save("c:\Test.mp3", Function(tagLibFile) tagLibFile.Tag.Title = "Test title name")

変更されたサブ:

Public Shared Sub Set_Tag_And_Save(ByVal File As String, _
                                   ByVal FieldSetter As Action(Of TagLib.File))

    TagFile = TagLib.File.Create(File)

    MsgBox(TagFile.Tag.Title) ' Result: Unbreakeable
    FieldSetter(TagFile)
    MsgBox(TagFile.Tag.Title) ' Result: Unbreakeable

    ' TagFile.Tag.Title = "Test title name"
    ' MsgBox(TagFile.Tag.Title) ' Result: "Test title name"

    TagFile.Save()

End Sub

Answer 1

私はそれを次のように呼び出すためにいくつかの変更を加えました：

TagLibSharp.Set_Tag_Fields("C:\Test.mp3", _
                           {Sub(x) x.Tag.Title = "Title Test", _
                            Sub(x) x.Tag.Performers = {"Artist Test"}, _
                            Sub(x) x.Tag.Album = "Album Test", _
                            Sub(x) x.Tag.Year = "2000"})

完全なヘルパー クラスは次のとおりです。

#Region " TagLib Sharp Helper "


' [ TagLib Sharp Helper ]
'
' // By Elektro H@cker
'
'
' Instructions:
' 1. Add a reference to "taglib-sharp.dll" into the project.
'
'
' Examples:
'
' MsgBox(TagLibSharp.FileIsCorrupt("C:\File.mp3")) ' Result: True or False
' MsgBox(TagLibSharp.FileIsWriteable("C:\File.mp3")) ' Result: True or False
' MsgBox(TagLibSharp.Get_Title("C:\File.mp3"))
' MsgBox(TagLibSharp.Get_Artist("C:\File.mp3"))
' MsgBox(TagLibSharp.Get_Album("C:\File.mp3"))
' MsgBox(TagLibSharp.Get_Genre("C:\File.mp3"))
' MsgBox(TagLibSharp.Get_Year("C:\File.mp3"))
' MsgBox(TagLibSharp.Get_Basic_TagInfo("C:\File.mp3"))
' TagLibSharp.RemoveTag("C:\File.mp3", TagLib.TagTypes.Id3v1 Or TagLib.TagTypes.Id3v2) ' Removes ID3v1 + ID3v2 Tags
' TagLibSharp.Set_Tag_Fields("C:\Test.mp3", Sub(x) x.Tag.Title = "Title Test"})
' TagLibSharp.Set_Tag_Fields("C:\Test.mp3", {Sub(x) x.Tag.Title = "Title Test", Sub(x) x.Tag.Performers = {"Artist Test"}})


Public Class TagLibSharp

''' <summary>
''' Stores the Taglib object.
''' </summary>
Private Shared TagFile As TagLib.File = Nothing

''' <summary>
''' Checks if file is possibly corrupted.
''' </summary>
Public Shared Function FileIsCorrupt(ByVal File As String) As Boolean

    Try
        Return TagLib.File.Create(File).PossiblyCorrupt

    Catch ex As Exception
        Throw New Exception(ex.Message)
        Return True

    Finally
        If TagFile IsNot Nothing Then TagFile.Dispose()

    End Try

End Function

''' <summary>
''' Checks if file can be written.
''' </summary>
Public Shared Function FileIsWriteable(ByVal File As String) As Boolean

Try
    Return TagLib.File.Create(File).Writeable

Catch ex As Exception
    Throw New Exception(ex.Message)
    Return True

Finally
    If TagFile IsNot Nothing Then TagFile.Dispose()

End Try

End Function

''' <summary>
''' Get TagTypes of file.
''' </summary>
Public Shared Function Get_Tags(ByVal File As String) As String

Try
    Return TagLib.File.Create(File).TagTypes.ToString

Catch ex As Exception
    Throw New Exception(ex.Message)
    Return String.Empty

Finally
    If TagFile IsNot Nothing Then TagFile.Dispose()

End Try

End Function

''' <summary>
''' Remove a entire Tag from file.
''' </summary>
Public Shared Sub RemoveTag(ByVal File As String, ByVal TagTypes As TagLib.TagTypes)

Try
    TagFile = TagLib.File.Create(File)
Catch ex As Exception
    Throw New Exception(ex.Message)
    Exit Sub
End Try

Try

    If Not TagFile.PossiblyCorrupt _
    AndAlso TagFile.Writeable Then

        TagFile.RemoveTags(TagTypes)
        TagFile.Save()

    End If

Catch ex As Exception
    Throw New Exception(ex.Message)

Finally
    If TagFile IsNot Nothing Then TagFile.Dispose()

End Try

End Sub

''' <summary>
''' Gets the Title tag field of file.
''' </summary>
Public Shared Function Get_Title(ByVal File As String) As String

Try
    Return TagLib.File.Create(File).Tag.Title

Catch ex As Exception
    Throw New Exception(ex.Message)
    Return String.Empty

Finally
    If TagFile IsNot Nothing Then TagFile.Dispose()

End Try

End Function

''' <summary>
''' Gets the Artist tag field of file.
''' </summary>
Public Shared Function Get_Artist(ByVal File As String) As String

Try
    Return TagLib.File.Create(File).Tag.Performers(0)

Catch ex As Exception
    Throw New Exception(ex.Message)
    Return String.Empty

Finally
    If TagFile IsNot Nothing Then TagFile.Dispose()

End Try

End Function

''' <summary>
''' Gets the Album tag field of file.
''' </summary>
Public Shared Function Get_Album(ByVal File As String) As String

Try
    Return TagLib.File.Create(File).Tag.Album

Catch ex As Exception
    Throw New Exception(ex.Message)
    Return String.Empty

Finally
    If TagFile IsNot Nothing Then TagFile.Dispose()

End Try

End Function

''' <summary>
''' Gets the Genre tag field of file.
''' </summary>
Public Shared Function Get_Genre(ByVal File As String) As String

Try
    Return TagLib.File.Create(File).Tag.Genres(0)

Catch ex As Exception
    Throw New Exception(ex.Message)
    Return String.Empty

Finally
    If TagFile IsNot Nothing Then TagFile.Dispose()

End Try

End Function

''' <summary>
''' Gets the Year tag field of file.
''' </summary>
Public Shared Function Get_Year(ByVal File As String) As String

Try
    Return TagLib.File.Create(File).Tag.Year

Catch ex As Exception
    Throw New Exception(ex.Message)
    Return String.Empty

Finally
    If TagFile IsNot Nothing Then TagFile.Dispose()

End Try

End Function

''' <summary>
''' Gets the basic tag fields of file.
''' </summary>
Public Shared Function Get_Basic_TagInfo(ByVal File As String) As String

Try
    TagFile = TagLib.File.Create(File)

    Return String.Format("Title: {1}{0}Artist: {2}{0}Album: {3}{0}Genre: {4}{0}Year: {5}", Environment.NewLine, _
                         TagFile.Tag.Title, _
                         TagFile.Tag.Performers(0), _
                         TagFile.Tag.Album, _
                         TagFile.Tag.Genres(0), _
                         TagFile.Tag.Year)

Catch ex As Exception
    Throw New Exception(ex.Message)
    Return String.Empty

Finally
    If TagFile IsNot Nothing Then TagFile.Dispose()

End Try

End Function

''' <summary>
''' Sets a Tag field.
''' </summary>
Public Shared Sub Set_Tag_Fields(ByVal File As String, _
                                   ByVal FieldSetter As Action(Of TagLib.File))

Try
    TagFile = TagLib.File.Create(File)
Catch ex As Exception
    Throw New Exception(ex.Message)
    Exit Sub
End Try

Try

    If Not TagFile.PossiblyCorrupt _
    AndAlso TagFile.Writeable Then

        FieldSetter(TagFile)
        TagFile.Save()

    End If

Catch ex As Exception
    Throw New Exception(ex.Message)

Finally
    If TagFile IsNot Nothing Then TagFile.Dispose()

End Try

End Sub

''' <summary>
''' Sets multiple Tag fields.
''' </summary>
Public Shared Sub Set_Tag_Fields(ByVal File As String, _
                                   ByVal FieldSetter() As Action(Of TagLib.File))

Try
    TagFile = TagLib.File.Create(File)
Catch ex As Exception
    Throw New Exception(ex.Message)
    Exit Sub
End Try

Try

    If Not TagFile.PossiblyCorrupt _
    AndAlso TagFile.Writeable Then

        For Each Field In FieldSetter
            Field(TagFile)
        Next

        TagFile.Save()

    End If

Catch ex As Exception
    Throw New Exception(ex.Message)

Finally
    If TagFile IsNot Nothing Then TagFile.Dispose()

End Try

End Sub

End Class

#End Region

Answer 2

(私の構文は C# です。VB の正確な構文はわかりません。)

持っているものでやりたいことを行う最も簡単な方法は、次の変更を加えることです。

1 - 型のパラメーターを 1 つ受け取るようにラムダ式を変更しますTagLib.File。

public void Set_Tag_And_Save(..., Action<TagLib.File> FieldSetter, ...)

2 - アクションを呼び出しに渡し、アクションにSet_Tag_And_Save値を設定します。

Set_Tag_And_Save("C:\Test.mp3", tagLibFile => tagLibFile.Tag.Album = "Test album name");

3 - 内でアクションを呼び出しSet_Tag_And_Saveます。

FieldSetter(TagFile);
TagFile.Save();