Trouble converting a date to a string and passing to SQL - vb.net

Question

I'm getting the following error message:
System.InvalidCastException: Conversion from string "select * from [tbl_FBNK_Limit_Hi" to type 'Integer' is not valid.
My setup is really pretty simple. Here is all the code:
Imports System.Data.OleDb
Public Class Form1
'Change Path Here:
Dim connString As String = "Provider=Microsoft.ACE.OLEDB.12.0; Data Source=path_here.accdb"
Dim MyConn As OleDbConnection
Dim da As OleDbDataAdapter
Dim ds As DataSet
Dim tables As DataTableCollection
Dim source1 As New BindingSource
Dim SqlStr As String
Dim startDate As String
Dim endDate As String
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
MyConn = New OleDbConnection
MyConn.ConnectionString = connString
ds = New DataSet
tables = ds.Tables
Dim startDate As DateTime = DateTimePicker1.Value.ToString("MM/dd/yyyy")
Dim endDate As DateTime = DateTimePicker2.Value.ToString("MM/dd/yyyy")
SqlStr = "select * from [tbl_Hist_Current] where AsOfDate >= #" & startDate & "# and AsOfDate <=#" & endDate & "#"
da = New OleDbDataAdapter(SqlStr, MyConn)
da.Fill(SqlStr, "tbl_Limit_Hist_Current")
Dim view As New DataView(tables(0))
source1.DataSource = view
DataGridView1.DataSource = view
End Sub
End Class
When I copy/paste the SqlStr into Access it works fine, so it's gotta be something with the way the dates are being handled, or not handled. Can someone here give me a nudge in the right direction?
Private Sub LoadData_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim connectionString As String = "Data Source=server_name;Initial Catalog=database_name;Integrated Security=True"
Dim SqlStr As String
Dim startDate As DateTime = DateTimePicker1.Value.ToString("MM/dd/yyyy")
Dim endDate As DateTime = DateTimePicker2.Value.ToString("MM/dd/yyyy")
SqlStr = "Select Field1, Field2, Field3, AsOfDate FROM [TBL_DATA_HIST] where AsOfDate >= '" & startDate & "' and AsOfDate <='" & endDate & "'"
Dim connection As New SqlConnection(connectionString)
Dim dataadapter As New SqlDataAdapter(SqlStr, connection)
Dim ds As New DataSet()
connection.Open()
dataadapter.Fill(ds, "TBL_DATA_HIST")
connection.Close()
DataGridView1.DataSource = ds
DataGridView1.DataMember = "TBL_DATA_HIST"
' Count rows in DG
Dim int As Integer
int = DataGridView1.Rows.Count()
TextBox1.Text = int
End Sub

Answer 1

You can use the following solution, using parameter placeholders:
'Change Path Here:
Dim connString As String = "Provider=Microsoft.ACE.OLEDB.12.0; Data Source=path_here.accdb"
Dim MyConn As OleDbConnection
Dim da As OleDbDataAdapter
Dim ds As DataSet
Dim tables As DataTableCollection
Dim source1 As New BindingSource
Dim SqlStr As String
Dim startDate As String
Dim endDate As String
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
MyConn = New OleDbConnection
MyConn.ConnectionString = connString
Dim startDate As DateTime = DateTimePicker1.Value
Dim endDate As DateTime = DateTimePicker2.Value
SqlStr = "select * from [tbl_Limit_Hist_Current] where AsOfDate >= ? and AsOfDate <= ?"
da = New OleDbDataAdapter(SqlStr, MyConn)
Dim selectCMD As New OleDbCommand(SqlStr, MyConn)
da.SelectCommand = selectCMD
selectCMD.Parameters.Add("#AsOfDate1", OleDbType.Date).Value = startDate
selectCMD.Parameters.Add("#AsOfDate2", OleDbType.Date).Value = endDate
ds = New DataSet
da.Fill(ds, "tbl_Limit_Hist_Current")
tables = ds.Tables
Dim view As New DataView(tables(0))
source1.DataSource = view
DataGridView1.DataSource = view
End Sub
You should also remove the ToString("MM/dd/yyyy") on the DateTimePicker values. On my system (german setup - dd.mm.yyyy date format by default) I got an error message like the following:
Invalid conversion of the string 11.13.2017 to type Date - translated from german
As Joel Coehoorn also mentioned in the comments, is it a performance waste and in some situations a security issue.