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   源码介绍

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Imports System.IO
Imports System.Collections



Public Class ImageViewer

    ' private member variables
    Private mFolder As String
    Private mImageList As ArrayList
    Private mImagePosition As Integer
    Private mPreviousImage As Image
    Private mCurrentImage As Image
    Private mNextImage As Image


    ''' <summary>
    ''' Default Constructor
    ''' </summary>
    ''' <remarks></remarks>
    Public Sub New()

        ' This call is required by the Windows Form Designer.
        InitializeComponent()

        ' Add any initialization after the InitializeComponent() call.

    End Sub



    ''' <summary>
    ''' Default load event handler
    ''' </summary>
    ''' <param name="sender"></param>
    ''' <param name="e"></param>
    ''' <remarks></remarks>
    Private Sub ImageViewer_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        ' do nothing

    End Sub


    ''' <summary>
    ''' Open the folder browse dialog and load 
    ''' the initial images
    ''' </summary>
    ''' <param name="sender"></param>
    ''' <param name="e"></param>
    ''' <remarks></remarks>
    Private Sub btnBrowse_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnBrowse.Click

        ' Label the folder browser dialog
        Me.folderBrowserDialog1.Description = "Select the image directory."

        ' disable create folder feature of folder browser
        Me.folderBrowserDialog1.ShowNewFolderButton = False

        ' display the folder browser
        Dim result As DialogResult = folderBrowserDialog1.ShowDialog()

        If result = DialogResult.OK Then

            ' on okay, set the image folder to the
            ' folder browser's selected path
            mFolder = folderBrowserDialog1.SelectedPath
            If (Not String.IsNullOrEmpty(mFolder)) Then
                txtImageDirectory.Text = mFolder
            Else
                ' exit if the user cancels
                Return
            End If

            ' initialize the image arraylist
            mImageList = New ArrayList()

            ' loop through the image directory
            ' and find all of the image files
            ' add the found files to the image
            ' list - add other image types if
            ' necessary
            Dim Dir As New DirectoryInfo(mFolder)
            Dim f As FileInfo
            For Each f In Dir.GetFiles("*.*")
                Select Case (f.Extension.ToUpper())
                    Case ".JPG"
                        mImageList.Add(f.FullName)
                    Case ".BMP"
                        mImageList.Add(f.FullName)
                    Case ".GIF"
                        mImageList.Add(f.FullName)
                    Case Else
                        ' skip file
                End Select
            Next

            ' set the starting position to 0
            ' and call the set images method
            ' to load the pictures
            mImagePosition = 0
            SetImages()

        End If

    End Sub



    ''' <summary>
    ''' This function is used to set the previous,
    ''' current, and next images into the 
    ''' correct picture boxes
    ''' </summary>
    ''' <remarks></remarks>
    Private Sub SetImages()

        ' clear any existing images
        ' memory will be an issue if
        ' cycling through a large
        ' number of images
        mPreviousImage = Nothing
        mNextImage = Nothing
        mCurrentImage = Nothing

        ' set the previous image
        If mImagePosition > 0 Then

            Try

                ' set delegate
                Dim prevCallback As Image.GetThumbnailImageAbort = _
                        New Image.GetThumbnailImageAbort(AddressOf ThumbnailCallback)

                ' get the previous image
                Dim prevBmp As _
                    New Bitmap(mImageList(mImagePosition - 1).ToString())

                ' thumbnail the image to the size
                ' of the picture box
                mPreviousImage = _
                prevBmp.GetThumbnailImage(160, 100, _
                        prevCallback, IntPtr.Zero)

                ' set the picture box image
                picPreviousImage.Image = mPreviousImage

                ' clear everything out
                prevBmp = Nothing
                prevCallback = Nothing
                mPreviousImage = Nothing

            Catch

                'stall if it hangs, the user can retry

            End Try

        Else

            ' at the limit clear the
            ' image
            picPreviousImage.Image = Nothing

        End If

        ' set current image
        If mImagePosition < mImageList.Count Then

            Try

                ' set delegate
                Dim currentCallback = _
                        New Image.GetThumbnailImageAbort(AddressOf ThumbnailCallback)

                ' get the current image
                Dim currentBmp As _
                        New Bitmap(mImageList(mImagePosition).ToString())

                ' thumbnail the image to the size
                ' of the picture box
                mCurrentImage = _
                currentBmp.GetThumbnailImage(320, 200, currentCallback, IntPtr.Zero)

                ' set the picture box image
                picCurrentImage.Image = mCurrentImage

                ' clear everything out
                currentBmp = Nothing
                mCurrentImage = Nothing
                currentCallback = Nothing

            Catch

                'stall if it hangs, the user can retry

            End Try

        End If


        ' set next image
        If mImagePosition < mImageList.Count - 1 Then

            Try

                ' set delegate
                Dim nextCallback As _
                    New Image.GetThumbnailImageAbort(AddressOf ThumbnailCallback)

                ' get the next image
                Dim nextBmp As _
                    New Bitmap(mImageList(mImagePosition   1).ToString())

                ' thumbnail the image to the size
                ' of the picture box
                mNextImage = _
                nextBmp.GetThumbnailImage(160, 100, nextCallback, IntPtr.Zero)

                ' set the picture box image
                picNextImage.Image = mNextImage

                ' clear everything out
                nextBmp = Nothing
                nextCallback = Nothing
                mNextImage = Nothing

            Catch

                'stall if it hangs, the user can retry

            End Try

        Else

            ' at the limit clear the
            ' image
            picNextImage.Image = Nothing

        End If

        ' call for garbage collection
        GC.Collect()

    End Sub



    ''' <summary>
    ''' Thumbnail image abort target
    ''' </summary>
    ''' <returns></returns>
    ''' <remarks></remarks>
    Public Function ThumbnailCallback() As Boolean

        Return False

    End Function




    ''' <summary>
    ''' Set the image position and reset all
    ''' of the images when the previous image
    ''' button is clicked
    ''' </summary>
    ''' <param name="sender"></param>
    ''' <param name="e"></param>
    ''' <remarks></remarks>
    Private Sub btnPreviousImage_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnPreviousImage.Click

        If (mImagePosition >= 0 And Not picPreviousImage.Image Is Nothing) Then
            mImagePosition -= 1
            SetImages()
        End If

    End Sub



    ''' <summary>
    ''' Set the image position and reset all
    ''' of the images when the next image
    ''' button is clicked
    ''' </summary>
    ''' <param name="sender"></param>
    ''' <param name="e"></param>
    ''' <remarks></remarks>
    Private Sub btnNextImage_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnNextImage.Click

        If (mImagePosition <= (mImageList.Count - 2)) Then
            mImagePosition  = 1
            SetImages()
        End If

    End Sub



    ''' <summary>
    ''' Open the current image using the default
    ''' program per the user's file associations
    ''' </summary>
    ''' <param name="sender"></param>
    ''' <param name="e"></param>
    ''' <remarks></remarks>
    Private Sub btnOpenImage_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnOpenImage.Click
        System.Diagnostics.Process.Start(mImageList(mImagePosition).ToString())
    End Sub


End Class