I have a windows forms application that runs two threads simultaneously, with the UI thread running in the task bar. The UI thread actually performs completely separate functionality from the other process, but in the case that a new user logs into the application, I need to pop up a setup window from the non-UI thread.
Here is the code from my Program.cs:
static void Main()
{
ThreadStart start = new ThreadStart(Waiting.wait);
Thread waiting = new Thread(start);
waiting.Start();
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(true);
Application.Run(TaskBarIcon.getInstance());
}
Currently, before TaskBarIcon can fully instantiate, one configuration method must be finished running in the waiting thread. This is achieved by passing a lock back and forth.
I would like to have this set up menu pop up while the configuration method is processing, and have the method wait to complete until the setup menu is done running. However, unless I run the set up menu directly from the Application.Run() method, I cannot even get the menu to show up properly.
I'm very new to C#....would be able to do this quickly in Java, but C# seems to do things differently.
Any suggestions or solutions would be greatly appreciated!
badPanda
I suspect what it is happening is that the setup menu form is not receiving windows messages on the worker thread and that is why it is not showing up. All forms and controls need a message pump to work properly. There are various different ways of getting a message pump started, but the two most applicable to you are:
Application.Run
Form.ShowDialog
If you call ShowDialog on the setup menu form then it should show up on the worker thread. Of course the call blocks until the form is closed so that will prevent the remainder of the configuration method from executing, but then again that may be exactly what you want.
If you want the main UI thread (the one calling Application.Run) to wait until this configuration method is finished then use a WaitHandle to signal when the configuration task is complete. It might look like the following.
static void Main()
{
var configured = new ManualResetEvent(false);
var worker = new Thread(
() =>
{
// Do some stuff here.
CallYourConfigurationMethod();
configured.Set() // Signal that configuration is complete.
// Do some more stuff here.
});
worker.Start();
configured.WaitOne();
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(true);
Application.Run(TaskBarIcon.getInstance());
}
Related
I have to show a progress window in a different thread.
This is what I've done:
Thread loadT = new Thread(new ThreadStart(() =>
{
Loading ldd = new Loading();
ldd.SetContentMessage("Loading...");
ldd.Closed += (s, ec) =>
Dispatcher.CurrentDispatcher.BeginInvokeShutdown(DispatcherPriority.Background);
ldd.ShowDialog();
}));
loadT.SetApartmentState(ApartmentState.STA);
loadT.Start();
//do something
loadT.Abort();
But I don't think this is the right way. I want to use this window for different processes and i also want to set the window on the top of the others. Which is the best approach?
Ty!
You should do this the other way around when you are waiting for data and stuff to load.
Loading ldd = new Loading();
ldd.SetContentMessage("Loading...");
ldd.ShowDialog();
Thread loadT = new Thread(new ThreadStart() =>
{
//Do stuff here
});
loadT.Start();
Then you can get setup some events and such to either post updates to the loading window, or just leave it as is. You can also either monitor the threads state within the Loading window and close itself when the thread is complete or close the window from the thread.
as an example you could modify Loading to take a Thread as its parameter.
Thread loadT = new Thread(new ThreadStart() =>
{
//Do stuff here
});
Loading ldd = new Loading(loadT);
ldd.ShowDialog();
You can then move the starting of the thread, and monitoring of the thread/closing the window into the Loading class and it can look after itself.
There are 900,000 ways you can do this. You can also use BackgroundWorkers instead of spawning a new Thread, or you can use async/await in .Net 4.5+. Threading like this has been exhaustively done in the past and there should be lots of resources on google to help you in whatever path you decide to take. The important takeaway from this is your window should really be on the UI thread, and your loading should be done on another thread, not the other way around.
You could refer to the following blog post for an example of how to launch a WPF window in a separate thread the right way: http://reedcopsey.com/2011/11/28/launching-a-wpf-window-in-a-separate-thread-part-1/.
But you won't be able to mix controls that are created on different threads. A control can only be accessed on the thread on which it was originally created so it makes no sense to create a control on one thread and then trying to use it on another because this simply won't work because of the thread affinity.
Displaying a stand-alone top-level read-only window during the time a long-running operation is in progress is fine but you should probably close this window as soon as the operation has completed. You won't be able to move controls from this window to another one that was created on another thread anyway.
I am working on understanding how to use BeginInvoke correctly. I wrote up a small test in a console app where all I am trying to do is use BeginInvoke to call a function to make a 100x100 Window with a title pop up. I am failing miserably. Here is what I have, I know this is probably just poor understanding of Threads (not my strong suit), but I'm stuck, no window pops up I just end up at my readline in Main waiting for a keypress. Execution starts at ThreadUITest.
static void ThreadUITest()
{
ThreadStart starter = new ThreadStart(threadFunc1);
Thread test = new Thread(starter);
test.IsBackground = true;
test.SetApartmentState(ApartmentState.STA);
test.Start();
}
static void threadFunc1()
{
dispatcher = Dispatcher.CurrentDispatcher; //Statically declared earlier
ThreadStart starter = new ThreadStart(threadFunc2);
Thread test = new Thread(starter);
test.IsBackground = true;
test.Start();
}
static void threadFunc2()
{
Action method = Draw;
Console.WriteLine("I'm here!");
//dispatcher.BeginInvoke( (Action)(() => {Draw();}),DispatcherPriority.Render, null);
dispatcher.BeginInvoke(method, DispatcherPriority.Send, null);
}
static void Draw()
{
Window win = new Window();
win.Height = 100;
win.Width = 100;
win.Title = "A Window!";
win.Show();
}
Thanks for any help.
You need to add the following at the bottom of your threadFunc1
// statically declared earlier, although you don't need to keep a reference to it as
// WPF will keep it in Application.Current
application = new Application();
application.Run(); // thread1 is now our "UI" thread
Why does this solve it?
The Dispatcher object provides an interface for getting a thread to do some work for you (via BeginInvoke or Invoke).
In order for a thread to be able to process any "do work" messages, it must be running some kind of event loop, where it sits and waits for the next message to process - if it weren't doing this, then it wouldn't be able to process anything, it would just be stuck.
Calling Dispatcher.CurrentDispatcher from thread1 will create a new dispatcher on that thread if there isn't one already there[1] - that gives us our interface to post messages to the thread.
What dispatcher.BeginInvoke does is add an entry into the message queue for that thread, however the thread isn't running any message loop yet. We can queue messages to it, but it won't pick them up and run them - this is why nothing happens.
So, we need to make that thread start running a message loop.
The Application.Run() method is the WPF framework method which does exactly that. The Application.Run method never returns (until you call Application.Shutdown anyway), it starts up a message loop to begin processing messages thereafter. I find it useful to think of it "taking over" the thread.
Now with this change, when thread2func calls dispatcher.BeginInvoke, the message loop code inside Application.Run goes "oh look, a message, I'll process it" - it gets the BeginInvoke method, and does what it's told (in this case, executing your Draw function), and all is well
Note: As per Ark-kun's answer You can also just call Dispatcher.Run to start a message loop on that thread without creating an Application object (Application.Run does this internally). Generally I find it nicer to create an application object though, as that's more "normal", and some other code you may write later on may expect an Application object to exist
[1] FYI, this is why calling Dispatcher.CurrentDispatcher is dangerous and you should avoid it. If you call Dispatcher.CurrentDispatcher from the existing UI thread, it returns you a reference to the correct dispatcher.
If you accidentally call it from another thread, logically, you'd think it would return a reference to the existing dispatcher. But no - instead, it creates a second dispatcher, pointing at our other thread - however our other thread won't be running a message loop, and we'll get stuck again. I'd suggest never calling Dispatcher.CurrentDispatcher except for the very first time.
Once your app is up and running, you generally don't need to do this anyway, as all WPF objects (Window, Button, etc) all have a Dispatcher property which you can use to get the correct dispatcher from anyway
Try calling Dispatcher.Run() in the end of threadFunc1.
I'm new to WPF (and computer science in general) and I was given a small project from my boss where there are 5 tabs, each that go to a different site. After logging in, the user is directed to the website of the 1st tab. In the background, the 4 other tabs should be loading in the background.
Each has the following name: "tabItem1", "tabItem2", "tabItem3", "tabItem4" up to "tabItem5"
Inside each there is a up to "webBrowser5".
I think that I have to use threading to load the pages in the background, but I'm not sure how to implement it. I tried creating 4 different threads in the MainWindow such as:
public MainWindow()
{
InitializeComponent();
Thread thread1 = new Thread(Update1);
thread1.SetApartmentState(ApartmentState.STA);
thread1.Start();
Thread thread2 = new Thread(Update2);
thread2.SetApartmentState(ApartmentState.STA);
thread2.Start();
Thread thread3 = new Thread(Update3);
thread3.SetApartmentState(ApartmentState.STA);
thread3.Start();
Thread thread4 = new Thread(Update4);
thread4.SetApartmentState(ApartmentState.STA);
thread4.Start();
}
private void Update1()
{
this.Dispatcher.BeginInvoke(DispatcherPriority.Normal,
(ThreadStart)delegate()
{
tabItem2.Focus();
}
);
}
private void Update2()
{
this.Dispatcher.BeginInvoke(DispatcherPriority.Normal,
(ThreadStart)delegate()
{
tabItem3.Focus();
}
);
}
//...Goes up to Update4
This seems to only focus on the last thread and also it doesn't do it the background. I appreciate any guidance and help. Thanks!
That IS what the dispatcher is doing, operating on the main thread. You told the main thread to set focus because the object is on the main thread.
The problem:
The answer lies in why you must do this. You cannot operate on a windows control in any other thread than the thread it was created on. You also can't create a control in one thread, and set it as a child of a control in another thread.
What this means to you... is that what your boss asked you to do can't be done. The only thing you can do in the background is calculate algorithms. At best, you'll be able to load data, and operate on data, and interpret data, but if you want to have that data be displayed in, or converted into, windows controls, you must do that on the main thread.
The only solution:
However, you can have multiple UIThreads. Which means you can create multiple Windows. So, the must-do alternative is to create windows on separate threads for each tab content, then host the thread-windows on each tab.
Threading windows
Host process window
Cross thread hosting
I do not agree with Xaade, I think you can do what you need using only this code:
Dispatcher.BeginInvoke((Action)(() =>
{
// load the pages
}), DispatcherPriority.Background, null);
That code will be executed in background, so, there you can load every webBrowser you need.
You just need to specify the DispatcherPriority to Background.
I am trying to run an application with at least two threads: One form for the user interface and one or more worker threads. They are jointly reading/writing from a static class through a number of other classes.
This is why I am passing an instance of the worker class to the display form. I guess that is why it goes wrong for me:
public class CoCoon
{
private Screen displayForm;
private Worker worker;
public ThreadedApp()
{
worker = new Worker (1024);
displayForm = new Screen(worker);
}
public void Run()
{
//thread 1: display form
Thread screenThread = new Thread(() => Application.Run(displayForm));
//thread 2: background worker
Thread workerThread = new Thread(worker.Run) {IsBackground = true};
screenThread.Start();
Thread.Sleep(1000); //if I don't wait a while, I get an ObjectDisposedException!
workerThread.Start();
}
The threads and objects are initiated just fine, but as soon after the Form_Load method is has been handled, an error is thrown on the Application.Run(displayForm) line above. It is an NotSupportedException, with a remark that I should use Control.Invoke. But I am not sure I understand, because I am not letting threads other than the display form's use the controls on it.
I am new to threading. Can anyone help me on my way? Thanks!
PS: One detail - I am developing this for the Windows Mobile platform.
EDIT After popular request hereby the Stack Trace
at Microsoft.AGL.Common.MISC.HandleAr(PAL_ERROR ar)\r\n at
System.Windows.Forms.Control.get_Visible()\r\n at
System.Windows.Forms.Form._SetVisibleNotify(Boolean fVis)\r\n at
System.Windows.Forms.Control.set_Visible(Boolean value)\r\n at
System.Windows.Forms.Application.Run(Form fm)\r\n at
CoCoonWM6.CoCoon.<Run>b__1()\r\n
I recommend that you only have one UI thread, the main thread. You can use your other threads for background operations, but keep all UI stuff on the main thread.
The UI thread should be the only one calling Application.Run. WinForms has other requirements for the UI thread (such as being STA), and those are satisfied by the main thread. In theory, it may be possible for WinForms to support two UI threads, but it's certainly not easy.
I normally recommend other forms of synchronization when you need to update UI controls from a background thread - TaskScheduler or SynchronizationContext. On the mobile platform, unfortunately, your only option is Control.Invoke.
Check out the stack trace for the exception (and post it). You are almost certainly accessing some Control from the worker thread.
This is how you can modify access to a Control (in this example a Label) after you find where you are accessing controls from non-UI threads:
if (label13.InvokeRequired)
{
ChangeTextDelegate changeText = new ChangeTextDelegate(anyChangeTextMethod);
label13.Invoke(changeText, new object[] { newText });
}
else
{
label13.Text = newText;
}
Looks like you're trying to use GUI elements in the background thread. That would explain why you have to call Sleep (otherwise the form and its controls don't finish loading before you try to use them) as well as the Control.Invoke exception (you can't use GUI elements from a non-UI thread). See the docs for Control.Invoke for how you should use it.
Since you don't have BackgroundWorker and Px in the CF, you're indeed forced to use threads directly - though the ThreadPool would probably be better than instantiating new threads, most of the time.
I have a Windows Form Application (Form1) that allow the user to open another Forms (FormGraph). In order to open the FormGraph App I use a thread that open it.
Here is the code that the thread is running:
private void ThreadCreateCurvedGraph()
{
FormGraph myGraph = new FormGraph();
myGraph.CreateCurvedGraph(...);
myGraph.Show();
}
My problem is that myGraph closed right after it's open.
1) Does anyone know why this is happening and how to make myGraph stay open?
2) After the user closed myGraph, How do I terminate the thread?
Many thanks!
The problem is not in the posted snippet. You'll need to start a new message loop with Application.Run() or Form.ShowDialog(). You'll also need to take care of thread properties so it is suitable to act as a UI thread. For example:
Thread t = new Thread(() => {
Application.Run(new Form2());
// OR:
//new Form2().ShowDialog();
});
t.SetApartmentState(ApartmentState.STA);
t.IsBackground = true;
t.Start();
There are some awkward choices here. The form cannot be owned by any form on your main thread, that usually causes Z-order problems. You'll also need to do something meaningful when the UI thread's main form is closed. Sloppily solved here by using IsBackground.
Windows was designed to support multiple windows running on one thread. Only use code like this if you really have to. You should never have to...
The main problem you ahve is that you do not establish a message pump in the new thread.
Check
Run multiple UI Threads
for a good overview how to run a high perforamnce user interface using multiple threads (one per form / group of forms).
What you basically miss is the call to Application.Run to set up the message pump on the separate UI thread.
I think once the last form of a message pump closes - it will dispose itself and end.
Note that all this ASSUMES you WANT to open the window in a separate UI thread... otherwise you need to invoke back to the main UI thread for the creation and all manipulation of the window, so it gets attached to the existing message pump. There are GOOD cases for both - one keeps thigns simple, the other allows a LOT more performance as every window has a separate message pump and can thus act individually - this is for example used a lot in trading applications which may need to update graphs on a number of screens and havea bottleneck if running single threaded in the UI.
As a rule of thumb you should avoid manipulating the UI from threads (creating a form is a sort of manipulation to the UI). You should always manipulate the UI from the main thread.
The form is closing because the thread has finished and is therefore free'd along with its resouces (the form). To make the thread stay running you need a loop
e.g.
private void ThreadCreateCurvedGraph()
{
FormGraph myGraph = new FormGraph();
myGraph.CreateCurvedGraph(...);
myGraph.Show();
while (myGraph.IsOpen)
{
//process incoming messages <- this could be fun on a thread....
}
}
You'll need a method of setting IsOpen (like a timeout or a button) and obviously you'll need to actually create IsOpen as a property of the form and set it to true when the form is created.
I'll add here the same as other users... You should have a good reason for not using the main thread.
If it takes a while to prepare the data for the form, you can do that in a separate thread to keep the application responsive. When the data is ready you can return the object to the main thread an let it show it.
You should declare a variable for the object in the form rather than locally in the method, so that it survives when you exit the thread.
When you are ready to show the form, you can use the Invoke method to make a method call that will be executed in the main thread.
do not create and show forms in non-main thread. do it in main form thread.
Or do this:
private void ThreadCreateCurvedGraph()
{
FormGraph myGraph = new FormGraph();
myGraph.CreateCurvedGraph(...);
Application.Run(myGraph);
}
but first version is better
Why are you creating a form on a new thread? There are times you need to use a new thread but other times you can use form.ShowDialog() on the main thread.
What about if you show the form as if it was a Dialog? You can use
private void ThreadCreateCurvedGraph()
{
FormGraph myGraph = new FormGraph();
myGraph.CreateCurvedGraph(...);
myGraph.ShowDialog();
}
This way the call will block until the myGraph form is closed. As you have the myGraph created on a separated thread calling the blocking ShowDialog should block only that thread.
Perhaps this is garbage collection:
After ThreadCreateCurvedGraph() exits, myGraph goes out of scope and closes.
You need to organise a way of the thread to hold on to the instance and wait (using a blocking wait) for it to close.
Edit: For instance add:
Application.Run(myGraph)
to the end of the method.
(See comments from TomTom)