C# と VB.NET の質問掲示板

VisualStudio2008　FrameWork2.0 VB

MDI親フォーム（Form1)より、コンボボックスを1つ配置したMDI子フォーム（Form2)を起動し閉じるを繰り返します。

Form2のコンボボックスのDataSourceに何も設定しない場合は、
GC.GetTotalMemory(True)のメモリ使用量はある一定で止まります。

しかしコンボボックスのDataSourceにDataTableを設定すると
GC.GetTotalMemory(True)のメモリ使用量がずっと増え続けます。
System.GC.Collect()を実行しても増え続けます。

どうして増え続けるのでしょうか？
また対応策などがありましたらご教授ください。
よろしくお願いします。

◆Form1.Designer.vb◆
<Global.Microsoft.VisualBasic.CompilerServices.DesignerGenerated()> _
Partial Class Form1
    Inherits System.Windows.Forms.Form

    'フォームがコンポーネントの一覧をクリーンアップするために dispose をオーバーライドします。
    <System.Diagnostics.DebuggerNonUserCode()> _
    Protected Overrides Sub Dispose(ByVal disposing As Boolean)
        Try
            If disposing AndAlso components IsNot Nothing Then
                components.Dispose()
            End If
        Finally
            MyBase.Dispose(disposing)
        End Try
    End Sub

    'Windows フォーム デザイナで必要です。
    Private components As System.ComponentModel.IContainer

    'メモ: 以下のプロシージャは Windows フォーム デザイナで必要です。
    'Windows フォーム デザイナを使用して変更できます。  
    'コード エディタを使って変更しないでください。
    <System.Diagnostics.DebuggerStepThrough()> _
    Private Sub InitializeComponent()
        Me.MenuStrip1 = New System.Windows.Forms.MenuStrip
        Me.Form2ToolStripMenuItem = New System.Windows.Forms.ToolStripMenuItem
        Me.MenuStrip1.SuspendLayout()
        Me.SuspendLayout()
        '
        'MenuStrip1
        '
        Me.MenuStrip1.Items.AddRange(New System.Windows.Forms.ToolStripItem() {Me.Form2ToolStripMenuItem})
        Me.MenuStrip1.Location = New System.Drawing.Point(0, 0)
        Me.MenuStrip1.Name = "MenuStrip1"
        Me.MenuStrip1.Size = New System.Drawing.Size(292, 24)
        Me.MenuStrip1.TabIndex = 1
        Me.MenuStrip1.Text = "MenuStrip1"
        '
        'Form2ToolStripMenuItem
        '
        Me.Form2ToolStripMenuItem.Name = "Form2ToolStripMenuItem"
        Me.Form2ToolStripMenuItem.Size = New System.Drawing.Size(62, 20)
        Me.Form2ToolStripMenuItem.Text = "form2(&O)"
        '
        'Form1
        '
        Me.AutoScaleDimensions = New System.Drawing.SizeF(6.0!, 12.0!)
        Me.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font
        Me.ClientSize = New System.Drawing.Size(292, 273)
        Me.Controls.Add(Me.MenuStrip1)
        Me.IsMdiContainer = True
        Me.MainMenuStrip = Me.MenuStrip1
        Me.Name = "Form1"
        Me.Text = "Form1"
        Me.MenuStrip1.ResumeLayout(False)
        Me.MenuStrip1.PerformLayout()
        Me.ResumeLayout(False)
        Me.PerformLayout()

    End Sub
    Friend WithEvents MenuStrip1 As System.Windows.Forms.MenuStrip
    Friend WithEvents Form2ToolStripMenuItem As System.Windows.Forms.ToolStripMenuItem

End Class

◆Form1.vb◆
Public Class Form1

    Private Sub Form2ToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Form2ToolStripMenuItem.Click
        System.GC.Collect()
        System.GC.WaitForPendingFinalizers()
        System.GC.Collect()

        Dim openfrm As Form = New Form2

        openfrm.MdiParent = Me
        'openfrm.FormBorderStyle = Windows.Forms.FormBorderStyle.None
        'openfrm.StartPosition = FormStartPosition.Manual
        'openfrm.Location = New Point(0, 0)
        'openfrm.Dock = DockStyle.Fill
        openfrm.Show()

    End Sub
End Class

◆Form2.Designer.vb◆
<Global.Microsoft.VisualBasic.CompilerServices.DesignerGenerated()> _
Partial Class Form2
    Inherits System.Windows.Forms.Form

    'フォームがコンポーネントの一覧をクリーンアップするために dispose をオーバーライドします。
    <System.Diagnostics.DebuggerNonUserCode()> _
    Protected Overrides Sub Dispose(ByVal disposing As Boolean)
        Try
            If disposing AndAlso components IsNot Nothing Then
                components.Dispose()
            End If
        Finally
            MyBase.Dispose(disposing)
        End Try
    End Sub

    'Windows フォーム デザイナで必要です。
    Private components As System.ComponentModel.IContainer

    'メモ: 以下のプロシージャは Windows フォーム デザイナで必要です。
    'Windows フォーム デザイナを使用して変更できます。  
    'コード エディタを使って変更しないでください。
    <System.Diagnostics.DebuggerStepThrough()> _
    Private Sub InitializeComponent()
        Me.Button1 = New System.Windows.Forms.Button
        Me.ComboBox1 = New System.Windows.Forms.ComboBox
        Me.SuspendLayout()
        '
        'Button1
        '
        Me.Button1.Location = New System.Drawing.Point(41, 141)
        Me.Button1.Name = "Button1"
        Me.Button1.Size = New System.Drawing.Size(75, 23)
        Me.Button1.TabIndex = 0
        Me.Button1.Text = "Button1(&O)"
        Me.Button1.UseVisualStyleBackColor = True
        '
        'ComboBox1
        '
        Me.ComboBox1.FormattingEnabled = True
        Me.ComboBox1.Location = New System.Drawing.Point(41, 36)
        Me.ComboBox1.Name = "ComboBox1"
        Me.ComboBox1.Size = New System.Drawing.Size(121, 20)
        Me.ComboBox1.TabIndex = 1
        '
        'Form2
        '
        Me.AutoScaleDimensions = New System.Drawing.SizeF(6.0!, 12.0!)
        Me.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font
        Me.ClientSize = New System.Drawing.Size(292, 273)
        Me.Controls.Add(Me.ComboBox1)
        Me.Controls.Add(Me.Button1)
        Me.Name = "Form2"
        Me.Text = "Form2"
        Me.ResumeLayout(False)

    End Sub
    Friend WithEvents Button1 As System.Windows.Forms.Button
    Friend WithEvents ComboBox1 As System.Windows.Forms.ComboBox
End Class

◆Form2.vb◆
Public Class Form2


    Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Me.Load
        Dim tbl As New DataTable
        tbl.Columns.Add("Key", GetType(Integer))
        tbl.Columns.Add("Value", GetType(String))

        tbl.Rows.Add(New Object() {1, "one"})
        tbl.Rows.Add(New Object() {2, "two"})

        With ComboBox1
            .DropDownStyle = ComboBoxStyle.DropDownList
            .ValueMember = "Key"
            .DisplayMember = "Value"
            .DataSource = tbl   '★ここをコメントにするとメモリが増えない。
            .SelectedIndex = -1
        End With

        Console.WriteLine(Me.Name & ":" & GC.GetTotalMemory(True))

    End Sub

    Private Sub Form2_Shown(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Shown
        Me.Button1.Focus()
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Me.Close()
    End Sub


End Class

>駄目だとしたらComboBoxのDatasourceを明示的に解放するには後Nothingいれるくらいかな。


またForm2のDisposedイベントで
以下のように2通りのCombobox.DataSouceにNothingを入れて、メモリ使用量を調べてみました。
どちらも結果はメモリ使用量が増え続けます。

パターン１
Private Sub Form2_Disposed(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Disposed
    Me.ComboBox1.DataSource = Nothing
End Sub

パターン２
Private Sub Form2_Disposed(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Disposed
    DirectCast(Me.ComboBox1.DataSource, DataTable).Dispose()
    Me.ComboBox1.DataSource = Nothing
End Sub

■No56734 (pon さん) に返信

 
> ◆Form1.vb◆
> Public Class Form1
> 
>     Private Sub Form2ToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Form2ToolStripMenuItem.Click
>         System.GC.Collect()
>         System.GC.WaitForPendingFinalizers()
>         System.GC.Collect()
> 
>         Dim openfrm As Form = New Form2
> 
>         openfrm.MdiParent = Me
>         'openfrm.FormBorderStyle = Windows.Forms.FormBorderStyle.None
>         'openfrm.StartPosition = FormStartPosition.Manual
>         'openfrm.Location = New Point(0, 0)
>         'openfrm.Dock = DockStyle.Fill
>         openfrm.Show()
> 
>     End Sub
> End Class

openfrm.Show()の後に
AddHandler openfrm.FormClosed, AddressOf Form2_Closed
を追加

次を定義
Private Sub Form2_Closed(ByVal sender As Object, ByVal e As EventArgs)
    Dim fm2 = DirectCast(sender, Form)
    fm2.Dispose()
End Sub


これでForm2が閉じたときにDisposeが動きます。


GC.Collectは頻繁に動かさない方がいいです。

Shuさん

Form1のコードを記載いただいたようにしたのですが、メモリ使用量は増え続けます。

Public Class Form1

    Private Sub Form2ToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Form2ToolStripMenuItem.Click
        'System.GC.Collect()
        'System.GC.WaitForPendingFinalizers()
        'System.GC.Collect()

        Dim openfrm As Form = New Form2
        AddHandler openfrm.FormClosed, AddressOf ChildFormClosed
        openfrm.MdiParent = Me
        'openfrm.FormBorderStyle = Windows.Forms.FormBorderStyle.None
        'openfrm.StartPosition = FormStartPosition.Manual
        'openfrm.Location = New Point(0, 0)
        'openfrm.Dock = DockStyle.Fill
        openfrm.Show()      

    End Sub

    Private Sub ChildFormClosed(ByVal sender As Object, ByVal e As Windows.Forms.FormClosedEventArgs)
        DirectCast(sender, Form).Dispose()
    End Sub
End Class

またForm2についてClosedイベントでComboboxのDataSourceにNothingを入れてみても、メモリ使用量は増え続けます。
Public Class Form2

    Private Sub Form2_FormClosed(ByVal sender As Object, ByVal e As System.Windows.Forms.FormClosedEventArgs) Handles Me.FormClosed
        Me.ComboBox1.DataSource = Nothing
    End Sub
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