如何显示 datagridview 看起来像是从 mysql 下载数据

Question

当数据从 mysql 加载到数据网格视图时它同时显示我想要做的是，当 datagridview 显示五行或七行时，它应该停止获取数据 4 到 5 秒，然后应该再次持续停止 5 秒就像是用于向用户显示 datagridview 从 mysql

下载数据

请有人帮助我@tim-schmelter

Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click

    MysqlConn = New MySqlConnection()

    ' Define the SQL to grab data from table.

    SQL = "SELECT * FROM dep0 "

    'Connection String

    MysqlConn.ConnectionString = "Server=sql2.freemysqlhosting.net;User Id=sql294434;Password=mI1*hrrD9*;Database=sql294434"

    ' Try, Catch, Finally

    Try

        MysqlConn.Open()
        ContactsCommand.Connection = MysqlConn
        ContactsCommand.CommandText = SQL
        ContactsAdapter.SelectCommand = ContactsCommand
        ContactsAdapter.Fill(ContactsData)
        DataGridView1.DataSource = ContactsData


    Catch myerror As MySqlException

        MessageBox.Show("Cannot connect to database: " & myerror.Message)

    Finally

        MysqlConn.Close()

        MysqlConn.Dispose()

    End Try

End Sub

Answer 1

更新了代码示例。

如果您需要以这种方式检索数据，您可以让 SQL 查询仅检索 5 到 7 行，将该数据作为数据源分配给 DataGridView，然后运行一个循环，使用 System.Threading.Thread.Sleep(5000)（告诉它等待 5 秒），每个循环让它再抓取 5 到 7 行，并且每次都将新数据源分配给 DataGridView。

或者您可以让它在计时器上检索数据。这样可以更顺利地更新表单。这是您如何操作的示例。

Private WithEvents myTimer As New Timer

Private Sub myTimer_Tick() Handles myTimer.Tick
    Try
        GetData()
    Catch ex As Exception
        'Error handeling
    End Try
End Sub

Private Sub Button3_Click(sender As System.Object, e As System.EventArgs) Handles btnGetData.Click
    Try
        myTimer.Interval = 5000
        myTimer.Start()
    Catch ex As Exception
        'Error handeling
    End Try
End Sub

Private Sub GetData()
    Dim MysqlConn As New Data.SqlClient.SqlConnection
    Dim ContactsCommand As New Data.SqlClient.SqlCommand
    Dim ContactsAdapter As New Data.SqlClient.SqlDataAdapter
    Dim ContactsData As New Data.DataTable
    'Declare Static variables so they retain their values for the next sub call.
    Static TopNumber As Integer = 5
    Static NewRowCount As Integer = 0
    Static OldRowCount As Integer = -1


    Try
        If OldRowCount < NewRowCount Then
            MysqlConn.ConnectionString = "Server=sql2.freemysqlhosting.net;User Id=sql294434;Password=mI1*hrrD9*;Database=sql294434"
            MysqlConn.Open()
            ContactsCommand.Connection = MysqlConn
            ContactsCommand.CommandText = "SELECT TOP " & TopNumber & " * FROM dep0 "
            ContactsAdapter.SelectCommand = ContactsCommand
            ContactsAdapter.Fill(ContactsData)
            DataGridView1.DataSource = ContactsData
            OldRowCount = NewRowCount
            NewRowCount = ContactsData.Rows.Count
            'Increment the variable to grab 5 more the next time.
            TopNumber += 5
        Else
            myTimer.Stop()
            MessageBox.Show("Done!")
        End If

    Catch ex As Exception
        'Error handling
    Finally
        MysqlConn.Close()
        MysqlConn.Dispose()
    End Try
End Sub

但我不建议以这种方式检索和显示数据，因为它会损害程序的性能。你所拥有的将带来更好的表现。

如何显示 datagridview 看起来像是从 mysql 下载数据

how to show datagridview look like it's downloading data from mysql

mysql

vb.net

visual-studio-2010

vb.net-2010