Serial Port Unauthorized Exception

I am trying to access RFID Reader through Arduino application which gives me the right output on control monitor.

But when I tried to access it through visual studio C#, it works only once and then gives me access is denied! And also stopped working on Arduino IDE.

//Function to initialize serial port

SerialPort RFIDPort
public SerialPort initializeRFIDPort()
{
try
{
RFIDPort = new SerialPort("COM4",9600,Parity.None,8, StopBits.One);

if (RFIDPort.IsOpen)
RFIDPort.Close();

if(!RFIDPort.IsOpen)
RFIDPort.Open();
}
catch (UnauthorizedAccessException ex) {MessageBox.Show( ex.Message); }
catch (Exception)
{
RFIDPort = null;
}

return RFIDPort;
}


I put the function here:

public products()
{
InitializeComponent();
initializeRFIDPort();
}


There is two scan button the first one for scanning and then add data to the database and the second button is to scan and search for data

private void ScanButton_Click(object sender, EventArgs e)
{
try
{
scanButtonIsClicked = true;

if (RFIDPort.IsOpen)
{
RFIDPort.DataReceived += serialPort1_DataReceived;
textBox1.Text = "";
}
else
MessageBox.Show("RFID Reader is not connected!");
}
catch (System.Exception)
{
MessageBox.Show("Please Try Again");
}
}

private void Searchbutton_Click(object sender, EventArgs e)
{
scansearchbtn = true;
scanButtonIsClicked = false;

try
{
if (RFIDPort.IsOpen)
{
RFIDPort.DataReceived += serialPort1_DataReceived;

textBox2.Text = "";

}
else
{
MessageBox.Show("RFID Reader is not connected!");
}
}
catch (IOException)
{
MessageBox.Show("Please reconnect your device ");
}
}

private void serialPort1_DataReceived(object sender, System.IO.Ports.SerialDataReceivedEventArgs e)
{
try
{
string line = RFIDPort.ReadLine();

if (scanButtonIsClicked == true)
this.BeginInvoke(new LineReceivedEvent(LineReceived), line);
else
this.BeginInvoke(new LineReceivedEvent(Line2Received), line);
}
catch (TimeoutException) { }
catch (Exception){ MessageBox.Show("Can't Read from RFID Device.Please try again"); }
}

private delegate void LineReceivedEvent(string line);

private void LineReceived(string line)
{
textBox2.Text = line;
}
private void Line2Received(string line)
{
textBox1.Text = line;
}


And then I closed serial port in Forum-Closing.
Please if anyone can lead me to the right way. I have try many times and it works randomly!
On Aruino side this is my code:

#include <SPI.h>
#include <MFRC522.h>

#define SS_PIN 10
#define RST_PIN 9

MFRC522 rfid(SS_PIN, RST_PIN); // Instance of the class

MFRC522::MIFARE_Key key;

// Init array that will store new NUID
byte nuidPICC[10];

void setup()
{
Serial.begin(9600);
SPI.begin(); // Init SPI bus
rfid.PCD_Init(); // Init MFRC522
for (byte i = 0; i < 6; i++)
{
key.keyByte[i] = 0xFF;
}
printHex(key.keyByte, MFRC522::MF_KEY_SIZE);
Serial.println();
}

void loop()
{

if ( ! rfid.PICC_IsNewCardPresent())
return;
if ( ! rfid.PICC_ReadCardSerial())
return;

// Serial.print(F("PICC type: "));
MFRC522::PICC_Type piccType = rfid.PICC_GetType(rfid.uid.sak);
// Serial.println(rfid.PICC_GetTypeName(piccType));

// Check is the PICC of Classic MIFARE type
if (piccType != MFRC522::PICC_TYPE_MIFARE_MINI && piccType !=
MFRC522::PICC_TYPE_MIFARE_1K && piccType != MFRC522::PICC_TYPE_MIFARE_4K)
{
Serial.println(F("Your tag is not of type MIFARE Classic."));
return;
}
// Store NUID into nuidPICC array
for (byte i = 0; i < 4; i++)
{
nuidPICC[i] = rfid.uid.uidByte[i];
}
printHex(rfid.uid.uidByte, rfid.uid.size);
Serial.println();
// Halt PICC
rfid.PICC_HaltA();
// Stop encryption on PCD
rfid.PCD_StopCrypto1();
}
void printHex(byte *buffer, byte bufferSize)
{
for (byte i = 0; i < bufferSize; i++) {
Serial.print(buffer[i] < 0x10 ? " 0" : " ");
Serial.print(buffer[i], HEX);
}
}


inside of your serialPort1_DataRecieved callback - try making your first line of code: RFIDPort.DataReceived -= serialPort1_DataReceived;
– Rick Riggs
Jun 27 at 17:21

RFIDPort.DataReceived -= serialPort1_DataReceived;

Thank u it first works when I run the program for 3 times but then gives the previous error!
– rosie
Jun 27 at 18:27

My guess is that after processing the line, you should try to clear the serial port's contents. It might be flooding (exceeding its limit). OR on the Arduino side, make sure that each line written replaces the last (NOT APPEND a new line).
– Rick Riggs
Jun 28 at 14:48

please recheck my Arduino code. Thank u
– rosie
Jun 29 at 9:47

before any of your Serial.println("...") statements my suggestion would be to issue Serial.flush(). For your reference here are the DOCS for the flush method. As for the printHex loop, just be sure to issue it before the loop, not exactly before the Serial.print(<byte>) statements.
– Rick Riggs
Jun 29 at 14:43

Serial.println("...")

Serial.flush()

printHex

Serial.print(<byte>)

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