c# - Cross-thread operation not valid: Control 'textBox1' accessed from a thread other than the thread it was created on

I want to send temperature value from a microcontroller using UART to C# interface and Display temperature on Label.Content. Here is my microcontroller code:

while(1) {
   key_scan(); // get value of temp
   if (Usart_Data_Ready())
   {
      while(temperature[i]!=0)
      {
         if(temperature[i]!=' ')
         {

            Usart_Write(temperature[i]);
            Delay_ms(1000);
         }
         i = i + 1;
      }
      i =0;
      Delay_ms(2000);
   }
}

and my C# code is:

private void serialPort1_DataReceived(object sender, System.IO.Ports.SerialDataReceivedEventArgs e)
{
   txt += serialPort1.ReadExisting().ToString();
   textBox1.Text = txt.ToString();
}

but exception arises there "Cross-thread operation not valid: Control 'textBox1' accessed from a thread other than the thread it was created on"
Please tell me how to get temperature string from my microcontroller and remove this Error!

Answer

The data received in your serialPort1_DataReceived method is coming from another thread context than the UI thread, and that's the reason you see this error.
To remedy this, you will have to use a dispatcher as descibed in the MSDN article:
How to: Make Thread-Safe Calls to Windows Forms Controls

So instead of setting the text property directly in the serialport1_DataReceived method, use this pattern:

delegate void SetTextCallback(string text);

private void SetText(string text)

{
  // InvokeRequired required compares the thread ID of the
  // calling thread to the thread ID of the creating thread.
  // If these threads are different, it returns true.
  if (this.textBox1.InvokeRequired)
  { 
    SetTextCallback d = new SetTextCallback(SetText);
    this.Invoke(d, new object[] { text });
  }
  else

  {
    this.textBox1.Text = text;
  }
}

So in your case:

private void serialPort1_DataReceived(object sender, System.IO.Ports.SerialDataReceivedEventArgs e)
{

  txt += serialPort1.ReadExisting().ToString();
  SetText(txt.ToString());
}