I am working on a project than involves making an image appear and then disappear after a fixed time. I thought that the correct function for that purpose would be Thread::Sleep() but it doesn't seem to work.
this->pictureTConf->Visible = true;
Thread::Sleep(5000);
this->pictureTConf->Visible = false;
With this code, the picture doesn't appear at any moment. Any thoughts? Thanks.
PD: Using Visual Studio, Windows forms and VC++.
Setting a member variable to true isn't enough because your call to Sleep() prevents the code from running the message loop. Try this instead: (This is just for sample purposes, you shouldn't do this in a "real" application.)
this->pictureTConf->Visible = true;
this->pictureTConf->Refresh();
Thread::Sleep(5000);
this->pictureTConf->Visible = false;
this->pictureTConf->Refresh();
Also, as Chuck pointed out, if you use a timer, you shouldn't need the calls to Refresh(). Everything will just work.
Related
I have looking at many threads about the exception "cannot pass a GCHandle across AppDomains" but I still don't get it....
I'm working with an RFID Reader which is driven by a DLL. I don't have source code for this DLL but only a sample to show how to use it.
The sample works great but I have to copy some code in another project to add the reader to the middleware Microsoft Biztalk.
The problem is that the process of Microsoft Biztalk works in another AppDomain. The reader handle events when a tag is read. But when I run it under Microsoft Biztalk I got this annoying exception.
I can't see any solution on how to make it work...
Here is some code that may be interesting :
// Let's connecting the result handlers.
// The reader calls a command-specific result handler if a command is done and the answer is ready to send.
// So let's tell the reader which functions should be called if a result is ready to send.
// result handler for reading EPCs synchronous
Reader.KSRWSetResultHandlerSyncGetEPCs(ResultHandlerSyncGetEPCs);
[...]
var readerErrorCode = Reader.KSRWSyncGetEPCs();
if (readerErrorCode == tKSRWReaderErrorCode.KSRW_REC_NoError)
{
// No error occurs while sending the command to the reader. Let's wait until the result handler was called.
if (ResultHandlerEvent.WaitOne(TimeSpan.FromSeconds(10)))
{
// The reader's work is done and the result handler was called. Let's check the result flag to make sure everything is ok.
if (_readerResultFlag == tKSRWResultFlag.KSRW_RF_NoError)
{
// The command was successfully processed by the reader.
// We'll display the result in the result handler.
}
else
{
// The command can't be proccessed by the reader. To know why check the result flag.
logger.error("Command \"KSRWSyncGetEPCs\" returns with error {0}", _readerResultFlag);
}
}
else
{
// We're getting no answer from the reader within 10 seconds.
logger.error("Command \"KSRWSyncGetEPCs\" timed out");
}
}
[...]
private static void ResultHandlerSyncGetEPCs(object sender, tKSRWResultFlag resultFlag, tKSRWExtendedResultFlag extendedResultFlag, tKSRWEPCListEntry[] epcList)
{
if (Reader == sender)
{
// Let's store the result flag in a global variable to get access from everywhere.
_readerResultFlag = resultFlag;
// Display all available epcs in the antenna field.
Console.ForegroundColor = ConsoleColor.White;
foreach (var resultListEntry in epcList)
{
handleTagEvent(resultListEntry);
}
// Let's set the event so that the calling process knows the command was processed by reader and the result is ready to get processed.
ResultHandlerEvent.Set();
}
}
You are having a problem with the gcroot<> helper class. It is used in the code that nobody can see, inside that DLL. It is frequently used by C++ code that was designed to interop with managed code, gcroot<> stores a reference to a managed object. The class uses the GCHandle type to add the reference. The GCHandle.ToIntPtr() method returns a pointer that the C++ code can store. The operation that fails is GCHandle.FromIntPtr(), used by the C++ code to recover the reference to the object.
There are two basic explanations for getting this exception:
It can be accurate. Which will happen when you initialized the code in the DLL from one AppDomain and use it in another. It isn't clear from the snippet where the Reader class object gets initialized so there are non-zero odds that this is the explanation. Be sure to keep it close to the code that uses the Reader class.
It can be caused by another bug, present in the C++ code inside the DLL. Unmanaged code often suffers from pointer bugs, the kind of bug that can accidentally overwrite memory. If that happens with the field that stores the gcroot<> object then nothing goes wrong for a while. Until the code tries to recover the object reference again. At that point the CLR notices that the corrupted pointer value no longer matches an actual object handle and generates this exception. This is certainly the hard kind of bug to solve since this happens in code you cannot fix and showing the programmer that worked on it a repro for the bug is very difficult, such memory corruption problems never repro well.
Chase bullet #1 first. There are decent odds that Biztalk runs your C# code in a separate AppDomain. And that the DLL gets loaded too soon, before or while the AppDomain is created. Something you can see with SysInternals' ProcMon. Create a repro of this by writing a little test program that creates an AppDomain and runs the test code. If that reproduces the crash then you'll have a very good way to demonstrate the issue to the RFID vendor and some hope that they'll use it and work on a fix.
Having a good working relationship with the RFID reader vendor to get to a resolution is going to be very important. That's never not a problem, always a good reason to go shopping elsewhere.
I notice Debug.Assert does not trigger in Metro apps, however, if the project is a traditional one like Console or WinForm, it does trigger. And yes, I am in Debug mode.
Is it a setting not properly set in Visual Studio (11 Beta)? Or Debug.Assert is intended to be disabled in metro apps?
I know many exceptions are swallowed during the execution of Metro apps, but Debug.Assert is so handy that I can't think of a reason why it should be disabled.
Seems like a bug. I would roll out my own assert method. Something like:
[Conditional("DEBUG")]
public static void Assert(bool condition)
{
if (!condition)
System.Diagnostics.Debugger.Break();
}
It does trigger, look in the Output window. It just doesn't automatically prompt you to ask if you want a debugger break and thus just keeps motoring.
The DefaultTraceListener.AssertUIEnabled property is false. That's an implementation problem, can't display a message box on top of Metro UI. Which does actually work but the monitor switches to the desktop, pretty undesirable when you would have liked to click No. Hard to solve and no doubt on the todo list. You can't easily get to the property to set it to true, it is inaccessible from the metadata. Filip's workaround sounds half-decent.
There is the same problem with F# in WinRT, in VS2013. The assert statement, which is an alias for System.Diagnostics.Debug.Assert, does not raise an exception, so unless you are watching the Output window then your assertions can fail without being noticed. Even if you are watching, it is hard to find the spot where the assertion was raised.
I followed Filip's suggestion and wrote a short utility, as follows:
namespace MyProj.Infrastructure
module Diagnostics =
let Assert condition = if not condition then
System.Diagnostics.Debugger.Break()
I chose Debugger.Break over raising an exception because it stops the debugger at the place the assertion fails. However, raising an exception is an acceptable alternative.
I didn't have any suitable global projects or modules already in my solution, so I had to create them just for this, which was quite annoying.
To stop my application from flickering, I tried to activate DoubleBuffering for all of my controls and subcontrols.
To achieve this, I added the follwoing codesnippet in my mainform:
protected override CreateParams CreateParams
{
get
{
CreateParams cp = base.CreateParams;
cp.ExStyle |= 0x02000000; //WS_EX_COMPOS
return cp;
}
}
The problem is, that with WindowsXP the cpu-load becomes almost 100% and keeps up. No problem on Windows7.
It looks for me, as it is the very same problem as in this question. Is there a "easy" solution in C#? Or asked in a different way -> What usually causes this behaviour? So I can find out the problem in my application.
UPDATE: Maybe some more information to help you folks help me. What I am trying to do is showing a semi-transparent form ontop of the mainform with an progressbar. This "progressBarForm" is in a second thread to have this progressbar running. On Win7 everything works fine, as mentioned above with WinXP (.net4, activated desktoptheme) there is 100% cpu-load after the progressbar was shown once - also the acutal payload-function needs much longer to complete - maybe because of the high-cpu-load done by the progressbar. Where and what should I check again? Some ideas?
Btw.: I don't think the thread is a problem, as when I show the form in the mainthread and don't refresh anything, the result (high cpu-load) is the same...
Is it possible to print in Silverlight without blocking the UI thread?
I have to print a lot of pages, and consequently my UI freezes for a while. I would like to print on a background thread instead (and update a progress bar if possible), but can't figure out how.
I tried calling the Print() method of my PrintDocument inside the DoWork() method of a BackgroundWorker, but that gives me an UnauthorizedAccessException "Invalid cross-thread access".
It seems that even initiating a PrintDocument is not possible outside the UI thread:
PrintDocument pd = new PrintDocument(); in BackgroundWorker.DoWork() throws the same exception.
I found a lot of posts where people say that printing has to happen on the UI thread, but no documentation of this. I'm new to multithreading, so any pointers in the right direction would be appreciated.
I had this problem and came across this question which unfortunately didn't have the answer i was hoping for. But I thought that for anyone else who comes across this problem, this may at least shed some light.
I was following this article on printing in Silverlight, It works like a charm for regular printing on the UI Thread, but for actually trying to print on a separate thread I don't think it's possible. I switched out the last line of code in the example
printDocument.Print("SLPrintDemo document");
with an alternate one to see if it would work
new Thread(() => printDocument.Print("SLPrintDemo document")).Start();
To see if the print job itself would spawn in a separate thread. However though the code compiles and runs fine, the document does not print. The reason seems to be that once the Print command is fired, it then fires up the printing options dialog for choosing printer and other options etc. At this point it is no longer on the UI thread so nothing happens ( No exceptions, so i'm assuming they're swallowed somewhere)
So as far as I can tell at the moment, there is no way to print in Silverlight that is not in the UI thread.
Use Dispatcher for updating your UI. For example:
Dispatcher.BeginInvoke(() =>
{
ProgressBar.Value = 100;
});
I am developing a Windows forms application which connects to a piece of hardware, acquires a lot of data (~1 GSample/sec), processes it, and spits it out to the screen upon a button click. I am now trying to automate the process in a loop that can be started/stopped at any time so I can monitor it whilst tweaking the input to the acquisition hardware. I thinks it's clear that I need to do this on a separate thread, but I'm having a heck of a time trying to do this in c++/cli - I have found a number of good examples using MFC, which is not supported by Express.
Specifically: My task is to press a button which is handled in Form1.h, to call a function in my main file Acquisition.cpp which contains the following code (currently an infinite loop)
void Form1::realTimeUpdate()
{
// live is a boolean variable set by a button on the form
while(live)
{
displayVariance(getVar(getQuadratures(100),nbrSamples));
}
}
I wish to execute this code in a separate thread so that the main program can listen for the user request to stop the operation. Without threading, I currently have to forcefully quit the program (or set it to run a fixed number of times) to stop it.
Is there any suggestions how I might go about running this code on a separate thread?
I've (unsuccessfully) tried a few things already:
Modifying the example given in This Microsoft Example. Problem: requires /clr:oldSyntax option which is incompatible with the other 1300 lines of code in the program.
Trying to do what I'd do in Java (Declare a global thread and start/stop it from any point in the code. Problem: Compiler won't let me declare a global System::Threading.Thread
this beautiful example. Problem: Requires MFC.
Any suggestions would be greatly appreciated!
You can use a BackgroundWorker or a Thread to handle this. You'll need to make sure that the portion of your work that updates the UI is marshaled back to the UI thread, however.
Here is a tutorial on threading in C++/CLI.
For the record, upon Reed's suggestion about using a BackgroundWorker, I sifted through the code at the bottom of this page and modified my code so that:
It created a new backgroundWorker BGWorker in which BGWorker->DoWork() called my realTimeUpdate() function.
A button on the main Form calls either RunWorkerAsync() or CancelAsync() depending on whether or not the process is running (checked by a boolean flag in my main program).
The realTimeUpdate() function is now passed a BackgroundWorker - realTimeUpdate(BackgroundWorker^ worker, DoWorkEventArgs ^ e) After each calculation is complete within the internal loop, it calls worker->ReportProgress(result) function. In the BGWorker->ProgressChanged() function a separate function, upDataUI(int) draws the result on the main form.
Thanks again for the help.