Develop Reference

How to safely give my function without making my main form stuck

I have made a WPF application which has a button to move some files attached
to the column cells from one column to another column. The moment when I press
the button it shows a nice animation and moves all files to the next column's cells.
But my real problem is once I give my function color_check(),
my application is getting stuck. I really don't know why. Is there
any help I can get out for this?
Code:
private void button3_Click(object sender, EventArgs e)
{
Hide();
bool done = false;
ThreadPool.QueueUserWorkItem((x) =>
{
using (var splashForm = new Form4())
{
splashForm.Show();
while (!done)
Application.DoEvents();
splashForm.Close();
}
});
move(); //file moving function
//color_check(); if i give this fn, my form stucks and comes to live after 10 - 20 sec
done = true;
MessageBox.Show("TEST FINISHED");
Show();
}
public void color_check() //this is my problem making fn
{
dataGridView1.Refresh();
string strVal = ini.ReadValue("Action", "Doc-Controller");
bool authenticated = true;
if (authenticated == UserInCustomRole(strVal))
{
foreach (DataGridViewRow row in dataGridView1.Rows)
{
// Application.DoEvents();
string fName1 = System.IO.Path.GetFileNameWithoutExtension(row.Cells[3].Value.ToString());
string fName2 = System.IO.Path.GetFileNameWithoutExtension(row.Cells[4].Value.ToString());
if (!string.IsNullOrEmpty(fName1) && !string.IsNullOrEmpty(fName2))
{
var f1 = GetValue(fName1.ToCharArray()[fName1.Length - 2]) * 16 + GetValue(fName1.ToCharArray()[fName1.Length - 1]);
var f2 = GetValue(fName2.ToCharArray()[fName2.Length - 2]) * 16 + GetValue(fName2.ToCharArray()[fName2.Length - 1]);
//if (System.IO.Path.GetFileName(fName1) != System.IO.Path.GetFileName(fName2))
if (f1 > f2)
{
//MessageBox.Show(fName1);
DataGridViewCellStyle style = new DataGridViewCellStyle();
style.BackColor = Color.Yellow;
row.Cells[3].Style = style;
}
else if (f2 > f1)
{
//MessageBox.Show(fName1);
DataGridViewCellStyle style = new DataGridViewCellStyle();
style.BackColor = Color.Yellow;
row.Cells[4].Style = style;
}
if (f1 == f2)
{
DataGridViewCellStyle style = new DataGridViewCellStyle();
style.BackColor = Color.Plum;
row.Cells[4].Style = style;
row.Cells[3].Style = style;
}
}
}
}

The issue is that your code which is invoked on button3_click() is blocking the UI thread. That's why it appears to freeze for a while - the code is executing, and once it's complete the UI thread becomes responsive again.
The way to resolve this is to perform your actions asynchronously on another thread. In .NET 4 and beyond, you can use Tasks and the async/await keywords to help you manage this. If you are working on a version older than .NET 4, then you'll want to take a look at BackgroundWorker or other threading options compatible with your version of .NET.
Note that if you want to modify the GUI in your async method, you may need to use a Dispatcher.Invoke() to do so safely.
Here are some links to help you understand some approaches available to you
C# Blog on Understanding a simple async program
MSDN reference for async/await
Related StackOverflow question on how to use BackgroundWorkers
Related StackOverflow question on how to access the UI thread directly

In a normal UI application, no 2 functions that work on the GUI will run at the same time. This would result in a lot of issues otherwise, which usually would cause the program to crash. For example there could be 2 functions running at the same time that each check if the same list has at least one element and then remove an element - because they run at the same time they first both check if the list has 1 element.
That's why GUI functions all run in the same thread, meaning they run only one at a time. While color_check runs, other functions don't run.
You can launch additional threads and do work on them that is executed in parallel, of you can speed up the color_check function, for example by breaking it up into parts which run at lower priority one at a time, using a dispatcher
Take this:
public void color_check() //this is my problem making fn
{
dataGridView1.Refresh();
string strVal = ini.ReadValue("Action", "Doc-Controller");
bool authenticated = true;
if (authenticated == UserInCustomRole(strVal))
{
foreach (DataGridViewRow row in dataGridView1.Rows)
{
ProcessRow(row);
}
}
}
and change it to this:
public void color_check() //this is my problem making fn
{
dataGridView1.Refresh();
string strVal = ini.ReadValue("Action", "Doc-Controller");
bool authenticated = true;
if (authenticated == UserInCustomRole(strVal))
{
foreach (DataGridViewRow row in dataGridView1.Rows)
{
Dispatcher.BeginInvoke(DispatcherPriority.Background, ()=>{Process(row);});
}
}
}
In this code, Dispatcher.BeginInvoke tells the UI thread that it should run Process(row), as soon as it finds the time. This might result in 200 Process(row) calls that are waiting to be executed. It's still all executed on the UI thread and only one thing at a time. If a mouse click happens after the first hundred have been completed, the GUI thread will first finish number onehunderd and one, and then handle the mouseclick, before picking up the remaining calls to process.
There's a disadvantage to this approach. By allowing other functions to be executed in between different calls to Process(row), you may get surprising results. Especially if these other processes also change the cell styles.

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)
{
}
}
}

WPF - print during a loop

I have a simple issue, but the solution appears to be tricky. I want to print using the WPF control canvas during a loop; but for each iteration, I want to udpate the canvas control.
If I want to print a canvas control in WPF, I can simply call
PrintDialog dialog = new PrintDialog();
dialog.PrintVisual(this.canvas, "");
And it prints as expected to my default printer. Wonderful.
However, if I want to perform this multiple times in a loop and make an update to the canvas during each iteration, only the final iteration of the loop is printed.
private void methodName()
{
for (int i = 0; i < 2; i++)
{
updateTextBox(i.ToString());
PrintDialog dialog = new PrintDialog();
dialog.PrintVisual(this.canvas, "");
}
}
private void updateTextBox(string text)
{
txtTextBox.Text = text;
}
Any idea what I need to do to ensure that I get 2 print outs, the first with the txtTextBox.Text value of 0, the second time it has the value of 1?

I am about to implement something similar in my application and found out that my previous answer wasn't good enough. The problem for me was that although the canvas is updated in each iteration, it has not yet rendered itself before being sent to PrintVisual. It surprises me that you get your final iteration printed, I only got the first one. Anyway, this is how I made it work, basically queueing the print command after the already pending render operation:
for (int i = 0; i < 2; i++)
{
updateTextBox(i.ToString());
this.canvas.InvalidateVisual(); // Maybe not needed in your case
PrintDialog dialog = new PrintDialog();
this.Dispatcher.Invoke(System.Windows.Threading.DispatcherPriority.Render, (Action)delegate()
{
dialog.PrintVisual(this.canvas, "" + i);
});
}
Yes it's somewhat similar (but not identical) to SalGad's answer and the post you're referring to, but I'm not able to comment that answer, so please try this out, it works for me.
I also had problems with disappearing prints when using empty description for the print jobs, thus the + i. Don't know if that is a generic problem, or just something with my printer setup.
I got the idea from this post, which also mentions an alternative solution using ViewBox.

OK
I solved it.
I removed all the dispatcher object methods so it runs on a single thread.
To update the canvas, I used the canvas.UpdateLayout() method.
I also ensured that the print had finished before updating the next canvas (the next iteration).
private void methodName()
{
for (int i = 0; i < 2; i++)
{
updateTextBox(i.ToString());
this.canvas.UpdateLayout();
PrintDialog dialog = new PrintDialog();
dialog.PrintVisual(this.canvas, "ABC");
dialog.PrintQueue.Refresh();
while (dialog.PrintQueue.NumberOfJobs != 0)
{
bool isQueued = false;
foreach (var job in dialog.PrintQueue.GetPrintJobInfoCollection())
{
if (job.Name == "ABC")
isQueued = true;
}
if (!isQueued)
break;
Thread.Sleep(500);
dialog.PrintQueue.Refresh();
}
}
}
private void updateTextBox(string text)
{
txtTextBox.Text = text;
}
I also could have just done thread.sleep(3000) - this worked as it was enough time to ensure the print job had completed, but it was also a little bit 'hopeful' and I wanted something more secure.
Thank you to everyone for your suggestions.

If you are going to call PrintVisual multiple times you have to look into PrintDocument and DocumentPaginator.

Just a guess, but it might be worth trying RenderTargetBitmap to force rendering the canvas in each iteration, and then create an Image with that source, which then can be sent to PrintVisual. See this post for code example:
Printing viewport

Just taking a shot here, but can you try refreshing the WPF canvas controls at the start of every for loop iteration? Here is the code snippet:
// declare this
public static class ExtensionMethods
{
private static Action EmptyDelegate = delegate() { };
public static void Refresh(this UIElement uiElement)
{
uiElement.Dispatcher.Invoke(DispatcherPriority.Render, EmptyDelegate);
}
}
// the loop
for (int i = 0; i < 2; i++)
{
updateTextBox(i.ToString());
PrintDialog dialog = new PrintDialog();
dialog.PrintVisual(this.canvas, "");
}
}
// update this method
private void updateTextBox(string text)
{
txtTextBox.Text = text;
txtTextBox.Refresh();
Thread.Sleep(500);
}
I am sourcing this idea from here

GTK+ widgets/windows being (randomly) corrupted, with what seems to be timers

I have recently implemented a scrolling text across an area of limited screen estate using a timers repeating every 100ms, and some simple string appending.
However, after this very implementation, I have come to realise that my GUI is getting randomly bugged/corrupted after a certain while. That is to say that some widgets/windows become completely white, and eventually the entire GUI turns white and unclickable.
What is weird is that there is no error debug output at all.
Having said that, I am using Mono with GTK-Sharp for the application. Does anyone have an idea or a possible clue how and why this is happening?
If not, how can I further debug this properly?
Thanks, really appreciate it.
PS: Sometimes, it takes up to 1.5 hours for the thing to start corrupting, it has random timeframes for it to start happening.
This is my the code implemented that caused this issue:
void ScrollSyncTo(object sender, System.Timers.ElapsedEventArgs e)
{
//initial check if it fits nicely alr
if (sync_to_full_txt.Length <= sync_to_max_char)
{
sync_to_timer.Stop();
return;
}
//check for pause
if (sync_to_pause >= 0)
{
sync_to_pause--;
return;
}
//check direction
int temp_psn;
string temp_str;
if (sync_to_direction)
{
temp_psn = sync_to_posn + 1;
if (sync_to_full_txt.Substring(temp_psn).Length < sync_to_max_char)
{
sync_to_pause = sync_to_break_steps;
sync_to_direction = false;
sync_to_posn = sync_to_full_txt.Length - 1;
System.GC.Collect();
return;
}
else
{
temp_str = sync_to_full_txt.Substring(temp_psn, sync_to_max_char);
}
}
else
{
temp_psn = sync_to_posn - 1;
if (temp_psn + 1 < sync_to_max_char)
{
sync_to_pause = sync_to_break_steps;
sync_to_direction = true;
sync_to_posn = 0;
System.GC.Collect();
return;
}
else
{
temp_str = sync_to_full_txt.Substring(temp_psn - sync_to_max_char + 1, sync_to_max_char);
}
}
//lets move it
sync_to.Text = temp_str;
sync_to_posn = temp_psn;
}

To program in GTK with multiple threads, you have to do a couple things to make your program thread-safe. Here is short explanation using C.
I'm more familiar with GTK in C, but I'm assuming it works the same in GTK#. So you have to call GLib.Thread.Init() and Gdk.Threads.Init() at the beginning of your program, bracket your call to Application.Run() with Gdk.Threads.Enter() and Gdk.Threads.Leave(), and also make sure any GTK and GDK calls in background threads (not GTK signal handlers) are between Gdk.Threads.Enter() and Gdk.Threads.Leave().

System.Timers.Timer callbacks come from a threadpool thread, but GTK objects can only safely be accessed from the GTK thread. I would suggest using GLib.Timeout, which runs on the GTK thread.

Problem While receiving events from a thread

I'm Doing a project on FileTransfer in which i have a listview , i will get events from one of my class file for updating the percentage of the file sent so far,after receiving it i will place the percentage in my listview ,while doing that the listview got
a flickering effect how to avoid it.i used application.doevents() but it doesnt works. i have seen in torrents while updating the percent the list doesnt get flickered
how to achieve this .
void Sender_Progress(int CurrentValue, string Ip) // here im receiving Events
{
try
{
//if (CurrentValue == 1)
// UpdateTimer.Enabled = true;
//list_send.Items[CurrentValue].SubItems[4].Text = Ip.ToString();
//Application.DoEvents();
obj = new object[] {CurrentValue, Ip };
list_send.Invoke(new UpdateList(UpList), obj);
}
catch(Exception ex)
{
MessageBox.Show(ex.Message);
}
}
public void UpList(int Val, string ind) // here im updating the listview
{
Application.DoEvents();
int index = 0;
index = Convert.ToInt32(ind);
index = index - 1;
list_send.Items[index].SubItems[4].Text = Val.ToString();
if (Val == 100)
{
list_send.Items[index].SubItems[2].Text = "Completed.";
//UpdateTimer.Enabled = false;
}
//Application.DoEvents();
}

Firstly, you don't need the DoEvents, since you are already correctly working on two threads. Remove that. After that, I expect the problem is simply doing too much too quickly. Is it possible to batch updates, and only send an update, say, every 20? 50? times? It isn't clear what the control is, but many have multiple-update modes; for example with ListView:
theList.BeginUpdate();
try {
// make multiple updates here...
} finally {
theList.EndUpdate();
}
I would then see about passing over a list of updates, say, every 20 times (unless each takes a considerable time) [note it must be a different list per Invoke, and you need to remember to send any remaining items at the end, too].

Use worker thread - it's available from the toolbox and has two events that are invoked in the main (UI) thread.
The Progress event can be used to signal the listbox that it need to refresh or that the task was completed.

i overcome the flickering effect succesfully,im getting events frequently ,i will get an integer everytime, i will store it in a variable and compare it with next variable received by the event if it matches i wont invoke the listview,otherwise i will invoke it.now the flickering goes away. thanks all.