Question

我刚刚开始使用Visual Basic（vb.net），并试图在TextBox中显示超过1个数据库行，到目前为止我有这个：

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

        Dim conn As MySqlConnection

        conn = New MySqlConnection
        conn.ConnectionString = connStr

        Try
            conn.Open()
        Catch myerror As MySqlException
            MsgBox("No connection")
        End Try

        Dim myAdaptor As New MySqlDataAdapter

        Dim sqlquery = "SELECT * FROM foo ORDER BY id DESC"
        Dim myCommand As New MySqlCommand()
        myCommand.Connection = conn
        myCommand.CommandText = sqlquery

        myAdaptor.SelectCommand = myCommand
        Dim myData As MySqlDataReader
        myData = myCommand.ExecuteReader()

        If myData.HasRows Then
            myData.Read()
            Viewer.Text = myData("foo1") & myData("foo2")

        End If

        myData.Close()
        conn.Close()

    End Sub

成功连接到数据库，但它只输出1行，如何才能输出更多？

Answer 1

您需要循环读取数据并在StringBuilder中逐行存储然后，当从读取循环退出时，设置文本框的Text属性

    Dim sb as StringBuilder = new StringBuilder()
    While myData.Read()
        sb.AppendLine(myData("foo1") & myData("foo2"))
    End While
    Viewer.Text = sb.ToString

当然，您的文本框应将MultiLine属性设置为True

除了直接回答您的问题之外，您的代码应该更改为在使用后处理连接和datareader，我也删除了DataAdapter，因为这里不需要

    Using conn = New MySqlConnection(connStr)
        Try
            conn.Open()
        Catch myerror As MySqlException
            MsgBox("No connection")
        End Try

        Dim sqlquery = "SELECT * FROM foo ORDER BY id DESC"
        Dim myCommand As New SqlCommand(sqlquery, conn)
        Using myData = myCommand.ExecuteReader()
            Dim sb as StringBuilder = new StringBuilder()
            While myData.Read()
                sb.AppendLine(myData("foo1") & myData("foo2"))
            End While
            Viewer.Text = sb.ToString        
        End Using
    End Using

Answer 2

你需要某种循环。我还会使用Using语句来确保即使在异常的情况下也会处理所有非托管资源（它也会关闭连接）：

Using conn As New MySqlConnection(connStr)
    Using myCommand As New MySqlCommand("SELECT * FROM foo ORDER BY id DESC", conn)
        Try
            conn.Open()
            Using myData = myCommand.ExecuteReader()
                If myData.HasRows Then
                    While myData.Read()
                        Dim line = String.Format("{0}{1}{2}",
                                                 myData.GetString(myData.GetOrdinal("foo1")),
                                                 myData.GetString(myData.GetOrdinal("foo1")),
                                                 Environment.NewLine)
                        viewer.Text &= line
                    End While
                End If
            End Using
        Catch ex As Exception
            MessageBox.Show(ex.ToString())
        End Try
    End Using
End Using

但是，如果您想要显示多条记录，我建议使用ListBox。它对许多项目更有效，并且它们也将它们彼此逻辑分开。

（只需将viewer.Text &= line替换为ListBox1.Items.Add(line)）

vb.net/mysql在TextBox中显示超过1行

2 个答案: