[VB.NET]MDI Thumbnail Preview

最近試著把MDI視窗加上Thumbnail Preview功能，找來找去找不到相關的技術文件，只好硬幹處理，這邊簡單記錄一下簡陋的作法。

要為MDI視窗加上Thumbnail Preview功能，必須知道如何透過複寫ProcessCmdKey把Ctrl+Tab切換MDI子視窗的動作給過濾掉，就像下面這樣： Protected Overrides Function ProcessCmdKey(ByRef msg As System.Windows.Forms.Message, ByVal keyData As System.Windows.Forms.Keys) As Boolean If keyData = (Keys.Control Or Keys.Tab) Then Return True End If Return MyBase.ProcessCmdKey(msg, keyData) End Function

了解如何過濾掉預設的切換動作後，我們必須改寫讓系統先彈出Thumbnail Preview對話盒，把對話盒放至中間，在Thumbnail Preview對話盒關閉時，把子視窗切至Thumbnail Preview對話盒最後選取的子視窗，像是下面這樣：

Protected Overrides Function ProcessCmdKey(ByRef msg As System.Windows.Forms.Message, ByVal keyData As System.Windows.Forms.Keys) As Boolean
    If keyData = (Keys.Control Or Keys.Tab) Then
        Dim thumbnailDlg As New ThumbnailDialog(Me)
        thumbnailDlg.ShowInTaskbar = False
        thumbnailDlg.Location = New Point(Me.Width / 2 - thumbnailDlg.Width / 2, Me.Height / 2 - thumbnailDlg.Height / 2)
        If thumbnailDlg.ShowDialog() = DialogResult.Cancel Then
            Return MyBase.ProcessCmdKey(msg, keyData)
        End If
        thumbnailDlg.SelectedChildForm.Activate()
        Return True
    End If
    Return MyBase.ProcessCmdKey(msg, keyData)
End Function

至於Thumbnail Preview對話盒則必須要做到放開Ctrl就關閉，與按下Ctrl + Tab切換子視窗選項的功能，簡單的範例如下：

Imports System.Windows.Forms

Public Class ThumbnailDialog

Private _mdiParent As Form
Private _thumbnailPool As Dictionary(Of Form, Image)

Private Property m_MDIParent As Form
    Get
        Return _mdiParent
    End Get
    Set(ByVal value As Form)
        _mdiParent = value
    End Set
End Property

Private ReadOnly Property m_ThumbnailPool As Dictionary(Of Form, Image)
    Get
        If _thumbnailPool Is Nothing Then
            _thumbnailPool = New Dictionary(Of Form, Image)
        End If
        Return _thumbnailPool
    End Get
End Property

Public ReadOnly Property SelectedChildForm As Form
    Get
        Return If(ListBox1.SelectedIndex = -1, Nothing, m_MDIParent.MdiChildren(ListBox1.SelectedIndex))
    End Get
End Property

Private Sub ThumbnailDialog_KeyUp(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles Me.KeyUp
    If Not e.Control Then
        DialogResult = If(ListBox1.SelectedIndex = -1, DialogResult.Cancel, DialogResult.OK)
        Me.Close()
    End If
End Sub

Protected Overrides Function ProcessCmdKey(ByRef msg As System.Windows.Forms.Message, ByVal keyData As System.Windows.Forms.Keys) As Boolean
    If keyData = (Keys.Control Or Keys.Tab) Then
        If ListBox1.Items.Count > 1 Then
            ListBox1.SelectedIndex = (ListBox1.SelectedIndex + 1) Mod ListBox1.Items.Count
        End If
        Return True
    End If
    Return MyBase.ProcessCmdKey(msg, keyData)
End Function

Private Sub ThumbnailDialog_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    Me.KeyPreview = True
    ListBox1.DisplayMember = "Text"
    ListBox1.DataSource = m_MDIParent.MdiChildren
    Dim childForm As Form = m_MDIParent.ActiveMdiChild
    If childForm Is Nothing Then
        Return
    End If
    ListBox1.SelectedItem = childForm
End Sub

Public Sub New(ByVal mdiParent As Form)

    ' This call is required by the designer.
    InitializeComponent()

    ' Add any initialization after the InitializeComponent() call.
    m_MDIParent = mdiParent
    PictureBox1.SizeMode = PictureBoxSizeMode.Zoom
End Sub

Private Sub ListBox1_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles ListBox1.SelectedIndexChanged
    Dim childForm As Form = m_MDIParent.MdiChildren(ListBox1.SelectedIndex)
    Dim thumbnailImage As Image = If(m_ThumbnailPool.ContainsKey(childForm), m_ThumbnailPool(childForm), Nothing)
    If thumbnailImage Is Nothing Then
        thumbnailImage = New Bitmap(childForm.Width, childForm.Height)
        m_ThumbnailPool.Add(childForm, thumbnailImage)
        childForm.DrawToBitmap(thumbnailImage, New Rectangle(0, 0, thumbnailImage.Width, thumbnailImage.Height))
    End If
    PictureBox1.Image = thumbnailImage
End Sub

End Class

下面是醜醜的執行範例圖(美工部分請自行補強)：

Download

MDIThumbnailPreview.zip

Download#

Download