I am working on Windows Forms application, that needs to start a big amount of async tasks. In other words, a small control panel, that will start and monitor the process (Task), started from this UI control panel.
But, after some researches, I realized, that there is no easy way to monitor variables' values from inside the Task.
Currently, I am looking for any way of monitoring progress in Task<>. Thinked, that I might start minimized process (Just basically copy&paste the whole code from task, that I need to start to a ConsoleApp, but, as always, that is not easy to catch the data from variables).
Any thoughts, how to do it correctly?
And found IProgress interface, but I didn't actually get the idea how it works. Just no examples.
Related
I have a Windows app that basically calls other classes and within thise stored procedures and ultimately creates a csv file of a lot of info. I need a progress bar that just runs until its done so the user can see something is happening. I have scoured the internet and cant seem to get this to work. I just want the bar to start running on a button click. Why does this seem so difficult? The closest I got is just starting the bar in marquee but it wont "start" until after the object has been filled which does me no good, I need it to start while the object is being filled. This is being done in C#. Any ideas?
You need to run the long running task in a separate thread so that the UI can update while the task runs.
See Windows Forms ProgressBar: Easiest way to start/stop marquee? for an example of setting this up.
I’ve got a process which will take a little under 5 seconds to complete. The user will most likely notice the program flicker for a few seconds after pushing the “go” button.
My question is:
Is this something that would normally be dumped onto a background worker, or is there another .NET method for handling small tasks, or is this something that shouldn’t be a concern?
FYI:
The process opens a user specified excel file, processes an unknown number of lines (max 1.5 million due to excel I believe), and queries a database (very quick query). So at the worst case scenario the user uploads a 1.5 million row excel file and is running on a very slow internet connection.
If you don't want the user to be able to do anything while the file is being uploaded, then you don't need to put it on a different thread.
If you want the user to be able to go on to other tasks while the file is uploading, put it on a different thread.
As a general rule of thumb, if I have a situation where I absolutely don't want the user to do anything while a long-running process is going, I disable the controls on the form until the task is complete, and usually use a status indicator to show that progress is happening.
My personal guideline for whether or not to allow user interaction is if the results of a process could be altered by a user action in mid-stream.
For example, one program that we have parses a bunch of queries on a highly normalized database (normalized to the point where reporting is sloooow) into "reportable" tables, and I don't want the user altering data in one of the source tables while the query is running, because it will give goofy results.
If there is no harm in allowing user interaction while the process is occuring, then put it in another thread.
Edit
Actually, on reading #UrbanEsc and #archer's comments, I agree with them. Still put it on a different thread and freeze the controls (and include a progress indicator where possible).
I would push this to a background worker. Doing so will keep the UI responsive. If the process ever does lag for more than a few seconds, users start getting nervous ...especially when the lagging process causes the UI to be 'frozen'.
From a user experience point of view it might be best to hand the job over to a different thread or an asynchronous worker and tell the user that his request is being processed in the background. Once the worker finishes, a success/failure message can be handled and shown to the user as required.
The cheapest way to handle the problem is to turn the cursor into an hourglass during the processing. That tells user please wait, I'm busy.
According to the budget (time and/or effort) you're willing to throw in it, using a backgroundworker and some reporting GUI is certainly a plus. But it's up to you according to your app.
For example, I'm currently modifying an in-house app that has 3 users. In that case, the hourglass is OK: All 3 of them will quickly learn they just have to wait. Don't get me wrong: this app is damn important. Without it, the small company that uses it would just die. But if I ask them for 2 hours of extra budget for a nice and tested little GUI, background thread, blah vs an hourglass, what do you think they'll say?
On the other hand, if it's an important operation in your flagship product, of course be nice to your users! Don't hesitate: background thread. Especially if the operation may actually take much longer than those 5 seconds.
Conclusion: Be pragmatic!
I would put it into a background worker or fire of a task if you are in .NET 4.0, for example:
void OnButtonClick(...)
{
new TaskFactory().StartNew(() => { /* your excel and query code */ });
}
I'll vote for the background worker process, since a frozen UI is like a frozen application, and most of users will think your application isn't doing anything at all.
UI thread for a progress bar or some animation, info text noticing what's going on + background worker thread = win
I think every process not related with the UI itself should be started as a separate thred or, in this case, as a bg worker. This will help to maintain the app healthy and easy to improve/fix in the future.
Also, as a user or tester, I really hate flicking and freezing windows...
Regards.
A general rule of thumb is any operation that takes a second or longer to complete requires some form of feedback to the user. This can be a progress bar, message, etc. Anything longer then that then the user becomes frustrated (not sure if they did something wrong, hate waiting, etc).
For operations like this that can take longer based on the environment (number of apps, available memory, data size, hard drive speed, etc) they should ALWAYS be put on a background thread and pipe messages back to the UI. I love the BackGroundWorker for this.
I'm writing a c# application that requires user authentication.
When the user hits the log in button, quite a bit of stuff is done in the background, but I'm having trouble informing the user that something is happening, and that the program isn't just frozen.
I have some hidden text fields that I would like to have show up after they log in, while this stuff is running, but I can't seem to get it to show up.
Basically, when the user hits the log in button, it checks to see if their credentials are correct, then the messages should show up, and then either some other functions might run, followed by a different form being shown.
After the credentials are checked, and I know that the user is valid, I tried running this:
please_wait.Visible = true;
But it doesn't change when it gets to that point in the code.
I've tried threading it, to see if that would help. Instead of calling the above line, I just start a thread that does it.
That doesn't work either. The field still doesn't show up.
If I return out of the function right after I either start the thread or change the Visible property, it works just fine.
How do I get it to work fine and have more code run after the change?
The problem isn't that you need to update the UI from a background thread. Rather, it's that you should be performing your long-running task in a background thread and marshalling updates to the foreground. This is frequently done via a BackgroundWorker with progress notification (on a progressbar, for example).
Basically, your UI foreground thread is either loaded or blocked doing work, so it isn't handling messages in its message queue to update your user interface.
Along with what Greg recommends (which is certainly the first step if you're not already doing it) you may also need to give up some quantum.
If you are taxing the scheduler, it's possible that the UI updates (which are pretty low priority) may be getting preempted until your worker is complete. Adding an Application.DoEvents (or maybe Thread.Sleep(1) in the background thread) could give the UI a little scheduler time to paint.
Have you tried adding a call to Application.DoEvents()? It's a hack, but it's all you sometimes need.
My program consists of a large graphing UI control that I need to spend about 15 seconds re-loading every once in a while. Because the updating code works primarily with the UI control (maybe 90% of it actually sets properties on the control), it would make sense to me to actually let the UI thread handle that. I really don't want the control to visually re-paint while it is loading in a separate thread from the UI.
I also want a progress bar to update as well that lives in the status bar of the same application window. Is there a way to break the rule in this case and re-paint only the progress bar, or should I just open a new application window for the progress bar to live in?
What would you do in this particular case?
If you can break your primary task (ie. updating the graph) in many steps, you can perform each step as a separate dispatcher message. This will allow other messages to be processed, including giving you the ability to update progress information.
The basic pattern is:
Invoke your primary task, passing in zero for the step.
Perform the step.
If there are more steps, queue another message, passing in step + 1.
You can then add in progress updates at the appropriate points in your code.
PS. Not saying this is your best option - hard to tell without knowing all the details. But this is an option.
It is not really true that there is only one UI thread in an application, it is just that most windows applications only ever create UI objects in one thread so this thread becomes "the" UI thread in the application. It is easy to understand why - this makes the code simpler to understand, and protects us from implicit thread binding issues between controls.
This suggests a possible idea, should it prove impossible to improve the speed of updating the control (which is what I would suggest to do first). Create the UI control on a separate thread. You need to make sure that the thread is suitable for UI, that is to say the threading model is STA, and that it will pump messages and not die before the control is destroyed. I don't know if you need to create the parent window in the UI thread as well, or just the control but it may be worth experimenting here.
Find a graphing UI control that is more efficient. Unless the UI thread yields to the message loop any other updates won't happen (and it will slow down your graph control's updates).
I would suggest using a progressbar in a new window (without the form headers). Make it paint the progress bar by reading the shared properties of a graph control. this way you can avoid the thread blocking (sluggish loading).. And it gives you good visual experience (progressive painting on both the controls).
I'm building a UI for a program, and I can't figure out why my progress bar won't become visible after the convert button is clicked.
private void convertButton_Click(object sender, EventArgs e)
{
toolStripProgressBar.Visible = true;
...
toolStripProgressBar.Visible = false;
}
I ran into a similar problem with tkinter in Python, and I had to call a function to update the idle tasks. Is there a way to do this with windows forms without using threads?
Edit: On a side note, this is a progress bar in a toolStrip that also contains a label that gets updated with status bar text. Is there any way to get the label on the left side and the progress bar on the other instead of right next to each other on the left?
Well, there is a way to do this without using threads (Application.DoEvents) but I strongly recommend against you using it. Re-entrancy is nasty, and you really don't want the UI thread tied up at all.
Use BackgroundWorker instead - it's easy, and it's pretty much designed for progress bars. It takes the hassle out of using a separate thread and reporting progress back to the UI thread. No need for Control.Invoke etc - it takes care of that for you.
There are lots of tutorials for BackgroundWorker - it shouldn't take you too long to get going with it.
Per the question you asked for the way to do this WITHOUT threads, that is to do it with Application.DoEvents();. (Just add that call right after setting the progress bar as visible.)
Now I do agree with Jon Skeet though that BackgroundWorker is a better way of doing this, but it does use a separate thread.
You need to execute your process in a thread separate from the UI thread, and then have it periodically report back to the UI thread with it's progress. If your convert operation is working inside the UI thread, it will simply go unresponsive until the operation is complete.
The progress bar can only become visible when it is allowed to paint which occurs during the processing of messages. Message processing cannot normally happen while you are in the middle of an event handler. If you want the progress bar to show up you will have to set the visiblitity to true, start a background thread to complete the work and return from the handler.
I'm guessing the problem is that the "..." in your code is a long-running process. UI updates are not instantaneous, but must run through the message queue in windows and then be painted to the screen. The queue is pumped and painting takes place in the same thread as your events.
As a result, any long-running tasks need to be moved to a different thread. More than that, your line line of code needs to called after that thread terminates. Otherwise you set the progress bar and then immediately turn it off again.
One way to do that is with a BackgroundWorker control.
Here go two links trying to explain you how things work:
(1) (2)
Now, I will try to explain it as shortly as I can. Most of what happens inside a windows forms application happens in a single thread, usually the same thread Main() runs in. If you open Program.cs, you will see that Main() has a line that looks like the following:
Application.Run(new Form1());
If you debug the application at any moment and examine the call stack, you will see it will trace back to that Run method. This means that a Windows Forms application is in fact a continuous run of the Run method. So, what is Run doing? Run is eating a message queue through which Windows sends messages to it. Run then dispatches those messages to the correct controls, which themselves do things like add text which corresponds to the key being pressed, redraw themselves, etc. Notice that all this happens during and endless loop running alongside a single thread, so weather you are typing or simply moving the window around, loads of those messages are being passed onto the application, which in turn is processing them and reacting accordingly, all in that single thread. Controls can also send messages to themselves through the queue and even you can place messages in the pump via Control.BeginInvoke. One of the things those controls do is to raise events according to what happens. So, if you click a button, the code you've written to handle that click will ultimately and indirectly be run by the Application.Run method.
Now, what is happening with your code is that even though you are changing the visible status of your progress bar to visible and then updating its Value, you are then changing its visibility to false, all in the same method. This means that only after you leave the method, will Application.Run() be able to continue iterating and consuming the message queue, effectively asking the progress bar to update its display. When that happens, you've already left the progress bar's visibility to false, the last thing you did before exiting the method. DoEvents() is a quick and dirty workaround to your problem as it reads the messages in the queue and processes them. I don't really feel comfortable using it as it can bring reentrancy problems.
Using threads is a good solution, but I would recommend using a ThreadPool thread instead of a custom thread in this kind of situation, as I tend to use custom threads only in cases where I have a limited number of long lived threads and I need to control their life cycles. The easiest and most practical way to use threads is to use the BackgroundWorker component, even though I would recommend going through the pains of understanding how to do Windows Forms multithreading with delegates if you want to really understand what is going on.
My solution is to call refresh on the status strip.
I believe this causes the UI thread to repaint the status strip.
toolStripStatusBar1.PerformStep();
statusStrip1.Refresh();
This is for .NET 4.0. Even though this question is old it was the first I found on googling this issue.