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MessageBox and while loop C#

I'm modifying existing C# code in order to pilote a piston. Every 30ms, I have a direct feedback of the position of this piston, through an event. The value is stored in a global variable I use to get the current position of the piston.
What I'm trying to achieve: for a given distance input (A->C), I want the piston to travel at full speed for 95% of the distance (A->B), and then slower for the remaining 5% (B->C).
I have access to a command that defines the speed and the destination of the piston : pos(velocity, destination).
However, if I write that code:
pos(fullSpeed,B);
pos(reducedSpeed, C);
the piston directly goes from fullSpeed to reducedSpeed
I tried to use a while loop to compare the current position of the piston with the goal destination, however, upon entering the while loop, the variable storing the piston position does not update anymore.
However, I noticed that by throwing a MessageBox in between, the position value keeps on getting updated, and I can simply click "ok" to launch the second command.
pos(fullSpeed,B);
MessageBox.show("Wait");
pos(reducedSpeed, C);
I would like to know why the "while" loop stops the update of the position variable but the MessageBox does not. I mean, as long as I don't click the "ok" button, the box is here preventing me from doing anything, which for me ressembles a while loop behaviour. Is there another way for me to do this instead of the MessageBox ?
I have little to no knowledge when it comes to C# and no support. I have tried to look in the documentation, but I did not find an answer (I have probably missed it). Any lead is more than welcome.
EDIT: I have no documentation for that code, and it is barely commented. Here is what I gathered (really hope it helps):
To move the piston, taht function is called:
MyEdc.Move.Pos(control, speed, destination, ref MyTan);
control simply define what we pilote (a distance or a load, it is an enum), and I have no idea what MyTan does. Only thing I know is that the MyEdc.Move.Pos returns an error code.
If I look at the definition of "pos", I am redirected to class
public DoPEmove Move;
containing among other things:
public DoPE.ERR Pos(DoPE.CTRL MoveCtrl, double Speed, double Destination, ref short Tan);
DoPE.ERR is also an type enum. However, I cannot reach the definition of a function named "Pos". Coud it be within the .dll included ?
The following is the code that allows me to access the position of the piston (without the global variables):
private int OnData(ref DoPE.OnData Data, object Parameter)
{
if (Data.DoPError == DoPE.ERR.NOERROR)
{
DoPE.Data Sample = Data.Data;
Int32 Time = Environment.TickCount;
if ((Time - LastTime) >= 300 /*ms*/)
{
LastTime = Time;
string text;
text = String.Format("{0}", Sample.Time.ToString("0.000"));
guiTime.Text = text;
text = String.Format("{0}", Sample.Sensor[(int)DoPE.SENSOR.SENSOR_S].ToString("0.000"));
guiPosition.Text = text;
text = String.Format("{0}", Sample.Sensor[(int)DoPE.SENSOR.SENSOR_F].ToString("0.000"));
guiLoad.Text = text;
text = String.Format("{0}", Sample.Sensor[(int)DoPE.SENSOR.SENSOR_E].ToString("0.000"));
guiExtension.Text = text;
}
}
return 0;
}
Which is called using
MyEdc.Eh.OnDataHdlr += new DoPE.OnDataHdlr(OnData);
I realise how little I know on how the soft operates, and how frustrating this is for you. If you think this is a lost cause, no problem, I'll try Timothy Jannace solution, and if it does not help me, I'll stick with the MessageBox solution. I just wanted to know why the MessageBox allowed me to sort of achieve my objectif, but the while loop did not, and how to use it in my advantage here.

I tried to use a while loop to compare the current position of the
piston with the goal destination, however, upon entering the while
loop, the variable storing the piston position does not update
anymore.
While you are in the while loop, your app can no longer receive and process the feedback event.
One possible solution would be to use async/await like this:
private const int fullSpeed = 1;
private const int reducedSpeed = 2;
private int currentPistonPositon = 0; // global var updated by event as you described
private async void button1_Click(object sender, EventArgs e)
{
int B = 50;
int C = 75;
pos(fullSpeed, B);
await Task.Run(() =>
{ // pick one below?
// assumes that "B" and "currentPistonPosition" can actually be EXACTLY the same value
while (currentPistonPositon != B)
{
System.Threading.Thread.Sleep(25);
}
// if this isn't the case, then perhaps when it reaches a certain threshold distance?
while (Math.Abs(currentPistonPositon - B) > 0.10)
{
System.Threading.Thread.Sleep(25);
}
});
pos(reducedSpeed, C);
}
Note the button1_Click method signature has been marked with async. The code will wait for the while loop inside the task to complete while still processing event messages because of the await. Only then will it move on to the second pos() call.
Thank you for your answer ! It works like a charm ! (good catch on the
EXACT value). I learnt a lot, and I am sure the async/await combo is
going to be very usefull in the future ! – MaximeS
If that worked well, then you might want to consider refactoring the code and making your own "goto position" method like this:
private void button1_Click(object sender, EventArgs e)
{
int B = 50;
int C = 75;
GotoPosition(fullSpeed, B);
GotoPosition(reducedSpeed, C);
}
private async void GotoPosition(int speed, int position)
{
pos(speed, position);
await Task.Run(() =>
{
while (Math.Abs(currentPistonPositon - position) > 0.10)
{
System.Threading.Thread.Sleep(25);
}
});
}
Readability would be greatly improved.
You could even get fancier and introduce a timeout concept into the while loop. Now your code could do something like below:
private void button1_Click(object sender, EventArgs e)
{
int B = 50;
int C = 75;
if (GotoPosition(fullSpeed, B, TimeSpan.FromMilliseconds(750)).Result)
{
if (GotoPosition(reducedSpeed, C, TimeSpan.FromMilliseconds(1500)).Result)
{
// ... we successfully went to B at fullSpeed, then to C at reducedSpeed ...
}
else
{
MessageBox.Show("Piston Timed Out");
}
}
else
{
MessageBox.Show("Piston Timed Out");
}
}
private async Task<bool> GotoPosition(int speed, int position, TimeSpan timeOut)
{
pos(speed, position); // call the async API
// wait for the position to be reached, or the timeout to occur
bool success = true; // assume we have succeeded until proven otherwise
DateTime dt = DateTime.Now.Add(timeOut); // set our timeout DateTime in the future
await Task.Run(() =>
{
System.Threading.Thread.Sleep(50); // give the piston a chance to update maybe once before checking?
while (Math.Abs(currentPistonPositon - position) > 0.10) // see if the piston has reached our target position
{
if (DateTime.Now > dt) // did we move past our timeout DateTime?
{
success = false;
break;
}
System.Threading.Thread.Sleep(25); // very small sleep to reduce CPU usage
}
});
return success;
}

If you're using events you are probably having concurrency issues. Especially with events being raised every 30ms!
A very simple way to handle concurrency is to use a lock object to prevent different threads from using contested resources simultaneously:
class MyEventHandler
{
private object _lockObject;
MyEventHandler()
{
_lockObject = new object();
}
public int MyContestedResource { get; }
public void HandleEvent( object sender, MyEvent event )
{
lock ( _lockObject )
{
// do stuff with event here
MyContestedResource++;
}
}
}
Keep in mind that is very simple and by no means perfect in every scenario. If you provide more information about how the events are raised and what you're doing with them people will be able to provide more help.
EDIT:
Using that signature you posted for the Pos method I was able to find documentation on the library you are using: https://www.academia.edu/24938060/Do_PE
The reason you only see the method signature when you goto definition is because the library has been compiled into a dll. Actually, it probably wouldn't be that useful to see the code anyway because it looks like the library is a C# wrapper around native (c or c++) code.
Anyways, I hope the documentation is helpful to you. If you look at page 20 there are some pointers on doing movement. This is going to be a challenge for a new programmer but you can do it. I would suggest you avoid using the event handler to drive your logic and instead stick with using the synchronous versions of commands. Using the synchronous commands your code should operate the same way it reads.

I believe what you'll want to do is add a call to:
Application.DoEvents();
This will allow your application to process posted messages (events), which will allow that global variable to be updated.
I just wanted to know why the MessageBox allowed me to sort of achieve my objectif, but the while loop did not, and how to use it in my advantage here.
The reason that works is because you're giving the WndProc a chance to process events which have been sent to the application. It's not an intended feature of that call to MessageBox.Show();, but it is a consequence. You can do the same thing with a call to Application.DoEvents(); without the interruption of the message box.

C# String comparison not working

I'm having this wierd problem within the application I'm currently working on.
string searchText = "onMouseOver=\"CallList_onMouseOver(this);\" id=\"";
List<int> searchOrders = AllIndexesOf(scraper.clientBrowser.DocumentText, searchText);
StringBuilder sb = new StringBuilder();
for (int i = 0; i < searchOrders.Count; i++)
{
string order = scraper.clientBrowser.DocumentText.Substring(searchOrders[i] + searchText.Length, 6);
scraper.clientBrowser.Document.GetElementById(order).InvokeMember("Click");
for (int j = 0; j < scraper.clientBrowser.Document.Window.Frames.Count; j++)
{
if (scraper.clientBrowser.Document.Window.Frames[j].Document != null && scraper.clientBrowser.Document.Window.Frames[j].Document.Body != null)
{
string orderText = scraper.clientBrowser.Document.Window.Frames[j].Document.Body.InnerText ?? "Nope";
//MessageBox.Show(j + Environment.NewLine + orderText);
if (!orderText.Contains("Nope"))
{
sb.AppendLine(orderText + Environment.NewLine);
}
}
}
}
Clipboard.SetText(sb.ToString());
The thing is, whenever I uncomment the MessageBox.Show, I can clearly see orderText is filled with another value than "Nope", the Stringbuilder gets filled, and the correct text is copied.
However if I comment the Messagebox.Show, the outcome of this loop is always "Nope". I'm stuck here, I have no idea what could cause something like this.
The scraper.clientBrowser is a System.Windows.Forms.WebBrowser.
Update:
Solved the issue by waiting for the document to be loaded, created this mechanism:
public bool DocumentLoaded
{
get { return documentLoaded; }
set { documentLoaded = value; }
}
private void wb_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{
this.DocumentLoaded = true;
this.clientBrowser = sender as WebBrowser;
}
void clientBrowser_Navigating(object sender, WebBrowserNavigatingEventArgs e)
{
this.DocumentLoaded = false;
}
Then in the class I'm using:
while(!scraper.DocumentLoaded)
{
System.Threading.Thread.Sleep(100);
}

It sounds like you need to ensure that the page is fully loaded, like there might be a race condition. I would suggest wiring up the WebBrowser.DocumentCompleted event, and then attempting your scrapping logic.
Update
I overlooked this initially, this certainly has something to do with your issue. The line where you are invoking a click, like so scraper.clientBrowser.Document.GetElementById(order).InvokeMember("Click");. This is done in the iteration, which will more than likely manipulate the DOM -- will it not? I suggest going about this problem entirely different. What are you trying to achieve exactly, (not how you're trying to do it)?
With this alone, I would suggest that you refer to this SO Q/A and look at how they're waiting for the click to finish.

Only one thing I can guest here:
When you uncomment MessageBox.Show, at the time the message box show the info, the clientBrowser use this time to finish loading page. Then when you press OK on message box, the page is load completed, so you get the result. When you comment it, you dont wai for page loaded, so the result is diffent.

Collection was modified in foreach loop C#

I know there are MANY similiar questions, but I can't seem to get to the bottom of this.
In my program I execute a verification method which should compare two ascii HEX files with eachother (one is local, the other is read from a USB device). Some code:
private void buttonVerify_Click(object sender, EventArgs e)
{
onlyVerifying = true;
Thread t = new Thread(verifyProgram);
}
private void verifyProgram()
{
verifying = true;
externalFlashFile.Clear();
// After this method is finished, the returned data will end up in
// this.externalFlashFile since this listen to the usb's returned data
hexFile.readExternalFlashForVerify(usbDongle, autoEvent);
externalFlashFile.RemoveAt(0);
//externalFlashFile.RemoveAt(externalFlashFile.Count - 1);
hexFile.verifyProgram(externalFlashFile);
}
public void verifyProgram(List<string> externalProgram)
{
byte[] originalFile = null; // Will be modified later with given size
byte[] externalFile = new byte[4096];
int k = 0, errors = 0;
// Remove last line which contains USB command data
externalProgram.RemoveAt(externalProgram.Count - 1);
foreach (String currentLine in externalProgram)
{
for (int i = 0; i < 64; i += 2)
{
string currentDataByte = currentLine.Substring(i, 2);
externalFile[k] = Convert.ToByte(currentDataByte, 16);
k++;
}
progress += steps;
}
//... compare externalFile and originalFile
When executing the readExternalFlashForVerify the USB is responding with requested data. This data is parsed and calls an eventhandler:
public void usbDongle_OnDataParsed(object sender, EventArgs e)
{
if (verifying)
{
usbDongle.receivedBytesString.Trim();
externalFlashFile.Add(usbDongle.receivedBytesString.Substring(2, 32 * 2));
// Allow hexFile continue its thread processing
autoEvent.Set();
}
}
The first run is always completes correctly. The following executions, at the third or fourth iteration of the foreach, I get an extra element in externalProgram. This is not a global variable (argument in function call) and the function is not called anywhere else. This ofcourse throws an exception.
I tried adding .ToList() to externalProgram in the foreach but that didn't do any difference. How can my externalProgram be modified during this execution?
EDIT: I never found the cause of this, but replacing the foreach with a hard-coded for-loop solved the issue at hand. Not an optimal solution, but don't have much time on this.
// The list should never be larger than 128 items
for (int j = 0; j < 0x7f ; j++)
{
string currentLine = externalProgram[j];
// ...

Usually when you receive an exception with a message like that it is caused by multiple accesses from different threads to a list.
What I suggest you is to use a lock when you add and remove items from that list, so you're sure the indexes to that collection are not changing. You have to think what would happen if you try to remove the last element (of index 3, for example) of a collection when someone else removes a previous item (changing the lenght of the collection to 3...).
This example: Properly locking a List<T> in MultiThreaded Scenarios? describes better what I mean.

Probably this line is a problem:
externalProgram.RemoveAt(externalProgram.Count - 1);
If verifyProgram is called multiple times, it will remove more and more lines from externalProgram list passed by reference

Have MessageBox appear once (code inside timer)

UPDATE: I've managed to fix my problem. Using the code below, I moved my MessageBox AFTER my XML saving and changed the Timer from 100ms to 400ms. I now have 1 box appear, thank god. Although If anyone has a short cut to updating a single value (ActReminded) in the List array(ActListTask), that'd be great to know.
I'm having a little issue with displaying the MessageBox. Show inside a timer without it spamming me. Here's the part of the code I've been working with:
public class ActiveTasks
{
//Properties here
}
public List<ActiveTasks> ActTaskList = new List<ActiveTasks>();
for (int i = 0; i < ListActive.Items.Count; i++)
{
if (DTime.Date == newDateTime.Date)
{
if (newDateTimeLeft.CompareTo(TimeSpan.Zero) <= 0 && ActTaskList[i].ActReminded != "true")
{
MessageBox.Show("!!!!");
ActTaskList.Add(new ActiveTasks()
{
ActTitle = ActTaskList[i].ActTitle,
ActDesc = ActTaskList[i].ActDesc,
ActDate = ActTaskList[i].ActDate,
ActTime = ActTaskList[i].ActTime,
ActStatus = ActTaskList[i].ActStatus,
ActReminded = "true",
ActRepeat = ActTaskList[i].ActRepeat
});
ListActive.Items.RemoveAt(i);
ActTaskList.RemoveAt(i);
XDocument XmlActTasks = GenerateActiveListToXML(ActTaskList);
}
}
}
I actually decided I may want to hold onto the reminder status, whether it has been shown or not as I wouldn't want a repeated reminder every time the program is opened. Since I don't know of a way to update an individual part of ActTaskList I just re-added it, and then deleted the original. This code manages to recognise that if it happens, it will change the reminder status from false, to true; after I've Ok'ed all the spam. So it will stop the MessageBox once I've managed to closed all the Messageboxes. However, it doesn't stop the spam. Would it be anything to do with the fact I've set the timer to 100ms? Or could their be an alternative way to make the messagebox appear without it being inside the timer?

The odds of the current time lining up exactly to the second what is happening in your loop is small. Why not treat newDateTime as a cut off point and just set a flag?
//Declare this outside of the loop
bool hasDisplayed = false;
//Inside the timer event handler
if (!hasDisplayed && DateTime.Now >= newDateTime)
{
hasDisplayed = true;
MessageBox.Show("!!!!!!!!!!!!!");
}

Can you do something like this?
Action message = () => MessageBox.Show("!!!!!!!!!!!!!"));
object lockOb = new object();
void timer_Elapsed(object sender, ElapsedEventArgs e)
{
lock(lockOb)
if(null != message)
{
message();
message = null;
}
}

You say you've already tried a boolean indicating the message has already been shown, I'm assuming because the code probably looked like it did below.
void TimerLoop()
{
bool msgAlreadyShown;
if(!msgAlreadyShown)
{
MessageBox.Show("!!!!!!!");
}
// Other work in your timer function
}
The problem with that code is that the bool will be set to false each time the function is called by the timer. You haven't posted much code, but you've at least stated what you're trying to accomplish, a timer that checks if a reminder should be presented to the user.
I'm about to make some wild guesses about how you've put together your software, there's a good chance it's way off, but I hope it might point you in the right direction. You could have some sort of reminder class like this:
public class Reminder
{
string Message { get; set;}
DateTime Alarm { get; set; }
bool IsDismissed { get; set; }
}
I'm assuming you might want to have multiple reminders that can be checked for in the timer loop, so your timer loop could look something like:
private List<Reminder> _activeReminders; // A list of reminders
void TimerLoop(object s, ElapsedEventArgs e)
{
lock(_activeReminders)
{
var now = DateTime.Now;
foreach(var reminder in _activeReminders)
{
// only run this code if the time has passed and it hasn't already
// been shown
if(now.CompareTo(reminder.Alarm) >= 0 && !reminder.IsDismissed)
{
MessageBox.Show(reminder.Message);
reminder.IsDismissed = true;
}
}
}
}
This is a pretty naive implementation, since you probably don't want to hold onto the reminders for forever and the reminders are never removed from the _activeReminders list, but you essentially just need to add some sort of state to determine if the reminder has already been shown.
Of course, this isn't a complete example either, since I never new up the _activeReminders field or add anything to it, but I think this might help get the idea of what you need to do across. Also, you might not care about multiple reminders, and your timer code could look nothing like this. The main idea was to show you how you can keep track of the state of a reminder, and tailor it to your own code. The above was just an example.
Also, I haven't actually tested it, so treat it more like pseudocode than anything else. However, the logic is sound, and should it should only cause the message box to appear once.

C# and Winforms TextBox control: How do I get the text change?

I have an event handler for the TextBox.TextChanged event on a form of mine. In order to support undo, I'd like to figure out exactly what has changed in the TextBox, so that I can undo the change if the user asks for it. (I know the builtin textbox supports undo, but I'd like to have a single undo stack for the whole application)
Is there a reasonable way to do that? If not, is there a better way of supporting such an undo feature?
EDIT: Something like the following seems to work -- are there any better ideas? (It's times like this that I really wish .NET had something like the STL's std::mismatch algorithm...
class TextModification
{
private string _OldValue;
public string OldValue
{
get
{
return _OldValue;
}
}
private string _NewValue;
public string NewValue
{
get
{
return _NewValue;
}
}
private int _Position;
public int Position
{
get
{
return _Position;
}
}
public TextModification(string oldValue, string newValue, int position)
{
_OldValue = oldValue;
_NewValue = newValue;
_Position = position;
}
public void RevertTextbox(System.Windows.Forms.TextBox tb)
{
tb.Text = tb.Text.Substring(0, Position) + OldValue + tb.Text.Substring(Position + NewValue.Length);
}
}
private Stack<TextModification> changes = new Stack<TextModification>();
private string OldTBText = "";
private bool undoing = false;
private void Undoit()
{
if (changes.Count == 0)
return;
undoing = true;
changes.Pop().RevertTextbox(tbFilter);
OldTBText = tbFilter.Text;
undoing = false;
}
private void UpdateUndoStatus(TextBox caller)
{
int changeStartLocation = 0;
int changeEndTBLocation = caller.Text.Length;
int changeEndOldLocation = OldTBText.Length;
while (changeStartLocation < Math.Min(changeEndOldLocation, changeEndTBLocation) &&
caller.Text[changeStartLocation] == OldTBText[changeStartLocation])
changeStartLocation++;
while (changeEndTBLocation > 1 && changeEndOldLocation > 1 &&
caller.Text[changeEndTBLocation-1] == OldTBText[changeEndOldLocation-1])
{
changeEndTBLocation--;
changeEndOldLocation--;
}
changes.Push(new TextModification(
OldTBText.Substring(changeStartLocation, changeEndOldLocation - changeStartLocation),
caller.Text.Substring(changeStartLocation, changeEndTBLocation - changeStartLocation),
changeStartLocation));
OldTBText = caller.Text;
}
private void tbFilter_TextChanged(object sender, EventArgs e)
{
if (!undoing)
UpdateUndoStatus((TextBox)sender);
}

You might be better off using the Enter and Leave events instead. When entering, store the current text in a class variable, then when leaving compare the new text to the old.

Yes, don't tie it directly to the textbox. Your forms' state should be in some model object somewhere that isn't directly tied to the form (MVC is one way to do this, MVVM is another). By decoupling them like that, you can compare the new textbox value to the current model value whenever a change request comes in.

Actually, all I can think of is having some kind of collection where you store different string versions (so you can undo many times, not just once).
I would store the reference to TextBox's collections in TextBox.Tag, so it is straightforward to store/use it.
Last but not least, you update your collection of strings during the event TextChange. With no much work, you can maintain a full history, gettinjg the previous value from your own structure.

This is probably overkill for what you're trying to accomplish, but CSLA support n-level undo. CSLA is a great business objects framework written by Rocky Lhotka. The business objects handle the undo history and it flows to the UI through data binding.
Switching your app to use CSLA would be a big commitment, but another option would be to look through the freely available source code to see how he implemented it.

I am actually making an own Syntax-Highlight-System so I also need to know the changed text.
My solution is to watch for an enter or space or an depositioning of the cursor.
As WinForms provide the Keydown event I used the KeyEventArguments (e) and converted them to a char.
After that I storage the char into a string like :
string i="";
i+=convertedToChar; // convertedToChar = kc.ConvertToString(e.KeyData)
And as soon as there is a enter or space or depositioning - "event" I delete the string.
Result:
If a user enters a few chars and hit space I am able to read the last chars (till the last space).
An advantage would be the fact that you can use any delimiter char for that (as soon as they are storaged and provided by e.KeyCode)
However I hope that this is a solution for everybody watching this after 9years :D.
It´s never too late.