Develop Reference

Why don't delays work when I'm attempting to flash an error message?

Problem: I'm working on a calculator as my first MVVM application and have come across an interesting problem that I would like to understand better. My noob problem is that I'm trying to flash an error message for an invalid input--in this case I don't want the user to use the negate operator in an invalid location. In order to flash the message across the screen, I'm saving the display in another variable, setting the display to say "Invalid Operation", then I'd like to delay for half a second and reset the display to what it was before (from the temp variable). My problem is that the display variable gets set but the actual display doesn't update to show the error message, no matter how long the delay is.
I've tried both blocking (Thread.Sleep) and non-blocking delays (Task.Delay) within the function, writing separate functions to set and reset the display, and delaying within the Negate function instead, but none of these attempts allow the display to update. The display works as expected when adding and deleting characters in other parts of the code, so I don't think there's an issue with that.
Is this some sort of piping issue (the delay function actually starts before it can call the Display property) or something else entirely? I've checked other posts on here and those solutions don't seem to solve my issue. I'd love feedback on why this doesn't work as I'd expect it to as well as more efficient/effective ways to code this. Here are the relevant code blocks:
public void Negate()
{
if (Display.Length > 0)
{
if (Display[Display.Length - 1].Equals('-'))
{
Display = Display.Substring(0, Display.Length - 1);
}
else if (Display[Display.Length - 1].Equals(' ') || Display[Display.Length - 1].Equals('(') ||
Display[Display.Length - 1].Equals('E') || Display[Display.Length - 1].Equals('^'))
{
Display += '-';
}
else
{
InvalidOperation();
}
}
else
{
Display = "-";
}
}
public void InvalidOperation()
{
tempDisplay = Display;
Display = "Invalid Operation";
Thread.Sleep(500);
Display = tempDisplay;
}
public string Display
{
get
{
return _display;
}
set
{
_display = value;
OnPropertyChanged();
}
}

UI will be updated only after method InvalidOperation execution is complete, so because in last line of the method you set value back to original - there are no updates in UI.
Asynchronous approach should work, because await operator will "pause" InvalidOperation method and return execution to the message loop which will update UI controls.
public async Task InvalidOperation()
{
tempDisplay = Display;
Display = "Invalid Operation";
await Task.Delay(2000);
Display = tempDisplay;
}

Find out which winforms controls are accessed from a background thread

We have built a huge winforms project, already in progress for multiple years.
Sometimes, our users get an exception which looks like this one.
The resolution of this problem seems to be:
don't acces UI components from a background thread
.
But since our project is a very big project with a lot of different threads, we don't succeed in finding all these.
Is there a way to check (with some tool or debugging option) which components are called from a background thread?
To clarify:
I created a sample winforms project with a single Form, containing two Button
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
button1.Text = "Clicked!";
}
private void button2_Click(object sender, EventArgs e)
{
Task.Run(() =>
{
button2.BackColor = Color.Red; //this does not throw an exception
//button2.Text = "Clicked"; //this throws an exception when uncommented
});
}
}
The background color of button2 is set to red when the button is clicked. This happens in a background thread (which is considered bad behavior). However, it doesn't (immediately) throw an exception. I would like a way to detect this as 'bad behavior'. Preferably by scanning my code, but if it's only possible by debugging, (so pausing as soon as a UI component is accessed from a background thread) it's also fine.

I've got 2 recommendations to use together, the first is a Visual Studio Plugin called DebugSingleThread.
You can freeze all the threads and work on one at a time (obviously the non-main-UI threads) and see each threads access to controls. Tedious I know but not so bad with the second method.
The second method is to get the steps in order to reproduce the problem. If you know the steps to reproduce it, it will be easier to see whats causing it. To do this I made this User Action Log project on Github.
It will record every action a user makes, you can read about it here on SO: User Activity Logging, Telemetry (and Variables in Global Exception Handlers).
I'd recommend you also log the Thread ID, then when you have been able to reproduce the problem, go to the end of the log and work out the exact steps. Its not as painful as it seems and its great for getting application telemetry.
You might be able to customise this project, eg trap a DataSource_Completed event or add a dummy DataSource property that sets the real Grids DataSource property and raises an INotifyPropertyChanged event - and if its a non-main thread ID then Debugger.Break();.
My gut feeling is you're changing a control's (eg a grid) data source in a background thread (for that non-freeze feel) and thats causing a problem with synchronisation. This is what happened to the other DevExpress customer who experienced this. Its discussed here in a different thread to the one you referenced.

Is your app set to ignore cross threading intentionally?
Cross-thread operations should be blowing up all the time in winforms. It checks for them like crazy in just about every method. for a starting point check out https://referencesource.microsoft.com/#System.Windows.Forms/winforms/Managed/System/WinForms/Control.cs.
Somewhere in your app, somebody might have put this line of code:
Control.CheckForIllegalCrossThreadCalls = False;
Comment that out and run the app, then follow the exceptions.
(Usually you can fix the problem by wrapping the update in an invoke, e.g., in a worker thread if you see textbox1.text=SomeString; change it to `textbox.invoke(()=>{textbox1.text=SomeString;});.
You may also have to add checking for InvokeRequired, use BeginInvoke to avoid deadlocks, and return values from invoke, those are all separate topics.
this is assuming even a moderate refactor is out of the question which for even a medium sized enterprise app is almost always the case.
Note: it's not possible to guarantee successful discovery of this case thru static analysis (that is, without running the app). unless you can solve the halting problem ... https://cs.stackexchange.com/questions/63403/is-the-halting-problem-decidable-for-pure-programs-on-an-ideal-computer etc...

I did this to search for that specific situation but of course, need to adjust it to your needs, but the purpose of this is to give you at least a possibility.
I called this method SearchForThreads but since it's just an example, you can call it whatever you want.
The main idea here is perhaps adding this Method call to a base class and call it on the constructor, makes it somewhat more flexible.
Then use reflection to invoke this method on all classes deriving from this base, and throw an exception or something if it finds this situation in any class.
There's one pre req, that is the usage of Framework 4.5.
This version of the framework added the CompilerServices attribute that gives us details about the Method's caller.
The documentation for this is here
With it we can open up the source file and dig into it.
What i did was just search for the situation you specified in your question, using rudimentary text search.
But it can give you an insight about how to do this on your solution, since i know very little about your solution, i can only work with the code you put on your post.
public static void SearchForThreads(
[System.Runtime.CompilerServices.CallerMemberName] string memberName = "",
[System.Runtime.CompilerServices.CallerFilePath] string sourceFilePath = "",
[System.Runtime.CompilerServices.CallerLineNumber] int sourceLineNumber = 0)
{
var startKey = "this.Controls.Add(";
var endKey = ")";
List<string> components = new List<string>();
var designerPath = sourceFilePath.Replace(".cs", ".Designer.cs");
if (File.Exists(designerPath))
{
var designerText = File.ReadAllText(designerPath);
var initSearchPos = designerText.IndexOf(startKey) + startKey.Length;
do
{
var endSearchPos = designerText.IndexOf(endKey, initSearchPos);
var componentName = designerText.Substring(initSearchPos, (endSearchPos - initSearchPos));
componentName = componentName.Replace("this.", "");
if (!components.Contains(componentName))
components.Add(componentName);
} while ((initSearchPos = designerText.IndexOf(startKey, initSearchPos) + startKey.Length) > startKey.Length);
}
if (components.Any())
{
var classText = File.ReadAllText(sourceFilePath);
var ThreadPos = classText.IndexOf("Task.Run");
if (ThreadPos > -1)
{
do
{
var endThreadPos = classText.IndexOf("}", ThreadPos);
if (endThreadPos > -1)
{
foreach (var component in components)
{
var search = classText.IndexOf(component, ThreadPos);
if (search > -1 && search < endThreadPos)
{
Console.WriteLine($"Found a call to UI thread component at pos: {search}");
}
}
}
}
while ((ThreadPos = classText.IndexOf("Task.Run", ++ThreadPos)) < classText.Length && ThreadPos > 0);
}
}
}
I hope it helps you out.
You can get the Line number if you split the text so you can output it, but i didn't want to go through the trouble, since i don't know what would work for you.
string[] lines = classText.Replace("\r","").Split('\n');

Try that:
public static void Main(string[] args)
{
// Add the event handler for handling UI thread exceptions to the event.
Application.ThreadException += new ThreadExceptionEventHandler(exception handler);
// Set the unhandled exception mode to force all Windows Forms errors to go through the handler.
Application.SetUnhandledExceptionMode(UnhandledExceptionMode.CatchException);
// Add the event handler for handling non-UI thread exceptions to the event.
AppDomain.CurrentDomain.UnhandledException += // add the handler here
// Runs the application.
Application.Run(new ......);
}
Then you can log the message and the call stack and that should give you enough information to fix the issue.

I recommend you update your GUI to handle this situation automatically for your convenience. You instead use a set of inherited controls.
The general principle here is to override the property Set methods in a way to make them Thread Safe. So, in each overridden property, instead of a straight update of the base control, there's a check to see if an invoke is required (meaning we're on a separate thread the the GUI). Then, the Invoke call updates the property on the GUI thread, instead of the secondary thread.
So, if the inherited controls are used, the form code that is trying to update GUI elements from a secondary thread can be left as is.
Here is the textbox and button ones. You would add more of them as needed and add other properties as needed. Rather than putting code on individual forms.
You don't need to go into the designer, you can instead do a find/replace on the designer files only. For example, in ALL designer.cs files, you would replace System.Windows.Forms.TextBox with ThreadSafeControls.TextBoxBackgroundThread and System.Windows.Forms.Button with ThreadSafeControls.ButtonBackgroundThread.
Other controls can be created with the same principle, based on which control types & properties are being updated from the background thread.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Forms;
namespace ThreadSafeControls
{
class TextBoxBackgroundThread : System.Windows.Forms.TextBox
{
public override string Text
{
get
{
return base.Text;
}
set
{
if (this.InvokeRequired)
this.Invoke((MethodInvoker)delegate { base.Text = value; });
else
base.Text = value;
}
}
public override System.Drawing.Color ForeColor
{
get
{
return base.ForeColor;
}
set
{
if (this.InvokeRequired)
this.Invoke((MethodInvoker)delegate { base.ForeColor = value; });
else
base.ForeColor = value;
}
}
public override System.Drawing.Color BackColor
{
get
{
return base.BackColor;
}
set
{
if (this.InvokeRequired)
this.Invoke((MethodInvoker)delegate { base.BackColor = value; });
else
base.BackColor = value;
}
}
}
class ButtonBackgroundThread : System.Windows.Forms.Button
{
public override string Text
{
get
{
return base.Text;
}
set
{
if (this.InvokeRequired)
this.Invoke((MethodInvoker)delegate { base.Text = value; });
else
base.Text = value;
}
}
public override System.Drawing.Color ForeColor
{
get
{
return base.ForeColor;
}
set
{
if (this.InvokeRequired)
this.Invoke((MethodInvoker)delegate { base.ForeColor = value; });
else
base.ForeColor = value;
}
}
public override System.Drawing.Color BackColor
{
get
{
return base.BackColor;
}
set
{
if (this.InvokeRequired)
this.Invoke((MethodInvoker)delegate { base.BackColor = value; });
else
base.BackColor = value;
}
}
}
}

Control.InvokeRequired changing throughout a method

Look at these screenshots. First shows a breakpoint in my code and shows current value of InvokeRequired.
Seconds screenshot shows value of InvokeRequired after pressing F10 (step over) one time in debugger (IF statement content is not entered, ELSE is).
What happens next, is InvalidOperationException on rtbOutput, because I try to change its fields in ReportProgress. Here is how I call OnProgressReported:
public event EventHandler<BuildProgressEventArgs> BuildProgresReported = delegate { };
public void InvokeReportBuildProgress(BuildProgress progress)
{
BuildProgresReported.Invoke(this, new BuildProgressEventArgs(progress));
}
How is this even possible? Is there other, better way to detect if Invoke should be called?
Update:
I have changed method code to the following:
public void OnProgressReported( object caller, BuildProgressEventArgs progressEventArgs )
{
if( rtbOutput.InvokeRequired )
{
Debug.WriteLine($"Invoke was required on thread: #{Thread.CurrentThread.ManagedThreadId} named '{Thread.CurrentThread.Name}'");
rtbOutput.BeginInvoke( new Action( () => OnProgressReported(caller, progressEventArgs) ) );
}
else
{
Debug.WriteLine($"Invoke was NOT required on thread: #{Thread.CurrentThread.ManagedThreadId} named '{Thread.CurrentThread.Name}'");
if ( this.IsDisposed )
{
throw new InvalidOperationException( "This form has been disposed" );
}
rtbOutput.Text = "abc";
rtbOutput.Text = "xxx";
//ReportProgress(progressEventArgs.Progress);
}
}
The only output is
Invoke was NOT required on thread: #15 named ''
and the method this throw an exception on line rtbOutput.Text = "abc";
HOWEVER! When the line rtbOutput.Text = "xxx"; is commented out, everything works fine, even though rtbOutput.Text = "abc"; is still present!
Update #2 - solution:
The problem was a window handle that was not yet created (I subscribe to an event right AFTER creating the window) I have to wait for handle to be created using
this.IsHandleCreated

Visual Studio during Debugging: The function evaluation requires all threads to run

I'm suddenly getting a strange error while debugging. Up to now the variable in the watch windows has been showing correctly. Now I am always getting this error message in the watch windows:
The function evaluation requires all threads to run
I am not able to check any variable anymore. I am not explicitly working with threads. What can I do to get it working again?
I already disabled, as mentioned in some forums, the function: "Enable property Evaluation and other implicit function Calls" in the option window of the debugger. But without success, and it gives me this error:
Error Implicit Function evaluation disabled by the user

From the msdn forum:
This isn't an error in and of itself, but more of a feature of your debugger.
Some properties require code to be executed in order for the property to be read, but if this requires cross-thread interaction, then other threads may have to run as well. The debugger doesn't do this automatically, but certainly can, with your permission.
Just click the little evaluate icon and it will run your code and evaluate the property.
For further details on this behaviour check this excelent article

I ran into this issue when just trying to get items from a table called "AGENCY" using Entity Framework:
var agencies = db.AGENCY.OrderBy(e => e.FULLNAME);
Hovering over agencies in debug mode, clicking to expand the options, and clicking Results would give the dreaded "The function evaluation requires all threads to run" with a "Do Not Enter" icon at the end that, on which, clicking did nothing.
2 possible solutions:
Add .ToList() at the end:
var agencies = db.AGENCY_TABLE.OrderBy(e => e.FULLNAME).ToList();
List<AGENCY_TABLE> agencies = db.AGENCY_TABLE.OrderBy(e => e.FULLNAME).ToList();
Credit goes to Hp93 for helping me come to this solution. In the comments on MUG4N's answer where I found this solution, it also mentions trying .Any() instead of .ToList(), but this gives a Boolean instead of a <T>, like <AGENCY> is, so it probably wouldn't help.
Workaround - try a different path in the debug options. I found that I could click on the "Non-Public Members" > "_internalQuery" > ObjectQuery > Results View and get my values that way.

MUG4N has indeed provided a correct answer however if you hover over the line of code in debug, you may be looking at something like the below. If so, click the little re-evaluate icon highlighted in the image below...
NB: I obtained this image by pinning, normally the re-evaluate icone are in the middle of the window and not down the left hand column.

You should make thread safe call because accessing Windows form controls are not Thread safe in multithreading.
This is my simple code which makes Thread safe call and sets Progress bar.
public partial class Form1 : Form
{// This delegate enables asynchronous calls for setting
// the text property on a TextBox control.
delegate void StringArgReturningVoidDelegate(string text);
private Thread demoThread = null;
public int Progresscount = 0;
static EventWaitHandle waithandler = new AutoResetEvent(false);
public Form1()
{
InitializeComponent();
}
public static bool CheckForInternetConnection()
{
try
{
using (var client = new WebClient())
{
using (var stream = client.OpenRead("http://www.google.com"))
{
return true;
}
}
}
catch
{
return false;
}
}
public void Progressincrement()
{
waithandler.WaitOne();
while (CheckForInternetConnection()==true)
{
if (Progresscount==100)
{
break;
}
SetLabel("Connected");
Progresscount += 1;
SetProgress(Progresscount.ToString());
Thread.Sleep(TimeSpan.FromSeconds(1));
}
if (Progresscount <100)
{
Startthread();
}
SetLabel("Completed");
}
public void Startthread ()
{
this.demoThread= new Thread(new ThreadStart(Progressincrement));
this.demoThread.Start();
SetLabel("Waiting for connection");
while (CheckForInternetConnection() == false) ;
waithandler.Set();
}
private void SetLabel(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.label1.InvokeRequired)
{
StringArgReturningVoidDelegate d = new StringArgReturningVoidDelegate(SetLabel);
this.Invoke(d, new object[] { text });
}
else
{
this.label1.Text = text;
}
}
private void SetProgress(string Value)
{
// 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.progressBar1.InvokeRequired)
{
StringArgReturningVoidDelegate d = new StringArgReturningVoidDelegate(SetProgress);
this.Invoke(d, new object[] {Value});
}
else
{
this.progressBar1.Value = Convert.ToInt32(Value);
}
}
private void Form1_Load(object sender, EventArgs e)
{
Startthread();
}
private void button1_Click(object sender, EventArgs e)
{
MessageBox.Show("Responsive");
}
}
For more information MSDN

This isn't an error, but more of a feature of your debugger.
The debugger doesn't do this automatically, but certainly can, with users permission. Just click the little space icon and it will run the code and evaluate the property.

I use the next workaround to pass:
var OtherThreadField = "";
Invoke(new MethodInvoker(delegate
{
OtherThreadField = ExecuteNeededMEthod();
}));
Now i have a value for OtherThreadField.

I faced the same issue and solved .The Issue arise due to username and password ,in SQL connection there is user and password but in code there no user and password. so I enable the user and the password and the issue solved

For me, this happened when trying to break on a line that accesses a complex object instance contained by a Settings Class.
A breakpoint on the following if results in Settings.Default.FindSettings with the value being "The function evaluation requires all threads to run." If I press the force eval button, it is null. Stepping with the force eval button click or not enters the if block and initializes the object. If I remove the breakpoint and add a new breakpoint following the if block, the Settings.Default.FindSettings deserializes properly with the expected values.
if (Settings.Default.FindSettings == null)
{
Settings.Default.FindSettings = new FindSettings();
}
After trial and error, I added the following code before the above if block to access the settings prior to breaking. This seems to reliably fix the problem. I do not need it in production so I wrap in conditional compiler directive. I have a comment in the code instead of a non-descript discard:
#if DEBUG
var _ = Settings.Default.FindSettings;
#endif
I am not sure if the above line would be optimized out in production since it has side effects. As I only need it while debugging, I have not checked.

Why would this progress bar code cause the progress bar to "hang"?

In the legacy code I'm working on, there are several file retrieval steps - first this set of data, then that set of data, which update a progress bar with a label displaying which portion of the process is currently active, and the progress bar itself, of course, updates its position. One portion of all this is hanging, though, and via the use of MessageBox.Show()s (I have to do it this way, can't step through it in the debugger), I've narrowed down where the hanging is occurring, but can't figure out why it's occurring.
Warning: the following code is unorthodox and may well warrant such warning signage as "Here be Dragons" or "This way lies madness." Proceed at your own risk/beware of the peril.
MessageBox.Show("Made it just before the pbDialog code");//<-- it hangs after this is displayed
using (pbDialog = new pbDialogs())
{
ProgressBar = new frmProgress( this, true);
ProgressBar.SetProgressLabelText("Vendor/Dept/Expense Data");
typeProgress = (int)ProgressStates.ProgressQRY;
ProgressBar.label1.Text += " (Receiving)";
if( pbDialog != null )
{
pbDialog.ShowDialog( ProgressBar, this );
}
else
{
ProgressBar.ShowDialog();
}
ProgressBar = null;
evt.Set();
}
MessageBox.Show("Made it just after the pbDialog code"); //This is not seen
pbDialog is declared in the same form as this code snippet:
public pbDialogs pbDialog;
pbDialogs is a class in another form (frmProgress.cs):
public class pbDialogs : IDisposable
ProgressBar is an instance of the anonymous class defined in frmProgress.cs (frmProgress, that is to say, which derives from System.Windows.Forms.Form)
public static frmProgress ProgressBar;
typeProgress is a locally defined int:
public static int typeProgress = 0;
evt is the name of the arg passed into the method from which this snippet originates:
private void FetchVendorDepartmentData(ManualResetEvent evt)
ManualResetEvent, as you may know, is a member of System.Threading
Does anybody see anything eyebrow-raising here (besides the general unorthodoxy of it all)?
UPDATE
I added more messages:
MessageBox.Show("Made it just before the pbDialog code");//<-- it hangs after this. TODO: Remove before deploying
using (pbDialog = new pbDialogs())
{
MessageBox.Show("Made it just before ProgressBar = new frmProgress");// TODO: Remove
ProgressBar = new frmProgress( this, true);
MessageBox.Show("Made it just after ProgressBar = new frmProgress");// TODO: Remove
ProgressBar.SetProgressLabelText("Vendor/Dept/Expense Data");
typeProgress = (int)ProgressStates.ProgressQRY;
MessageBox.Show("Made it just after assignment to typeProgress");// TODO: Remove
ProgressBar.label1.Text += " (Receiving)";
if( pbDialog != null )
{
MessageBox.Show("pbDialog was not null");// TODO: Remove
pbDialog.ShowDialog( ProgressBar, this );
}
else
{
MessageBox.Show("pbDialog was null");// TODO: Remove
ProgressBar.ShowDialog();
}
ProgressBar = null;
MessageBox.Show("ProgressBar set to null");// TODO: Remove
evt.Set();
MessageBox.Show("evt.Set called");// TODO: Remove
}
MessageBox.Show("Made it just after the pbDialog code");//TODO: Remove
}
...and the last one I see is, "pbDialog was not null"
UPDATE 2
In accord with the answer from "500 - Internal Server Error," I prepended a line to show the ProgressBar:
ProgressBar.ShowDialog();
if( pbDialog != null ) . . .
...but it makes no diff; in fact, with that I don't even make it as far as without it - I don't see the "pbDialog was not null" message.
Apologies in advance to Billy Blake, but: What the hammer? What the chain? What the anvil? What dread grasp is going on here?
UPDATE 3
So apparently either of these lines cause the hang:
ProgressBar.ShowDialog(); // with this, "pbDialog was not null" is not seen
pbDialog.ShowDialog( ProgressBar, this ); // if make it to here (line above commented out), "ProgressBar set to null" is not seen.
UPDATE 4
The problem may not be in this code after all, as I found another spot in the same class that uses the exact same code, and that portion of the data retrieval completes just fine...

You are specifying that you want ProgressBar as the modal owner of pbDialog here:
pbDialog.ShowDialog( ProgressBar, this );
but it doesn't look like you've actually shown ProgressBar (the owner) yet at this point.