顯示從一個MySQL查詢獲得的值到一個VB.net文本框

我想顯示一個值，我obatain從一個文本框中的COUNT（*）查詢在VB.NET中，而不是顯示獲取的值，它顯示實際查詢。顯示從一個MySQL查詢獲得的值到一個VB.net文本框

這裏是我的代碼：

Imports MySql.Data.MySqlClient 
Public Class Statistics 
Dim conn As MySqlConnection 
Dim command As MySqlCommand 
Dim query As String 
Dim dadapter As New MySqlDataAdapter 

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click 
    conn = New MySqlConnection 
    conn.ConnectionString = 
     "server=localhost;userid=root;database=librarydatabase" 
    Dim reader As MySqlDataReader 


    Try 
     conn.Open() 
     query = "SELECT COUNT(*) FROM login where users='" & Username.Text & "'" 


     command = New MySqlCommand(query, conn) 
     reader = command.ExecuteReader 

     dadapter.SelectCommand = command 
     If reader.HasRows Then 
      reader.Read() 
      takenout.Text = (query) 


     End If 

     conn.Close() 
    Catch ex As MySqlException 
     MessageBox.Show(ex.Message) 
    Finally 
     conn.Dispose() 

    End Try 

End Sub

這裏是我的程序的截圖：

當試圖修復我改變它與takenout取代takenout.Text =（查詢）的代碼。文本=（reader.read（））和刪除reader.read（））的上方和dadapter.SelectCommand =命令

這裏是改變的代碼：

Imports MySql.Data.MySqlClient 

Public Class Statistics 
Dim conn As MySqlConnection 
Dim command As MySqlCommand 
Dim query As String 
Dim dadapter As New MySqlDataAdapter 

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click 
    conn = New MySqlConnection 
    conn.ConnectionString = 
     "server=localhost;userid=root;database=librarydatabase" 
    Dim reader As MySqlDataReader 

    Try 
     conn.Open() 
     query = "SELECT COUNT(*) FROM login where users='" & Username.Text & "'" 


     command = New MySqlCommand(query, conn) 
     reader = command.ExecuteReader 


     If reader.HasRows() Then 

      takenout.Text = (reader.Read()) 


     End If 

     conn.Close() 
    Catch ex As MySqlException 
     MessageBox.Show(ex.Message) 
    Finally 
     conn.Dispose() 

    End Try 

End Sub

此代碼無法解決問題，而是在按下按鈕時在文本框中顯示true，無論用戶名文本框中的內容如何。

這裏是一個圖像：

來源

2016-12-15 The Shayaan

而不是一味地試圖隨機碼，你應該花10分鐘在MSDN怎麼看[DBDataReader（https://msdn.microsoft.com/en-us/library/system.data.common。 dbdatareader（v = vs.110）.aspx）的作品。一旦你讀取（）一行，你就需要獲取數據。但對於只能返回一行的'Count（）'查詢，您不需要讀取器，'command.ExecuteScalar（）'將返回值 – Plutonix

使用command.ExecuteScalar()代替。

來源

2016-12-15 10:06:32 Dai

使用command.executescalar（）可以解決問題。

這裏是一個固定代碼的副本，如果其他人有類似的問題，並希望看到一個工作的例子。

Public Class Statistics 
Dim conn As MySqlConnection 
Dim command As MySqlCommand 
Dim query As String 
Dim dadapter As New MySqlDataAdapter 

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click 
    conn = New MySqlConnection 
    conn.ConnectionString = 
    "server=localhost;userid=root;database=librarydatabase" 
    Dim numtakenout As String 

    Try 
     conn.Open() 
     query = "SELECT COUNT(*) FROM login where users='" & Username.Text & "'" 


     command = New MySqlCommand(query, conn) 


     numtakenout = Convert.ToString(command.ExecuteScalar()) 


     takenout.Text = numtakenout 




     conn.Close() 
    Catch ex As MySqlException 
     MessageBox.Show(ex.Message) 
    Finally 
     conn.Dispose() 

    End Try 

End Sub

來源

2016-12-15 15:59:13

顯示從一個MySQL查詢獲得的值到一個VB.net文本框

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