主题：[求助]怎样判断一个文本是否在占用？

窗口计时器里面写了这个代码：

Dim fileName As String = "d:\data.txt"

Dim inUse As Boolean = True
Dim fs As system.io.FileStream = Nothing
Try
    fs = New system.io.FileStream(fileName, system.io.FileMode.Open, system.io.FileAccess.Read, system.io.FileShare.None)
    inUse = False
Catch ex As Exception
   
Finally
    If (fs IsNot Nothing) Then
        fs.Close()
    End If
End Try

If inUse = True Then
e.Form.Controls("Label1").text = "空闲"
Else
e.Form.Controls("Label1").text = "占用"
End If

窗口上做了个按钮，写入文本得代码：

FileSys.WriteAllText("d:\data.txt", "I Like Foxtable", True)

首次打开窗口得时候显示“空闲”，写入文本一次之后就一直是“占用”状态。怎么回事？