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How do I update the GUI from another thread?
(47 answers)
Closed 5 years ago.
I recently started learning C#, I am trying to repeat a method every minute with help of a timer. The method changes the value of the label. However, I get the following error:
$exception {"Cross-thread operation not valid: Control 'label1'
accessed from a thread other than the thread it was created
on."} System.Exception {System.InvalidOperationException}
I have tried searching for a solution and each thread confuses me. I don't just need the correct code but also explanation as I want to learn manipulating UI with help of Timers and Threading.
The following is my code:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Timers;
using System.Windows.Forms;
namespace Winforms_Timer_and_Thread
{
public partial class Form1 : Form
{
System.Timers.Timer myTimer = new System.Timers.Timer();
public Form1()
{
myTimer.Enabled = true;
InitializeComponent();
}
public void startMethod(object senter, ElapsedEventArgs e)
{
int cntr = 0;
cntr++;
label1.Text = "Executed: " + cntr.ToString();
}
private void button1_Click(object sender, EventArgs e)
{
label1.Text = "Started!";
myTimer.Enabled = true;
myTimer.Interval=(1*60*1000);
myTimer.Elapsed += new System.Timers.ElapsedEventHandler(startMethod);
}
}
}
If you change to use a System.Windows.Forms.Timer, you won't have that problem, since it's executed in the same UI thread.
You only have to change:
The type of the timer from System.Timers.Timer to System.Windows.Forms.Timer
The event that gets subscribed to from Elapsed to Tick
The event signature, where ElapsedEventArgs e becomes EventArgs e
You also only need to subscribe to the event once, not each time the timer is enabled, so move that to the Form_Load event instead, along with the Interval assignment (although that can be changed any time).
You also might want to store the counter variable outside of the StartMethod, so it increments each time it's executed, and then reset it to zero each time you start the timer:
public partial class Form1 : Form
{
readonly System.Windows.Forms.Timer myTimer = new System.Windows.Forms.Timer();
private int tickCounter;
public Form1()
{
InitializeComponent();
myTimer.Interval = (int)TimeSpan.FromMinutes(1).TotalMilliseconds;
myTimer.Tick += StartMethod;
}
private void StartMethod(object sender, EventArgs e)
{
tickCounter++;
label1.Text = "Number of executions: " + tickCounter;
}
private void button1_Click(object sender, EventArgs e)
{
tickCounter = 0;
label1.Text = "Started!";
myTimer.Enabled = true;
}
}
Related
I am trying to write an application the is constantly searching for host on a lan. When I run this as a console as the countdown.Wait() seems to work fine. However when I bring the code into a windows form the countdown.Signal() does not seem to decrement its counter. Not sure what the problem is.
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Net.NetworkInformation;
using System.Diagnostics;
using System.Net;
using System.Threading;
namespace Multi_Threaded
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
PortScanner ps = new PortScanner();
ps.ProbeCompleted += new PingProbeCompleted(ps_ProbeCompleted);
ps.run_ping_probe();
}
void ps_ProbeCompleted(object sender, PingProbeCompletedArguments e)
{
MessageBox.Show("I found " + e.ip_adresses_list_of_host.Count.ToString() + "host(s)");
}
}
public delegate void PingProbeCompleted(object sender,PingProbeCompletedArguments e);
public class PingProbeCompletedArguments : EventArgs
{
public List<string> ip_adresses_list_of_host;
}
public class PortScanner
{
public event PingProbeCompleted ProbeCompleted;
static List<string> ip_adresses = new List<string>();
static CountdownEvent countdown;
public void run_ping_probe()
{
ip_adresses.Clear();
countdown = new CountdownEvent(1);
string ipBase = "10.125.";
for (int sub = 0; sub < 14; sub++)
{
for (int i = 1; i < 255; i++)
{
string ip = ipBase + sub.ToString() + "." + i.ToString();
Ping p = new Ping();
p.PingCompleted += new PingCompletedEventHandler(p_PingCompleted);
countdown.AddCount();
p.SendAsync(ip, 100, ip);
}
}
countdown.Signal();
countdown.Wait();
PingProbeCompletedArguments e = new PingProbeCompletedArguments();
e.ip_adresses_list_of_host = ip_adresses;
ProbeCompleted(this, e);
}
private void p_PingCompleted(object sender, PingCompletedEventArgs e)
{
string ip = (string)e.UserState;
if (e.Reply.Status == IPStatus.Success)
{
ip_adresses.Add(ip + "\t" + e.Reply.RoundtripTime + " ms");
}
countdown.Signal();
}
}
Yes, your code deadlocks when you use it in a Winforms project. The problem is that the Ping class makes a best effort to raise the PingCompleted event on the same thread that called SendAsync(). It uses the AsyncOperationManager.CreateOperation() method to do so.
Problem is, that actually works in a Winforms app. It tries to raise the event on the main thread. But that cannot work since you blocked the main thread with the countdown.Wait() call. The ping cannot complete since the main thread is blocked. The main thread cannot complete since the ping doesn't complete. Deadlock city.
It works in a Console mode app since it doesn't have a synchronization provider like Winforms does. The PingComplete event will be raised on a threadpool thread.
Blocking the UI thread is fundamentally flawed. The quick fix is to run the code on a worker thread. Beware that this makes the ProbeCompleted event fired on that worker as well. Use Control.BeginInvoke() to marshal it to the UI thread. Or use BackgroundWorker.
private void Form1_Load(object sender, EventArgs e) {
PortScanner ps = new PortScanner();
ps.ProbeCompleted += new PingProbeCompleted(ps_ProbeCompleted);
ThreadPool.QueueUserWorkItem((w) => ps.run_ping_probe());
}
And don't forget to remove the extra Signal() call.
your wait handler is run under a thread from the threadpool.
you need to get back into the UI thread to have the UI updated (due to the message loop that the UI runs on) - for that you use SynchronizationContext
Here more info on how to you it:
http://www.codeproject.com/KB/threads/SynchronizationContext.aspx
I am developing a game in Windows Phone 8 SDK
and i need a countdown timer.
i implemented a Dispatcher timer , on the first time CLICK
The timer decrease with no errors !
but if i press RESET (Which it should reset to 60 SECONDS and start countdown)
it Resets to 60 BUT it Decreases "2 Seconds" every second !
and if i press one more time RESET , it Decreases by 3 Seconds every second
Sample code i wrote with the same idea of my app: (and same wrong
results)
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Navigation;
using Microsoft.Phone.Controls;
using Microsoft.Phone.Shell;
using PhoneApp3.Resources;
using System.Windows.Threading;
namespace PhoneApp3
{
public partial class MainPage : PhoneApplicationPage
{
private DispatcherTimer time = new DispatcherTimer(); // DISPATCHER TIMER
private int left;
// Constructor
public MainPage()
{
InitializeComponent();
}
//Starting Countdown
private void Start_Click_1(object sender, RoutedEventArgs e)
{
left = 60; // time left
time.Interval = TimeSpan.FromSeconds(1);
time.Tick += time_Tick;
time.Start();
}
void time_Tick(object sender, EventArgs e)
{
left--; // decrease
txt.Text = Convert.ToString(left); // update text
}
private void reset_Click(object sender, RoutedEventArgs e)
{
time.Stop();
Start_Click_1(null, null); // RE - START
}
}
}
Every time you press reset, and Start_Click_1 runs again, you're subscribing to time_Tick again:
time.Tick += time_Tick;
So after pressing Reset 3 times, you're subscribed 3 times, and the following line of code is running 3 times every time the tick event fires:
left--;
Move the subscription to your constructor:
public MainPage()
{
InitializeComponent();
time.Tick += time_Tick;
}
//Starting Countdown
private void Start_Click_1(object sender, RoutedEventArgs e)
{
left = 60; // time left
time.Interval = TimeSpan.FromSeconds(1);
time.Start();
}
As Hans said in the comments, you are incorrectly adding the event handler every time the button is clicked.
You should call this code
time.Interval = TimeSpan.FromSeconds(1);
time.Tick += time_Tick;
in the constructor, instead of the event handler.
I am trying to write an application the is constantly searching for host on a lan. When I run this as a console as the countdown.Wait() seems to work fine. However when I bring the code into a windows form the countdown.Signal() does not seem to decrement its counter. Not sure what the problem is.
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Net.NetworkInformation;
using System.Diagnostics;
using System.Net;
using System.Threading;
namespace Multi_Threaded
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
PortScanner ps = new PortScanner();
ps.ProbeCompleted += new PingProbeCompleted(ps_ProbeCompleted);
ps.run_ping_probe();
}
void ps_ProbeCompleted(object sender, PingProbeCompletedArguments e)
{
MessageBox.Show("I found " + e.ip_adresses_list_of_host.Count.ToString() + "host(s)");
}
}
public delegate void PingProbeCompleted(object sender,PingProbeCompletedArguments e);
public class PingProbeCompletedArguments : EventArgs
{
public List<string> ip_adresses_list_of_host;
}
public class PortScanner
{
public event PingProbeCompleted ProbeCompleted;
static List<string> ip_adresses = new List<string>();
static CountdownEvent countdown;
public void run_ping_probe()
{
ip_adresses.Clear();
countdown = new CountdownEvent(1);
string ipBase = "10.125.";
for (int sub = 0; sub < 14; sub++)
{
for (int i = 1; i < 255; i++)
{
string ip = ipBase + sub.ToString() + "." + i.ToString();
Ping p = new Ping();
p.PingCompleted += new PingCompletedEventHandler(p_PingCompleted);
countdown.AddCount();
p.SendAsync(ip, 100, ip);
}
}
countdown.Signal();
countdown.Wait();
PingProbeCompletedArguments e = new PingProbeCompletedArguments();
e.ip_adresses_list_of_host = ip_adresses;
ProbeCompleted(this, e);
}
private void p_PingCompleted(object sender, PingCompletedEventArgs e)
{
string ip = (string)e.UserState;
if (e.Reply.Status == IPStatus.Success)
{
ip_adresses.Add(ip + "\t" + e.Reply.RoundtripTime + " ms");
}
countdown.Signal();
}
}
Yes, your code deadlocks when you use it in a Winforms project. The problem is that the Ping class makes a best effort to raise the PingCompleted event on the same thread that called SendAsync(). It uses the AsyncOperationManager.CreateOperation() method to do so.
Problem is, that actually works in a Winforms app. It tries to raise the event on the main thread. But that cannot work since you blocked the main thread with the countdown.Wait() call. The ping cannot complete since the main thread is blocked. The main thread cannot complete since the ping doesn't complete. Deadlock city.
It works in a Console mode app since it doesn't have a synchronization provider like Winforms does. The PingComplete event will be raised on a threadpool thread.
Blocking the UI thread is fundamentally flawed. The quick fix is to run the code on a worker thread. Beware that this makes the ProbeCompleted event fired on that worker as well. Use Control.BeginInvoke() to marshal it to the UI thread. Or use BackgroundWorker.
private void Form1_Load(object sender, EventArgs e) {
PortScanner ps = new PortScanner();
ps.ProbeCompleted += new PingProbeCompleted(ps_ProbeCompleted);
ThreadPool.QueueUserWorkItem((w) => ps.run_ping_probe());
}
And don't forget to remove the extra Signal() call.
your wait handler is run under a thread from the threadpool.
you need to get back into the UI thread to have the UI updated (due to the message loop that the UI runs on) - for that you use SynchronizationContext
Here more info on how to you it:
http://www.codeproject.com/KB/threads/SynchronizationContext.aspx
In the designer i put backgroundworker and i have two events: Do Work and Progress Changed.
I used breakpoint and its getting inside the Do Work event but it never get into the Progress Changed event. Its never stop there like the event isnt working. Why the progrss changed event isnt working ?
This is the code:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using Google.GData.Client;
using Google.GData.Extensions;
using Google.GData.Extensions.MediaRss;
using Google.GData.YouTube;
using Google.YouTube;
using System.Threading;
namespace YoutubeTesting
{
public partial class Form1 : Form
{
YouTubeRequestSettings settings;
YouTubeRequest request;
string devkey = "AI39si6xhSQXx95FTYIACWPfq-lLIphblgaReuz9z6VEjR1Q6YjrV6FRN2U6FN6P6-lGF2OYaUZhCVOKJ_MCk4o6kPeUszvf5A";
string username = "chocolade13091972#gmail.com";
string password = "password";
public Form1()
{
InitializeComponent();
worker.RunWorkerAsync();
}
private void Form1_Load(object sender, EventArgs e)
{
}
private void upload()
{
try
{
settings = new YouTubeRequestSettings("You Manager", devkey, username, password);
settings.Timeout = -1;
request = new YouTubeRequest(settings);
Video video = new Video();
video.Title = "test";
video.Tags.Add(new MediaCategory("Comedy", YouTubeNameTable.CategorySchema));
video.Keywords = "Comedy";
video.Private = false;
video.MediaSource = new MediaFileSource("d:\\VIDEO0037.3gp", "video/3gp");
request.Upload(video);
MessageBox.Show("Successfully Uploaded");
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
}
private void worker_DoWork(object sender, DoWorkEventArgs e)
{
upload();
}
private void worker_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
textBox1.Text = e.ProgressPercentage.ToString();
}
}
}
You need to report the progress using worker.ReportProgress()
From MSDN:
If you need the background operation to report on its progress, you
can call the ReportProgress method to raise the ProgressChanged event.
The WorkerReportsProgress property value must be true, or
ReportProgress will throw an InvalidOperationException.
It is up to you to implement a meaningful way of measuring your
background operation's progress as a percentage of the total task
completed.
The call to the ReportProgress method is asynchronous and returns
immediately. The ProgressChanged event handler executes on the thread
that created the BackgroundWorker.
You have to set this.
backgroundWorker.WorkerReportsProgress = true;
Gets or sets a value indicating whether the BackgroundWorker can
report progress updates.
EDIT
If still not working checks whether you have bind the event properly in the designer code. Or just add something like below in your class.
backgroundWorker1.ProgressChanged += new System.ComponentModel.ProgressChangedEventHandler(this.worker_ProgressChanged);
In your Upload method you have to report progress. Otherwise above event won't fire. Keep in mind that, it's not easy to report actual progress always.
Below is an example code for a DoWork method. Look at here if you want to see a complete example.
static void bw_DoWork (object sender, DoWorkEventArgs e)
{
for (int i = 0; i <= 100; i += 20)
{
if (_bw.CancellationPending) { e.Cancel = true; return; }
_bw.ReportProgress (i);
Thread.Sleep (1000); // Just for the demo... don't go sleeping
} // for real in pooled threads!
e.Result = 123; // This gets passed to RunWorkerCompleted
}
I am tryig to fade-in a windows form using c# but it doesnt seem to work after I have shown the form. Is it possible to change the forms opacity after Ive shown it?
Code:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Timers;
namespace ToolStrip
{
public partial class Form1 : Form
{
Form ToolForm = new ToolForm();
Form PropForm = new PropertyGrid();
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
ToolForm.FormBorderStyle = FormBorderStyle.FixedToolWindow;
ToolForm.Owner = this;
ToolForm.Show();
ToolForm.Location = new Point(50, 50);
}
private void button2_Click(object sender, EventArgs e)
{
PropForm.FormBorderStyle = FormBorderStyle.FixedToolWindow;
PropForm.Owner = this;
PropForm.Show();
PropForm.Location = new Point(50, 50);
System.Timers.Timer aTimer = new System.Timers.Timer(10000);
aTimer.Elapsed += new ElapsedEventHandler(OnTimedEvent);
aTimer.Interval = 2000;
aTimer.Enabled = true;
Console.WriteLine("Press the Enter key to exit the program.");
Console.ReadLine();
}
private void OnTimedEvent(object source, ElapsedEventArgs e)
{
PropForm.Opacity = PropForm.Opacity - 0.25;
Console.WriteLine(PropForm.Opacity);
}
}
}
because you r using System.Timers.Timer which is a multithread timer, in it's OnTimedEvent() it calls control created by another thread, which cause exception.
If you use System.Windows.Forms.Timer, it will work. i tested.
Using your code (and creating the other necessary Form classes), I get a cross-threading exception the first time the timer fires and the event handler is called, as Benny suggests.
Making changes to your code to check InvokeRequired in the timer event handler, and use Invoke if necessary to change PropForm.Opacity, results in the opacity changing after the form is shown, as required.
Note that you probably want to start with an Opacity of 0, and increase it gradually - otherwise your form will start off completely solid and gradually fade out
I will mention in passing that Opacity will have no effect on some versions of Windows, though you say you have Opacity effects working elsewhere, so it shouldn't be that in this case.
Ive gotten it to work without timers:
int Loop = 0;
for (Loop = 100; Loop >= 5; Loop -= 10)
{
this.PropForm.Opacity = Loop / 95.0;
this.PropForm .Refresh();
System.Threading.Thread.Sleep(100);
}
but i cant seem to change this example to fade-in instead of out.