I can't stop my app because I have a while loop, so the gui doesn't let me click the stop button, it looks something like:
private void btnStart_Click(object sender, EventArgs e)
{ while(true)
{
//some code here
}
}
//some methods here
private void btnStop_Click(object sender, EventArgs e)
{
Application.Exit();
}
Firstly if you're running some sort of long running background job then you should not be doing that in the UI thread, because as you state, you cannot then do anything else in the UI thread to stop the loop. You'll need to defer that work to a secondary thread, or a timer, or something outside of the context of the UI thread. You can Google many different ways to achieve this.
Secondly, if you need to stop the loop then change the while condition for the loop from true to some other monitorable condition, e.g. a variable called keepRunning, which you can then set from within the btnStop_Click method. Of course if you adopt my advice in the first point then there may be some other way to stop the loop from running, e.g. if it's a timer then you can stop that timer in the appropriate way.
Thirdly, you should wait for the background operation to stop before closing the application.
Related
I am using C#,.Net4.0 and Visual Studio 2010 and I am trying to get this behaviour from my windows form application when the user click on a button:
A GUI LED starts to blink
A long rung operation starts
When the operation at point 2 ends the LED stops blinking
private void Btn_WebService_Click(object sender, EventArgs e)
{
Thread_Blink = new Thread(() => { LED_Blink(LED.WS); });
Thread_Blink.Start();
// Do something that takes time.. Let's imulate with a sleep
Thread.Sleep(2000);
Thread_Blink.Abort();
}
I also tried using 3 different events and/or timers..
private void Btn_WebService_MouseDown(object sender, MouseEventArgs e)
{
Timer_Blink.Enabled = true;
}
private void Btn_WebService_Click(object sender, EventArgs e)
{
// Do something that takes time.. Let's imulate with a sleep
Thread.Sleep(2000);
}
private void Btn_WebService_MouseUp(object sender, MouseEventArgs e)
{
Timer_Blink.Enabled = false;
}
The result is always the same: The LED starts to blink only AT THE END of the long running operation (Thread.Sleep(2000);) and suddenly STOPS so that you can't see anything. Why does this happen and how can I get the desired behaviour?
I add further infos. I tried to use BackgroundWorked and implemented the wanted behavour in this way:
private void Btn_WebService_Click(object sender, EventArgs e)
{
BlinkWorker.RunWorkerAsync(LED.WS);
LedOn(LED.WS);
TestWebService(); // This method takes about 2 seconds to answer..
LedOff(LED.WS);
BlinkWorker.CancelAsync();
}
While the TestWebService() is running I get the LED off(LedOn(LED.WS);). When the TestWebService()has finished the LED comes on.
The BlinkWorker still does not work if started and cancelled inside the Click event.
FYI: If I make a button that starts the blinking and another button that stops it, it works perfectly.
The problem is, you're tying up the UI thread inside that Thread.Sleep. The UI thread is special - it's the only one that can make changes to the UI - so whilst it's busy sleeping, it's not able to service any attempts from your BackgroundWorker or LED_Blink timer callback to change the UI state.
So, you need to not tie up the UI thread. You need to put the Thread.Sleep code (or it's actual real equivalent) into the BackgroundWorkers DoWork handler, or use other means to avoid blocking the UI thread.
Common approaches today would be to make use of async/await if the real work you're trying to do already offers an asynchronous alternative (e.g. await Task.Delay(2000); would be the equivalent of your current Thread.Sleep(2000);). Unfortunately, using async and await would require you to move to a later version of .NET/Visual Studio - but you ought to be considering that anyway. 2010 is quite dated (and also, IMO, probably the worst one to stop on - it was notoriously slow), and .NET 4.0 (as opposed to .NET 4.5.2 or later) is no longer supported.
I would propose that you take a look at the BackgroundWorker class and the ReportProgress method.
I'm trying to use background worker to update a text label continuously, but for DoWork, if no loop used, it will only execute once, but if infinite loop is used, it freezes the GUI, any idea to solve this? Really appreciate!!! I'm pretty new to C# and still trying to learn.
Here's my code:
This in the main form:
backgroundWorkerX.DoWork += backgroundWorkerX_DoWork;
backgroundWorkerX.ProgressChanged += backgroundWorkerX_ProgressChanged;
backgroundWorkerX.WorkerReportsProgress = true;
backgroundWorkerX.RunWorkerAsync();
Then:
public void backgroundWorkerX_DoWork(object sender, DoWorkEventArgs e)
{
X = -(RSSI_PI1_ST1);
backgroundWorkerX.ReportProgress(X);
}
public void backgroundWorkerX_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
label9.Text = e.ProgressPercentage.ToString();
}
public void backgroundWorkerX_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
}
[...] if no loop used, it will only execute once
This is the expected behavior. It will do the thing it's expected and then call RunWorkerCompleted.
[...] but if infinite loop is used, it freezes the GUI.
You don't present a loop in your question. So I'll make an assumption and will give you an educated guess that it actually consumes all the CPU, and therefore crashes the GUI.
// I assume that you loop like this somehow.
do
{
X = -(RSSI_PI1_ST1);
backgroundWorkerX.ReportProgress(X);
} while (true);
Try to add something to "slow it down" once in a while. Otherwise it will just run and run as fast as possible, and therefore consume all the CPU available. Remember that everytime you use ReportProgress it will be rendered by the GUI-thread. And this will execute very often and not leave a lot of resources for the GUI thread to respond to other things. Below I use Thread.Sleep, which will pause the thread for half a second. But remember that you will only want to do this in a background thread.
do
{
X = -(RSSI_PI1_ST1);
backgroundWorkerX.ReportProgress(X);
Thread.Sleep(500);
} while (true);
I would also consider doing this another way. If you actually have the need of pausing the thread, you might as well do it with a Timer. Thread.Sleep will lock the thread, and may therefore not be what you really want. From this answer:
Process() // method to be called after regular interval in Timer
{
// lengthy process, i.e. data fetching and processing etc.
// here comes the UI update part
Dispatcher.Invoke((Action)delegate() { /* update UI */ });
}
In my solution I got a user interface where some word automation is started by a buttonclick (lets call that button wordStart). I want to break this word automation with another buttonclick (lets call that button wordBreak).
However when I click the wordStart the user interface freezes while doing the work and it's not possible for me to click the wordBreak button.
I'm still a bit new to programming so for me this must be because the application is single threaded or atleast I could solve it with multithreading.
So this is a 2 in 1 question.
1. Is it possible to stop the execution of code with a single threaded application?
2. How do I stop the execution of code?
For question number 2 I looked a bit around the internet and found these methods which I think will work, but other suggestions are welcome:
Application.Exit
Application.Shutdown
Environment.Exit
EDIT:
As I thought this should be done with multi threading. I don't have that much experience with that so I've added this code to the question if anyone would like to help me out here. In the meantime I will look for a solution to this myself.
private void generateButton_Click(object sender, EventArgs e)
{
//Thread or backgroundworker should handle this event?
commandsChosed(); //Event to be throwed - this starts the word automation
}
private void stopButton_Click(object sender, EventArgs e)
{
//Stop/pause the working thread
}
No, by using only a single thread it gets blocked until the execution is finished. If you want to be able to cancel/pause it, you need to use another thread for the operation. For instance you can use BackgroundWorker.
Just wanted to post my answer to my own question here in case anyone had a similar problem.
As suggested by others on this question I wasn't able to implement it with a backgroundworker since it doesn't allow OLE functions like use of clipboard and such - but this is specific for what my thread is handling. A backgroundworker could definitely be useful in a lot of situations - but it can't be set to STA since it's from the threadpool.
Thread workerThread;
private void generateButton_Click(object sender, EventArgs e)
{
generateButton.Visible = false;
stopButton.Visible = true;
//Setting up a background thread
workerThread = new Thread(new ThreadStart(handleGenerateButtonClick));
workerThread.SetApartmentState(ApartmentState.STA); //In STA state the thread can use OLE functions like clipboard and handle some UI components as well.
workerThread.IsBackground = true; //It shuts down if the mainthread shuts down
workerThread.Start();
try
{
//Checking whether the currentThread is not the workerThread before blocking the currentThread until workerThread has terminated
if (Thread.CurrentThread != workerThread)
{
//Wait until workerThread has terminated
workerThread.Join();
}
//Sets the window buttons after workerThread has finished
if (!workerThread.IsAlive)
{
generateButton.Visible = true;
stopButton.Visible = false;
}
}
catch
{
}
}
private void stopButton_Click(object sender, EventArgs e)
{
generateButton.Visible = true;
stopButton.Visible = false;
//Stops the worker thread
workerThread.Abort();
}
I've got a GUI interface which has a start and a cancel button. After starting, the main thread which is the GUI thread, is creating a second thread which will do the actual work. When pressing the cancel button, all it does is set a boolean value which tells the working thread to stop its work and end. The problem is that the main GUI thread remain stuck even though I'm sure that the working thread has finished what it was doing. Why is that?
Here is some of the code:
private Thread workerThread;
private SomeClass fs;
private void buttonSearch_Click(object sender, EventArgs e)
{
//do some initializations
fs = new SomeClass();
workerThread = new Thread(fs.WorkMethod);
workerThread.Start();
}
private void buttonCancel_Click(object sender, EventArgs e)
{
fs.StopWork();
workerThread.Join();
}
inside SomeClass:
private bool keepWorking;
public void StopWork()
{
keepWorking= false;
}
public void WorkMethod()
{
if (keepWorking)
{
//do some stuff with recursion
}
}
does someone know why won't the main thread wake up after calling join?
I have also tried debugging to see what happens if I change the keepWorking variable to false manually and the method does reach its' end.
Your WorkMethod has a call to Invoke in there that is invoking a delegate to run on the UI thread and then block until it finishes. Since your UI thread is currently blocking on the call to Join waiting for the background thread, the UI thread is unable to call that delegate.
You now have both threads each waiting on the other, and no progress is being made. This is called a "deadlock".
Also, keepWorking should be marked as volatile as it's being accessed from multiple threads; as it stands the background thread can be accessing an outdated/cached value of that variable for quite some time after the main thread changes it. Marking it as volatile prevents the runtime from making such optimizations.
The solution here is to not block the UI thread with a call to Join. If you need to have some code execute when the background thread ends then you'll need to asynchronously fire that code when the thread finishes instead of synchronously blocking.
I am a newbie in .net world so i am facing some problem,please help me out, here is one of them,I have a for loop and i have a backgroundWorker control and a progressBar Control and also have 1 button that id:"btnPause".So my requirement is when my form will load the peogressbar will show the progress how much it has completed ,whenever i click on the button(btnPause) the button text need to b change and set the text as pause, then whenever i clicked again on that button it need to be resume from the value it got paused.Please help me.
Thanks in advance.
My approach to this would be to use a boolean flag to let me know whether or not the operation is paused (and perhaps a second one letting me know whether or not the operation is cancelled). When the user presses the pause button, you set the IsPaused flag to true so that when the worker begins processing the next item, it can check this flag and know to go into a wait state.
There are a few ways to keep the BackgroundWorker in this paused state. My approach would be to use a ManualResetEvent. This allows the BackgroundWorker thread to enter a sleep state and come out when the event is set. I think this is better than using a while loop with a sleep body because the thread stays asleep until the event is set, rather than waking up to check if it should still be asleep. When the user wishes to continue, it can set this event and let the Background worker continue.
So the code would look a little like this:
private void backgroundWorker_doWork(object sender, DoWorkEventArgs args)
{
//Initialize any pre-work stuff here.
while(!finished)
{
if (Paused)
m_evtPause.WaitOne();
if (Cancelled)
break;
//lengthy thread procedure code.
}
}
Try to use this
class MyWorkerClass
{
volatile bool m_bPaused = false;
// Public property to control worker execution
public bool Paused
{
get { return m_bPaused; }
set { m_bPaused = value; }
}
long ThreadFunc (BackgroundWorker worker, DoWorkEventArgs e)
{
...
// While Paused property set to true
while (m_bPaused)
{
// Pause execution for some time
System.Threading.Thread.Sleep (100);
}
}
}