VB.net检查数组元素是否存在

Question

我有2个子例程调用另一个来写入日志文件。数据放在一个名为LogData（）的数组中。子例程1包含3个元素，而子例程2包含4.如果我只使用所有LogData（）元素编写日志，则在子例程1运行时会出错，因为它不包含LogData（3）中的任何元素。我如何检查LogData元素（3）是否保存一个值，如果是，将它写入日志？我试着用下面的if语句，但这样的错误：

If (Not LogData(3) Is Nothing) Then 
w.WriteLine("Address : {0}", LogData(3)) 
End If 

我也试过：

If LogData.Count > 2 Then 
If Not arrayList(yourIndex) Is Nothing Then 

如果我只是写LogData（）日志文件，我可以只使用一个循环。不过，因为我在每个元素之间添加文本，所以我无法做到这一点。

子1：

 Dim appData As String = GetFolderPath(SpecialFolder.ApplicationData) 
     Dim LogPath As String = appData & "\myApplication" 
     Dim LogData() As String = {Username, Action, Domain} 
     If (Not System.IO.Directory.Exists(LogPath)) Then 
      System.IO.Directory.CreateDirectory(LogPath) 
     End If 
     Using w As StreamWriter = File.AppendText(LogPath & "\log.txt") 
      Log(LogData, w) 
     End Using 

子2：

 Dim appData As String = GetFolderPath(SpecialFolder.ApplicationData) 
     Dim LogPath As String = appData & "\myApplication" 
     Dim LogData() As String = {Username, Action, Domain, Address} 
     If (Not System.IO.Directory.Exists(LogPath)) Then 
      System.IO.Directory.CreateDirectory(LogPath) 
     End If 
     Using w As StreamWriter = File.AppendText(LogPath & "\log.txt") 
      Log(LogData, w) 
     End Using 

日志子：阵列的

Public Shared Sub Log2(LogData As Array, w As TextWriter) 
    w.Write(vbCrLf) 
    w.WriteLine("Log Entry   : {0} - {1}", DateTime.Now.ToLongTimeString(), DateTime.Now.ToLongDateString()) 
    w.WriteLine("username : {0}", LogData(0)) 
    w.WriteLine("Action : {0}", LogData(1)) 
    w.WriteLine("Domain : {0}", LogData(2)) 
    If (Not LogData(3) Is Nothing) Then 
     w.WriteLine("Address : {0}", LogData(3)) 
    End If 
    w.WriteLine("Application version: " & Application.ProductVersion) 
    w.WriteLine("-------------------------------") 
End Sub 

Answer 1

检查长度

Public Shared Sub Log2(LogData() As String, w As IO.TextWriter) 
    w.Write(vbCrLf) 
    w.WriteLine("Log Entry   : {0} - {1}", DateTime.Now.ToLongTimeString(), DateTime.Now.ToLongDateString()) 
    w.WriteLine("username : {0}", LogData(0)) 
    w.WriteLine("Action : {0}", LogData(1)) 
    w.WriteLine("Domain : {0}", LogData(2)) 

    If LogData.Length = 4 Then'<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 
     w.WriteLine("Address : {0}", LogData(3)) 
    End If 

    w.WriteLine("Application version: " & Application.ProductVersion) 
    w.WriteLine("-------------------------------") 
End Sub