I have a method UploadReportNotifier() which is subscribed to an event, which is raised once i have finished uploading data to a database. In UploadReportNotifier() i want to reset some values on my GUI, ie progressbars etc, but i want there to be a time delay between doing this.
Is it possible to create a thread inside UploadReportNotifier() and call thread.Sleep, or is the timer() class more appropriate?
Thanks for your help.
If your goal is to wait a few amount of time after the execution of UploadReportNotifier before updating all your GUI controls, then a timer would be a good solution IMO.
In your UploadReportNotifier method, you can create and start a timer so your "update my GUI" code will be executed after a few time. Don't forget to stop/dispose your timer after your GUI update as you probably don't want it to be executed multiple time.
You could use the System.Windows.Forms.Timer timer class (as you may know, there are multiple timer classes available).
This one is not the most accurate one, but it executes the code in the UI thread, so you won't deal with cross-thread exceptions when modiying your UI.
I see you have found your solution. I just want to mention that in this situation you should always choose timers over Thread + Sleep, which imo is just an ugly hack that should be avoided always.
Timers are great because they are also capable of executing their code on the GUI thread, so you don't need to use Invoke or BeginInvoke. For example System.Windows.Forms.Timer for WinForms or System.Windows.Threading.DispatcherTimer for WPF.
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?
In the quest to keep interfaces responsive I'd like to know which tasks on the Dispatcher/message pump take too long. This includes both WPF-internals as well as stuff I push on the Dispatcher by the way of BeginInvoke().
I've already thought about wrapping BeginInvoke() to measure this for me, but this captures only my own code and I fear that it might be too much overhead.
Any ideas/suggestions?
Why not subscribe to the events in the Dispatcher.Hooks property (DispatcherHooks class).
There is an OperationPosted event and an Operationcompleted event
e.g. in Winforms I'd write...
// on UI Thread
BackgroundWorker workerThread = new BackgroundWorker();
workerThread.DoWork += new DoWorkEventHandler(LoadChildren);
workerThread.RunWorkerCompleted += new RunWorkerCompletedEventHandler(OnLoadChildrenCompleted);
while (workerThread.IsBusy)
{
Application.DoEvents();
}
In WPF what is the equivalent of Application.DoEvents in Winforms?
I have a property called Children in my ViewModel class. A HierarchicalDataTemplate has been setup to read Items from the Children property.
A TreeView displays the nodes. When the user expands a node, the children of the node are generated from the results of this property
public Node Children
{
get
{
// 1. time-consuming LINQ query to load children from a SQL DB
// 2. return results
}
}
So I'd like to run 1. on a background thread and wait for it to complete before returning the results... keeping the UI responsive.
Googling led me to this page which has uses DispatcherFrames to simulate the above method. But this seems to be too much work.. which hints at 'Am I doing this right?'
As I understand it, you've got this sort of flow:
Do some prep work (UI thread)
Do some background work (other thread)
Do some finishing work (UI thread)
You want to wait for the second bullet to finish before running the code in the third.
The easiest way to do that is make the second bullet's code call back into the UI thread (in the normal way) to trigger the third bullet to execute. If you really, really want to use local variables from the method, you could always use an anonymous method or lambda expression to create the delegate to pass to the background worker - but normally it would be cleaner to just have a "PostBackgroundWork" method or something like that.
EDIT: This wouldn't be nice for a property as you've shown in your edited question, but I'd refactor that as a request to fetch the children with a callback when it's completed. This avoids the whole mess of reentrancy, and makes it clearer what's actually going on.
Calling DoEvents on the UI thread in a loop like this is not recommended practice in WinForms or WPF.
If your application can't continue until this thread has finished its work, then why is it on another thread?
If some parts of your application can continue, then disable those bits that can't and reenable them when your completion callback is called. Let the rest of the system get on with its stuff. No need for the loop with DoEvents in it, this is not good practice.
Take a look at the community content on MSDN.
This is a good article on DoEvents.
In WPF what is the equivalent of Application.DoEvents in Winforms?
There is none built-in, but you can easily write your own. Indeed, WPF gives you more power around message processing than does Winforms. See my blog post on Dispatcher Frames here. It includes an example showing you how to simulate Application.DoEvents().
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.