Is there any way to load window inside the background worker thread without using showdialog()? the background worker only terminate only after getting some input from the window. Here the issue is window shown but the button and other controls are not rendered even we don't have control over any of the window.
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
// acquire form
Acquire aq = new Acquire(Handle);
aq.Show();
do
{
// waiting for image
} while (!aq.isImageReady);
// doing Image operation
}
You can show the dialog before you start the background worker, and declare a volatile var that you can change/check in the background worker and keep it running until it will have your desired value, that will be achieved once the dialog is closed.
The problem might be because you're using the background thread to show the window instead of the main UI thread of the process. Winform controls either throw exceptions or behave incorrectly if they are not used on the proper thread. In this case, the problem might be that your main window is running on the main UI thread while this additional dialog window is being created and shown by a different thread.
Try raising an event from the background thread to let the UI know that it requires input from the user. The UI can then handle displaying the dialog and responding to the user's input by passing the data back to the background thread.
In order to prevent the background thread from proceeding any further, create a System.Threading.AutoResetEvent object (a WaitHandle) and call the WaitOne method on that object immediately after raising the event to notify the UI to show the dialog. When the UI responds to the user input by passing the data back to the background thread, that code can call the Set method on the AutoResetEvent object, allowing the background thread to proceed.
Related
I am using background worker in my win form application I am showing progress bar form for a long running process and that long running process is on background worker.
Note: I have used background worker for showing progress bar in marquee style.
Problem I am facing is due to background worker my User interface gets responsive, but I don't want it to be responsive.
My code is as below:
ProgressBarForm progForm = new ProgressBarForm();
progForm.Show();
BackgroundWorker worker = new BackgroundWorker();
worker.DoWork+= myMethod;
worker.RunWorkerAsync();
Considering that you are using a form to display the progress, you can use ShowDialog instead of Show. This will open the window as a modal dialog, blocking UI actions to your underlying window until the progress window is closed.
Some things to consider:
ShowDialog is a blocking call, so call it after starting the background worker.
Make sure the user can't close the window, and programmatically close the window yourself after the background worker completes.
If you don't want your user interface to be used, set .Enabled = false; on each of the form controls, then reverse the changes in _RunWorkerCompleted.
Just remember to leave any cancel / close buttons enabled :)
I have a modal dialog with a cancel button only which pops up when the user clicks on a button. Aftre the modal dialog pops up, I would like to start a long process which monitors external event. If the event happens, then the dialog will be closed automatically. The user can cancel the monitoring process by clicking the cancel button.
I assigned the process start to the Shown event
private void ProceedForm_Shown(object sender, System.EventArgs e)
{
controller.StartSwiping();
}
The process itself is a loop
public void StartSwiping()
{
Status status;
do
{
status = CallForFeedback();
} while (status == Status.Pending);
form.DialogResult = DialogResult.OK;
form.Close();
}
The process starts fine, but the dialog does not pop up, so the user can non cancel the process. I also tried to assign the start to the Load event, but nothing changed.
Is there any way to Show the dialog and after that start the process?
Thanks
Your problem is that you are doing everything in the UI thread. You need to put you status monitoring loop in a separate thread so that the UI thread can remain responsive.
There are several ways you can do this, but one easy place to start is with the BackgroundWorker class
Use a Task to do your LongRunning events:
CancellationTokenSource _cancelationTokenSource = new CancellationTokenSource();
new Task(() =>
{
//Do LongRunning task
}, _cancelationTokenSource.Token, TaskCreationOptions.LongRunning).Start();
Use the _cancelationTokenSource to cancel the task when needed.
I would move the long running code onto a background thread as you are blocking the UI thread, which is why the UI never displays.
Use a background worker class for the controller functionality http://msdn.microsoft.com/en-us/library/cc221403(v=vs.95).aspx
When the work is completed on the background worker (i.e. the event is received) then you can use the following mechanism to callback onto the UI thread:
http://msdn.microsoft.com/en-us/library/ms171728(v=vs.80).aspx
Note: the article says you can turn off the crossthreadexception this would be considered bad practice, instead handle it the correct way using the InvokeRequired check and then invoke method on the windows form.
Others have suggested using a BackgroundWorker, or some other sort of background thread. While in many cases this is appropriate here, there is likely an even better solution. You're not just doing some long running task, you're waiting for something to happen. Rather than constantly polling...whatever it is, you should be using events. There should be an event that is triggered when you are done, and you should subscribe to that event to do whatever you need to do (i.e. close the dialog) when the correct conditions are met.
I have a main form that contains an edit control that occupies the entire form. There is another worker thread that constantly writes log messages to this edit control. Now I want to show a dialog box with just a cancel button while the main UI's edit control is displaying stuff. The problem is that the cancel dialog is non-responsive while the updates are happening behind it and I cannot click on the cancel button. Any idea on how to resolve it. I was thinking of creating another UI thread and show the cancel button from it. Any other alternatives?
EDIT#1
I should clarify that I already use a worker thread to do the work.
DisplayLogs() is in a seperate thread.
DisplayLogs() is called from other threads.
LogMessage is the delegate that points to the method UpdateMessage in main UI.
The control used is a TextBox. I have tried other controls like listview,
richtextboxsand, etc. still the same result.
Worker Thread
void DisplayLogs()
{
lock (this)
{
while (logQueue.Count > 0)
{
string logMessagemessage = logQueue.Dequeue();
LogMessage(string.Concat(logMessagemessage, Environment.NewLine));
}
}
}
Main UI
public void UpdateMessage( string message)
{
if (!txtLog.IsHandleCreated)
{
return;
}
if (txtLog.InvokeRequired)
txtLog.BeginInvoke( new UpdateLogDelegate( UpdateLog), message);
else
txtLog.AppendText(message);
}
The main solution is to offload the expensive code onto a background worker and leave your UI thread responsive for UI actions. Your form can then simply show a modal dialog or something.
MSDN - How to use a Background Worker
In this situation it's necessary to move the majority of the work to a new thread, and clear up the UI thread for cancel messages etc.
You are going about this backwards. The main thread should, in theory, always be available to accept user input. Anything that may block for extended periods of time (heavy computation, database access, network access) should be done in a background thread. The idea is to have the edit control's data being computed and populated by a background thread (BackgroundWorker objects work nicely here) so that the main thread is always available if the user clicks on the cancel button.
Your problem is that the your UI thread is ALWAYS busy. I am saying this assuming that the number of items in logQueue is quite large. The while loop doesn't quit till the queue is empty. So it keeps hitting the UI thread with request for updates.
Also the if (txtLog.InvokeRequired) is kind of pointless because you are always calling the method from a worker thread.
So, since a .net WinForm application has only a single UI, which in your case is too busy to process other notifications, the new window appears stuck (because the paint messages are stuck in the message queue and cannot be processed as it is already flooded with the text box update messages)
You could stick an Application.DoEvents inside your loop which will give the message loop some time to process the pending notifications. However this is kind of a hack, in my opinion, as the UI behavior is sometimes not predictable. It may lead to things like stuttering while moving a dialog, delayed responses to click events etc.
Another point, MessageBox.Show or a Form.ShowDialog (if this is what you are using for the cancel button) is a blocking call. The thread on which you show it WILL hang till you dismiss the dialog. Try Form.Show and set the parent property to the main form.
Another alternative is to add a timer and process only X notifications per Y seconds. This will give the UI thread some breathing room for performing other activities.
So I have a thread in my application, which purpose is to listen to messages from the server and act according to what it recieves.
I ran into a problem when I wanted to fire off a message from the server, that when the client app recieves it, the client app would open up a new form. However this new form just freezes instantly.
I think what's happening is that the new form is loaded up on the same thread as the thread listening to the server, which of course is busy listening on the stream, in turn blocking the thread.
Normally, for my other functions in the clients listening thread, I'd use invokes to update the UI of the main form, so I guess what I'm asking for is if here's a way to invoke a new form on the main form.
I assume this is Windows Forms and not WPF? From your background thread, you should not attempt to create any form, control, etc or manipulate them. This will only work from the main thread which has a message loop running and can process Windows messages.
So to get your code to execute on the main thread instead of the background thread, you can use the Control.BeginInvoke method like so:
private static Form MainForm; // set this to your main form
private void SomethingOnBackgroundThread() {
string someData = "some data";
MainForm.BeginInvoke((Action)delegate {
var form = new MyForm();
form.Text = someData;
form.Show();
});
}
The main thing to keep in mind is that if the background thread doesn't need any response from the main thread, you should use BeginInvoke, not Invoke. Otherwise you could get into a deadlock if the main thread is busy waiting on the background thread.
You basically gave the answer yourself - just execute the code to create the form on the GUI thread, using Invoke.
Ok, so I found something weird over the weekend. I have a WPF app that spawns off some threads to perform background work. Those background threads then Post work items to my Synchronization Context. This is all working fine except for one case. When my threads finish sometimes they will post an action onto the dispatcher that will open up a Popup window. What ends up happening is that if 2 threads both post an action on the Dispatcher it starts processing one, then if I open up a Popup window with Window.ShowDialog(); the current execution path pauses waiting for feedback from the dialog box as it should. But the problem arises that when the dialog box opens the Dispatcher then goes and starts immediately starts running the second action that was posted. This results in two code paths being executed. The first one with a message box being held open, while the second one is running wild because my application state is unknown because the first action never completed.
I've posted some example code to demonstrate the behavior I'm talking about. What should happen is that if I post 2 actions and the 1st one opens up a dialog box the second action shouldn't run until after the 1st action has been completed.
public partial class Window1 : Window {
private SynchronizationContext syncContext;
public Window1() {
InitializeComponent();
syncContext = SynchronizationContext.Current;
}
private void Button_ClickWithout(object sender, RoutedEventArgs e) {
// Post an action on the thread pool with the syncContext
ThreadPool.QueueUserWorkItem(BackgroundCallback, syncContext);
}
private void BackgroundCallback(object data) {
var currentContext = data as SynchronizationContext;
System.Console.WriteLine("{1}: Thread {0} started", Thread.CurrentThread.ManagedThreadId, currentContext);
// Simulate work being done
Thread.Sleep(3000);
currentContext.Post(UICallback, currentContext);
System.Console.WriteLine("{1}: Thread {0} finished", Thread.CurrentThread.ManagedThreadId, currentContext);
}
private void UICallback(object data) {
System.Console.WriteLine("{1}: UI Callback started on thread {0}", Thread.CurrentThread.ManagedThreadId, data);
var popup = new Popup();
var result = popup.ShowDialog();
System.Console.WriteLine("{1}: UI Callback finished on thread {0}", Thread.CurrentThread.ManagedThreadId, data);
}
}
The XAML is just a Window with a button that calls Button_ClickWithout OnClick. If you push the button twice and wait 3 seconds, you will see you get 2 dialogs popping up one over the other, where the expected behavior would be the first one pops up, then once it's closed the second one will pop up.
So my question is: Is this a bug ? or how do I mitigate this so I can have only one action be processed at a time when the first action halts execution with a Window.ShowDialog() ?
Thanks,
Raul
As I'm awaiting an answer on my question (Advice on using the Dispatcher Priority and Binding) I thought that would pay-it-forward™.
What you are experiencing is Nested Pumping on the Dispatcher. I recommend reading the MSDN article on the WPF Threading Model, especially the section titled 'Technical Details and Stumbling Points' that is two-thirds down the page. The sub-section describing the Nested Pumping is copied below for convenience.
Nested Pumping
Sometimes it is not feasible to completely lock up the UI thread.
Let’s consider the Show method of the MessageBox class. Show doesn’t
return until the user clicks the OK button. It does, however, create a
window that must have a message loop in order to be interactive. While
we are waiting for the user to click OK, the original application
window does not respond to user input. It does, however, continue to
process paint messages. The original window redraws itself when
covered and revealed.
Some thread must be in charge of the message box window. WPF could
create a new thread just for the message box window, but this thread
would be unable to paint the disabled elements in the original window
(remember the earlier discussion of mutual exclusion). Instead, WPF
uses a nested message processing system. The Dispatcher class includes
a special method called PushFrame, which stores an application’s
current execution point then begins a new message loop. When the
nested message loop finishes, execution resumes after the original
PushFrame call.
In this case, PushFrame maintains the program context at the call to
MessageBox.Show, and it starts a new message loop to repaint the
background window and handle input to the message box window. When the
user clicks OK and clears the pop-up window, the nested loop exits and
control resumes after the call to Show.
A modal dialog box does not prevent the owner window from processing messages, otherwise you'd see it fail to redraw as the modal dialog was moved over its surface (just as an example).
In order to achieve what you want, you have to implement your own queue on the UI thread, possibly with some synchronization to "wake it up" when the first work item arrives.
EDIT:
Also if you examine the call stack of the UI thread while the 2nd modal dialog box is up, you might find out that it has the first ShowDialog call above it in the stack.
EDIT #2:
There might be an easier way of doing this, without implementing your own queue. If instead of the SynchronizationContext, you would use the Dispatcher object, you would be able to call BeginInvoke on it with a priority of DispatcherPriority.Normal, and it will get queued properly (check).