如何从满足条件的文本文件中返回字符串？

Question

 Public Sub openDB()
        Dim Lines As New List(Of String)

        Try
            ' Open the file using a stream reader.
            Using sr As New StreamReader("Config.txt")
                Dim line As String
                ' Read the stream to a string and write the string to the console.
                line = sr.ReadLine()
                Do Until String.IsNullOrEmpty(line)
                    Lines.Add(line)
                    line = sr.ReadLine
                Loop
            End Using
        Catch e As Exception
            Console.WriteLine("The file could not be read:")
            Console.WriteLine(e.Message)
        End Try

        Dim dbname As String = g_DatabaseName
        Dim server As String = Lines.Where(Function(str) str.Contains("server =")).ToString
        Dim user As String = ""
        Dim password As String = ""

        conn = New MySqlConnection
        conn.ConnectionString = String.Format("server={0}; user id={1}; password={2}; database={3}; pooling=false; Convert Zero Datetime=True", server, user, password, dbname)
        conn.Open()
    End Sub

我尝试从文本文件中返回一些字符串，所以我使用 StreamReader 读取文件并将它们存储到列表中。现在我尝试声明一个变量以从字符串列表中获取“localhost”，但下面的代码不适用于我。

Dim server As String = Lines.Where(Function(str) str.Contains("server =")).ToString

Answer 1

Enumerable.Where 不会返回单个字符串，而是可能返回多个字符串，使用ToString 不会为您提供第一个匹配行，而只是System.Linq.Enumerable+WhereArrayIterator1[System.String] 类型的名称。

要么将其声明为IEnumerable(Of String)，要么使用First/FirstOrDefault 来获取匹配条件的第一行：

Dim serverLine As String = Lines
    .Where(Function(str) str.Contains("server ="))
    .FirstOrDefault()

你也可以使用FirstOrDefault的重载（Nothing如果没有这样的行）：

Dim serverLine As String = Lines.FirstOrDefault(Function(str) str.Contains("server ="))

提取Localhost：

Dim server As String = serverLine.Substring(serverLine.IndexOf("server =") + "server =".Length).Trim(""""c, " "c)