I've created a TimerManager class for my WPF application.
This class handles the start and stop the dispatcher timer.
Here is the class:
public static class TimerManager
{
static DispatcherTimer disTimer;
static Model m = Model.GetInstance();
static TimerManager()
{
disTimer = new DispatcherTimer();
disTimer.Tick += disTimer_tick;
disTimer.Interval = new TimeSpan(0, 0, 1);
}
public static void StartTimer()
{
disTimer.Start();
}
public static void StopTimer()
{
disTimer.Stop();
}
private static void disTimer_tick(object sender, EventArgs e)
{
m.Tick++;
}
}
And I've created a Model class that represents the ticking in the UI.
(Binding in MainWindow.xaml -> xy textbox text field "{Binding Tick}").
class Model : INotifyPropertyChanged
{
private Model()
{
}
static Model instance;
public static Model GetInstance()
{
if (instance == null)
{
instance = new Model();
}
return instance;
}
int tick;
public event PropertyChangedEventHandler PropertyChanged;
public void OnNotifyPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChangedEventArgs e = new PropertyChangedEventArgs(propertyName);
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, e);
}
}
public int Tick
{
get
{
return tick;
}
set
{
tick = value;
OnNotifyPropertyChanged();
}
}
}
And here is the MainWindow class:
Model m;
public MainWindow()
{
InitializeComponent();
m = Model.GetInstance();
this.DataContext = m;
}
private void startButton_Click(object sender, RoutedEventArgs e)
{
ThreadPool.QueueUserWorkItem(o =>
{
TimerManager.StartTimer();
});
//TimerManager.StartTimer();
}
private void stopButton_Click(object sender, RoutedEventArgs e)
{
TimerManager.StopTimer();
}
When I click the start button I use the ThreadPool.QueueUserWorkItem() method. In that method, I start the timer but the timer tick is not run at every one second.
When I don't use ThreadPool this works. But this solution is not good for me; ThreadPool is important for me because I use an HTTP web server (in local).
My question is: why is the ticking not working if I use ThreadPool?
The DispatcherTimer object has thread affinity. That is, it is tied to a specific thread. In particular, it is designed specifically to raise its Tick event in the thread in which it was created, using the Dispatcher for that thread.
Your ThreadManager class's static constructor will be called when the type is first used. In your non-working example, this occurs in the queued work item method, causing the static constructor to be executed in the thread pool thread used to execute that work item method. This in turn causes the DispatcherTimer object you create to be owned by that thread, and to have its Tick event raised in that thread by the Dispatcher for that thread.
Except, thread pool threads don't have Dispatchers. So there's no Dispatcher there to raise the Tick event for the DispatcherTimer object. Even if there was, without a call to Application.Run() to have the dispatcher loop executed, the Dispatcher wouldn't actually get to dispatch anything, including the Tick event.
What you need is to make sure that when you create the DispatcherTimer object, the code that creates that object is executed in the dispatcher thread, which is your main UI thread.
There are a couple of ways to do that. IMHO, the best way is to make your ThreadManager class not a static class and to create an instance of it in your MainWindow constructor. For example:
class TimerManager
{
DispatcherTimer disTimer;
Model m = Model.GetInstance();
public TimerManager()
{
disTimer = new DispatcherTimer();
disTimer.Tick += disTimer_tick;
disTimer.Interval = new TimeSpan(0, 0, 1);
}
public void StartTimer()
{
disTimer.Start();
}
public void StopTimer()
{
disTimer.Stop();
}
private void disTimer_tick(object sender, EventArgs e)
{
m.Tick++;
}
}
and:
public partial class MainWindow : Window
{
TimerManager _timerManager = new TimerManager();
public MainWindow()
{
InitializeComponent();
this.DataContext = Model.GetInstance();
}
private void startButton_Click(object sender, RoutedEventArgs e)
{
ThreadPool.QueueUserWorkItem(o =>
{
_timerManager.StartTimer();
});
}
private void stopButton_Click(object sender, RoutedEventArgs e)
{
_timerManager.StopTimer();
}
}
Since you know your MainWindow object has to be created in the dispatcher thread, and you know that non-static field initialization happens at the same time the constructor is called, in that same dispatcher thread, the above ensures that your TimerManager object is created in the dispatcher thread.
This gives you complete control over the lifetime of the TimerManager object, particularly when it's created but of course also when it can be discarded. Given the nature of the DispatcherTimer object itself, it's my opinion that this is better than maintaining a statically-held instance.
This approach also gives you the option of having a manager object for each dispatcher thread (in rare cases, a program might have more than one…you should try very hard to avoid getting into that situation, but it can be useful for types to at least be compatible with such a situation).
That said, if you really want to keep the static implementation, you can do that by providing a method that can be called explicitly when you want to initialize the class, so you can make sure that the initialization happens in the right thread:
static class TimerManager
{
static DispatcherTimer disTimer;
static Model m = Model.GetInstance();
public static void Initialize()
{
disTimer = new DispatcherTimer();
disTimer.Tick += disTimer_tick;
disTimer.Interval = new TimeSpan(0, 0, 1);
}
public static void StartTimer()
{
disTimer.Start();
}
public static void StopTimer()
{
disTimer.Stop();
}
private static void disTimer_tick(object sender, EventArgs e)
{
m.Tick++;
}
}
Then in your MainWindow class:
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
this.DataContext = Model.GetInstance();
StaticTimerManager.Initialize();
}
private void startButton_Click(object sender, RoutedEventArgs e)
{
ThreadPool.QueueUserWorkItem(o =>
{
StaticTimerManager.StartTimer();
});
}
private void stopButton_Click(object sender, RoutedEventArgs e)
{
StaticTimerManager.StopTimer();
}
}
All you need to do here is make sure you call the Initialize() method from the main UI thread where you actually have a running dispatcher, before you attempt to call either of the other two static methods in the class.
This approach could also be made to work with multiple threads (i.e. if you have more than one dispatcher thread), but it would be trickier, especially if you want to be able to call the StartTimer() method from a different thread that actually owns the timer object. I'd recommend against the static class approach if you really did wind up in that situation.
Related
I have an application that takes a Wireshark capture file and feeds it (all the containing packets) into a network adapter.
Currently my application is a big mess - countless global variables & every task opened within a seperate BackgroundWorker instance etc...
To clarify - the purpose of using BackgroundWorkers here (more specifically the DoWork, RunWorkerCompleted events and the WorkerReportsProgress property) is to prevent the packet feeding operations from freezing my UI. To stop an operation, I need access to these workes - for now, global variables are used to achieve this.
So the question is - should I place my BackgroundWorker objects inside a Singleton-type class and then call this object when necessary?
From a technical point of view is possible, after all the singleton pattern is a design pattern that restricts the instantiation of a class to one object
you can try something like this
public class BackWorkerSingleton
{
private BackgroundWorker _backgroundWorker;
private static readonly object myLock = new object();
private static BackWorkerSingleton _backWorkerSingleton = new BackWorkerSingleton();
public delegate void ReportProgressEventHandler(object sender,MyEventsArgs e);
public event ReportProgressEventHandler ReportProgress = delegate{ };
private BackWorkerSingleton()
{
_backgroundWorker = new BackgroundWorker();
_backgroundWorker.DoWork += new DoWorkEventHandler(_backgroundWorker_DoWork);
_backgroundWorker.ProgressChanged += new ProgressChangedEventHandler(_backgroundWorker_ProgressChanged);
}
void _backgroundWorker_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
this.ReportProgress( this, new MyEventsArgs(){Progress = e.ProgressPercentage});
}
void _backgroundWorker_DoWork(object sender, DoWorkEventArgs e)
{
// do your work here
}
public void StartTheJob()
{
_backgroundWorker.RunWorkerAsync();
}
public static BackWorkerSingleton Worker
{
get
{
lock (myLock)
{
if (_backWorkerSingleton == null)
{
_backWorkerSingleton = new BackWorkerSingleton();
}
}
return _backWorkerSingleton;
}
}
}
class MyEventsArgs:EventArgs
{
public int Progress { get; set; }
}
and here the report progress
private void Form1_Load(object sender, EventArgs e)
{
BackWorkerSingleton.Worker.ReportProgress += new BackWorkerSingleton.ReportProgressEventHandler(Worker_ReportProgress);
}
void Worker_ReportProgress(object sender, MyEventsArgs e)
{
}
and call it like this
BackWorkerSingleton.Worker.StartJob()
I have a listbox with filenames. When the selected index is changed I load the file.
I want something like jQuery's HoverIntent that delays the action of loading the file for a short time so the user can use the down arrow and quickly cycle through the items in the list without the application trying to load each one. Thread.Sleep pauses the whole app so a user can't select another list item until the sleep completes, this is obviously not what I want.
This will work if your using WinForms, make a call to the InitTimer method in the Form constructor.
Load the file in the _timer_Tick event handler. To change the delay set the Interval property in InitTimer to another value.
private System.Windows.Forms.Timer _timer;
private void InitTimer()
{
_timer = new Timer { Interval = 500 };
_timer.Tick += _timer_Tick;
}
private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
{
_timer.Stop();
_timer.Start();
}
private void _timer_Tick(object sender, EventArgs e)
{
_timer.Stop();
// TODO: Load file here
}
Use Threading to separate the loading from your GUI.
This should get you started:
public partial class MainWindow : Window
{
CancellationTokenSource cts;
bool loading;
private void SelectedIndexChanged(int index)
{
if (loading)
cts.Cancel();
cts = new CancellationTokenSource();
var loader = new Task.Delay(1000);
loader.ContinueWith(() => LoadFile(index))
.ContinueWith((x) => DisplayResult(x));
loader.Start();
}
private void DisplayResult(Task t)
{
// TODO: Invoke this Method to MainThread
if (!cts.IsCancellationRequested)
{
// Actually display this file
}
}
Could not test, as I'm still on .net 4 whereas Task.Delay() is .net 4.5
You may need to add another field in the form for the file content transfer from the tasks to the GUI.
Winforms:
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private CancellationTokenSource _cancel;
private object _loadLock = new object();
private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
{
lock (_loadLock)
{
handleCancellation();
var loader = new Task((chosenFileItemInListbox) =>
{
Thread.Sleep(1000);
LoadFile(chosenFileItemInListbox);
}, listBox1.SelectedItem, _cancel.Token);
}
}
private bool handleCancellation()
{
bool cancelled = false;
lock (_loadLock)
{
if (_cancel != null)
{
if (!_cancel.IsCancellationRequested)
{
_cancel.Cancel();
cancelled = true;
}
_cancel = null;
}
}
return cancelled;
}
private void LoadFile(object chosenFileItemInListbox)
{
if (handleCancellation())
{
return;
}
}
}
The code above could also be applied to WPF, but WPF contains some built in magic for handling delays and cancellation of previous updates.
<ListBox SelectedItem="{Binding Path=SelectedFile, Delay=1000}" />
I am new to C# and am having trouble figuring out how to pass an event from a thread up to the GUI form thread. Any help would be appreciated. All of the examples I find are WAY too complicated. I just want to start with one event from the treat up to the GUI and have the GUI do something (right now, anything).
namespace testEvents
{
public delegate void StuffHappenedDel( MessageEventArgs e);
public partial class Form1 : Form
{
workerThread thread;
int j = 0;
public Form1()
{
InitializeComponent();
thread = new workerThread();
thread.Start();
}
private void button1_Click(object sender, EventArgs e)
{
thread.Stop();
}
private void StuffHappenedDel(Object seder, EventArgs e)
{
j++;
}
}
public class workerThread
{
Thread worker;
private bool _quit = false;
/* I don't think this next line is correct*/
public event StuffHappenedDel StuffHappened;
protected virtual void OnStuffHappened(MessageEventArgs e)
{
if (StuffHappened != null)
StuffHappened( e);
}
public void Start()
{
ThreadStart start = new ThreadStart(Run);
worker = new Thread(start);
worker.Start();
}
private void Run()
{
int i = 0;
while (!_quit)
{
Thread.Sleep(1000);
i++;
OnStuffHappened(new MessageEventArgs(false, "it worked!"));
Console.WriteLine(string.Format("Slept {0} seconds.",i));
}
Console.WriteLine("Thread exiting");
}
}
public class MessageEventArgs : EventArgs
{
public MessageEventArgs(bool Error, string message)
{
IsError = Error;
Message = message;
}
public bool IsError { get; set; }
public string Message { get; set; }
}
}
You need to register Form1 as a listener for the event. First, add a method like the following to Form1:
private void thread_SuffHappened(MessageEventArgs e)
{
MessageBox.Show("Stuff happened!");
}
And in Form1's constructor, register as a listener like so:
public Form1()
{
InitializeComponent();
thread = new workerThread();
thread.StuffHappened += new StuffHappenedDel(thread_StuffHappened);
thread.Start();
}
Do you have to use this custom threading system, or are you able to use BackgroundWorkers? BackgroundWorkers haven an event ProgressChanged which fires on the thread that created the BackgroundWorker.
Alternatively, if you attach a handler to a background event from the UI thread, the work is still done on the background thread.
thread.StuffHappenedDel += new EventHandler<MessageEventArgs>(StuffHappenedDel);
Therefore, you need to marshall the data to the UI thread. One way is by using BeingInvoke.
private void StuffHappenedDel(object sender, MessageEventArgs e)
{
this.myControl.BeginInvoke( new Action(
() =>
{
//UI thread work (likely anything that affects UI. Heavy
//processing can continue on the bg thread outside this code block
}));
}
Also, you can use if (myControl.InvokeRequired) to check if you need to marshall data when changing a particular control.
if (this.InvokeRequired)
{
this.Invoke((Action)(() =>
{
//UI thread stuff
}
));
}
Edit to clarify
Your thread object that you've created needs to attach an event handler to the StuffHappenedDel event. To do this, you use something like this
thread.StuffHappenedDel += new EventHandler<MessageEventArgs>(StuffHappenedDel);
before you call thread.Start(). Now, this handler is called
private void StuffHappenedDel(Object seder, MessageEventArgs e)
{
j++;
}
whenever your event is fired.
If you want to make changes to any UI elements, you need to use the Invoke method described above.
Look into the Background Worker Class. Also, you can always fire an event that is handled by your GUI Class (though not on the GUI Thread) and then call Invoke
After adding Service Reference to my Phone Application (for example http://www.deeptraining.com/webservices/weather.asmx?op=GetWeather), I tried to use AutoResetEvent for emulation syncronous method calling. But after calling WaitOne, method Set is never called. Why? Is it a bug?
public partial class MainPage : PhoneApplicationPage
{
private readonly AutoResetEvent _autoResetEvent = new AutoResetEvent(false);
private string _result;
// Constructor
public MainPage()
{
InitializeComponent();
}
private void button1_Click(object sender, RoutedEventArgs e)
{
var weatherSoapClient = new WeatherSoapClient();
weatherSoapClient.GetWeatherCompleted += weatherSoapClient_GetWeatherCompleted;
weatherSoapClient.GetWeatherAsync("Pekin");
_autoResetEvent.WaitOne(); // Program stop hire
textBlock1.Text = _result;
}
void weatherSoapClient_GetWeatherCompleted(object sender, GetWeatherCompletedEventArgs e)
{
_result = e.Result;
_autoResetEvent.Set(); // Never invoke! Why???
}
}
In WP7, HTTP responses are processed on the UI thread. Bocking the UI thread prevents the response from being processed.
I added an event handler to my code and it broke all access to the CollectionViewSources in the SystemHTA class saying "The calling thread cannot access this object because a different thread owns it". My class was working when "this.systemHTA = new SystemHTA();" was placed outside of the DeviceManager_StateChanged() function.
public partial class MainWindow : Window
{
private DeviceManager DeviceManager = DeviceManager.Instance;
public SystemHTA systemHTA;
public MainWindow()
{
InitializeComponent();
}
private void Window_Loaded(object sender, RoutedEventArgs e)
{
DeviceManager.StateChanged += new EventHandler<DeviceManagerStateChangedEventArgs>(DeviceManager_StateChanged);
DeviceManager.Initialize();
}
void DeviceManager_StateChanged(object sender, DeviceManagerStateChangedEventArgs e)
{
if (e.State == DeviceManagerState.Operational)
{
this.systemHTA = new SystemHTA();
}
}
private void button1_Click(object sender, RoutedEventArgs e)
{
this.systemHTA.GetViewSourceTest();
}
}
public class SystemHTA
{
private CollectionViewSource _deviceTestSource;
public SystemHTA()
{
_deviceTestSource = new CollectionViewSource();
_deviceTestSource.Source = CreateLoadData<HWController>.ControllerCollection;
}
public void GetViewSourceTest()
{
ListCollectionView view = (ListCollectionView)_deviceTestSource.View; //This creates an error saying a thread already owns _deviceTestSource
}
}
This is not about 'Thread Locking' but about the well known problem that a GUI (either WPF or WinForms) is not threadsafe and in a Debug build there is active checking for cross-thread calls.
So you already know the solution: create the SystemHTA object on the main thread. Your problem may shift to loading it from the DeviceMgr stuff, you may have to use Control.Dispatcher.Invoke() here.
I ended up replacing the CollectionViewSource with an ObservableCollection and everything works fine.