Develop Reference

Event handler fires twice

i am an engineering student and i am currently working on my final year project. i am trying to build a rfid-based parking lot management system in C#. based on some research i have written the following code to read data from rfid reader but i am facing this problem. the event handler
which i use to read the received data fires twice, which i don't understand how...i did some research on the internet and found many people are facing similar problem of an event handler firing twice but most of them are button-click events. i could only find a few threads on custom event handler but those solutions don't seem to work in my project. any possible solutions to this problem?
private void Parking_layout_Load(object sender, EventArgs e)
{
foreach (string port in System.IO.Ports.SerialPort.GetPortNames())
{
comboBox1.Items.Add(port);
if (comboBox1.Items.Count > 0)
comboBox1.SelectedIndex = comboBox1.Items.Count - 1;
}
RFID = new SerialPort();
RFID.PortName = comboBox1.Text;
RFID.BaudRate = 9600;
RFID.DataBits = 8;
RFID.Parity = Parity.None;
RFID.StopBits = StopBits.One;
RFID.Open();
RFID.DataReceived += new SerialDataReceivedEventHandler(RFID_DataReceived);
}
private void RFID_DataReceived(object sender, SerialDataReceivedEventArgs e)
{
try
{
tag_id = RFID.ReadExisting().ToString();
SetLabel(tag_id);
}
catch (Exception ex)
{
throw new Exception(ex.Message);
}
}
the RFID_DataReceived executes twice. if i put a messageBox.show() statement to test it, it shows the message twice. how do i fix this problem?

Set a break point on the RFID_DataReceived method in order to see why it is firing twice. You can then take a look at the stack window to see the stack trace of the code.
You can also do the same for the original method Parking_layout_Load to see if perhaps it is being called more then once from another piece of code. You can also place code inside the function in order for the stacktrace to be written to the output window.
private void RFID_DataReceived(object sender, SerialDataReceivedEventArgs e)
{ Debug.WriteLine("StackTrace: '{0}'", Environment.StackTrace);
try
{
tag_id = RFID.ReadExisting().ToString();
SetLabel(tag_id);
}
catch (Exception ex)
{
throw new Exception(ex.Message);
}
}
For even more detail then use the stacktrace class as in this example : StackTrace Class
Environment.StackTrace Property
How to: Use the Call Stack Window

What is the incoming data? Looking at your code, I notice you have the line
RFID.DataBits = 8;
In .NET, a char is 2 bytes. If you are reading a character from your device, then it would in fact need to call your event handler twice to process all 16 bits. Can you change the value to 16?

Prevent other Methods from running under a condition is met in a previous Method

My problem is when the user clicks on myButton the program operates perfectly fine. But if the user was to input a value less than 3 in the first textbox a message box will appear to the user stating that the value must be greater than 3 metres. If you click OK the next method in myButton runs anyway and the result message box appears anyway.
I've tried looking around to solve this problem of mine using Nested For Loops but failed to get them to work (most likely a fault on my end). I also prefer not to use Goto because it isn't exactly good programming practice to use. Of course you can tell me otherwise if you want :) .
// Button
private void myButton_Click(object sender, EventArgs e)
{
checkIfNumericalValue();
testIfTextBoxOnesMinimumIsMet();
testIfTextBoxTwosMinimumIsMet();
displayResultToUser();
resetOrClose();
}
// Textbox One
public void testIfTextBoxOnesMinimumIsMet()
{
if (length < 3)
{
MessageBox.Show("length must be greater than 3 metres");
}
}
Help would be greatly appreciated this is also my second attempt at C# on Visual Studio 2012. Do not worry this has nothing to do with my year 10 schooling as my school doesn't have a programming subject. This problem occurs in testIfTextBoxOnesMinimumIsMet() and testIfTextBoxOnesMinimumIsMet() as well but if someone can help me with this one method I should be able to fix the rest :)

You could throw an exception from your inner functions and catch it from your button's function, something like this:
// Button
private void myButton_Click(object sender, EventArgs e)
{
try
{
checkIfNumericalValue();
testIfTextBoxOnesMinimumIsMet();
testIfTextBoxTwosMinimumIsMet();
displayResultToUser();
resetOrClose();
}
catch (ArgumentException ex)
{
// The error message we defined at the exception we threw
MessageBox.Show(ex.Message);
}
}
// Textbox One
public void testIfTextBoxOnesMinimumIsMet()
{
if (length < 3)
{
throw new ArgumentException("Length must be greater than 3 meters.");
}
}
An alternative would be to deal with the validation within your button like so:
// Button
private void myButton_Click(object sender, EventArgs e)
{
checkIfNumericalValue();
if (length < 3)
{
MessageBox.Show("Length must be greater than 3 meters.");
return;
}
testIfTextBoxTwosMinimumIsMet();
displayResultToUser();
resetOrClose();
}
What happens above is that the return will leave that function without further processing anything else.

So, if I'm understanding this correctly, if the text boxes contain numerical values, text box 1 meets the minimum and text box 2 meets the minimum, you want to displayResultToUser() and then resetOrClose().
If that's the case, you can have the 3 methods checkIfNumericalValue(), testIfTextBoxOnesMinimumIsMet() and testIfTextBoxTwosMinimumIsMet() return a bool depending on what the minimum condition is and then write something like this:
private void myButton_Click(object sender, EventArgs e)
{
if (checkIfNumericalValue() && testIfTextBoxOnesMinimumIsMet(Convert.ToInt32(txtBoxOne.Text)) && testIfTextBoxTwosMinimumIsMet(Convert.ToInt32(txtBoxTwo.Text)))
{
displayResultToUser();
resetOrClose();
}
}
public bool testIfTextBoxOnesMinimumIsMet(int length)
{
if (length < 3)
{
MessageBox.Show("length must be greater than 3 metres");
return false;
}
return true;
}

It appears that you need some other variable to track whether or not you have encountered errors. To do this, you could have a bool noErrors variable defined, and you should return a boolean from your error check methods that is True if there were no errors, otherwise False. This way you know if you ran into any problems.
Finally, you should check for the state of errrorsFound before running any of your other methods.
For example:
// Button
private void myButton_Click(object sender, EventArgs e)
{
bool noErrors =
isNumericalValue() &&
textBoxOnesMinimumIsMet() &&
textBoxTwosMinimumIsMet();
if (noErrors)
{
displayResultToUser();
resetOrClose(); // I'm not sure if this should happen regardless of errors?
}
}
// Textbox One
public bool textBoxOnesMinimumIsMet()
{
if (length < 3)
{
MessageBox.Show("length must be greater than 3 metres");
return false;
}
return true;
}

How to display data received from serial port in a textbox without the text disappearing in Visual Studio C#?

So, I'm trying to develop a simple application in visual C# which gets data from serial port and displays it in a textbox (to monitor temperature). I'm acquiring and displaying the data successfully, using the DataReceived event to update a global string variable and a timer to update the text field on my text box, as shown:
private void port_DataReceived_1(object sender, SerialDataReceivedEventArgs e)
{
try
{
globalVar.updateTemp = port.ReadLine(); //This is my global string
}
catch (IOException)
{
}
catch (InvalidOperationException)
{
}
catch (TimeoutException)
{
}
}
private void timer1_Tick(object sender, EventArgs e)
{
tempDisplayBox.Text = globalVar.updateTemp; //This is my textbox updating
}
The only issue I have is that the value shown in the textbox keeps flashing, making it hard to read. My timer is set to trigger every 10 ms (which should be fast enough, right?). Is there any way to make it more stable? I realize this may be a newb question, but to be fair I am a newb :) Any help is appreciated! Thanks!

Do you really need it updating every 10ms? What about every 500 ms or if not that then 100ms. 100ms will require your update method run 10 times less and therefore update 10 times less. The flickering you are expiriencing is due to the refresh speed. You could create custom method which will only update the temp only when target Label or textBox value is different than source port. But that will only sort the flickering when temp is steady, when temp will start vary it will bring back the flickering. Good luck ;-)
UPDATE
Hi I tried to reproduce the conditions and could not make my textbox nor Label flash. The way I tested it was by assigning int ntick = 0; and then increment the ++ntick; inside of the timer_tick method. The results didn't make any of the controls flash and were updated even every milisecond at some point. I also tried string.Format to put some load on the method. Is your app responsive?

The trick is to use double buffering. This way the operating system will redraw the Control off-screen, and only show the control when it is fully redrawn.
I have had the same problem, and solved it by extending the TextBox control like this:
public FastLogBox()
{
InitializeComponent();
_logBoxText = new StringBuilder(150000);
timer1.Interval = 20;
timer1.Tick += timer1_Tick;
timer1.Start();
SetStyle(ControlStyles.DoubleBuffer, true);
}
void timer1_Tick(object sender, EventArgs e)
{
if (_timeToClear)
{
_logBoxText.Clear();
_timeToClear = false;
}
if (_logQueue.Count <= 0) return;
while (!_logQueue.IsEmpty)
{
string element;
if (!_logQueue.TryDequeue(out element)) continue;
{
_logBoxText.Insert(0, element + "\r\n");
}
}
if (_logBoxText.Length > 150000)
{
_logBoxText.Remove(150000, _logBoxText.Length - 150001);
}
Text = _logBoxText.ToString();
}
public new void Clear()
{
_timeToClear = true;
while (!_logQueue.IsEmpty)
{
string element;
_logQueue.TryDequeue(out element);
}
}
public void AddToQueue(string message)
{
_logQueue.Enqueue(message);
}
}
I also use a timer and a concurrentQueue to avoid using Invoke to update the control from another thread. I also use a StringBuilder to prepare the string before putting it into the TextBox. StringBuilder is faster when building larger strings.

You can use ReadExisting() to read the whole data at a time.
You need to handle DataReceived Event of SerialPort
serialPort1.ReadExisting();
Sample:
private void serialPort1_DataReceived(object sender, System.IO.Ports.SerialDataReceivedEventArgs e)
{
String myData=serialPort1.ReadExisting();
}
Example Code: Here i would like to show you the code to Read Data(RFID Tag Code which is basically of length 12)
String macid = "";
private void DoWork()
{
Invoke(
new SetTextDeleg(machineExe ),
new object[] { macid });
macid = "";
}
private void serialPort1_DataReceived(object sender, System.IO.Ports.SerialDataReceivedEventArgs e)
{
string str1;
macid += serialPort1.ReadExisting();
if (macid.Length == 12)
{
macid = macid.Substring(0, 10);
Thread t = new Thread(new ThreadStart(DoWork));
t.Start();
}
}
public void machineExe(string text)
{
TextBox1.Text=text;
}

Thank you so much for the answers! I found a way to work around this issue:
Instead of replacing the contents of my textbox by rewriting the TextBox.Text property - which, as HenningNT implied, refreshes the control and causes the flickering - I'm now using the TextBox.AppendText method. Though, as I want to display only one line of data at a time, I use the textbox in multiline mode and the Environment.NewLine to jump to a new line before appending the text. As for the method of updating, I've gone back to using the timer because with the invoke method was crashing my application when I close the form, for some reason. Also, enabling double buffering didn't do me much good, although I guess I was doing it wrong... It still flickers a bit, but it's much better now :) I know this is not really a perfect solution (much more of a workaround), so I'll keep looking for it. If I find it, I'll be sure to update it here ;) My code:
private void timer1_Tick(object sender, EventArgs e) //Timer to update textbox
{
if (tempDisplayBox.Text != globalVar.updateTemp) //Only update if temperature is different
{
try
{
tempDisplayBox.AppendText(Environment.NewLine);
tempDisplayBox.AppendText(globalVar.updateTemp);
}
catch (NullReferenceException)
{
}
}
}

'index was outside the bounds of the array' exception handling error

I am using the below code to find the base address of a running process. It's within a timer control for other purposes. If the target process is not running I want to display "Process is not running" in the label text, but keep checking for the running process and when/if found continue with the next code block. I have tried a few ways I thought would work, such as a 'try' with exception handling, but the form I am using to hold the label just freezes, I am quit new to c#. Here is the code,
private void timer1_Tick(object sender, EventArgs e)
{
#region BaseAddress
Process[] test = Process.GetProcessesByName("process");
int Base = test[0].MainModule.BaseAddress.ToInt32();
#endregion
//Other code
}
The exception when run is: "IndexOutOfRange exception was unhandled" - Index was outside the bounds of the array. Hopefully someone can help. Thanks.

private void timer1_Tick(object sender, EventArgs e)
{
#region BaseAddress
Process[] test = Process.GetProcessesByName("process");
if (test.Length > 0)
{
int Base = test[0].MainModule.BaseAddress.ToInt32();
}
else
{
myLabel.Text = "Process is not running";
}
#endregion
//Other code
}

Rather than use a try–catch block to handle the error, you should check whether the process was found before trying to access it:
private void timer1_Tick(object sender, EventArgs e)
{
#region BaseAddress
Process[] test = Process.GetProcessesByName("process");
if (test.Any())
{
// Process is running.
int Base = test[0].MainModule.BaseAddress.ToInt32();
// Perform any processing you require on the "Base" address here.
}
else
{
// Process is not running.
// Display "Process is not running" in the label text.
}
#endregion
//Other code
}

I think that the Process with the name "process" does not exist. You need to give a real processname. So the array does not contain any elements. Try debugging to see if the array contains any elements and add error handling or a verification that the array length is higher than 0 before doing the second line of your code.

WPF RichTextBox as a text queue for logging purposes

I would like to use a RichTextBox WPF control to print log outputs, but I am wondering what is the most efficient way to remove the "oldest" lines after there are for example more than 10,000 lines displayed, if it is possible to actually implement a queue behaviour, especially as there is no easy "Text" property to play with.
Unfortunately, I am not able to achieve this result with nlog either probably due to a bug or a limitation.

You can use a Queue<string> to store your log messages, and display them using the RichTextBox.Lines property.
For example:
private const int _maxCapacity = 10000;
private Queue<string> _messageQueue = new Queue<string>(_maxCapacity);
private void button1_Click(object sender, EventArgs e)
{
if (_messageQueue.Count >= _maxCapacity)
{
_messageQueue.Dequeue();
}
_messageQueue.Enqueue("message " + _count++.ToString());
richTextBox1.Lines = _messageQueue.ToArray();
}
If you want the most recent messages to appear on top, reverse the queue:
richTextBox1.Lines = _messageQueue.Reverse().ToArray();

If you extend the original control with a LineCount int property, it is possible to use this (inspired by some code given here):
if (this.MaxLines > 0)
{
this.lineCount++;
if (this.lineCount > this.MaxLines)
{
tr = new TextRange(rtbx.Document.ContentStart, rtbx.Document.ContentEnd);
tr.Text = tr.Text.Remove(0, tr.Text.IndexOf('\n'));
this.lineCount--;
}
}
//And for auto scrolling
if (this.AutoScroll)
{
rtbx.ScrollToEnd();
}