How use BackgroundWorker thread In My App

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C#

SQL

.NET

WPF

C#4.0

Hi Every Body.
I Have CircularProgressBar that is a User Control.I Create a Window with Name Of Printer And Add CircularProgressBar to it.
In my App I will When I connect to Sql And Load Data CircularProgressBar is shown And when this Loading finished it disappear.
then I use BackgroundWorker thread for this Mean.this is my code:
in public

Printer p = new Printer();
BackgroundWorker bw = new BackgroundWorker();
bw.WorkerReportsProgress = true;
bw.WorkerSupportsCancellation = true;
bw.DoWork += new DoWorkEventHandler(bw_DoWork);
bw.ProgressChanged += new ProgressChangedEventHandler(bw_ProgressChanged);
bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bw_RunWorkerCompleted);

When Button View Clicked:

private void View_Click(object sender, RoutedEventArgs e)
      {
           bw.RunWorkerAsync();

      }
  private void bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
      {
          p.Close();
      }

      private void bw_ProgressChanged(object sender, ProgressChangedEventArgs e)
      {
      }

      private void bw_DoWork(object sender, DoWorkEventArgs e)
      {
          Dispatcher.BeginInvoke(new Action(() =>
          {
              p.Show();
              ViewTabelsData();
          }));
      }

But It Do not work Correctly.

When Button View first clicked CircularProgressBar just for few seconds shown (that more less than it must shown)and then disappear.when button view for second time pressed I get this Exception: System.InvalidOperationException "Cannot set Visibility or call Show, ShowDialog, or WindowInteropHelper.EnsureHandle after a Window has closed."


Where is my Bug?What the best way I do it?