I am trying to create a time clock for clocking in and out in C# with windows forms. I would like to have the current time displayed on the screen constantly. I also want to be able to ping the bosses wifi on his or her phone, then use that to determine if they are in the building. I tried using threads, but then they can't update the UI. I also tried using timers, but it was super laggy. I also tried a background worker, but I think that you can't update the UI with a background worker. I would like to be able to update the time every second, and check if the boss is there every minute or so. Please help me find a way to do this without slowing everything down.
You can actually do many things from background call, updating UI is simplest.
Put following code in your background call where UI update is required. UI just needs to invoked from its own thread.
this.Invoke((MethodInvoker)delegate {
LabelStatus.Text = "Yeah its working";
Label2.Text = "Updated UI";
// do your stuff on UI thread
});
Related
I am developing one chat application in windows phone. I am using Deployment.Current.Dispatcher.BeginInvoke method to update the UI, but at the time of using Dispatcher.BeginInvoke the screen will struck. How to solve this or any way to update the UI without stuck?
If you use the dispatcher then you will execute the given code in the UI thread. And while you execute code in the UI thread, the UI is stuck. There's no way around that, so you must make sure to execute only the absolute minimum amount of code in the UI thread. The common pattern is to retrieve/compute the data in a background thread, then switch to the UI only to update the controls. The BackgroundWorker class is a convenient helper to reach this result.
I'm new to developing Winform application (using C# .NET)
My application will freeze and sometimes even showing "not responding" when there are too many operations running behind, especially when it involves a lot of data reading/writing to/from database. The application did NOT crash though, it just freeze until the all code behind were finish executing.
My question is, how do I "unfreeze" the application. For example, the user can still click the "cancel" button to terminate whatever the operation is running, or show a progress bar or something like that?
Your application freezes because it has single thread, which is responsible both for drawing UI and doing other 'heavy' operations (reading/writing to database). When thread is busy with database, it cannot refresh UI. You should perform 'heavy' operations in background thread(s). Thus main thread will be responsible only for refreshing UI and it will be always ready to do that. Use BackgroundWorker component to run some operations on background threads.
Suggested reading: BackgroundWorker Class Sample for Beginners and How to: Use a Background Worker
A windows application will stop working if you are using a System.Timers.Timer.
To fix this, change System.Timers.Timer by System.Windows.Forms.Timer
Greetings
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.
I have a windows form simply like this: 1) a button when clicked will perform an operation taking a long time to complete, 2) a label showing how much percentage of the progress is going on.
In the long operation I mentioned, I write the code to update the Text property of the label but it doesn't work!
Please help me to show the progress status correctly.
You can take a look at the BackgroundWorker class (see the MSDN overview). It allows you to run some long-running operation in background and report progress updates (percentage) and completion from the background task to the user interface. Note that you'll need to calculate the progress percentage yourself.
However, the BackgroundWorker class takes care of other tricky aspects, such as sending your progress reports to the main GUI thread (where you can safely update the user interface).
Your going to want to create a worker thread that performs the task and occasionally reports its update to the form thread. If you do all of your work in the UI thread, your UI will be locked and won't update the progress/label correctly.
Before you start the worker thread, calculate the total number of steps you believe the process will take. Start the worker thread. After each unit of work, you Invoke an update method on the UI thread to increment the process.
You'll want to look at the BackgroundWorker class.
If your application will have several of these, I recommend creating a process interface (e.g. IProgressProcess). This interface will contain methods for executing a process and reporting updates. You will create all of your process classes by implementing from this interface. Write a control that contains a progress bar and accepts an IProgressProcess through a constructor or property. It can then use your custom process to execute and move along the progress bar. Then you can have your custom progress control send events when the process is complete or canceled.
This usually happens if you try to update the UI on the same thread where the operation is occurring. There are a couple of different ways that you could accomplish this.
You can update the UI with the BeginInvoke method.
You can use a BackgroundWorker component.
The reason that you don't see any change, is that the change causes a message to redraw the label, but the main thread is busy working so it doesn't respond to the message.
The simplest solution would be to just call the Application.DoEvents after updating the label. That works as a quick fix for your immediate problem, but it still will leave the application unresponsive in any other way.
The good solution would to start the operation in a separate thread. That way your main thread is free to handle messages while the operation is running. However working in a separate thread means a litte more work when communicating with the UI. If you want to update controls, you have to use the Invoke method to start a method that runs in the main thread so that it has access to the controls. Alternatively you can just update a variable in the thread, and have a timer control that periodically checks for changes in the variable and updates the label accordingly.
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.