Private Sub TextBox1_Validating(ByVal sender As Object, _
ByVal e As System.ComponentModel.CancelEventArgs) _
Handles TextBox1.Validating

    ' If nothing is entered,
    ' an ArgumentException is caught; if an invalid directory is entered, 
    ' a DirectoryNotFoundException is caught. An appropriate error message 
    ' is displayed in either case.
    Try
        Dim directory As New System.IO.DirectoryInfo(TextBox1.Text)
        directory.GetFiles()
        ErrorProvider1.SetError(TextBox1, "")

    Catch ex1 As System.ArgumentException
        ErrorProvider1.SetError(TextBox1, "Please enter a directory")

    Catch ex2 As System.IO.DirectoryNotFoundException
        ErrorProvider1.SetError(TextBox1, _
        "The directory does not exist." & _
        "Try again with a different directory.")
    End Try

End Sub

' This method handles the LostFocus event for TextBox1 by setting the 
' dialog's InitialDirectory property to the text in TextBox1.
Private Sub TextBox1_LostFocus(ByVal sender As Object, _
    ByVal e As System.EventArgs) Handles TextBox1.LostFocus
    OpenFileDialog1.InitialDirectory = TextBox1.Text
End Sub


' This method demonstrates using the ErrorProvider.GetError method 
' to check for an error before opening the dialog box.
Private Sub Button1_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles Button1.Click

    'If there is no error, then open the dialog box.
    If ErrorProvider1.GetError(TextBox1) = "" Then
        Dim dialogResult As DialogResult = OpenFileDialog1.ShowDialog()
    End If

End Sub

    private void textBox1_Validating(object sender, 
        System.ComponentModel.CancelEventArgs e)
    {
        // If nothing is entered,
        // an ArgumentException is caught; if an invalid directory is entered, 
        // a DirectoryNotFoundException is caught. An appropriate error message 
        // is displayed in either case.
        try
        {
            System.IO.DirectoryInfo directory = 
                new System.IO.DirectoryInfo(textBox1.Text);
            directory.GetFiles();
            errorProvider1.SetError(textBox1, "");

        }
        catch(System.ArgumentException ex1)
        {
            errorProvider1.SetError(textBox1, "Please enter a directory");

        }
        catch(System.IO.DirectoryNotFoundException ex2)
        {
            errorProvider1.SetError(textBox1, "The directory does not exist." +
                "Try again with a different directory.");
        }

    }

    // This method handles the LostFocus event for textBox1 by setting the 
    // dialog's InitialDirectory property to the text in textBox1.
    private void textBox1_LostFocus(object sender, System.EventArgs e)
    {
        openFileDialog1.InitialDirectory = textBox1.Text;
    }

    // This method demonstrates using the ErrorProvider.GetError method 
    // to check for an error before opening the dialog box.
    private void button1_Click(System.Object sender, System.EventArgs e)
    {
        //If there is no error, then open the dialog box.
        if (errorProvider1.GetError(textBox1)=="")
        {
            DialogResult dialogResult = openFileDialog1.ShowDialog();
        }
    }

private:
   void TextBox1_Validating( Object^ sender,
      System::ComponentModel::CancelEventArgs^ e )
   {
      // If nothing is entered,
      // an ArgumentException is caught; if an invalid directory is entered, 
      // a DirectoryNotFoundException is caught. An appropriate error message 
      // is displayed in either case.
      try
      {
         System::IO::DirectoryInfo^ directory = gcnew System::IO::DirectoryInfo( TextBox1->Text );
         directory->GetFiles();
         ErrorProvider1->SetError( TextBox1, "" );
      }
      catch ( System::ArgumentException^ ) 
      {
         ErrorProvider1->SetError( TextBox1, "Please enter a directory" );
      }
      catch ( System::IO::DirectoryNotFoundException^ ) 
      {
         ErrorProvider1->SetError( TextBox1, "The directory does not exist."
         "Try again with a different directory." );
      }
   }

   // This method handles the LostFocus event for TextBox1 by setting the 
   // dialog's InitialDirectory property to the text in TextBox1.
   void TextBox1_LostFocus( Object^ sender, System::EventArgs^ e )
   {
      OpenFileDialog1->InitialDirectory = TextBox1->Text;
   }

   // This method demonstrates using the ErrorProvider.GetError method 
   // to check for an error before opening the dialog box.
   void Button1_Click( System::Object^ sender, System::EventArgs^ e )
   {
      //If there is no error, then open the dialog box.
      if ( ErrorProvider1->GetError( TextBox1 )->Equals( "" ) )
      {
         ::DialogResult dialogResult = OpenFileDialog1->ShowDialog();
      }
   }

The following code example demonstrates validating the TextBox1 object's text. 
It also demonstrates handling the text box’s LostFocus event by setting the file dialog's InitialDirectory
property to the text in TextBox1. The code example used the ErrorProvider.GetError method to check for an error before opening the file dialog.

To run this example paste the following code into a form containing a TextBox named TextBox1, an OpenFileDialog named OpenFileDialog1, a button named Button1, and an ErrorProvider named ErrorProvider1.