I want to show progress bar while my application create complex screen. my code is:
protected override void LoadSubject(object sender)
{
var win = new Spinner();
win.Show();
Thread th = new Thread(() =>
{
LoadSubjectImpl(sender);
win.Dispatcher.BeginInvoke(new Action(() => win.Close()));
});
th.Start();
}
private void LoadSubjectImpl(object sender)
{
Application.Current.Dispatcher.BeginInvoke(new Action(() =>
{
StartServiceWorkflow(sender);
})
);
}
its works fine, but the progress bar freeze...
I must use the dispatcher in background thread because of "InvalidOperationException" and I think that the problem, but what can I do?
spinner = costum progressbar.
You will have no luck trying to achieve what you have described. If you'd read closely that InvalidOperationException you would know that you cannot manipulate UI from background thread. What you have done using Dispatcher is synchronizing StartServiceWorkflow to UI thread. So your code is executing in it - that causes the freeze.
To achieve some user experience enhancement you can delegate to background thread tasks like reading form database or processing data that is to be displayed.
Related
I have Window 1 in which on button click i am opening Window 2 in new thread.
Following is my code
private void Button_Click_2(object sender, RoutedEventArgs e)
{
Thread thread = new Thread(() =>
{
Scanner w = new Scanner();
w.Show();
w.Closed += (sender2, e2) =>
w.Dispatcher.InvokeShutdown();
System.Windows.Threading.Dispatcher.Run();
});
thread.SetApartmentState(ApartmentState.STA);
thread.Start();
}
Window 2 has form I am getting form values on Button click
private void EnterProduct(object sender, RoutedEventArgs e)
{
var data = ProductDetailsData;
LoadCurrentBetween objMain = new LoadCurrentBetween(); //new MainWindow();
objMain.fillorderform(data);
}
on button click of window 2 i am passing values of form to another View
public void fillorderform(dynamic data)
{
this.Dispatcher.Invoke(() =>
{
LoadCurrentdetails.Part = data.Part;
LoadCurrentBetween loadCurrentbtw = new LoadCurrentBetween();
Switcher.Switch(loadCurrentbtw);
});
} public static class Switcher
{
public static MainWindow pageSwitcher;
public static void Switch(UserControl newPage)
{
pageSwitcher.Navigate(newPage);
}
}
Following code is giving error at "this.Content = nextPage;"
The calling thread cannot access this object because a different thread owns it.
public void Navigate(UserControl nextPage)
{
this.Dispatcher.Invoke(() =>
{
var aa = nextPage.Dispatcher.CheckAccess();
this.Content = nextPage;
});
}
I have seen similar Questions asked by other developers but i am not getting how to fix.
pls help
WPF is very strict (compared to Windows forms) about requiring methods which update UI elements to be done on the main/UI thread. So you definitely want both windows to be in the main/UI thread. The error that you are seeing is what happens if you try to do UI work in WPF from a different thread, so you absolutely have to stop doing that. It's OK to have multiple windows open, all on the same UI thread.
If one of your windows is doing heavyweight processing that makes the UI lock up, then the easiest thing is probably to add the async keyword to your button click event, and put the work you are doing in another method which has an async keyword. Then, when you call the helper method, you use the await keyword.
I agree with others that BackgroundWorker and Task are two other ways to accomplish heavyweight processing in a background thread while still having a responsive UI. Tasks are easier to use than BackgroundWorker.
If you are using a BackgroundWorker, it may be good enough to use the RunWorkerCompleted event. If so, look at this post: How to use WPF Background Worker. If you are using a BackgroundWorker and you need to call a custom method in your UI class from the background thread, then pass the Dispatcher object for your window/dialog to the background thread (or get access to it some other way), and when it needs to call back into the UI, use Invoke with the Dispatcher object. By using Invoke, the method you are calling from the background thread will be executed on the UI thread.
According to answer for this question Why Thread.Join() DOES NOT hang my application when called on UI thread? thread.Join should not hang UI if it called from STA thread. I used the same code as in linked question
private void button1_Click(object sender, EventArgs e)
{
string retValue = "";
Thread thread = new Thread(
() =>
{
retValue = LongRunningHeavyFunction();
});
thread.Start();
thread.Join();
button1.Text = retValue;
}
private string LongRunningHeavyFunction()
{
Thread.Sleep(5000);
return "Done";
}
Method Main in class Program marked as [STAThread]. But when I press button UI is freezed, I can't drag window etc. I'm confused. Am I missed something? Why UI is freezed in my case?
Thread.Sleep causes UI to freeze.
If you want to wait for a while in LongRunningHeavyFunction(), use a timer object.
Here is an example, how to use timer:
How to use a timer to wait?
thread.Join() tells the current thread to await thread. In this case, the current thread is the GUI thread, and you're telling it to await the worker thread. As a result, your GUI thread does nothing until the worker thread completes. And since the GUI thread is doing nothing, it isn't handling normal GUI activities, causing the freeze.
The solution is to not block your GUI. Instead, run your long-running process without awaiting it, such that your GUI thread can keep responding to the user. Then, once the long-running process does complete, use the GUI dispatcher to call back to set the result.
The code might look something like this:
private void button1_Click(object sender, EventArgs e)
{
Thread thread = new Thread(
() =>
{
// Perform work
var retValue = LongRunningHeavyFunction();
// Call the GUI thread
button1.Dispatcher.BeginInvoke(() =>
{
// .Dispatcher called the GUI thread.
// This code happens back in the GUI thread once the
// worker thread has completed.
button1.Text = retValue;
});
});
thread.Start();
}
private string LongRunningHeavyFunction()
{
Thread.Sleep(5000);
return "Done";
}
I have faced with a problem of threads synchronization. My presenter analyzes some sensors and update UI form. I moved updating code into separate thread. It works fine, but if the user stops presenter when it is updating the view, the software freezes - I found that it happens when view.UpdateUI working (it just set some labels using Invoke). Where my problem is? I use compact framework 3.5 and Windows CE 5
using System.Threading;
class MyPresenter
{
UserControl view;
private Thread thread;
private ManualResetEvent cancelEvent;
public void Start()
{
cancelEvent = new ManualResetEvent(false);
thread = new Thread(UpdateView) { IsBackground = true };
thread.Start();
}
public void Stop()
{
if (thread != null) {
cancelEvent.Set();
thread.Join();
thread = null;
}
}
private void UpdateView()
{
while (cancelEvent.WaitOne(1000, false) == false) {
// analyze something
view.UpdateUI(...);
}
}
}
Don't update the UI thread directly from within a worker thread. Use a delegate instead.
For example: How to update the GUI from another thread in C#?
If your background thread is blocked calling your UI (via Control.Invoke), and then your UI thread is blocked calling your Stop method with its thread.Join() you've got yourself a classic fatal embrace. You should get rid of the Join and instead have the background thread raise one last event / notification when the Stop completes so the UI can deal with that (enable/disable buttons etc).
How would I update the UI in my Windows Phone app from a while, foreach, for, etc loop?
Have you considered using additional thread for this?
public MainPage()
{
InitializeComponent();
Thread thread = new Thread(() => ReadFile(/*params*/));
thread.Start();
}
private void ReadFile(/*params*/)
{
while(/*condition*/)
{
/* READ FILE */
//send task to UI thread to add object to list box
Dispatcher.BeginInvoke(() => listBox1.Items.Add("YOUR OBJECT"));
}
}
Long term action is happening in non-UI thread, what makes that UI thread doesn`t get frozen. In every loop iteration, non-UI Thread sends action via Dispatcher.BeginInvoke to UI thread to add new object to listbox.
I have two threads.
Thread 1: WPF thread. Shows a Window with all the information.
Thread 2: Loops constantly, receiving information & updates the Window in thread 1.
I have the following interfaces.
IModuleWindow
{
void AddModule(IModule module);
void RemoveModule(IModule module);
}
IModule
{
UserControl GetSmallScreen();
UserControl GetBigScreen();
}
IModuleWindow is implemented by the WPF window in Thread 1
IModule is implemented by an object, is instantiated in Thread 2, and then sent to thread 1.
I want to Add the UserControls in IModule to the Window object in thread 1, and show them. IModule objects get updated constantly in thread 2 and they have to change their text.
Basically the idea is that this program is supposed to show the state of objects in thread 2 , which gets updated constantly.
What is the best way to accomplish this in WPF?
IMO the best idea is to use BackgroundWorker, with the very handy ReportProgress method and ProgressChanged event.
The ProgressChanged event is raised on the GUI thread, so you can perform your updates to the GUI directly. Here's how you code should look like:
// initialize the worker
BackgroundWorker backgroundWorker1 = new BackgroundWorker();
backgroundWorker1.WorkerReportsProgress = true;
backgroundWorker1.DoWork += new DoWorkEventHandler(backgroundWorker1_DoWork);
backgroundWorker1.ProgressChanged += new ProgressChangedEventHandler(backgroundWorker1_ProgressChanged);
backgroundWorker1.RunWorkerAsync();
// thread 2 (BackgroundWorker)
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
// main loop
while(true)
{
// time-consuming work
// raise the event; use the state object to pass any information you need
ReportProgress(0, state);
}
}
// this code will run on the GUI thread
private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
// get your state back
object state = e.UserState;
// update GUI with state
}
It helped me lot to understand what i must do.
The scenario must be like that:
ObservableCollection images = new ObservableCollection();
TaskFactory tFactory = new TaskFactory();
tFactory.StartNew(() =>
{
for (int i = 0; i < 50; i++)
{
//GET IMAGE Path FROM SERVER
System.Windows.Application.Current.Dispatcher
.BeginInvoke((Action)delegate()
{
// UPDATE PROGRESS BAR IN UI
});
images.Add(("");
}
}).ContinueWith(t =>
{
if (t.IsFaulted)
{
// EXCEPTION IF THREAD IS FAULT
throw t.Exception;
}
System.Windows.Application.Current.Dispatcher
.BeginInvoke((Action)delegate()
{
//PROCESS IMAGES AND DISPLAY
});
});
You must use System.Windows.Application.Current.Dispatcher.BeginInvoke() for updating UI in WPF.
It would be nice to be able to use controls created at another thread,
thats what I want ideally
The short answer: forget it.
A UI control belongs to a single UI thread only. The best you can do here, is to create controls in main thread, prepare data in background thread, and update controls' properties in main (UI) thread again.
For data preparation I recommend use TPL.