C#, threading and GUI help needed

g'day guys,
just have a problem here that i have no idea how to fix. I am doing a small project which involves a GUI and serial data. The GUI is being run by the main thread and since the data variables that hold my incoming serial data need to be updated continuously, these are being updated in a second thread. The problem is when i need to update some textboxes on the GUI, these need to be updated with data from the secondary thread and that is where my problem lies. I cant update them directly from the secondary thread and i have no idea how i would transfer data from my secondary thread and work out a system of updating them from main thread. I have put my code below:
Any help would be great.

 

 public MainWindow() 
    { 
        Serial = new Thread(ReadData); 
        InitializeComponent(); 
        int Count = 0; 
        for (Count = 0; Count < portlist.Length; Count++) 
        { 
            ComPortCombo.Items.Add(portlist[Count]); 
        } 
    } 
 
    private void StartDataButton_Click(object sender, RoutedEventArgs e) 
    { 
        SerialData = new SerialPort(ComPortCombo.Text, 19200, Parity.None, 8, StopBits.One); 
        SerialData.Open(); 
        SerialData.WriteLine("P"); 
        Serial.Start(); 
        StartDataButton.IsEnabled = false; 
        EndDataButton.IsEnabled = true; 
        ComPortCombo.IsEnabled = false; 
        CurrentSpeed = 0; 
        MaximumSpeed = 0; 
        Time = 0; 
        DistanceTravelled = 0; 
        MotorOutput = 0; 
        RiderInput = 0; 
        SaveData[0] = ""; 
        SaveData[1] = ""; 
        SaveData[2] = ""; 
        SaveData[3] = ""; 
        SaveDataButton.IsEnabled = false; 
        if (SerialData.IsOpen) 
        { 
            ComPortStatusLabel.Content = "OPEN"; 
            SerialData.NewLine = "/n"; 
            SerialData.WriteLine("0"); 
            SerialData.WriteLine("/n"); 
        } 
    } 
 
    private void EndDataButton_Click(object sender, RoutedEventArgs e) 
    { 
        SerialData.Close(); 
        SaveDataButton.IsEnabled = true; 
        SerialData.WriteLine("1"); 
        SerialData.WriteLine("0"); 
        if (!SerialData.IsOpen) 
        { 
            ComPortStatusLabel.Content = "CLOSED"; 
        } 
        int i = 0; 
        for (i = 0; i < 4; i++) 
        { 
            if (i == 0) 
            { 
                SaveDataString = "MaximumSpeed during the Ride was = " + Convert.ToString(MaximumSpeed) + "m/h"; 
                SaveData[i] = SaveDataString; 
            } 
            if (i == 1) 
            { 
                SaveDataString = "Total Distance Travelled = " + Convert.ToString(DistanceTravelled) + "m"; 
                SaveData[i] = SaveDataString; 
            } 
            if (i == 2) 
            { 
                SaveDataString = "Maximum Rider Input Power = " + Convert.ToString(maximumRiderInput) + "Watts"; 
                SaveData[i] = SaveDataString; 
            } 
            if (i == 3) 
            { 
                SaveDataString = "Maximum Motor Output Power = " + Convert.ToString(MaximumMotorOutput) + "Watts"; 
                SaveData[i] = SaveDataString; 
            } 
        } 
    } 
 
    private void SaveDataButton_Click(object sender, RoutedEventArgs e) 
    { 
        //File.WriteAllBytes(directory + "image" + imageNO + ".txt", ); //saves the file to Disk     
        File.WriteAllLines(directory + "BikeData.txt", SaveData); 
    } 
 
    public void ReadData() 
    { 
        int counter = 0; 
 
        while (SerialData.IsOpen) 
        { 
            if (counter == 0) 
            { 
                //try 
                //{ 
                    InputSpeed = Convert.ToInt16(SerialData.ReadChar()); 
                    CurrentSpeed = InputSpeed; 
                    if (CurrentSpeed > MaximumSpeed) 
                    { 
                        MaximumSpeed = CurrentSpeed; 
                    } 
                    SpeedTextBox.Text = "Current Wheel Speed = " + Convert.ToString(CurrentSpeed) + "Km/h"; 
                    DistanceTravelled = DistanceTravelled + (Convert.ToInt16(CurrentSpeed) * Time); 
                    DistanceTravelledTextBox.Text = "Total Distance Travelled = " + Convert.ToString(DistanceTravelled) + "Km"; 
                //} 
                //catch (Exception) { } 
            } 
            if (counter == 1) 
            { 
                try 
                { 
                    RiderInput = Convert.ToInt16(SerialData.ReadLine()); 
                    if (RiderInput > maximumRiderInput) 
                    { 
                        maximumRiderInput = RiderInput; 
                    } 
                    RiderInputTextBox.Text = "Current Rider Input Power =" + Convert.ToString(RiderInput) + "Watts"; 
                } 
                catch (Exception) { } 
            } 
            if (counter == 2) 
            { 
                try 
                { 
                    MotorOutput = Convert.ToInt16(SerialData.ReadLine()); 
                    if (MotorOutput > MaximumMotorOutput) 
                    { 
                        MaximumMotorOutput = MotorOutput; 
                    } 
 
                    MotorOutputTextBox.Text = "Current Motor Output = " + Convert.ToString(MotorOutput) + "Watts"; 
                } 
                catch (Exception) { } 
            } 
            counter++; 
            if (counter == 3) 
            { 
                counter = 0; 
            } 
        } 
    } 
 
    private void ComPortCombo_SelectionChanged(object sender, SelectionChangedEventArgs e) 
    { 
        StartDataButton.IsEnabled = true; 
    } 
 
 
    private void Window_Closed(object sender, RoutedEventArgs e) 
    { 
        if (SerialData.IsOpen) 
        { 
            SerialData.Close(); 
        } 
    }