Data updation and deletion error - vb.net

Question

I have a DataGrid and many text fields to add data into the database. When i add a new data, it gets updated in the database and in the data grid.But when i delete the data, it gets deleted only from the database. It doesn't get updated in the data grid.
When i try to update the data, it updates only one record at a time.when i try for another record it gives me a error "The variable name '#date' has already been declared. Variable names must be unique within a query batch or stored procedure." I have to close and reopen the form to update a new record.
Imports System.Data.SqlClient
Public Class Form
Dim con As New SqlClient.SqlConnection("Server = DEL-PC; Database=Shj; Trusted_Connection=yes;")
Dim cmd As New SqlCommand
Dim dr As SqlDataReader
Dim ds As DataSet
Dim da As SqlDataAdapter
Private Sub Form_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
SqlDataAdapter1.Fill(DataSet11)
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles newbtn.Click
If RegNoTextBox.Text <> "" Then
cmd.Connection = con
con.Open()
cmd.CommandText = "insert into WaterProofing(Date,RegNo) values ('" & DateDateTimePicker.Value & "','" & RegNoTextBox.Text & "')"
cmd.ExecuteNonQuery()
Call showdata()
con.Close()
Else
MessageBox.Show("Please enter registration number")
End If
End Sub
//updation
Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles editbtn.Click
cmd.Parameters.AddWithValue("#date", DateDateTimePicker.Value)
cmd.Parameters.AddWithValue("#regno", RegNoTextBox.Text)
cmd.Connection = con
con.Open()
cmd.CommandText = "update WaterProofing set RegNo= #regno where date=#date"
cmd.ExecuteNonQuery()
Call showdata()
con.Close()
MessageBox.Show("Details Updated!")
End Sub
Private Sub Button4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles deletebtn.Click
cmd.Connection = con
con.Open()
cmd.CommandText = "delete from WaterProofing where date='" & DateDateTimePicker.Value & "'"
cmd.ExecuteNonQuery()
Call showdata()
con.Close()
MessageBox.Show("Details Deleted!")
End Sub
Sub showdata()
SqlDataAdapter1.Fill(DataSet11, "WaterProofing")
With DataGridView
.Update()
End With
End Sub
End Class
Please help me in deletion and updating.

Answer 1

You're adding parameters before declaring CommandText at Button2_Click
Try it in this way:
Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles editbtn.Click
Try
Dim command As New SqlCommand
con.Open()
command.Connection = con
command.CommandText = "update WaterProofing set RegNo= #regno where date=#date"
command.Parameters.AddWithValue("#date", DateDateTimePicker.Value)
command.Parameters.AddWithValue("#regno", RegNoTextBox.Text)
command.ExecuteNonQuery()
con.Close()
Call showdata()
MessageBox.Show("Details Updated!")
Catch ex as Exception
MessageBox.Show(ex.Message)
End try
End Sub
UPDATE
Basically you have to do the same thing when you load the DataGridView for the first time in order to refresh the DataGridView with the current data from database after deleting or updating records, so your ShowData Sub might look something like this
Private Sub ShowData()
Dim Connection As SqlConnection
Connection = New SqlConnection("YourConnectionString")
Try
Connection.Open()
Dim SQL As String = "SELECT Field1, Field2, Field3 FROM Table"
Dim DS As New DataSet
Dim Adapter As New SqlDataAdapter(SQL, Connection)
Adapter.Fill(DS)
DataGridView.DataSource = DS.Tables(0)
DataGridView.Refresh()
Catch ex As Exception
MessageBox(ex.Message)
Finally
Connection.Close()
End Try
End Sub

Answer 2

Private Sub Button4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles deletebtn.Click
Try
Dim command As New SqlCommand
con.Open()
command.Connection = con
command.CommandText = "delete from WaterProofing where date='" & DateDateTimePicker.Value & "'"
command.ExecuteNonQuery()
con.Close()
Call ShowData_Delete()
MessageBox.Show("Details Deleted!")
Catch ex As Exception
MessageBox.Show(ex.Message)
Finally
End Try
End Sub
Private Sub ShowData_Delete()
Dim Connection As SqlConnection
Try
Connection = New SqlConnection("Server = DEL-PC; Database=Shj; Trusted_Connection=yes;")
Connection.Open()
Dim SQL As String = "SELECT * from WaterProofing"
Dim DS As New DataSet
Dim Adapter As New SqlDataAdapter(SQL, Connection)
Adapter.Fill(DS)
DataGridView1.DataSource = DS.Tables(0)
DataGridView1.Refresh()
Catch ex As Exception
MessageBox.Show(ex.Message)
Finally
Connection.Close()
End Try
End Sub