I have a list with hundreds items,
when I try to sort the items, it always blocking my program.
It' so too annoying.
I try to use Task.Run(), It doesn't work.
private void resultListView_ColumnClick(object sender, ColumnClickEventArgs e)
{
// doesn't work
Task.Run(() => ListViewOperate((ListView)sender, ListViewOP.SORT));
// doesn't work
resultListView.BeginUpdate();
ListViewOperate((ListView)sender, ListViewOP.SORT);
resultListView.EndUpdate();
}
private delegate void ListViewOperateDelegate(System.Windows.Forms.ListView liv,
ListViewOP op);
private void ListViewOperate(System.Windows.Forms.ListView liv, ListViewOP op)
{
if (liv.InvokeRequired)
{
var addDele = new ListViewOperateDelegate(ListViewOperate);
liv.Invoke(addDele, new object[] { liv, op});
}
else
{
if (op == ListViewOP.SORT)
{
liv.BeginUpdate();
liv.Sort();
liv.EndUpdate();
}
}
}
The trick you are trying to use, doesn't work here, because you are starting the
ListViewOperator on a thread/task but the callback checks if it is started on the UI thread. If it isn't on the UI thread, invoke it on the UI thread. So what benefits did you gain? none..
You should check the Virtual Mode. With the virtual mode you are able to sort it (a copy) of the list on a task/thread and then swap the list "variable" and trigger the listview to refresh it self.
Here is an Example
I have a method which consists of two lists (1. items to search and 2. workers to search with). Each worker takes an item from the list, searches for it, and add the results to a global results list which update the UI thread (a listview).
This is what I came up with so far:
List<Result> allResults = new List<Result>();
var search = new Search(workers);
//Will be full with items to search for
var items= new ConcurrentBag<item>();
while (items.Any())
{
foreach (var worker in workers)
{
if (!items.Any())
break;
IEnumerable<Result> results = null;
Task.Factory.StartNew(() =>
{
if (ct.IsCancellationRequested)
return;
items.TryTake(out Item item);
if (item == null)
return;
results= search.DoWork(worker, item);
}, ct);
if (results?.Any() ?? false)
{
allResults.AddRange(reults);
}
//Update UI thread here?
}
}
The workers should search in parallel and their results added to the global results list. This list will then refresh the UI.
Am I on the right track with the above approach? Will the workers run in parallel? Should I update the UI thread within the task and use BeginInvoke?
This will run parallel searches from the list items up to a specified number of workers without blocking the UI thread and then put the results into a list view.
private CancellationTokenSource _cts;
private async void btnSearch_Click(object sender, EventArgs e)
{
btnSearch.Enabled = false;
lvSearchResults.Clear();
_cts = new CancellationTokenSource();
AddResults(await Task.Run(() => RunSearch(GetItems(), GetWorkerCount(), _cts.Token)));
btnSearch.Enabled = true;
}
private void btnCancel_Click(object sender, EventArgs e)
{
_cts?.Cancel();
}
private List<Result> RunSearch(List<Item> items, int workerCount, CancellationToken ct)
{
ConcurrentBag<List<Result>> allResults = new ConcurrentBag<List<Result>>();
try
{
Parallel.ForEach(items, new ParallelOptions() { MaxDegreeOfParallelism = workerCount, CancellationToken = ct }, (item) =>
{
Search search = new Search(); // you could instanciate this elseware as long as it's thread safe...
List<Result> results = search.DoWork(item);
allResults.Add(results);
});
}
catch (OperationCanceledException)
{ }
return allResults.SelectMany(r => r).ToList();
}
private void AddResults(List<Result> results)
{
if (results.Count > 0)
lvSearchResults.Items.AddRange(results.Select(r => new ListViewItem(r.ToString())).ToArray());
}
If your are working with Windows form, you can refer to How do I update the GUI from another thread?
If you are working with WPF. You can find your UI Dispatcher and use the dispatcher to update UI. Usually, even you try to update UI in a loop, it may not update the UI immediately. If you want to force to update UI, you can use DoEvents() method. The DoEvents() method also works for WPF. But try to avoid using DoEvents().
I am currently writing my first program on C# and I am extremely new to the language (used to only work with C so far). I have done a lot of research, but all answers were too general and I simply couldn't get it t work.
So here my (very common) problem:
I have a WPF application which takes inputs from a few textboxes filled by the user and then uses that to do a lot of calculations with them. They should take around 2-3 minutes, so I would like to update a progress bar and a textblock telling me what the current status is.
Also I need to store the UI inputs from the user and give them to the thread, so I have a third class, which I use to create an object and would like to pass this object to the background thread.
Obviously I would run the calculations in another thread, so the UI doesn't freeze, but I don't know how to update the UI, since all the calculation methods are part of another class.
After a lot of reasearch I think the best method to go with would be using dispatchers and TPL and not a backgroundworker, but honestly I am not sure how they work and after around 20 hours of trial and error with other answers, I decided to ask a question myself.
Here a very simple structure of my program:
public partial class MainWindow : Window
{
public MainWindow()
{
Initialize Component();
}
private void startCalc(object sender, RoutedEventArgs e)
{
inputValues input = new inputValues();
calcClass calculations = new calcClass();
try
{
input.pota = Convert.ToDouble(aVar.Text);
input.potb = Convert.ToDouble(bVar.Text);
input.potc = Convert.ToDouble(cVar.Text);
input.potd = Convert.ToDouble(dVar.Text);
input.potf = Convert.ToDouble(fVar.Text);
input.potA = Convert.ToDouble(AVar.Text);
input.potB = Convert.ToDouble(BVar.Text);
input.initStart = Convert.ToDouble(initStart.Text);
input.initEnd = Convert.ToDouble(initEnd.Text);
input.inita = Convert.ToDouble(inita.Text);
input.initb = Convert.ToDouble(initb.Text);
input.initc = Convert.ToDouble(initb.Text);
}
catch
{
MessageBox.Show("Some input values are not of the expected Type.", "Wrong Input", MessageBoxButton.OK, MessageBoxImage.Error);
}
Thread calcthread = new Thread(new ParameterizedThreadStart(calculations.testMethod);
calcthread.Start(input);
}
public class inputValues
{
public double pota, potb, potc, potd, potf, potA, potB;
public double initStart, initEnd, inita, initb, initc;
}
public class calcClass
{
public void testmethod(inputValues input)
{
Thread.CurrentThread.Priority = ThreadPriority.Lowest;
int i;
//the input object will be used somehow, but that doesn't matter for my problem
for (i = 0; i < 1000; i++)
{
Thread.Sleep(10);
}
}
}
I would be very grateful if someone had a simple explanation how to update the UI from inside the testmethod. Since I am new to C# and object oriented programming, too complicated answers I will very likely not understand, I'll do my best though.
Also if someone has a better idea in general (maybe using backgroundworker or anything else) I am open to see it.
First you need to use Dispatcher.Invoke to change the UI from another thread and to do that from another class, you can use events.
Then you can register to that event(s) in the main class and Dispatch the changes to the UI and in the calculation class you throw the event when you want to notify the UI:
class MainWindow : Window
{
private void startCalc()
{
//your code
CalcClass calc = new CalcClass();
calc.ProgressUpdate += (s, e) => {
Dispatcher.Invoke((Action)delegate() { /* update UI */ });
};
Thread calcthread = new Thread(new ParameterizedThreadStart(calc.testMethod));
calcthread.Start(input);
}
}
class CalcClass
{
public event EventHandler ProgressUpdate;
public void testMethod(object input)
{
//part 1
if(ProgressUpdate != null)
ProgressUpdate(this, new YourEventArgs(status));
//part 2
}
}
UPDATE:
As it seems this is still an often visited question and answer I want to update this answer with how I would do it now (with .NET 4.5) - this is a little longer as I will show some different possibilities:
class MainWindow : Window
{
Task calcTask = null;
void buttonStartCalc_Clicked(object sender, EventArgs e) { StartCalc(); } // #1
async void buttonDoCalc_Clicked(object sender, EventArgs e) // #2
{
await CalcAsync(); // #2
}
void StartCalc()
{
var calc = PrepareCalc();
calcTask = Task.Run(() => calc.TestMethod(input)); // #3
}
Task CalcAsync()
{
var calc = PrepareCalc();
return Task.Run(() => calc.TestMethod(input)); // #4
}
CalcClass PrepareCalc()
{
//your code
var calc = new CalcClass();
calc.ProgressUpdate += (s, e) => Dispatcher.Invoke((Action)delegate()
{
// update UI
});
return calc;
}
}
class CalcClass
{
public event EventHandler<EventArgs<YourStatus>> ProgressUpdate; // #5
public TestMethod(InputValues input)
{
//part 1
ProgressUpdate.Raise(this, status); // #6 - status is of type YourStatus
// alternative version to the extension for C# 6+:
ProgressUpdate?.Invoke(this, new EventArgs<YourStatus>(status));
//part 2
}
}
static class EventExtensions
{
public static void Raise<T>(this EventHandler<EventArgs<T>> theEvent,
object sender, T args)
{
if (theEvent != null)
theEvent(sender, new EventArgs<T>(args));
}
}
#1) How to start the "synchronous" calculations and run them in the background
#2) How to start it "asynchronous" and "await it": Here the calculation is executed and completed before the method returns, but because of the async/await the UI is not blocked (BTW: such event handlers are the only valid usages of async void as the event handler must return void - use async Task in all other cases)
#3) Instead of a new Thread we now use a Task. To later be able to check its (successfull) completion we save it in the global calcTask member. In the background this also starts a new thread and runs the action there, but it is much easier to handle and has some other benefits.
#4) Here we also start the action, but this time we return the task, so the "async event handler" can "await it". We could also create async Task CalcAsync() and then await Task.Run(() => calc.TestMethod(input)).ConfigureAwait(false); (FYI: the ConfigureAwait(false) is to avoid deadlocks, you should read up on this if you use async/await as it would be to much to explain here) which would result in the same workflow, but as the Task.Run is the only "awaitable operation" and is the last one we can simply return the task and save one context switch, which saves some execution time.
#5) Here I now use a "strongly typed generic event" so we can pass and receive our "status object" easily
#6) Here I use the extension defined below, which (aside from ease of use) solve the possible race condition in the old example. There it could have happened that the event got null after the if-check, but before the call if the event handler was removed in another thread at just that moment. This can't happen here, as the extensions gets a "copy" of the event delegate and in the same situation the handler is still registered inside the Raise method.
I am going to throw you a curve ball here. If I have said it once I have said it a hundred times. Marshaling operations like Invoke or BeginInvoke are not always the best methods for updating the UI with worker thread progress.
In this case it usually works better to have the worker thread publish its progress information to a shared data structure that the UI thread then polls at regular intervals. This has several advantages.
It breaks the tight coupling between the UI and worker thread that Invoke imposes.
The UI thread gets to dictate when the UI controls get updated...the way it should be anyway when you really think about it.
There is no risk of overrunning the UI message queue as would be the case if BeginInvoke were used from the worker thread.
The worker thread does not have to wait for a response from the UI thread as would be the case with Invoke.
You get more throughput on both the UI and worker threads.
Invoke and BeginInvoke are expensive operations.
So in your calcClass create a data structure that will hold the progress information.
public class calcClass
{
private double percentComplete = 0;
public double PercentComplete
{
get
{
// Do a thread-safe read here.
return Interlocked.CompareExchange(ref percentComplete, 0, 0);
}
}
public testMethod(object input)
{
int count = 1000;
for (int i = 0; i < count; i++)
{
Thread.Sleep(10);
double newvalue = ((double)i + 1) / (double)count;
Interlocked.Exchange(ref percentComplete, newvalue);
}
}
}
Then in your MainWindow class use a DispatcherTimer to periodically poll the progress information. Configure the DispatcherTimer to raise the Tick event on whatever interval is most appropriate for your situation.
public partial class MainWindow : Window
{
public void YourDispatcherTimer_Tick(object sender, EventArgs args)
{
YourProgressBar.Value = calculation.PercentComplete;
}
}
You're right that you should use the Dispatcher to update controls on the UI thread, and also right that long-running processes should not run on the UI thread. Even if you run the long-running process asynchronously on the UI thread, it can still cause performance issues.
It should be noted that Dispatcher.CurrentDispatcher will return the dispatcher for the current thread, not necessarily the UI thread. I think you can use Application.Current.Dispatcher to get a reference to the UI thread's dispatcher if that's available to you, but if not you'll have to pass the UI dispatcher in to your background thread.
Typically I use the Task Parallel Library for threading operations instead of a BackgroundWorker. I just find it easier to use.
For example,
Task.Factory.StartNew(() =>
SomeObject.RunLongProcess(someDataObject));
where
void RunLongProcess(SomeViewModel someDataObject)
{
for (int i = 0; i <= 1000; i++)
{
Thread.Sleep(10);
// Update every 10 executions
if (i % 10 == 0)
{
// Send message to UI thread
Application.Current.Dispatcher.BeginInvoke(
DispatcherPriority.Normal,
(Action)(() => someDataObject.ProgressValue = (i / 1000)));
}
}
}
Everything that interacts with the UI must be called in the UI thread (unless it is a frozen object). To do that, you can use the dispatcher.
var disp = /* Get the UI dispatcher, each WPF object has a dispatcher which you can query*/
disp.BeginInvoke(DispatcherPriority.Normal,
(Action)(() => /*Do your UI Stuff here*/));
I use BeginInvoke here, usually a backgroundworker doesn't need to wait that the UI updates. If you want to wait, you can use Invoke. But you should be careful not to call BeginInvoke to fast to often, this can get really nasty.
By the way, The BackgroundWorker class helps with this kind of taks. It allows Reporting changes, like a percentage and dispatches this automatically from the Background thread into the ui thread. For the most thread <> update ui tasks the BackgroundWorker is a great tool.
If this is a long calculation then I would go background worker. It has progress support. It also has support for cancel.
http://msdn.microsoft.com/en-us/library/cc221403(v=VS.95).aspx
Here I have a TextBox bound to contents.
private void backgroundWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
Debug.Write("backgroundWorker_RunWorkerCompleted");
if (e.Cancelled)
{
contents = "Cancelled get contents.";
NotifyPropertyChanged("Contents");
}
else if (e.Error != null)
{
contents = "An Error Occured in get contents";
NotifyPropertyChanged("Contents");
}
else
{
contents = (string)e.Result;
if (contentTabSelectd) NotifyPropertyChanged("Contents");
}
}
You are going to have to come back to your main thread (also called UI thread) in order to update the UI.
Any other thread trying to update your UI will just cause exceptions to be thrown all over the place.
So because you are in WPF, you can use the Dispatcher and more specifically a beginInvoke on this dispatcher. This will allow you to execute what needs done (typically Update the UI) in the UI thread.
You migh also want to "register" the UI in your business, by maintaining a reference to a control/form, so you can use its dispatcher.
Thank God, Microsoft got that figured out in WPF :)
Every Control, like a progress bar, button, form, etc. has a Dispatcher on it. You can give the Dispatcher an Action that needs to be performed, and it will automatically call it on the correct thread (an Action is like a function delegate).
You can find an example here.
Of course, you'll have to have the control accessible from other classes, e.g. by making it public and handing a reference to the Window to your other class, or maybe by passing a reference only to the progress bar.
Felt the need to add this better answer, as nothing except BackgroundWorker seemed to help me, and the answer dealing with that thus far was woefully incomplete. This is how you would update a XAML page called MainWindow that has an Image tag like this:
<Image Name="imgNtwkInd" Source="Images/network_on.jpg" Width="50" />
with a BackgroundWorker process to show if you are connected to the network or not:
using System.ComponentModel;
using System.Windows;
using System.Windows.Controls;
public partial class MainWindow : Window
{
private BackgroundWorker bw = new BackgroundWorker();
public MainWindow()
{
InitializeComponent();
// Set up background worker to allow progress reporting and cancellation
bw.WorkerReportsProgress = true;
bw.WorkerSupportsCancellation = true;
// This is your main work process that records progress
bw.DoWork += new DoWorkEventHandler(SomeClass.DoWork);
// This will update your page based on that progress
bw.ProgressChanged += new ProgressChangedEventHandler(bw_ProgressChanged);
// This starts your background worker and "DoWork()"
bw.RunWorkerAsync();
// When this page closes, this will run and cancel your background worker
this.Closing += new CancelEventHandler(Page_Unload);
}
private void bw_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
BitmapImage bImg = new BitmapImage();
bool connected = false;
string response = e.ProgressPercentage.ToString(); // will either be 1 or 0 for true/false -- this is the result recorded in DoWork()
if (response == "1")
connected = true;
// Do something with the result we got
if (!connected)
{
bImg.BeginInit();
bImg.UriSource = new Uri("Images/network_off.jpg", UriKind.Relative);
bImg.EndInit();
imgNtwkInd.Source = bImg;
}
else
{
bImg.BeginInit();
bImg.UriSource = new Uri("Images/network_on.jpg", UriKind.Relative);
bImg.EndInit();
imgNtwkInd.Source = bImg;
}
}
private void Page_Unload(object sender, CancelEventArgs e)
{
bw.CancelAsync(); // stops the background worker when unloading the page
}
}
public class SomeClass
{
public static bool connected = false;
public void DoWork(object sender, DoWorkEventArgs e)
{
BackgroundWorker bw = sender as BackgroundWorker;
int i = 0;
do
{
connected = CheckConn(); // do some task and get the result
if (bw.CancellationPending == true)
{
e.Cancel = true;
break;
}
else
{
Thread.Sleep(1000);
// Record your result here
if (connected)
bw.ReportProgress(1);
else
bw.ReportProgress(0);
}
}
while (i == 0);
}
private static bool CheckConn()
{
bool conn = false;
Ping png = new Ping();
string host = "SomeComputerNameHere";
try
{
PingReply pngReply = png.Send(host);
if (pngReply.Status == IPStatus.Success)
conn = true;
}
catch (PingException ex)
{
// write exception to log
}
return conn;
}
}
For more information: https://msdn.microsoft.com/en-us/library/cc221403(v=VS.95).aspx
I am aware that you need to use a Dispatcher to update items in the UI thread from a worker thread. To confirm my understanding, when you get the Dispatcher associated with current object is it always the UI dispatcher if my class inherits from the UserControl class? In which cases is it not the UI dispatcher?
Anyway, in the following code, I am creating a query and starting it asynchronously and when it completes, it sets the itemsource on one of my UI elements. I also am adding items to an observable collection that a UI element uses as its itemsource. When this is ran, it works fine and isn't fussing at me to use a dispatcher and update the UI that way. Why is that?
private void UserControl_Loaded(object sender, RoutedEventArgs e)
{
QueryTask queryTask = new QueryTask(URL);
queryTask.ExecuteCompleted += new EventHandler<QueryEventArgs>(queryTask_ExecuteCompleted);
queryTask.Failed += new EventHandler<TaskFailedEventArgs>(queryTask_Failed);
Query query = new Query();
query.Where = "Field <> 'XXX'";
query.OutFields.Add("*");
queryTask.ExecuteAsync(query);
BuildingsOrganizationList.ItemsSource = organizationList;
}
void queryTask_ExecuteCompleted(object sender, QueryEventArgs e)
{
FeatureSet featureSet = e.FeatureSet;
foreach (KeyValuePair<string, string> columns in featureSet.FieldAliases)
{
TypeGrid.Columns.Add(new DataGridTextColumn()
{
Header = columns.Key,
Binding = new System.Windows.Data.Binding("Attributes[" + columns.Key + "]"),
CanUserSort = true
});
}
TypeGrid.ItemsSource = featureSet.Features;
TypeBusyIndicator.IsBusy = false;
testing();
}
private void testing()
{
List<string> temp = new List<string>();
temp.Add("Item 1");
temp.Add("Item 2");
temp.Add("Item 3");
foreach (string org in temp)
{
organizationList.Add(org);
}
}
Because even though the processing is done asynchronously, you retrieve the result in your UI thread (an event is NOT thread), and update it from there.
If, however, you put the code inside queryTask_ExecuteCompleted in a Task:
Task.Factory.StartNew(() =>
{
//code of queryTask_ExecuteCompleted here
});
You will get your exception.
The ExecuteCompleted event happens on the same thread that calls ExecuteAsync.
I'm trying to create parallel execution of a function in wpf c# which also runs actions on the UI. But when running there is always an exception at methods on UI Controls: The calling thread cannot access this object because a different thread owns it. The exception is always called on the second instance of the loop being run, so it isn't possible to manipulate the UI in two parallel running instances?
Is it possible to acces the UI in parallel?
Code:
do
{
if (listBox_Copy.SelectedIndex < listBox_Copy.Items.Count - 1)
{
listBox_Copy.SelectedIndex = listBox_Copy.SelectedIndex + 1;
listBox_Copy.ScrollIntoView(listBox_Copy.SelectedItem);
}
listBox_Copy.Focus();
huidigitem = listBox_Copy.SelectedItem as ListBoxItem;
currentitemindex = listBox_Copy.SelectedIndex;
currentitem = listBox_Copy.ItemContainerGenerator.ContainerFromIndex(currentitemindex) as ListBoxItem;
itemgrid = FindVisualChild<Grid>(currentitem);
senderbutton = (Button)sender;
Button playcues = itemgrid.FindName("Playbutton") as Button;
cuetrigger = itemgrid.FindName("cuetrigger") as TextBlock;
Jobs.Add(playcues);
} while (cuetrigger.Text != "go");
Parallel.ForEach(Jobs, playcues => { play(playcues, new RoutedEventArgs()); });
And then it crashes at the play function
private void play(object sender, System.Windows.RoutedEventArgs e)
{
Grid itemgrid = VisualTreeHelperExtensions.FindAncestor<Grid>(playcue);
...
}
It is not possible to access the UI from a background thread, all your updates must be on the main thread. You can do this by using the Dispatcher
Something like this
Action x = (Action)delegate {
//do my UI updating
};
Dispatcher.Invoke(x, new object[] { });
The trick is to use an IProgress<T> to report updates to the main thread. The IProgress<T> constructor accepts an anonymous function that will be run in the main thread and can thus update the UI.
Quoting from https://blog.stephencleary.com/2012/02/reporting-progress-from-async-tasks.html :
public async void StartProcessingButton_Click(object sender, EventArgs e)
{
// The Progress<T> constructor captures our UI context,
// so the lambda will be run on the UI thread.
var progress = new Progress<int>(percent =>
{
textBox1.Text = percent + "%";
});
// DoProcessing is run on the thread pool.
await Task.Run(() => DoProcessing(progress));
textBox1.Text = "Done!";
}
public void DoProcessing(IProgress<int> progress)
{
for (int i = 0; i != 100; ++i)
{
Thread.Sleep(100); // CPU-bound work
if (progress != null)
progress.Report(i);
}
}
Now, a little bit of self-promotion :) I created an IEnumerable<T> extension to run a parallel for with event callbacks that can directly modify the UI. You can have a look at it here:
https://github.com/jotaelesalinas/csharp-forallp
Hope it helps!