診間報到系統-3(FileSystemWatcher)

由於診間報到系統，護士瑞及電視牆兩隻程式需要交換資料去觸發畫面更新事件。過去，常用timer設定long loop的方式來取得特定目錄的檔案更新，現在則打算用FileSystemWatcher的事件觸發來執行。一方面提昇反應時間，另一方面也是自我提昇。

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
 ' 1.引用類別
 Dim watcher As New FileSystemWatcher()
 ' 2.設定監聽路徑
 watcher.Path = "C:\Temp"
 ' 3.過濾監聽條件
 watcher.Filter = "*.txt"
 ' 4.設定監看類型
 watcher.NotifyFilter = NotifyFilters.FileName
 ' 5.設定監聽項目
 AddHandler watcher.Created, AddressOf watcher_Created
 ' 6.開啟監聽事件
 watcher.EnableRaisingEvents = True
End Sub

Private Shared locker As Object = New [Object]()
Private Sub watcher_Created(ByVal sender As Object, ByVal e As FileSystemEventArgs)
 SyncLock locker
  Dim file As New FileInfo(e.FullPath)
            Dim intCounter As Integer = 0
            Do While file.IsLocked()
                System.Threading.Thread.Sleep(100)
                intCounter += 1
                If intCounter >= 100 Then Exit Sub
            Loop
   
   string readText = file.ReadAllText();
 End SyncLock
End Sub

Module clsExtension

    <Extension()> _
    Public Function IsLocked(ByVal file As FileInfo) As Boolean
        Dim stream As FileStream = Nothing

        Try
            stream = file.Open(FileMode.Open, FileAccess.ReadWrite, FileShare.None)
        Catch ex_IsLocked As IOException
            'the file is unavailable because it is:
            'still being written to
            'or being processed by another thread
            'or does not exist (has already been processed)
            Return True
        Finally
            If stream IsNot Nothing Then
                stream.Close()
            End If
        End Try

        'file is not locked
        Return False
    End Function

    <Extension()> _
    Public Function ReadAllText(ByVal file As FileInfo) As String
        Try
            Using reader As StreamReader = file.OpenText()
                Return reader.ReadToEnd()
            End Using
        Catch ex_ReadAllText As Exception
            Return Nothing
        End Try
    End Function

End Module

參考資料
[1] [VB.NET][C#.NET] 使用 FileSystemWatcher 監看資料夾 是否被變更
[2] Wait Until File Is Completely Written