VB.NET Backgroundworker only show loading form once? - vb.net

Question

I have a button on a form which basically get data from my database as below.
Private Sub ToolStripButton1_Click(sender As Object, e As EventArgs)
Handles ToolStripButton1.Click
BackgroundWorker1.RunWorkerAsync()
Loading_Screen.ShowDialog()
End Sub
The loading screen is called after my code (obtain data from database) is run in backgroundworker.
When backgroundworker is done, I close the loading form as below
Private Sub BackgroundWorker1_RunWorkerCompleted(sender As Object, e As RunWorkerCompletedEventArgs)
Handles BackgroundWorker1.RunWorkerCompleted
DataGridView1.DataSource = bSource
SDA.Update(dataTable)
ToolStripLabel1.Text = "RESULT : " + DataGridView1.RowCount.ToString
Loading_Screen.Close()
End Sub
This only works when I started the application for the first time. Whenever I click the button again, the loading form will not show anymore but the code still runs fine. Any idea?
The loading form has no code at all, just a running progress bar every time it is loaded.
What I have done but no luck :
Me.Refresh() the main form after calling loading form.
Me.Refresh() the loading form when on load function.
Tried loadingform.hide() instead of show()
Tried both show() and showdialog()
Tried creating new instance of the loading form.
Me.dispose() loading form on closing function
Me.dispose() main form on closing function
Setting loading form as top most.
UPDATE (I will keep updating my progress here)
As many of you asked to create a new instance, here is what I already did
Private Sub ToolStripButton1_Click(sender As Object, e As EventArgs) Handles ToolStripButton1.Click
BackgroundWorker1.RunWorkerAsync()
ldScreen = New Loading_Screen()
ldScreen.ShowDialog()
Me.Refresh()
End Sub
Then, in run completed,
Private Sub BackgroundWorker1_RunWorkerCompleted(sender As Object, e As RunWorkerCompletedEventArgs) Handles BackgroundWorker1.RunWorkerCompleted
DataGridView1.DataSource = bSource
SDA.Update(dataTable)
ToolStripLabel1.Text = "RESULT : " + DataGridView1.RowCount.ToString
ldScreen.Close()
BackgroundWorker1.Dispose()
End Sub
In my loading form, the code is only this
Private Sub Loading_Screen_FormClosing(sender As Object, e As FormClosingEventArgs) Handles Me.FormClosing
Me.Dispose()
End Sub
Private Sub Loading_Screen_Load(sender As Object, e As EventArgs) Handles Me.Load
Me.Refresh()
End Sub
UPDATE 2
By stripping out most of my code and putting system thread sleep in backgroundworker do work, the loading form shows up properly. So here is my code in backgroundworkerdowork on what is actually happening.
Private Sub BackgroundWorker1_DoWork(sender As Object, e As DoWorkEventArgs) Handles BackgroundWorker1.DoWork
Connect2Database()
Try
sqlCommand.CommandText = "Select * from kup_table" 'Load full database into gridview
SDA.SelectCommand = sqlCommand
SDA.Fill(dataTable)
bSource.DataSource = dataTable
mySqlConn.Close()
Catch ex As MySqlException
MsgBox(ex.ToString)
If mySqlConn.State = ConnectionState.Open Then
mySqlConn.Close()
End If
Finally
mySqlConn.Dispose()
End Try
'System.Threading.Thread.Sleep(2000)
End Sub
And here is the Connect2Database function codes
Private Sub Connect2Database()
sqlCommand = New MySqlCommand
dataTable = New DataTable
SDA = New MySqlDataAdapter
bSource = New BindingSource
Try
dataTable.Clear()
mySqlConn.ConnectionString = connString
sqlCommand.Connection = mySqlConn
mySqlConn.Open()
Catch ex As MySqlException
MsgBox(ex.ToString)
If mySqlConn.State = ConnectionState.Open Then
mySqlConn.Close()
End If
End Try
End Sub
UPDATE 3
What I have noticed is that when my System.Threading.Thread.Sleep(2000) is not commented, the loading screen will show up normally. But if I changed it to System.Threading.Thread.Sleep(1), loading screen does not shows up. Why is this happening? Code runs super fast after the first time?

Answer 1

This is because calling Close() disposes the Form. So either you have to create a new instance of the form every time, or you need to use Hide(). Judging by your question, I think you want the former.

Answer 2

have you tried to create a new instance of the form?
Private Sub ToolStripButton1_Click(sender As Object, e As EventArgs)
Handles ToolStripButton1.Click
Dim frm As New Loading_Screen
BackgroundWorker1.RunWorkerAsync()
frm.ShowDialog()
End Sub