I am having a class that has a timer, on timer elapsed I need to check a class level variable _isModelShutdown to determine whether to raise an event or not. The problem is that the timer is not able to get the latest value from the class level variable _isModelShutdown. I tried it by changing that variable to static variable, but that doesn't solve my problem, because this class is called by multiple threads. So, when I am in timer elapsed, the variable seems to get the default value of false instead of true which was set by an Consumer_Channel_ModelShutdown event saying shutdown happened. I think that another thread has already updated the static variable to false.
Workflow: When channel shutdown happens, Consumer_Channel_ModelShutdown is fired, that sets _isModelShutdown=true. Timer should check for _isModelShutdown==true to invoke Channel_Failure event. The reason why i can't do all this in the Consumer_Channel_ModelShutdown event is that RabbitMQ says shutdown callback is not a safe place to open another channel as it throws time out error on channel creation code. Hope this gives more clarity to the problem.
public class SomeClass
{
public event Func<string> Channel_Failure;
IModel consumerChannel = null;
private static bool _isModelShutdown = false;
public SomeClass(RabbitMQConnectionInfo rabbitMQConnectionInfo, Func<string> handleFailure)
{
if (handleFailure != null)
{
Channel_Failure = handleFailure;
}
consumerChannel = rabbitMQConnectionInfo.Connection.CreateModel();
// Some more code
if (connected) return;
StartTimer((int)reconnectionInterval);
}
private void StartTimer(int waitIntervalBeforeReconnecting)
{
double interval = 30000;
var retryTimer = new Timer(interval)
{
AutoReset = true //run once
};
retryTimer.Elapsed += (sender, eventArgs) =>
{
RetryTimerElapsed((Timer)sender);
}
retryTimer.Start();
}
private void RetryTimerElapsed(IDisposable sender)
{
if (_isModelShutdown) // This is the problem statement, how to access class level variable??
{
Channel_Failure?.Invoke(source);
_isModelShutdown = false;
}
}
private void Consumer_Channel_ModelShutdown(object sender, Client.ShutdownEventArgs reason)
{
_isModelShutdown = true;
}
}
Is there a better way to handle this scenario, any help would be appreciated.
Let's say i have created a class name myClass and this class has a property named myValue with any type, doesn't matter, like:
class myClass
{
public delegate void OverTheLimitDlg(int arg);
public event OverTheLimitDlg OverTheLimit;
public myClass()
{
myValue = 0;
}
private int myvalue = 0;
public int myValue
{
get { return myvalue;}
set
{
myValue = value;
if(value > 5)
OvertheLimit(value);
}
}
}
I have a winforms label named myLabel on form and i create an object typed myClass at Form Load event, subscribe its OverTheLimit event and start backgroundworker:
myClass myObj;
private void Form_Load(object sender, EventArgs e)
{
myObj = new myClass();
myObj.OverTheLimit += SubsMethod;
backgroundworker.RunWorkerAsync();
}
private void backgroundworker_DoWork(...)
{
myObj.myValue = 10;
//Some expressions.
}
private void SubsMethod(int someInt)
{
myLabel.Text = "Oh it's over the limit!";
}
Summary: i create a class that an object instantiated from it can fire an event. I make the object fire the event in a thread and it runs a method that affects a GUI object, an object created and runs at another thread. I didn't try it ever. What is going to happen in a situation like this? Does it cause error? Thanks.
What is going to happen in a situation like this?
myLabel.Text = "Oh it's over the limit!";
This line will throw an InvalidOperationException when it tries to edit the myLabel from the BackgroundWorker thread. WinForms controls must be changed from the thread that they are created on, this is why Control.InvokeRequired exists.
You can use the following modified version of SubsMethod() which will check if the event handler is running on another thread and then invoke the label change on the GUI thread if necessary.
private void SubsMethod(int someInt)
{
if (myLabel.InvokeRequired) {
myLabel.Invoke(new MethodInvoker(()=>SubsMethod(someInt)));
return;
}
myLabel.Text = "Oh it's over the limit!";
}
I'm trying to call method Run in script1. Then from script1 call method alert or wait and try to update statusLabel in Form1. But this code has an error.
static Label status = this.Controls.Find("statusLabel", true).FirstOrDefault() as Label;
This code will only work in Form1. Because this return error in another classes. Maybe it is not correct and you know better solution.
P.S. I know how to solve this problem (see below "Not the best solution"), but the code will be ~ 10-30 new lines.
Project
Form1.cs
public partial class Form1 : Form
{
private void statusLabel_Click(object sender, EventArgs e)
{
}
private void Form1_Load(object sender, EventArgs e)
{
script1.Run();
...
script30.Run();
}
}
function.cs (Frequently used functions)
public class function
{
static Label statusLabel = this.Controls.Find("statusLabel", true).FirstOrDefault() as Label;
static public void alert(string str)
{
statusLabel.Text = str;
}
static public void wait(int sec)
{
int i = 0;
while (i++ < sec)
{
statusLabel.Text = "Wait: " + (sec+1-i).ToString();
Thread.Sleep(1000);
}
}
}
script1.cs (script1,script2 ... it is about 30 mini programs)
public class script1
{
static public void Run()
{
function.alert("Script1 is running");
function.wait(5);
function.alert("Script1 is done");
}
}
Not the best solution
remove in function.cs
static Label status = this.Controls.Find("statusLabel", true).FirstOrDefault() as Label;
Form1.cs
public partial class Form1 : Form
{
private void Form1_Load(object sender, EventArgs e)
{
script1.Run(this.statusLabel);
}
}
function.cs
public class function
{
private Label _statusLabel;
public scriptClass(Label statusLabel)
{
_statusLabel = statusLabel;
}
}
script1.cs (script1,script2 ... it is about 30 mini programs)
public class script1
{
static public void Run(Label statusLabel)
{
function _function = new function(statusLabel);
}
}
The statusLabel object is owned by, and should be encapsulated and hidden by, the Form1 class. To ensure good decoupling of your classes, as well as proper data hiding, only the Form1 class should be directly accessing it. And it should (by default) be able to access it via a field named statusLabel (i.e. no need to call this.Controls.Find() (nor should that even work from the function class, since that class also is not the owner of the object, nor of a Controls property).
The correct way to do this is for the script1 class to expose a StatusText property, and an event that is raised when the property value changes. There are two canonical ways to implement the event:
Implement an event named StatusTextChanged
Implement the INotifyPropertyChanged interface
Note that in your example, #2 is not an option because you are using static classes to implement your scripts. IMHO this is inadvisable for a variety of reasons, but since #1 is a perfectly fine solution I won't belabor that point. :)
The first looks like this:
class script1
{
public static string StatusText { get; private set; }
public static event EventHandler StatusTextChanged;
static public void Run()
{
ChangeStatusText("Script1 is running");
function.wait(5);
ChangeStatusText("Script1 is done");
}
static void ChangeStatusText(string text)
{
StatusText = text;
EventHandler handler = StatusTextChanged;
if (handler != null)
{
handler(null, EventArgs.Empty);
}
}
}
Then in Form1:
public partial class Form1
{
private void Form1_Load(object sender, EventArgs e)
{
script1.StatusTextChanged += (sender1, e1) => statusLabel.Text = script1.Text;
script1.Run();
...
script30.StatusTextChanged += (sender1, e1) => statusLabel.Text = script30.Text;
script30.Run();
}
}
Note in the above, each scriptX class has to reimplement the event. You could instead make a base class that each of the scriptX classes inherits, and which contains the event in question. Then the Form1 class need only subscribe to the one base class event. It would also address, or at least minimize the hassle of, the issue of leaving event handlers subscribed to 30 different events.
Of course, in this case then the Form1 class won't know which script is updating the text, but maybe that doesn't matter in your case.
Also note that if you did make the scriptX classes non-static, you might then again run into the issue of having to subscribe multiple times. But that is much more easily handled, since it seems certain in that case you'd use a base class, and so it would be easy to generalize the "subscribe, run script, unsubscribe" logic into a helper method.
I have a windows form with a button.
I click the button and it starts a method in a separate class. I start this method in a separate thread.
When this class.method finishes it raises an event back to the windows form class.
When this happens I start another method in that separate class that tells a system.windows.form timer (declared in that class) to be enabled and thus start processing.
But the timer does not start (I did put a break point inside the 'tick' event).
I am assuming that it is because I declared the timer outside of the calling thread right at the start of my code.
Normally, I would use this to invoke a method on the same thread...
this.invoke(mydelegatename, any pars);
But, 'this' cannot be called with an class because unassumingly it is related to the UI thread.
I know this all looks bad architecture and I can easily solve this problem by moving the timer to the UI thread (windows form class).
But, I have forgotten how I did this many years ago and it really is an attempt to encapsulate my code.
Can anyone enlighten me pls?
Thanks
The Code:
[windows class]
_webSync = new WebSync(Shared.ClientID);
_webSync.evBeginSync += new WebSync.delBeginSync(_webSync_evBeginSync);
Thread _thSync = new Thread(_webSync.PreConnect);
_thSync.Start();
private void _webSync_evBeginSync()
{
_webSync.Connect();
}
[WebSync class]
private System.Windows.Forms.Timer _tmrManifestHandler = new System.Windows.Forms.Timer();
public WebSyn()
{
_tmrManifestHandler.Tick += new EventHandler(_tmrManifestHandler_Tick);
_tmrManifestHandler.Interval = 100;
_tmrManifestHandler.Enabled = false;
}
public delegate void delBeginSync();
public event delBeginSync evBeginSync;
public void PreConnect()
{
while (true)
{
if (some condition met)
{
evBeginSync();
return ;
}
}
}
public void Connect()
{
_tmrManifestHandler.Enabled = true;
_tmrManifestHandler.Start();
}
private void _tmrManifestHandler_Tick(object sender, EventArgs e)
{
//NOT BEING 'HIT'
}
You have to call _tmrManifestHandler.Start(); enabling is not enough.
Using a System.Windows.Forms.Timer on another thread will not work.
for more info look here.
Use a System.Timers.Timer instead, be carefull of CrossThreadExceptions if you are using accessing UI elements.
public class WebSync
{
private System.Timers.Timer _tmrManifestHandler = new System.Timers.Timer();
public WebSync(object id)
{
_tmrManifestHandler.Elapsed += new System.Timers.ElapsedEventHandler(_tmrManifestHandler_Tick);
_tmrManifestHandler.Interval = 100;
_tmrManifestHandler.Enabled = false;
}
public delegate void delBeginSync();
public event delBeginSync evBeginSync;
public void PreConnect()
{
while (true)
{
if (true /* just for testing*/)
{
evBeginSync();
return;
}
}
}
public void Connect()
{
_tmrManifestHandler.Enabled = true;
_tmrManifestHandler.Start();
}
private void _tmrManifestHandler_Tick(object sender, EventArgs e)
{
//NOT BEING 'HIT'
}
}
I am currently having a hardtime understanding and implementing events in C# using delagates. I am used to the Java way of doing things:
Define an interface for a listener type which would contain a number of method definitions
Define adapter class for that interface to make things easier if I'm not interested in all the events defined in a listener
Define Add, Remove and Get[] methods in the class which raises the events
Define protected fire methods to do the dirty work of looping through the list of added listeners and calling the correct method
This I understand (and like!) - I know I could do this exactly the same in c#, but it seems that a new (better?) system is in place for c#. After reading countless tutorials explaining the use of delegates and events in c# I still am no closer to really understanding what is going on :S
In short, for the following methods how would I implement the event system in c#:
void computerStarted(Computer computer);
void computerStopped(Computer computer);
void computerReset(Computer computer);
void computerError(Computer computer, Exception error);
^ The above methods are taken from a Java application I once made which I'm trying to port over to c#.
Many many thanks!
You'd create four events, and methods to raise them, along with a new EventArgs-based class to indicate the error:
public class ExceptionEventArgs : EventArgs
{
private readonly Exception error;
public ExceptionEventArgs(Exception error)
{
this.error = error;
}
public Error
{
get { return error; }
}
}
public class Computer
{
public event EventHandler Started = delegate{};
public event EventHandler Stopped = delegate{};
public event EventHandler Reset = delegate{};
public event EventHandler<ExceptionEventArgs> Error = delegate{};
protected void OnStarted()
{
Started(this, EventArgs.Empty);
}
protected void OnStopped()
{
Stopped(this, EventArgs.Empty);
}
protected void OnReset()
{
Reset(this, EventArgs.Empty);
}
protected void OnError(Exception e)
{
Error(this, new ExceptionEventArgs(e));
}
}
Classes would then subscribe to the event using either a method or a an anonymous function:
someComputer.Started += StartEventHandler; // A method
someComputer.Stopped += delegate(object o, EventArgs e)
{
Console.WriteLine("{0} has started", o);
};
someComputer.Reset += (o, e) => Console.WriteLine("{0} has been reset");
A few things to note about the above:
The OnXXX methods are protected so that derived classes can raise the events. This isn't always necessary - do it as you see fit.
The delegate{} piece on each event declaration is just a trick to avoid having to do a null check. It's subscribing a no-op event handler to each event
The event declarations are field-like events. What's actually being created is both a variable and an event. Inside the class you see the variable; outside the class you see the event.
See my events/delegates article for much more detail on events.
You'll have to define a single delegate for that
public delegate void ComputerEvent(object sender, ComputerEventArgs e);
ComputerEventArgs would be defined like this:
public class ComputerEventArgs : EventArgs
{
// TODO wrap in properties
public Computer computer;
public Exception error;
public ComputerEventArgs(Computer aComputer, Exception anError)
{
computer = aComputer;
error = anError;
}
public ComputerEventArgs(Computer aComputer) : this(aComputer, null)
{
}
}
The class that fires the events would have these:
public YourClass
{
...
public event ComputerEvent ComputerStarted;
public event ComputerEvent ComputerStopped;
public event ComputerEvent ComputerReset;
public event ComputerEvent ComputerError;
...
}
This is how you assign handlers to the events:
YourClass obj = new YourClass();
obj.ComputerStarted += new ComputerEvent(your_computer_started_handler);
Your handler is:
private void ComputerStartedEventHandler(object sender, ComputerEventArgs e)
{
// do your thing.
}
The main difference is that in C# the events are not interface-based. Instead, the event publisher declares the delegate which you can think of as a function pointer (although not exactly the same :-)). The subscriber then implements the event prototype as a regular method and adds a new instance of the delegate to the event handler chain of the publisher. Read more about delegates and events.
You can also read short comparison of C# vs. Java events here.
First of all, there is a standard method signature in .Net that is typically used for events. The languages allow any sort of method signature at all to be used for events, and there are some experts who believe the convention is flawed (I mostly agree), but it is what it is and I will follow it for this example.
Create a class that will contain the event’s parameters (derived from EventArgs).
public class ComputerEventArgs : EventArgs
{
Computer computer;
// constructor, properties, etc.
}
Create a public event on the class that is to fire the event.
class ComputerEventGenerator // I picked a terrible name BTW.
{
public event EventHandler<ComputerEventArgs> ComputerStarted;
public event EventHandler<ComputerEventArgs> ComputerStopped;
public event EventHandler<ComputerEventArgs> ComputerReset;
...
}
Call the events.
class ComputerEventGenerator
{
...
private void OnComputerStarted(Computer computer)
{
EventHandler<ComputerEventArgs> temp = ComputerStarted;
if (temp != null) temp(this, new ComputerEventArgs(computer)); // replace "this" with null if the event is static
}
}
Attach a handler for the event.
void OnLoad()
{
ComputerEventGenerator computerEventGenerator = new ComputerEventGenerator();
computerEventGenerator.ComputerStarted += new EventHandler<ComputerEventArgs>(ComputerEventGenerator_ComputerStarted);
}
Create the handler you just attached (mostly by pressing the Tab key in VS).
private void ComputerEventGenerator_ComputerStarted(object sender, ComputerEventArgs args)
{
if (args.Computer.Name == "HAL9000")
ShutItDownNow(args.Computer);
}
Don't forget to detach the handler when you're done. (Forgetting to do this is the biggest source of memory leaks in C#!)
void OnClose()
{
ComputerEventGenerator.ComputerStarted -= ComputerEventGenerator_ComputerStarted;
}
And that's it!
EDIT: I honestly can't figure out why my numbered points all appear as "1." I hate computers.
there are several ways to do what you want. The most direct way would be to define delegates for each event in the hosting class, e.g.
public delegate void ComputerStartedDelegate(Computer computer);
protected event ComputerStartedDelegate ComputerStarted;
public void OnComputerStarted(Computer computer)
{
if (ComputerStarted != null)
{
ComputerStarted.Invoke(computer);
}
}
protected void someMethod()
{
//...
computer.Started = true; //or whatever
OnComputerStarted(computer);
//...
}
any object may 'listen' for this event simply by:
Computer comp = new Computer();
comp.ComputerStarted += new ComputerStartedDelegate(
this.ComputerStartedHandler);
protected void ComputerStartedHandler(Computer computer)
{
//do something
}
The 'recommended standard way' of doing this would be to define a subclass of EventArgs to hold the Computer (and old/new state and exception) value(s), reducing 4 delegates to one. In this case that would be a cleaner solution, esp. with an Enum for the computer states in case of later expansion. But the basic technique remains the same:
the delegate defines the signature/interface for the event handler/listener
the event data member is a list of 'listeners'
listeners are removed using the -= syntax instead of +=
In c# events are delegates. They behave in a similar way to a function pointer in C/C++ but are actual classes derived from System.Delegate.
In this case, create a custom EventArgs class to pass the Computer object.
public class ComputerEventArgs : EventArgs
{
private Computer _computer;
public ComputerEventArgs(Computer computer) {
_computer = computer;
}
public Computer Computer { get { return _computer; } }
}
Then expose the events from the producer:
public class ComputerEventProducer
{
public event EventHandler<ComputerEventArgs> Started;
public event EventHandler<ComputerEventArgs> Stopped;
public event EventHandler<ComputerEventArgs> Reset;
public event EventHandler<ComputerEventArgs> Error;
/*
// Invokes the Started event */
private void OnStarted(Computer computer) {
if( Started != null ) {
Started(this, new ComputerEventArgs(computer));
}
}
// Add OnStopped, OnReset and OnError
}
The consumer of the events then binds a handler function to each event on the consumer.
public class ComputerEventConsumer
{
public void ComputerEventConsumer(ComputerEventProducer producer) {
producer.Started += new EventHandler<ComputerEventArgs>(ComputerStarted);
// Add other event handlers
}
private void ComputerStarted(object sender, ComputerEventArgs e) {
}
}
When the ComputerEventProducer calls OnStarted the Started event is invoked which in turn will call the ComputerEventConsumer.ComputerStarted method.
The delegate declares a function signature, and when it's used as an event on a class it also acts as a collection of enlisted call targets. The += and -= syntax on an event is used to adding a target to the list.
Given the following delegates used as events:
// arguments for events
public class ComputerEventArgs : EventArgs
{
public Computer Computer { get; set; }
}
public class ComputerErrorEventArgs : ComputerEventArgs
{
public Exception Error { get; set; }
}
// delegates for events
public delegate void ComputerEventHandler(object sender, ComputerEventArgs e);
public delegate void ComputerErrorEventHandler(object sender, ComputerErrorEventArgs e);
// component that raises events
public class Thing
{
public event ComputerEventHandler Started;
public event ComputerEventHandler Stopped;
public event ComputerEventHandler Reset;
public event ComputerErrorEventHandler Error;
}
You would subscribe to those events with the following:
class Program
{
static void Main(string[] args)
{
var thing = new Thing();
thing.Started += thing_Started;
}
static void thing_Started(object sender, ComputerEventArgs e)
{
throw new NotImplementedException();
}
}
Although the arguments could be anything, the object sender and EventArgs e is a convention that's used very consistently. The += thing_started will first create an instance of the delegate pointing to target method, then add it to the event.
On the component itself you would typically add methods to fire the events:
public class Thing
{
public event ComputerEventHandler Started;
public void OnStarted(Computer computer)
{
if (Started != null)
Started(this, new ComputerEventArgs {Computer = computer});
}
}
You must test for null in case no delegates have been added to the event. When you make the method call however all delegates which have been added will be called. This is why for events the return type is void - there is no single return value - so to feed back information you would have properties on the EventArgs which the event handlers would alter.
Another refinement would be to use the generic EventHandler delegate rather than declaring a concrete delegate for each type of args.
public class Thing
{
public event EventHandler<ComputerEventArgs> Started;
public event EventHandler<ComputerEventArgs> Stopped;
public event EventHandler<ComputerEventArgs> Reset;
public event EventHandler<ComputerErrorEventArgs> Error;
}
Thank you all so much for your answers! Finally I'm starting to understand what is going on. Just one thing; It seems that if each event had a different number/type of arguments I'd need to create a different :: EventArgs class to deal with it:
public void computerStarted(Computer computer);
public void computerStopped(Computer computer);
public void computerReset(Computer computer);
public void breakPointHit(Computer computer, int breakpoint);
public void computerError(Computer computer, Exception exception);
This would require three classses to deal with the events!? (Well two custom, and one using the default EventArgs.Empty class)
Cheers!
Ok, FINAL clarification!: So this is pretty much the best I can do code-wise to implement those events?
public class Computer {
public event EventHandler Started;
public event EventHandler Stopped;
public event EventHandler Reset;
public event EventHandler<BreakPointEvent> BreakPointHit;
public event EventHandler<ExceptionEvent> Error;
public Computer() {
Started = delegate { };
Stopped = delegate { };
Reset = delegate { };
BreakPointHit = delegate { };
Error = delegate { };
}
protected void OnStarted() {
Started(this, EventArgs.Empty);
}
protected void OnStopped() {
Stopped(this, EventArgs.Empty);
}
protected void OnReset() {
Reset(this, EventArgs.Empty);
}
protected void OnBreakPointHit(int breakPoint) {
BreakPointHit(this, new BreakPointEvent(breakPoint));
}
protected void OnError(System.Exception exception) {
Error(this, new ExceptionEvent(exception));
}
}
}