WPF

private void StartStopRecBtn_Click(object sender, RoutedEventArgs e)<br />
        {<br />
            if (!recordingStatus)<br />
            {<br />
                ReadOnlyCollection<AudioCaptureDevice> devices = CaptureDeviceConfiguration.GetAvailableAudioCaptureDevices();<br />
                if (devices.Count == 0)<br />
                    return;<br />
 <br />
                if (!CaptureDeviceConfiguration.AllowedDeviceAccess)<br />
                {<br />
                    CaptureDeviceConfiguration.RequestDeviceAccess();<br />
 <br />
                }<br />
                    if (CaptureDeviceConfiguration.AllowedDeviceAccess)<br />
                    {<br />
                        recImg.Source = new BitmapImage(new Uri("Images/StopRecording.jpg", UriKind.RelativeOrAbsolute));<br />
                        if (audioSink == null)<br />
                        {<br />
                            capture = new CaptureSource();<br />
                            capture.AudioCaptureDevice = CaptureDeviceConfiguration.GetDefaultAudioCaptureDevice();<br />
                            capture.VideoCaptureDevice = null;<br />
                            audioSink = new MemoryStreamAudioSink();<br />
                            audioSink.CaptureSource = capture;<br />
                        }<br />
                        else<br />
                        {<br />
 <br />
                            audioSink.CaptureSource.Stop();<br />
                            audioSink = null;<br />
                        }<br />
 <br />
                            try<br />
                            {<br />
 <br />
                                if (audioSink != null)<br />
                                    audioSink.CaptureSource.Start();<br />
                                else<br />
                                    StatusText.Text = "Not ready to Record..";<br />
                            }<br />
                            catch (InvalidOperationException ex)<br />
                            {<br />
                                MessageBox.Show("There was a problem starting the webcam " +<br />
                                                "If using a Mac, verify default device settings." +<br />
                                                "Right click app to access the Configuration settings." + ex.Message + " " + ex.InnerException);<br />
                            }<br />
 <br />
                        Thread.Sleep(TimeSpan.FromSeconds(0.5));<br />
                        recordingStatus = true;<br />
                    }<br />
                }<br />
            else<br />
            {<br />
                recordingStatus = false;<br />
                StatusText.Text = "Ready to Record..";<br />
                recImg.Source = new BitmapImage(new Uri("Images/StartRecording.jpg", UriKind.RelativeOrAbsolute));<br />
                audioSink.CaptureSource.Stop();<br />
                <br />
            }<br />
        }

private bool IsDecimal(string text)
        {
            bool blnValidDecimal = false;
            foreach (char c in text)
            {
                if (Char.IsNumber(c))
                {
                    blnValidDecimal = true;
                }
                if (char.IsDigit(c))
                {
                    blnValidDecimal = true;
                }
            }
            return blnValidDecimal;
        }

        private void txtAvgGrade_PreviewTextInput(object sender, TextCompositionEventArgs e)
        {
            e.Handled = !IsDecimal(e.Text);
        }

private static bool IsEmailAllowed(string text)
        {
            Regex regEMail = new Regex(@"^[a-zA-Z][\w\.-]{2,28}[a-zA-Z0-9]@[a-zA-Z0-9][\w\.-]*[a-zA-Z0-9]\.[a-zA-Z][a-zA-Z\.]*[a-zA-Z]$");
            return !regEMail.IsMatch(text);
        }

        private void txtEmail_PreviewTextInput(object sender, TextCompositionEventArgs e)
        {
            e.Handled = !IsEmailAllowed(e.Text);            
        } 

private void txtEmail_Validating(object sender, CancelEventArgs e)
        {
            System.Text.RegularExpressions.Regex rEMail = new System.Text.RegularExpressions.Regex(@"^[a-zA-Z][\w\.-]{2,28}[a-zA-Z0-9]@[a-zA-Z0-9][\w\.-]*[a-zA-Z0-9]\.[a-zA-Z][a-zA-Z\.]*[a-zA-Z]$");
            if (txtEmail.Text.Length > 0)
            {
                if (!rEMail.IsMatch(txtEmail.Text))
                {
                    MessageBox.Show("E-Mail expected", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
                    txtEmail.SelectAll();
                    e.Cancel = true;
                }
            }
        }