I have a DevExpress GridControl oneway binding to a tableview in the viewmodel. There are about 20 background threads querying data from databases and update the tableview individually. The update to the table view is guardard with lock for async update. Dispatcher is used for refreshing the main UI thread. I also have another button to cancel the database and update functions via CancellationTokenSource.
However, when the applicatoin runs, I have to click the cancellation button many times in order to execute code in the cancel command. In another word, the UI Main thread is busy refreshing the GridControl and it blocks the Cancel Button.
Is there a way to achive this function?
Edit: Found this method helps a lot await Dispatcher.Yield(DispatcherPriority.ApplicationIdle);
It simply gives other UI controls a chance to be executed.
Creates an awaitable object that asynchronously yields control back to the current dispatcher and provides an opportunity for the dispatcher to process other events. (MSDN)
AFAIK, UI stands for User Interface, where main part is User! User is not robot, it is a person, which uses your application. You do not need to query data updates so often on UI thread. Why do you need 20 threads for database query operation? You have the single GridControl, which can show only several rows at time on the screen, 20, 50, 100 (no more). So, I suggest you to have only one thread for reading data from database, and do it once per 2-5 seconds, in order to provide User with some interactivity. For this purpose, TPL - is the good choice. Using it with CancellationToken - is good way to support cancellation with your scenario. Between database queries you can do the following:
while (true)
{
myToken.ThrowIfCancellationRequested();
// database query here
myToken.WaitHandle.WaitOne(2000)
}
Also, before updating source collection, you can use the following:
GridControl.BeginDataUpdate();
//Update your source collection
GridControl.EndDataUpdate();
This will prevent DevExpress control from listening CollectionChanged event, or any other, because on each Add/Remove action DevExpress call UpdateLayout() method, which is no so fast as we want to.
if layout is invalid in either respect, the UpdateLayout call will redo the entire layout. Therefore, you should avoid calling UpdateLayout after each incremental and minor change in the element tree.
Related
I have some UI task which took to long. I have some 'home made' property grid ( I uses an ItemControl , where item template uses a ContentControl, the item itself holds the datatemplate to be used in the Content control.).
The application is Shapes viewer, where each shape has its properties. each time the user clicks on some shape, the property grid shows its properties (60 different properties).
The updates process takes something about 1-2 sec. while this updating the application freeze.
Is there any way to do the updating of the property grid in the background?
Is there any way to stop last updating?
Regards, Leon
You should implement the MVVM pattern to make sure that your UI controls is a way to DISPLAY your data rather than be the HOLDER of data.
You can then choose to do various background tasks and only update VM content when ready.
Check out this video:
http://blog.lab49.com/archives/2650
you need to work with thread and dispatcher to do this.
Dispatcher in WPF/SL - http://www.switchonthecode.com/tutorials/working-with-the-wpf-dispatcher
In order to use another thread you have some options:
Threadpool (TaskClass only On .Net 4) - http://msdn.microsoft.com/en-us/library/3dasc8as(v=vs.80).aspx
Thread class - http://msdn.microsoft.com/en-us/library/aa645740(v=vs.71).aspx
BackgroundWorker Class - http://msdn.microsoft.com/en-us/library/cc221403(v=vs.95).aspx
The 3rd option is the easiest if you don't know how to work with threads.
I guess what taking so long is the fetching the properties so what you need to do is to perform the fetch in another thread and then to use Dispatcher in this thread to update your datagrid,
you have to use Dispatcher to update your GUI from another thread.
In my WPF app, I need to run an expensive operation on my UI thread (let's call it ExpensiveUIOperation()), and I want to keep the UI up to date to track it's progress.
To track progress, I simply have a TextBlock, whose Text property is bound to an integer dependency property PercentageComplete. During ExpensiveUIOperation(), I simply set the value of PercentageComplete as required.
Now, I understand enough about threading to know that if I simply ran ExpensiveUIOperation() on my UI thread, that the TextBlock would not appear to keep up to date, as the UI thread would be blocked, stopping any interface updates.
And so I thought I could do it asynchronously like this:
Dispatcher.BeginInvoke(new Action(ExpensiveUIOperation), DispatcherPriority.Background);
But that is still not working. The text block is not visually updated until the operation completes.
Is there a way to do this?
Unfortunately in this situation I cannot use a background thread, as the operation makes heavy use of objects owned by the UI thread.
Unfortunately in this situation I cannot use a background thread, as the operation makes heavy use of objects owned by the UI thread.
That is not a good enough reason to abuse the UI-thread like this. Use the Dispatcher when accessing those elements (see the treading model reference), or properly bind your view to relevant properties and you will not even need to do that as updates are queued to the UI internally.
You're stuck, UI operations have to occur on the UI thread, and while that occurs no UI updates will happen. You could do the equivalent of an Application.DoEvents in WPF by creating a new dispatcher frame (http://dedjo.blogspot.com/2007/08/how-to-doevents-in-wpf.html) but it is dangerous, you will catch the UI in the middle of updates and not a good thing to do.
Is the expensive UI operation really a CPU-intensive, UI-only operation? Nothing that can be done with a View Model object graph and then finally bound to the UI, for example?
Im working on a reporting system, a series of DocumentPage are to be created through a DocumentPaginator. These documents include a number of WPF components that are to be instantiated so the paginator includes the correct things when later sent to the XpsDocumentWriter (which in turn is sent to the actual printer).
My problem now is that the DocumentPage instances take quite a while to create (enough for Windows to mark the application as frozen) so I tried to create them in a background thread, which is problematic since WPF expects the attributes on them to be set from the GUI thread. I would also like to have a progress bar showing up, indicating how many pages have been created so far. Thus, it looks like Im trying to get two things to happen in parallell on the GUI.
The problem is hard to explain and Im really not sure how to tackle it. In short:
Create a series of DocumentPage's.
These include WPF components
These are to be created on a background thread, or use some other trick so the application isnt frozen.
After each page is created, a WPF ProgressBar should be updated.
If there is no decent way to do this, alternate solutions and approaches are more than welcome.
You should be able to run the paginator in a background thread as long as the thread is STA.
After you've set up your thread, try this prior to running it.
thread.SetApartmentState(ApartmentState.STA);
If you really must be on the GUI thread, then check out the Freezable class, as you might have to move the objects from your background thread to the GUI thread.
If the portions that require the UI thread are relatively small, you can use the Dispatcher to perform those operations without blocking the UI. There's overhead associated with this, but it may allow the bulk of the calculations to occur in the background and will interleave the work on the UI thread with other UI tasks. You can update the progress bar with the Dispatcher as well.
My guess is that everything that is time-consuming to create is within your Visual. If so, there is an easy solution: Don't create actual DocumentPage objects and their associated Visuals until DocumentPaginator.GetPage() is called.
As long as the code that consumes your document only requests one or two pages at a time there will be no performance bottleneck.
If you're printing to the printer or to a file, everything can be done on a background thread, but if you're displaying onscreen you only need to display a few DocumentPages at a time anyway. In either case you won't get any UI lockups.
The worst case scenario would be an app that displays pages in a thumbnail view. In this case, I would:
The thumbnail view would bind its ItemsSource to a "RealizedPages" collection which initially is filled with dummy pages
Whenever a dummy page is measured, it queues a dispatcher operation at DispatcherPriority.Background to call DocumentPaginator.GetPage() and then replace the dummy page in the RealizedPages collection with the real page.
If there are performance concerns even with realizing a single page because of the number of separate items, this same general approach can be used within whatever ItemsControl on the page has the large number of items.
One more note: The XPS printing system doesn't ever process more than one DocumentPage at a time, so if you know that's your client you can actually just keep returning the same DocumentPage over and over again with appropriate modifications.
Elaborating further on Ray Burns' answer: Couldn't you have your dataprocessing done in a class on a background thread and then databind the DocumentPage's properties to this class when the processing is done?
A little late to the game on this one, but I just worked out a solution to this so I thought I would share. In order to display the UI elements they have to be created on the UI thread on which they will be displayed. Since the long running task is on the UI thread, it will prevent a progress bar from updating. To get around this, I created the progress bar on a new UI thread and created the pages on the main UI thread.
Thread t = new Thread(() =>
{
ProgressDialog pd = new ProgressDialog(context);
pd.WindowStartupLocation = System.Windows.WindowStartupLocation.CenterScreen;
pd.Show();
System.Windows.Threading.Dispatcher.Run();
});
t.SetApartmentState(ApartmentState.STA);
t.IsBackground = true;
t.Start();
Action(); //we need to execute the action on the main thread so that UI elements created by the action can later be displayed in the main UI
'ProgressDialog' was my own WPF window for displaying progress information.
'context' holds the progress data for my progress dialog. It includes a cancelled property so that I can abort the action running on the main thread. It also includes a complete property so the progress dialog can close when the Action has finished.
'Action' is the method used to create all the UI elements. It monitors the context for the cancel flag and stops generating the UI elements if the flag is set. It sets the complete flag when it is done.
I don't remember the exact reason I had to set Thread 't' to an STA thread and IsBackground to true, but I am pretty sure it won't work without them.
Our app's master/details view uses a datagridview as the master, and a custom control as the details view. The details view takes a long time to compute and render, making cursoring up/down the master view painfully slow.
Therefore, we'd like the details view to run asynchronously (in a separate UI thread) with change notifications from the master.
Creating a form in a separate thread is relatively straightforward, as Application.Run takes a form parameter.
Is there a way to run a winforms control on a separate thread? I'm aware that native windows in different threads can have a parent/child relationship, just not sure how to set that up using winforms.
TIA,
Updating the UI from a Secondary Thread
http://msdn.microsoft.com/en-us/magazine/cc188732.aspx
Intuitively, you also ought to be able to accomplish the same thing by using a BackgroundWorker. The BackgroundWorker is designed to update UI things like progress bars while executing stuff in the background, and it can be cancelled during its operation.
Is the slowdown caused by the loading of the data, or the population of the UI itself?
Most of the time it's the former, so if that's the case, then the logic that does the data loading should be abstracted into a different thread. The UI code can live in the main thread since updates are quick. You could use either a Thread or a BackgroundWorker in this situation. The key is to separate your data loading from your GUI population.
If you are firing off the update of the detail view in code, you can greatly improve the usability by sleeping 500ms between the time that the user selects the master record, and the time you update the detail view.
This gives the user 1/2 second to scroll to the next record without the details view updating at all.
If you're taking a speed hit during rendering, you should consider suspending layout until the form has completed updating, and then refresh the visible display once at the end.
this.SuspendLayout();
// Do control stuff here
this.ResumeLayout();
If that doesn't help, try this:
[DllImport("user32.dll")]
public static extern bool LockWindowUpdate(IntPtr hWndLock);
//
LockWindowUpdate(this.Handle);
// Do control stuff here
this.Refresh(); //Forces a synchronous redraw of all controls
LockWindowUpdate(IntPtr.Zero);
http://social.msdn.microsoft.com/Forums/en-US/winforms/thread/8a5e5188-2985-4baf-9a0e-b72064ce5aeb
I'm currently designing/reworking the databinding part of an application that makes heavy use of winforms databinding and updates coming from a background thread (once a second on > 100 records).
Let's assume the application is a stock trading application, where a background thread monitors for data changes and putting them onto the data objects. These objects are stored in a BindingList<> and implement INotifyPropertyChanged to propagate the changes via databinding to the winforms controls.
Additionally the data objects are currently marshalling the changes via WinformsSynchronizationContext.Send to the UI thread.
The user is able to enter some of the values in the UI, which means that some values can be changed from both sides. And the user values shouldn't be overritten by updates.
So there are several question coming to my mind:
Is there a general design-guildline how to do that (background updates in databinding)?
When and how to marshal on the UI thread?
What is the best way of the background thread to interact with
binding/data objects?
Which classes/Interfaces should be used? (BindingSource, ...)
...
The UI doesn't really know that there is a background thread, that updates the control, and as of my understanding in databinding scenarios the UI shouldn't know where the data is coming from... You can think of the background thread as something that pushes data to the UI, so I'm not sure if the backgroundworker is the option I'm searching for.
Sometimes you want to get some UI response during an operation in the data-/business object (e.g. setting the background during recalculations). Raising a propertychanged on a status property which is bound to the background isn't enough, as the control get's repainted after the calculation has finished? My idea would be to hook on the propertychanged event and call .update() on the control...
Any other ideas about that?
This is a hard problem since most “solutions” lead to lots of custom code and lots of calls to BeginInvoke() or System.ComponentModel.BackgroundWorker (which itself is just a thin wrapper over BeginInvoke).
In the past, I've also found that you soon wish to delay sending your INotifyPropertyChanged events until the data is stable. The code that handles one propriety-changed event often needs to read other proprieties. You also often have a control that needs to redraw itself whenever the state of one of many properties changes, and you don’t wan the control to redraw itself too often.
Firstly, each custom WinForms control should read all data it needs to paint itself in the PropertyChanged event handler, so it does not need to lock any data objects when it was a WM_PAINT (OnPaint) message. The control should not immediately repaint itself when it gets new data; instead, it should call Control.Invalidate(). Windows will combine the WM_PAINT messages into as few requests as possible and only send them when the UI thread has nothing else to do. This minimizes the number of redraws and the time the data objects are locked. (Standard controls mostly do this with data binding anyway)
The data objects need to record what has changed as the changes are made, then once a set of changes has been completed, “kick” the UI thread into calling the SendChangeEvents method that then calls the PropertyChanged event handler (on the UI thread) for all properties that have changed. While the SendChangeEvents() method is running, the data objects must be locked to stop the background thread(s) from updating them.
The UI thread can be “kicked” with a call to BeginInvoke whenever a set of update have bean read from the database. Often it is better to have the UI thread poll using a timer, as Windows only sends the WM_TIMER message when the UI message queue is empty, hence leading to the UI feeling more responsive.
Also consider not using data binding at all, and having the UI ask each data object “what has changed” each time the timer fires. Databinding always looks nice, but can quickly become part of the problem, rather then part of the solution.
As locking/unlock of the data-objects is a pain and may not allow the updates to be read from the database fast enough, you may wish to pass the UI thread a (virtual) copy of the data objects. Having the data object be persistent/immutable so that any changes to the data object return a new data object rather than changing the current data object can enable this.
Persistent objects sound very slow, but need not be, see this and that for some pointers. Also look at this and that on Stack Overflow.
Also have a look at retlang - Message-based concurrency in .NET. Its message batching may be useful.
(For WPF, I would have a View-Model that sets in the UI thread that was then updated in ‘batches’ from the multi-threaded model by the background thread. However, WPF is a lot better at combining data binding events then WinForms.)
Yes all the books show threaded structures and invokes etc. Which is perfectly correct etc, but it can be a pain to code, and often hard to organise so you can make decent tests for it
A UI only needs to be refreshed so many times a second, so performance is never an issue, and polling will work fine
I like to use a object graph that is being continuously updated by a pool of background threads. They check for actual changes in data values and when they notice an actual change they update a version counter on the root of the object graph (or on each main item whatever makes more sense) and updates the values
Then your foreground process can have a timer (same as UI thread by default) to fire once a second or so and check the version counter, and if it changes, locks it (to stop partial updates) and then refreshes the display
This simple technique totally isolates the UI thread from the background threads
There is an MSDN article specific on that topic. But be prepared to look at VB.NET. ;)
Additionally maybe you could use System.ComponentModel.BackgroundWorker, instead of a generic second thread, since it nicely formalize the kind of interaction with the spawned background thread you are describing. The example given in the MSDN library is pretty decent, so go look at it for a hint on how to use it.
Edit:
Please note: No marshalling is required if you use the ProgressChanged event to communicate back to the UI thread. The background thread calls ReportProgress whenever it has the need to communicate with the UI. Since it is possible to attach any object to that event there is no reason to do manual marshalling. The progress is communicated via another async operation - so there is no need to worry about neither how fast the UI can handle the progress events nor if the background thread gets interruped by waiting for the event to finish.
If you prove that the background thread is raising the progress changed event way too fast then you might want to look at Pull vs. Push models for UI updates an excellent article by Ayende.
I just fought a similar situation - badkground thread updating the UI via BeginInvokes. The background has a delay of 10ms on every loop, but down the road I ran into problems where the UI updates which sometimes get fired every time on that loop, can't keep up with teh freq of updates, and the app effectively stops working (not sure what happens- blew a stack?).
I wound up adding a flag in the object passed over the invoke, which was just a ready flag. I'd set this to false before calling the invoke, and then the bg thread would do no more ui updates until this flag is toggled back to true. The UI thread would do it's screen updates etc, and then set this var to true.
This allowed the bg thread to keep crunching, but allowed the ui to shut off the flow until it was ready for more.
Create a new UserControl, add your control and format it (maybe dock = fill) and add a property.
now configure the property to invoke the usercontrol and update your element, each time you change the property form any thread you want!
thats my solution:
private long value;
public long Value
{
get { return this.value; }
set
{
this.value = value;
UpdateTextBox();
}
}
private delegate void Delegate();
private void UpdateTextBox()
{
if (this.InvokeRequired)
{
this.Invoke(new Delegate(UpdateTextBox), new object[] {});
}
else
{
textBox1.Text = this.value.ToString();
}
}
on my form i bind my view
viewTx.DataBindings.Add(new Binding("Value", ptx.CounterTX, "ReturnValue"));
This is a problem that I solved in Update Controls. I bring this up not to suggest you rewrite your code, but to give you some source to look at for ideas.
The technique that I used in WPF was to use Dispatcher.BeginInvoke to notify the foreground thread of a change. You can do the same thing in Winforms with Control.BeginInvoke. Unfortunately, you have to pass a reference to a Form object into your data object.
Once you do, you can pass an Action into BeginInvoke that fires PropertyChanged. For example:
_form.BeginInvoke(new Action(() => NotifyPropertyChanged(propertyName))) );
You will need to lock the properties in your data object to make them thread-safe.
This post is old but I thought I'd give options to others. It seems once you start doing async programming and Windows Forms databinding you end up with problems updating Bindingsource datasource or updating lists bound to windows forms control. I am going to try using Jeffrey Richters AsyncEnumerator class from his powerthreading tools on wintellect.
Reason:
1. His AsyncEnumerator class automatically marshals background threads to UI threads so you can update controls as you would doing Synchronous code.
2. AsyncEnumerator simplifies Async programming. It does this automatically, so you write your code in a Synchronous fashion, but the code is still running in an asynchronous fashion.
Jeffrey Richter has a video on Channel 9 MSDN, that explains AsyncEnumerator.
Wish me luck.
-R
I am late to the party but I believe this is still a valid question.
I would advise you to avoid using data binding at all and use Observable objects instead.
The reason is, data binding looks cool and when implemented the code looks good, but data binding miserably fails when there is lot os asynchronous UI update or multi-threading as in your case.
I have personally experienced this problem with asynchronous and Databinding in prod, we even didn't detect it in testing, when users started using all different scenarios things started to break down.