Imports System.Runtime.InteropServices

Public Class Form1

    Inherits System.Windows.Forms.Form

    Implements IMessageFilter

‘ API申明

    Const WM_DROPFILES = &H233  ‘拖放文件消息

    <DllImport("shell32.dll")> Public Shared Sub DragFinish(ByVal hDrop As Integer)

    End Sub

    <DllImport("shell32.dll")> Public Shared Sub DragAcceptFiles(ByVal hwnd As Integer, ByVal fAccept As Boolean)

    End Sub

    <DllImport("shell32.dll")> Public Shared Function DragQueryFile(ByVal HDROP As Integer, ByVal UINT As Integer, ByVal lpStr As System.Text.StringBuilder, ByVal ch As Integer) As Integer

    End Function

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

        Application.AddMessageFilter(Me)

        DragAcceptFiles(TextBox1.Handle.ToInt32, True)

End Sub

Function PreFilterMessage(ByRef m As Message) As Boolean Implements IMessageFilter.PreFilterMessage

        If m.Msg = WM_DROPFILES Then

            '设置拖放的动作

            Dim nfiles As Int16

            nfiles = DragQueryFile(m.WParam.ToInt32, -1, Nothing, 0)

            Dim i As Int16

            Dim sb As New System.Text.StringBuilder(256)

            Dim sFirstFileName As String '记录第一个文件名

            TextBox1.Clear()

            For i = 0 To nfiles - 1

                DragQueryFile(m.WParam.ToInt32, i, sb, 256)

                If i = 0 Then sFirstFileName = sb.ToString

                TextBox1.AppendText(ControlChars.CrLf & sb.ToString)

            Next

            DragFinish(m.WParam.ToInt32) '拖放完成

            '显示文件内容

            Dim fs As New System.IO.FileStream(sFirstFileName, IO.FileMode.Open)

            Dim sr As New System.IO.StreamReader(fs, System.Text.Encoding.GetEncoding("gb2312"))

            TextBox1.AppendText(ControlChars.CrLf & sr.ReadToEnd().ToString)

            fs.Close()

            sr.Close()

        End If

        Return False

End Function

Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)

        If disposing Then

            If Not (components Is Nothing) Then

                components.Dispose()

            End If

        End If

        Application.RemoveMessageFilter(Me)

        DragAcceptFiles(TextBox1.Handle.ToInt32, False)

        MyBase.Dispose(disposing)

   End Sub