MenuStrip からの Me.Close で例外発生(.NET Framework 3.5 + VB2008)

Question

MenuStrip からの終了について質問があります。

 

以下のコードにて、MenuStripItem から Me.Close を呼び出した後に例外が発生します。

 

Code Snippet

Public Class Form1

    Friend WithEvents MenuStrip1 As System.Windows.Forms.MenuStrip
    Friend WithEvents TopMenuToolStripMenuItem As System.Windows.Forms.ToolStripMenuItem
    Friend WithEvents EndMenuToolStripMenuItem1 As System.Windows.Forms.ToolStripMenuItem
    Friend WithEvents EndMenuToolStripMenuItem2 As System.Windows.Forms.ToolStripMenuItem

    Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

        Me.MenuStrip1 = New System.Windows.Forms.MenuStrip
        Me.TopMenuToolStripMenuItem = New System.Windows.Forms.ToolStripMenuItem
        Me.EndMenuToolStripMenuItem1 = New System.Windows.Forms.ToolStripMenuItem
        Me.EndMenuToolStripMenuItem2 = New System.Windows.Forms.ToolStripMenuItem
        Me.MenuStrip1.SuspendLayout()
        Me.SuspendLayout()

        Me.MenuStrip1.Items.AddRange(New System.Windows.Forms.ToolStripItem() {Me.TopMenuToolStripMenuItem})
        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 = 0
        Me.MenuStrip1.Text = "MenuStrip1"

        Me.TopMenuToolStripMenuItem.DropDownItems.AddRange(New System.Windows.Forms.ToolStripItem() {Me.EndMenuToolStripMenuItem1, Me.EndMenuToolStripMenuItem2})
        Me.TopMenuToolStripMenuItem.Name = "TopMenuToolStripMenuItem"
        Me.TopMenuToolStripMenuItem.Size = New System.Drawing.Size(64, 20)
        Me.TopMenuToolStripMenuItem.Text = "親メニュー"

        Me.EndMenuToolStripMenuItem1.Name = "EndMenuToolStripMenuItem"
        Me.EndMenuToolStripMenuItem1.Size = New System.Drawing.Size(152, 22)
        Me.EndMenuToolStripMenuItem1.Text = "終了メニュー(例外発生)"

        Me.EndMenuToolStripMenuItem2.Name = "EndMenuToolStripMenuItem"
        Me.EndMenuToolStripMenuItem2.Size = New System.Drawing.Size(152, 22)
        Me.EndMenuToolStripMenuItem2.Text = "終了メニュー(正常終了)"

        Me.Controls.Add(Me.MenuStrip1)
        Me.MenuStrip1.ResumeLayout(False)
        Me.MenuStrip1.PerformLayout()

        AddHandler TopMenuToolStripMenuItem.DropDownItemClicked, AddressOf MenuToolStripMenuItem_DropDownItemClicked
        AddHandler EndMenuToolStripMenuItem2.Click, AddressOf EndMenuToolStripMenuItem2_Click

    End Sub

    Private Sub MenuToolStripMenuItem_DropDownItemClicked(ByVal sender As Object, ByVal e As System.Windows.Forms.ToolStripItemClickedEventArgs)
        Select Case True
            Case e.ClickedItem Is EndMenuToolStripMenuItem1
                Me.Close()      ' 例外発生
        End Select
    End Sub

    Private Sub EndMenuToolStripMenuItem2_Click(ByVal sender As Object, ByVal e As System.EventArgs)
        Me.Close()      ' 正常終了
    End Sub

End Class

 

 

このようなコードはまずいのでしょうか？

 

よろしくお願いします。

Answer 1

Me.Close()でエラーなのではなく、Me.Close()でFormのDisposeが実行されるので、このイベント呼び出し元がDisposeされたオブジェクトにアクセスしてエラーになっているのだと思われます。

 

Code Snippet

    Private Sub MenuToolStripMenuItem_DropDownItemClicked(ByVal sender As Object, ByVal e As ToolStripItemClickedEventArgs)
        Select Case True
            Case e.ClickedItem Is EndMenuToolStripMenuItem1
                CType(sender, ToolStripMenuItem).DropDown.Close()
                Me.Close()      ' 例外発生
        End Select
    End Sub

 

 

他にもComboboxのドロップダウン中に操作してエラーが発生したりするので、DropDown中に何かを削除したりするときはDropDownを閉じておくのが無難なのでしょう。

Answer 2

なるほど！非常に分かりやすい回答をありがとう御座います。

 

ComboBox でも気をつける事にします。

 

ありがとう御座いました。