Fire event in WPF

I have a textbox that stores data from INotifyPropertyChanged

an MVVM model.

I want to optimize it as such: when I close the window, no data should fit into the textbox; and when i open the textbox it should start transmitting data again.

This is my viewmodel code:

public class serial : NotifyPropertyChanged
{
    private string luminRecevied;

    public string LuminRecevied
    {
        get { return luminRecevied; }
        set 
        {

            if (this.luminRecevied == value)
                return;

            this.luminRecevied = value ;

            this.InvokePropertyChanged("LuminRecevied");

        }
    }
}

      

        
        
        
      

    

this is my model code:

 //This is where the Outgoing Ports are Tapped and the data is displayed to the serial Monitor.
 var rawPacket = e.Value as RawPacket; // Data recived from the port after tapped 
 StringBuilder sb = new StringBuilder();

 for (int i = 0; i < rawPacket.RawData.Length; i++)
 {
     sb.Append(rawPacket.RawData[i].ToString("X2"));
 }

 this.serialData.LuminRecevied += "RX:"+sb.ToString() + Environment.NewLine;