We Keep Coding

Update a control in the UI from a different thread

I have a M2MQTT client subscribed to a topic in the DashboardViewModel class. On message receive, the UI gets updated by calling Writelog.
public class DashboardViewModel : Object, IDashboardViewModel
{
private IDashboardView View { get; }
public DashboardViewModel(IDashboardView view)
{
View = view;
mqttClient = new MqttClient("localhost");
mqttClientId = Guid.NewGuid().ToString();
mqttClient.MqttMsgPublishReceived += mqttClient_MsgPublishReceived;
mqttClient.Subscribe(new string[] { "Home/Temperature" }, new byte[] { MqttMsgBase.QOS_LEVEL_EXACTLY_ONCE });
mqttClient.Connect(mqttClientId);
//...
}
private void mqttClient_MsgPublishReceived(object sender, MqttMsgPublishEventArgs eventArgs)
{
string message = Encoding.UTF8.GetString(eventArgs.Message);
View.Writelog(message);
}
}
The textbox on FrmMain does not update; tbxLogs.InvokeRequired always returns false, i.e. tbxLogs.AppendText always executes. Any suggestions please?
public partial class FrmMain : Form, IDashboardView
{
private IDashboardViewModel dashboardViewModel = null;
private delegate void WriteLogCallback(string text);
public FrmMain()
{
InitializeComponent();
}
public void Writelog(string text)
{
if (tbxLogs.InvokeRequired)
{
WriteLogCallback callback = new WriteLogCallback(Writelog);
tbxLogs.Invoke(callback, new object[] { text });
}
else
{
tbxLogs.AppendText(text + "\n");
}
}
}

I think you need to use dispatcher :)
Dispatcher.CurrentDispatcher.BeginInvoke(DispatcherPriority.ApplicationIdle, new Action<String>(Writelog), message);
inside of this method
private void mqttClient_MsgPublishReceived(object sender, MqttMsgPublishEventArgs eventArgs)
{
string message = Encoding.UTF8.GetString(eventArgs.Message);
//here instead of View.Writelog(message);
}

How to implement monitor and system.threading for the smokers situation

The problem that I am working on deals with out to use a functional Lock, or monitor structure, to provided exclusive access to only one member on separate threads. Below, is my class definition of the monitor (note that it is different than the actual monitor class given by c# library). What I am trying to do is make pictureboxes appear or disappear on my form.
I have attempted to add in an instance of the form so I can access the individual pictureboxes, however, my program seems to freeze.
namespace SmokersProblem
{
class monitor
{
Form1 form = new Form1();
Random num = new Random();
object obj = new object();
public monitor()
{
}
public void agent(){
form.pictureBox4.Visible = false;
int r = num.Next(1, 4);
if (r == 1)
{
// put lighter and paper on table
smoker1();
}
else if (r == 2)
{
// put lighter and tobacco on table
smoker2();
}
else
{
// put paper and tobacco on table
smoker3();
}
}
public void smoker1()
{
//lock (obj)
//{
form.pictureBox9.Visible = true;
form.pictureBox1.Visible = false;
System.Threading.Thread.Sleep(5000);
//agent();
// }
}
public void smoker2()
{
//lock (obj)
//{
form.pictureBox10.Visible = true;
form.pictureBox3.Visible = false;
System.Threading.Thread.Sleep(5000);
//agent();
//}
}
public void smoker3()
{
//lock (obj)
//{
form.pictureBox11.Visible = true;
form.pictureBox2.Visible = false;
System.Threading.Thread.Sleep(5000);
//agent();
// }
}
}
}
Below is my form code, as you can see here, i try to create three seperate threads, one for each smoker.
namespace SmokersProblem
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
Random rnd = new Random();
int num = rnd.Next(1, 4);
Object obj = new Object();
}
private void Form1_Load(object sender, EventArgs e)
{
}
private void button1_Click(object sender, EventArgs e)
{
pictureBox1.Visible = true;
pictureBox2.Visible = true;
pictureBox3.Visible = true;
pictureBox8.Visible = false;
pictureBox7.Visible = false;
pictureBox6.Visible = false;
monitor one = new monitor();
one.agent();
Thread vone = new Thread(one.smoker1);
Thread two = new Thread(one.smoker2);
Thread three = new Thread(one.smoker3);
vone.Start();
two.Start();
three.Start();
}
}
}

After implementing this, I went looking for the Smoker Thread Problem that it looks like OP is trying to implement. This code should be easily adaptable to that problem.
The reason your UI is freezing is that you're calling one.agent() without putting it in a new thread. one.agent() sleeps, which keeps your UI from processing events.
OK, I've implemented some code to do the smoker problem with labels. Obviously it could be improved, for instance by not coupling the form to the threads.
I put two different locking mechanisms in, and left one commented out.
Essentially, there are three labels that can either be "Smoking" or "Not Smoking". The main UI thread creates three threads:
Smoker1
Smoker2
Smoker3
Each of the threads continually tries to take the lock in a while loop. When they take the lock, they set their label to "Smoking", wait a few seconds, and then set their label to "Not Smoking". This uses thread safe code from this answer.
public partial class Form1 : Form
{
private bool running = false;
public Label OneLabel { get; set; }
public Label TwoLabel { get; set; }
public Label ThreeLabel { get; set; }
private MyMonitor one;
private Thread vone;
private Thread two;
private Thread three;
public Form1()
{
InitializeComponent();
OneLabel = new Label();
OneLabel.Text = "Not Smoking";
OneLabel.Location = new Point(10, 50);
OneLabel.AutoSize = true;
this.Controls.Add(OneLabel);
TwoLabel = new Label();
TwoLabel.Text = "Not Smoking";
TwoLabel.Location = new Point(150, 50);
this.Controls.Add(TwoLabel);
ThreeLabel = new Label();
ThreeLabel.Text = "Not Smoking";
ThreeLabel.Location = new Point(300, 50);
this.Controls.Add(ThreeLabel);
}
private void MainButton_Click(object sender, EventArgs e)
{
if (!running)
{
vone.Start();
two.Start();
three.Start();
MainButton.Text = "Stop";
running = true;
}
else
{
one.RequestStop();
MainButton.Text = "Run";
running = false;
}
}
private void Form1_Load(object sender, EventArgs e)
{
one = new MyMonitor(this);
vone = new Thread(one.Smoker1);
two = new Thread(one.Smoker2);
three = new Thread(one.Smoker3);
}
private void Form1_FormClosing(object sender, FormClosingEventArgs e)
{
if (running)
{
one.RequestStop();
running = false;
}
}
}
class MyMonitor
{
private int x = 1;
private Object obj = new Object();
private Form1 _form;
bool _finished = false;
public MyMonitor(Form1 form)
{
_form = form;
}
public void Smoker1()
{
while (!_finished)
{
//lock (obj)
//{
// _form.OneLabel.SetPropertyThreadSafe(() => _form.OneLabel.Text, "Smoking");
// System.Threading.Thread.Sleep(2000);
// _form.OneLabel.SetPropertyThreadSafe(() => _form.OneLabel.Text, "Not Smoking");
//}
try
{
Monitor.Enter(obj);
try
{
_form.OneLabel.SetPropertyThreadSafe(() => _form.OneLabel.Text, "Smoking");
System.Threading.Thread.Sleep(2000);
_form.OneLabel.SetPropertyThreadSafe(() => _form.OneLabel.Text, "Not Smoking");
}
finally
{
Monitor.Exit(obj);
}
}
catch (SynchronizationLockException SyncEx)
{
Console.WriteLine(SyncEx.Message);
}
}
}
public void Smoker2()
{
while (!_finished)
{
//lock (obj)
//{
// _form.TwoLabel.SetPropertyThreadSafe(() => _form.TwoLabel.Text, "Smoking");
// System.Threading.Thread.Sleep(2000);
// _form.TwoLabel.SetPropertyThreadSafe(() => _form.TwoLabel.Text, "Not Smoking");
//}
try
{
Monitor.Enter(obj);
try
{
_form.TwoLabel.SetPropertyThreadSafe(() => _form.TwoLabel.Text, "Smoking");
System.Threading.Thread.Sleep(2000);
_form.TwoLabel.SetPropertyThreadSafe(() => _form.TwoLabel.Text, "Not Smoking");
}
finally
{
Monitor.Exit(obj);
}
}
catch (SynchronizationLockException SyncEx)
{
Console.WriteLine(SyncEx.Message);
}
}
}
public void Smoker3()
{
while (!_finished)
{
//lock (obj)
//{
// _form.ThreeLabel.SetPropertyThreadSafe(() => _form.ThreeLabel.Text, "Smoking");
// System.Threading.Thread.Sleep(2000);
// _form.ThreeLabel.SetPropertyThreadSafe(() => _form.ThreeLabel.Text, "Not Smoking");
//}
try
{
Monitor.Enter(obj);
try
{
_form.ThreeLabel.SetPropertyThreadSafe(() => _form.ThreeLabel.Text, "Smoking");
System.Threading.Thread.Sleep(2000);
_form.ThreeLabel.SetPropertyThreadSafe(() => _form.ThreeLabel.Text, "Not Smoking");
}
finally
{
Monitor.Exit(obj);
}
}
catch (SynchronizationLockException SyncEx)
{
Console.WriteLine(SyncEx.Message);
}
}
}
public void RequestStop()
{
_finished = true;
}
}
//Thread Safe Extension Method
public static class Extensions
{
private delegate void SetPropertyThreadSafeDelegate<TResult>(Control #this, Expression<Func<TResult>> property, TResult value);
public static void SetPropertyThreadSafe<TResult>(this Control #this, Expression<Func<TResult>> property, TResult value)
{
var propertyInfo = (property.Body as MemberExpression).Member as PropertyInfo;
if (propertyInfo == null ||
!#this.GetType().IsSubclassOf(propertyInfo.ReflectedType) ||
#this.GetType().GetProperty(propertyInfo.Name, propertyInfo.PropertyType) == null)
{
throw new ArgumentException("The lambda expression 'property' must reference a valid property on this Control.");
}
if (#this.InvokeRequired)
{
#this.Invoke(new SetPropertyThreadSafeDelegate<TResult>(SetPropertyThreadSafe), new object[] { #this, property, value });
}
else
{
#this.GetType().InvokeMember(propertyInfo.Name, BindingFlags.SetProperty, null, #this, new object[] { value });
}
}
}

my program seems to freeze
My one.agent() is the part of the code that allows one of the smokers
to be called on, so they can smoke. Why wouldnt I want it in the main
code?
Because you shouldn't be using Sleep() from the main UI thread, which is what happens when you call one.agent() from the Button Click event. When Sleep(5000) is hit, you're telling the forms main UI thread to not do ANYTHING for five seconds, thus the freezing you're seeing.
To fix this, you'd need agent() to execute smoker1(), smoker2(), or smoker3() in a separate thread like you're doing down below.
There are several other problems with the code, however, that must also be addressed before you can "fix" your code...
The next problem lies in you creating a new instance of Form1() inside your monitor() class. This instance of Form1() is not the same one that is visible on your screen. Acting upon it is modifying an invisible form that has never even been shown. To act upon the form that is actually visible on your screen would require you to either (a) pass a reference to it into your monitor() class when you create it, or (b) have your monitor() class raise custom events that Form1() subscribes to, again when it creates monitor().
The last problem lies in you attempting to change UI controls from within a thread other than the main UI thread. This will result in a cross-thread exception (unless you've turn this off, which you shouldn't). There are various ways to overcome this problem, the most basic of which involves using delegates and the Invoke() method of the Form/Control to which you are trying to update.

Access control element from static thread function

I ve read lots of information about this stuff and i tried this:
class Server
{
...
public Server(int Port, ListBox ex_lb, PictureBox ex_pb)
{
ServerWork = new Thread(() => ServerFunction(Listener, ex_lb, ex_pb));
ServerWork.Start();
}
static void ServerFunction(TcpListener ex_listener, ListBox ex_lb, PictureBox ex_pb)
{
//and any access to ex_lb throws exception, didnt debug to access to ex_pb
}
}
this:
private static IncomingDataClass g_IDC = new IncomingDataClass();
private class IncomingDataClass
{
static string data = "";
public string Data
{
get { return data; }
set {
data = value;
SomeEvent(this,null,data);
}
}
}
void IncomingDataClass_SomeEvent(object sender, EventArgs e, string ex_data)
{
if (ex_data.Contains("listbox"))
{
ex_data = ex_data.Remove(ex_data.IndexOf("listbox"), "listbox".Length);
listBox1.Items.Add(ex_data);
}
}
delegate void MyEventHandler(object sender, EventArgs e, string ex_data);
static event MyEventHandler SomeEvent;
// in form load event
SomeEvent += IncomingDataClass_SomeEvent;
class Server
{
...
public Server(int Port, ListBox ex_lb, PictureBox ex_pb)
{
ServerWork = new Thread(() => ServerFunction(Listener));
ServerWork.Start();
}
static void ServerFunction(TcpListener ex_listener)
{
//and any change of g_IDC.Data throws exception here
}
}
this:
private static ListBox listBox1 = new ListBox();
private void Form1_Load(object sender, EventArgs e)
{
...
listBox1.FormattingEnabled = true;
listBox1.Location = new System.Drawing.Point(12, 256);
listBox1.Name = "listBox1";
listBox1.Size = new System.Drawing.Size(258, 108);
listBox1.TabIndex = 6;
Controls.Add(listBox1);
}
//anyways, even if i create new ListBox lb = listBox1 in ServerFunction(..), it throws System.InvalidOperationException => Access attempt to listBox1 not from thread where is was created.
What do i do wrong? I thought that creating static control is an ultimate problem solve for this, but even this doesnt work...

If I remember correctly in order to update the UI from another thread you need to use this invocation:
this.Invoke((MethodInvoker)delegate
{
MethodForUpdatingUI();
});
This will start MethodForUpdatingUI() from the UI thread, enabling you to access the controls.
So, for use this in your code I'll try to change IncomingDataClass_SomeEvent:
void IncomingDataClass_SomeEvent(object sender, EventArgs e, string ex_data)
{
this.Invoke((MethodInvoker)delegate
{
UpdateListBox(ex_data);
});
}
UpdateListBox(string ex_data)
{
if (ex_data.Contains("listbox"))
{
ex_data = ex_data.Remove(ex_data.IndexOf("listbox"), "listbox".Length);
listBox1.Items.Add(ex_data);
}
}
Please feel free to correct me if this is not the case you are asking for or this is a bad pratice. I've not tested the code.

You can only manipulate UI controls from UI thread. It doesn't matter if those controls are static or not, afaik. Use Dispatcher object or SynchronizationContext object to modify controls from different thread.

Logging information to a windowed textbox

I am working on converting a console application into a windowed format and as someone who knows little about it but has had experience with a similar application already in window format in the past I figured it wouldn't be too hard.
So I created a form and added a textbox to it just to get the logging information to start with.
This console app used to run in a single thread, I have since added a second thread to allow the form to run side by side with the console for testing. (it runs fine in a single thread strangely now too).
This is the code I am using to write text to the form except that I am not getting ANYTHING at all on the form.
static Form1 f = new Form1();
delegate void SetTextCallback(string s);
private void SetText(string text)
{
// InvokeRequired required compares the thread ID of the
// calling thread to the thread ID of the creating thread.
// If these threads are different, it returns true.
if (f.textBox1.InvokeRequired)
{
SetTextCallback d = new SetTextCallback(SetText);
f.textBox1.Invoke(d, new object[] { text });
}
else
{
f.textBox1.AppendText(text);
}
}
I can confirm that there is text entering the "text" variable but it is not getting to the form.
Any help would be appreciated.
This is the full file:
using System;
using System.Windows.Forms;
using Chraft.Properties;
using System.IO;
using Chraft.Plugins.Events.Args;
using Chraft.Plugins.Events;
namespace Chraft
{
public class Logger
{
private StreamWriter WriteLog;
private Server Server;
internal Logger(Server server, string file)
{
Server = server;
try
{
WriteLog = new StreamWriter(file, true);
WriteLog.AutoFlush = true;
}
catch
{
WriteLog = null;
}
}
~Logger()
{
try
{
WriteLog.Close();
}
catch
{
}
}
public void Log(LogLevel level, string format, params object[] arguments)
{
Log(level, string.Format(format, arguments));
}
public void Log(LogLevel level, string message)
{
//Event
LoggerEventArgs e = new LoggerEventArgs(this, level, message);
Server.PluginManager.CallEvent(Event.LOGGER_LOG, e);
if (e.EventCanceled) return;
level = e.LogLevel;
message = e.LogMessage;
//End Event
LogToConsole(level, message);
LogToForm(level, message);
LogToFile(level, message);
}
private void LogToConsole(LogLevel level, string message)
{
if ((int)level >= Settings.Default.LogConsoleLevel)
{
Console.WriteLine(Settings.Default.LogConsoleFormat, DateTime.Now, level.ToString().ToUpper(), message);
}
}
static Form1 f = new Form1();
delegate void SetTextCallback(string s);
private void SetText(string text)
{
// InvokeRequired required compares the thread ID of the
// calling thread to the thread ID of the creating thread.
// If these threads are different, it returns true.
if (f.textBox1.InvokeRequired)
{
SetTextCallback d = new SetTextCallback(SetText);
f.textBox1.Invoke(d, new object[] { text });
}
else
{
f.textBox1.AppendText(text);
}
}
private void LogToForm(LogLevel level, string message)
{
if ((int)level >= Settings.Default.LogConsoleLevel)
{
SetText(DateTime.Now + level.ToString().ToUpper() + message);
}
}
private void LogToFile(LogLevel level, string message)
{
if ((int)level >= Settings.Default.LogFileLevel && WriteLog != null)
WriteLog.WriteLine(Settings.Default.LogFileFormat, DateTime.Now, level.ToString().ToUpper(), message);
}
public void Log(Exception ex)
{
//Event
LoggerEventArgs e = new LoggerEventArgs(this, LogLevel.Debug, ex.ToString(), ex);
Server.PluginManager.CallEvent(Event.LOGGER_LOG, e);
if (e.EventCanceled) return;
//End Event
Log(LogLevel.Debug, ex.ToString());
}
public enum LogLevel : int
{
Trivial = -1,
Debug = 0,
Info = 1,
Warning = 2,
Caution = 3,
Notice = 4,
Error = 5,
Fatal = 6
}
}
}

The problem is that you are creating two Form objects. One that is created in your Program.cs file:
Application.Run(new Form1());
And the one you created in your logger class
Form f = new Form1();
The one passed to Application.Run is the one that the user is interacting with. It has become visible and responds to user interaction because of the Application.Run call.
The one you created on your logger class just sits there in memory. Its TextBox is happily adding the text you ask it to, but that one isn't visible anywhere.
There are many ways to handle this situation. You could gain access to the correct Form object through Application.OpenForms, but a more appropriate way to handle it would be to add an event on the logger that the form can subscribe to and it can handle updating the TextBox in response to the event.
Updated
class LoggerLogEventArgs : EventArgs
{
public LoggerLogEventArgs(string message)
{
this.message = message;
}
private string message;
public string Message { get { return message; } }
}
class Logger
{
public event EventHandler<LoggerLogEventArgs> Logged;
protected virtual void OnLogged(LoggerLogEventArgs e)
{
EventHandler<LoggerLogEventArgs> handler = Logged;
if (handler != null)
handler(this, e);
}
// I would change this method name to LogToEvent
private void LogToForm(LogLevel level, string message)
{
if ((int)level >= Settings.Default.LogConsoleLevel)
{
OnLogged(new LoggerLogEventArgs(message));
}
}
}
class Form1 : Form
{
// Subscribe to the logger only when we are ready to display text
protected override void OnHandleCreated(EventArgs e)
{
base.OnHandleCreated(e);
GetLog().Logged += new EventHandler<LoggerLogEventArgs>(logger_Logged);
}
// Unsubscribe from the logger before we are no longer ready to display text
protected override void OnHandleDestroyed(EventArgs e)
{
GetLog().Logged -= new EventHandler<LoggerLogEventArgs>(logger_Logged);
base.OnHandleDestroyed(e);
}
private void logger_Logged(object sender, LoggerLogEventArgs e)
{
if (InvokeRequired)
BeginInvoke(new EventHandler<LoggerLogEventArgs>(logger_Logged), e);
else
textBox1.AppendText(e.Message);
}
}

hello i try this it works ( I make a console application and I add a windows form)
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Security.Permissions;
using System.Windows.Forms;
namespace ConsoleApplication6
{
class Program
{
delegate void SetTextCallback(string s);
static Form1 f;
static void Main(string[] args)
{
f = new Form1();
f.Show();
SetText("test");
Console.ReadLine();
}
private static void SetText(string text)
{
// InvokeRequired required compares the thread ID of the
// calling thread to the thread ID of the creating thread.
// If these threads are different, it returns true.
if (f.textBox1.InvokeRequired)
{
SetTextCallback d = new SetTextCallback(SetText);
f.textBox1.Invoke(d, new object[] { text });
}
else
{
f.textBox1.AppendText(text);
}
}
}
}

Thread safe form manipulation between two forms (WinForms C#)

I have two forms, the main form and one that pops up as a modal dialog. From a process spawned in the main form, I want to dynamically update the text on the modal dialog. Here's what I have:
In the main form, I do this:
// show the wait modal
var modal = new WaitDialog { Owner = this };
// thread the packaging
var thread = new Thread(() => Packager.PackageUpdates(clients, version, modal));
thread.Start();
// hopefully it worked ...
if (modal.ShowDialog() != DialogResult.OK)
{
throw new Exception("Something failed, miserably.");
}
The PackageUpdates method takes the modal dialog, and does this:
// quick update and sleep for a sec ...
modal.SetWaitLabelText("Downloading update package...");
Thread.Sleep(2000);
modal.SetWaitLabelText("Re-packaging update...");
To be thread safe, I do this in the modal dialog:
public void SetWaitLabelText(string text)
{
if (lblWaitMessage.InvokeRequired)
{
Invoke(new Action<string>(SetWaitLabelText), text);
}
else
{
lblWaitMessage.Text = text;
}
}
Everything works great ... most of the time. Every three or four times that the modal pops up, I get an exception on the lblWaitMessage.Text = text; and it's not invoking the command.
Am I missing something in this setup?

Like #Hans Passant pointed out, you should wait for the modal.Load-event. One good option is to use the ManualResetEvent to inform your thread to wait until that happens.
The WaitOne method will block the thread until the Set method is called. Here's a very simple setup which should do the trick.
public partial class Form1 : Form
{
ManualResetEvent m_ResetEvent;
public Form1()
{
InitializeComponent();
m_ResetEvent = new ManualResetEvent(false);
}
private void button1_Click(object sender, EventArgs e)
{
Dialog d = new Dialog { Owner = this, ResetEvent = m_ResetEvent };
var thread = new Thread(new ParameterizedThreadStart(DoSomething));
thread.Start(d);
if (d.ShowDialog() != System.Windows.Forms.DialogResult.OK)
{
throw new Exception("Something terrible happened");
}
}
private void DoSomething(object modal)
{
Dialog d = (Dialog)modal;
// Block the thread!
m_ResetEvent.WaitOne();
for (int i = 0; i < 1000; i++)
{
d.SetWaitLabelText(i.ToString());
Thread.Sleep(1000);
}
}
}
And here is the modal form
public partial class Dialog : Form
{
public Form Owner { get; set; }
public ManualResetEvent ResetEvent { get; set; }
public Dialog()
{
InitializeComponent();
}
public void SetWaitLabelText(string text)
{
if (label1.InvokeRequired)
{
Invoke(new Action<string>(SetWaitLabelText), text);
}
else
{
label1.Text = text;
}
}
private void Dialog_Load(object sender, EventArgs e)
{
// Set the event, thus unblocking the other thread
ResetEvent.Set();
}
}

I think you should rewrite the code to let thread.Start() isn't called before modal.ShowDialog().
As a workaround, you can try this:
public void SetWaitLabelText(string text) {
Invoke(new Action<string>(SetWaitLabelText2), text);
}
void SetWaitLabelText2(string text) {
lblWaitMessage.Text = text;
}
The first method always uses Invoke, regardless the value of InvokeRequired. The second method actually does the thing. This pattern is usable when you always call the function from another thread.