We Keep Coding

How do I create a public action, but keep the invoke private?

Let say I have an action like this:
public Action OnSomeAction;
I would like to be able to subscribe to this action from outside of the class, but not be able to invoke it:
OnSomeAction.Invoke();
Is there a way to do this without making the action private and creating methods for subscribing and unsubscribing like this:
private Action _someAction;
public void Subscribe(Action listener)
{
_someAction += listener;
}
public void Unsubscribe(Action listener)
{
_someAction -= listener;
}
private void Invoke()
{
_someAction.Invoke();
}

Are you looking for event?
public class MyClass {
// Let firing event be private
private void onMyAction() {
Action action = MyAction;
if (action != null)
action();
}
public void FireDemo() {
onMyAction();
}
//TODO: I've put Action, but, probably, EventHandler will be a better choice
// while event itself (subscribe / unsubscribe) being public
public event Action MyAction;
}
Demo:
MyClass myClass = new MyClass();
var first = () => {Console.WriteLine("I'm the first")};
var second = () => {Console.WriteLine("I'm the second")};
var none = () => {Console.WriteLine("I should not fire")};
myClass.MyAction += first;
myClass.MyAction += second;
myClass.MyAction += none;
// Unsubsribe
myClass.MyAction -= none;
// Direct attempt will NOT compile:
// myClass.MyAction();
myClass.FireDemo();

Although this looks a lot like events. You can achieve it using Action too. Consider following code which is almost same as you suggested:
private List<Action> _someActionList = new List<Action>();
public void Subscribe(Action listener)
{
_someActionList.Add(listener);
}
public void Unsubscribe(Action listener)
{
_someActionList.Remove(listener);
}
private void Invoke()
{
foreach(action in _someActionList)
{
action();
}
}
I hope this is exactly what you want to do. If not then please elaborate further.

Joining a thread started with StartNew()

When using the StartNew() method to kick off a process on a new thread, I need to figure out how to make another call into this object in that same thread (I assume this would be some sort of Join operation?).
The following example is dumbed down to illustrate the meat of what I am trying to do. I am well aware it is severely lacking in basic concurrency considerations. But I didn't want to cloud the code with all of that logic, so please forgive me on that.
The following console app shows what I am trying to accomplish. Assume on the StartNew() call a new thread with ID 9976 is created and the method invoked there. I would like the subsequent call to ProcessImmediate() in the file system watcher change event handler to be made on thread 9976 as well. As it stands, the call would share the same thread that is used for the file system watcher change event.
Can this be done, and if so, how?
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
var runner = new Runner();
runner.Run();
Console.ReadKey();
}
}
public class Runner
{
private Activity _activity = null;
private FileSystemWatcher _fileSystemWatcher;
public void Run()
{
_activity = new Activity();
// start activity on a new thread
Task.Factory.StartNew(() => _activity.Go());
_fileSystemWatcher = new FileSystemWatcher();
_fileSystemWatcher.Filter = "*.watcher";
_fileSystemWatcher.Path = "c:\temp";
_fileSystemWatcher.Changed += FileSystemWatcher_Changed;
_fileSystemWatcher.EnableRaisingEvents = true;
}
private void FileSystemWatcher_Changed(object sender, FileSystemEventArgs e)
{
// WANT TO CALL THIS FOR ACTIVITY RUNNING ON PREVIOUSLY CALLED THREAD
_activity.ProcessImmediate();
}
}
public class Activity
{
public void Go()
{
while (!Stop)
{
// for purposes of this example, magically assume that ProcessImmediate has not been called when this is called
DoSomethingInteresting();
System.Threading.Thread.Sleep(2000);
}
}
protected virtual void DoSomethingInteresting() { }
public void ProcessImmediate()
{
// for purposes of this example, assume that Go is magically in its sleep state when ProcessImmediate is called
DoSomethingInteresting();
}
public bool Stop { get; set; }
}
}
* UPDATE *
Thanks for the excellent responses. I took Mike's suggestion and implemented it for my console app. Below is the full working code which also includes the use of a cancellation token. I post this in case someone else might find it useful.
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
var runner = new Runner();
runner.Run();
Console.ReadKey();
runner.Stop();
Console.ReadKey();
}
}
public class Runner
{
private Activity _activity = null;
private FileSystemWatcher _fileSystemWatcher;
private CancellationTokenSource _cts = new CancellationTokenSource();
public void Stop() { _cts.Cancel(); }
public void Run()
{
_activity = new Activity();
// start activity on a new thread
var task = new Task(() => _activity.Go(_cts.Token), _cts.Token, TaskCreationOptions.LongRunning);
task.Start();
_fileSystemWatcher = new FileSystemWatcher();
_fileSystemWatcher.Filter = "*.watcher";
_fileSystemWatcher.Path = "C:\\Temp\\FileSystemWatcherPath";
_fileSystemWatcher.Changed += FileSystemWatcher_Changed;
_fileSystemWatcher.EnableRaisingEvents = true;
}
private void FileSystemWatcher_Changed(object sender, FileSystemEventArgs e)
{
// WANT TO CALL THIS FOR ACTIVITY RUNNING ON PREVIOUSLY CALLED THREAD
_activity.ProcessImmediate();
}
}
public class Activity : IDisposable
{
private AutoResetEvent _processing = new AutoResetEvent(false);
public void Go(CancellationToken ct)
{
Thread.CurrentThread.Name = "Go";
while (!ct.IsCancellationRequested)
{
// for purposes of this example, magically assume that ProcessImmediate has not been called when this is called
DoSomethingInteresting();
_processing.WaitOne(5000);
}
Console.WriteLine("Exiting");
}
protected virtual void DoSomethingInteresting()
{
Console.WriteLine(string.Format("Doing Something Interesting on thread {0}", Thread.CurrentThread.ManagedThreadId));
}
public void ProcessImmediate()
{
// for purposes of this example, assume that Go is magically in its sleep state when ProcessImmediate is called
_processing.Set();
}
public void Dispose()
{
if (_processing != null)
{
_processing.Dispose();
_processing = null;
}
}
}
}

First, you should use TaskCreationOptions.LongRunning if you are creating a task that will not complete quickly. Second, use an AutoResetEvent to signal the waiting thread to wake up. Note that below ProcessImmediate will return before DoSomethingInteresting has completed running on the other thread. Example:
using System.Threading;
public class Activity : IDisposable
{
private AutoResetEvent _processing = new AutoResetEvent(false);
public void Go()
{
while (!Stop)
{
// for purposes of this example, magically assume that ProcessImmediate has not been called when this is called
DoSomethingInteresting();
_processing.WaitOne(2000);
}
}
protected virtual void DoSomethingInteresting() { }
public void ProcessImmediate()
{
_processing.Set();
}
public bool Stop { get; set; }
public void Dispose()
{
if (_processing != null)
{
_processing.Dispose();
_processing = null;
}
}
}

User mike has given a better solution, which will be appropriate when you like to call the same method immediately. If you want to call a different methods immediately I'll expand mike's answer to achieve that.
using System.Threading;
public class Activity : IDisposable
{
private AutoResetEvent _processing = new AutoResetEvent(false);
private ConcurrentQueue<Action> actionsToProcess = new ConcurrentQueue<Action>();
public void Go()
{
while (!Stop)
{
// for purposes of this example, magically assume that ProcessImmediate has not been called when this is called
DoSomethingInteresting();
_processing.WaitOne(2000);
while(!actionsToProcess.IsEmpty)
{
Action action;
if(actionsToProcess.TryDeque(out action))
action();
}
}
}
protected virtual void DoSomethingInteresting() { }
public void ProcessImmediate(Action action)
{
actionsToProcess.Enqueue(action);
_processing.Set();
}
public bool Stop { get; set; }
public void Dispose()
{
if (_processing != null)
{
_processing.Dispose();
_processing = null;
}
}
}

To execute different methods on the same thread you can use a message loop that dispatches incoming requests. A simple option would be to use the event loop scheduler of the Reactive Extensions and to "recursively" schedule your Go() function - if in the mean time a different operation is scheduled it would be processed before the next Go() operation.
Here is a sample:
class Loop
: IDisposable
{
IScheduler scheduler = new EventLoopScheduler();
MultipleAssignmentDisposable stopper = new MultipleAssignmentDisposable();
public Loop()
{
Next();
}
void Next()
{
if (!stopper.IsDisposed)
stopper.Disposable = scheduler.Schedule(Handler);
}
void Handler()
{
Thread.Sleep(1000);
Console.WriteLine("Handler: {0}", Thread.CurrentThread.ManagedThreadId);
Next();
}
public void Notify()
{
scheduler.Schedule(() =>
{
Console.WriteLine("Notify: {0}", Thread.CurrentThread.ManagedThreadId);
});
}
public void Dispose()
{
stopper.Dispose();
}
}
static void Main(string[] args)
{
using (var l = new Loop())
{
Console.WriteLine("Press 'q' to quit.");
while (Console.ReadKey().Key != ConsoleKey.Q)
l.Notify();
}
}

How to publish and subscribe to events across different classes

Goal: To change a image on a form when either udp or tcp uses its send method
Problem: I have no idea how to get the event, eventhandler and delegates set up correctly
Send Interface
interface ISendData
{
void Send();
}
Tcp Connection class
//Need some type of delegate??
public class TCPconnection : ISendData
{
void Send()
{
//how invoke/fire a send Event?
}
}
UDP Connection class
//Need some type of delegate??
public class UDPConnection : ISendData
{
void Send()
{
//how invoke/fire a send event?
}
}
the winform which 'should' subscribe to seeing the fired events
public class myForm
{
private DataWatcher datawatcher = new DataWatcher();
private Image statusIndicator = null;
public myform()
{
initComponents();
datawatcher.DataSendActive += new DataWatcherSendHandler(DataSending);
datawatcher.DataSendInactive += new DataWatcherSendHandler(NoDataSending);
}
public void DataSending(object sender, DataWatcherArgs e)
{
statusIndicator = Properties.resources.greenLight;
}
public void NoDataSending(object sender, DataWatcherArgs e)
{
statusIndicator = Properties.resources.redLight;
}
}
The Event/Event handler?? But I really have no Idea what I'm doing here to make this work
public delegate void EventHandler(object sender, EventArgs e);
class DataWatcher
{
public event EventHandler DataSendActive;
public event EventHandler DataSendInactive;
protected virtual void onDataSendActive(System.EventArgs e)
{
if (DataSendActive != null)
{
DataSendActive(this, e);
}
}
protected virtual void onDataSendInactive(System.EventArgs e)
{
if (DataSendInactive != null)
{
DataSendInactive(this, e);
}
}
}

There are many conventions used to do this. Here's my little implementation.
public enum ActivityState
{
Sending,
Receiving,
Idle
}
public interface IDataTransferManager
{
// This event will fire when the activity state changes.
// note that Action<T> is introduced in .NET 3.5
// if you're using .NET 2.0, you can use a delegate.
event Action<ActivityState> DataActivityStateChange;
void Send(byte[] data);
//byte[] Receive();
// ... more methods ... //
}
Now the TcpConnection class will implement this.
public class TcpConnection : IDataTransferManager
{
public event Action<ActivityState> DataActivityStateChange;
public void Send(byte[] data)
{
// we're sending data. fire the change event
FireDataActivityStateChange(ActivityState.Sending);
//TODO: send the data
// we're done sending. Fire the change event
FireDataActivityStateChange(ActivityState.Idle);
}
private void FireDataActivityStateChange(ActivityState state)
{
// helper method, so I don't have to check the event
// to avoid null reference exceptions.
if (DataActivityStateChange != null)
DataActivityStateChange(state);
}
}
Here's the setup for your Form.
class MyForm // :Form
{
IDataTransferManager dataManager;
public MyForm()
{ // here, usually an instance will be passed in,
// so there's only one instance throughout the application.
// let's new up an instance for explanation purposes.
dataManager = new TcpConnection();
dataManager.DataActivityStateChange += (state) =>
{
// NOTE: if you don't like inline,
// you can point this labda to a method.
switch (state)
{
case ActivityState.Sending:
// change the image to the spinning toilet ball
break;
case ActivityState.Receiving:
// change the image to the spinning toilet ball, but reverse :P
break;
case ActivityState.Idle:
// hide it ?
break;
}
};
}
}

Here is a simple example of how you could implement an event for sending and not sending and subscribe to it
public class Connection
{
//Set up an event
public event EventHandler DataSending;
public event EventHandler DataNotSending
//This method will trigger the event for sending
private void OnDataSending()
{
if (DataSending!= null) { DataSending(this, EventArgs.Empty); }
}
//this method will trigger the event for finished sending
private void OnDataNotSending()
{
if (DataNotSending!= null) { DataNotSending(this, EventArgs.Empty); }
}
//This method performs your send logic
public void Send()
{
//Call your method that tells the event to be raised
OnDataSending();
//Then put your send code
OnDataNotSending(); //we're done!
}
}
This is how you use it in a consuming program
public class myForm
{
//This method is the one that sets up the
//instance and subscribes to the event
public myForm()
{
Connection con = new Connection();
con.DataSending += new EventHandler(con_DataSending);
con.DataNotSending += new EventHander(con_DataNotSending);
}
void con_DataSending(object sender, EventArgs e)
{
//Put your subscription logic here.
//Whatever you want to do in response to a send
}
void con_DataNotSending(object sender, EventArgs e)
{
//Put your subscription logic here.
//Respond to it not sending
}
}

Updating a C# 2.0 events example to be idiomatic with C# 3.5?

I have a short events example from .NET 2.0 that I've been using as a reference point for a while. We're now upgrading to 3.5, though, and I'm not clear on the most idiomatic way to do things. How would this simple events example get updated to reflect idioms that are now available in .NET 3.5?
// Args class.
public class TickArgs : EventArgs {
private DateTime TimeNow;
public DateTime Time {
set { TimeNow = value; }
get { return this.TimeNow; }
}
}
// Producer class that generates events.
public class Metronome {
public event TickHandler Tick;
public delegate void TickHandler(Metronome m, TickArgs e);
public void Start() {
while (true) {
System.Threading.Thread.Sleep(3000);
if (Tick != null) {
TickArgs t = new TickArgs();
t.Time = DateTime.Now;
Tick(this, t);
}
}
}
}
// Consumer class that listens for events.
public class Listener {
public void Subscribe(Metronome m) {
m.Tick += new Metronome.TickHandler(HeardIt);
}
private void HeardIt(Metronome m, TickArgs e) {
System.Console.WriteLine("HEARD IT AT {0}",e.Time);
}
}
// Example.
public class Test {
static void Main() {
Metronome m = new Metronome();
Listener l = new Listener();
l.Subscribe(m);
m.Start();
}
}

// Args class.
public class TickArgs : EventArgs {
private DateTime TimeNow;
// Auto property used
public DateTime Time { get; set; }
}
// Producer class that generates events.
public class Metronome {
public event TickHandler Tick;
public delegate void TickHandler(Metronome m, TickArgs e);
public void Start() {
while (true) {
System.Threading.Thread.Sleep(3000);
// Thread safety introduced
TickHandler ticker = Tick;
if (ticker != null) {
// Object initialiser added
TickArgs t = new TickArgs {
Time = DateTime.Now;
}
ticker(this, t);
}
}
}
}
// Consumer class that listens for events.
public class Listener {
public void Subscribe(Metronome m) {
// Event handler replaced with llambda function
m.Tick += (mm, e) => System.Console.WriteLine("HEARD IT AT {0}",e.Time)
}
}
// Example.
public class Test {
static void Main() {
Metronome m = new Metronome();
Listener l = new Listener();
l.Subscribe(m);
m.Start();
}
}
You can improve the Tick event like this
// Producer class that generates events.
public class Metronome {
// Add a dummy event handler and ensure that there's no unsafe thread issues
public event TickHandler Tick = (m, e) => {};
public delegate void TickHandler(Metronome m, TickArgs e);
public void Start() {
while (true) {
System.Threading.Thread.Sleep(3000);
// no need to check for null before calling
Tick(this, new TickArgs { Time = DateTime.Now; });
}
}
}
I don't have a compile to hand but you can improve the Tick event like this I think
// Producer class that generates events.
public class Metronome {
// Add a dummy event handler and ensure that there's no unsafe thread issues
public event EventHandler<TickArgs> Tick = (m, e) => {};
public void Start() {
while (true) {
System.Threading.Thread.Sleep(3000);
// no need to check for null before calling
Tick(this, new TickArgs { Time = DateTime.Now; });
}
}
}

For a start, you shouldn't define your own delegate types for events. Instead, use System.EventHandler<T> or System.EventHandler.
Also, you can use auto-implemented properties for your TickArgs class (which, incidentally, should really be called TickEventArgs, in accord with .NET conventions):
public class TickEventArgs : EventArgs
{
public DateTime Time
{
get;
set;
}
}
As for the events themselves, there are some gotchas that you should know about in .NET which you can read about in some of John Skeet's multithreading articles:
http://www.yoda.arachsys.com/csharp/events.html
Note that events in .NET 4 work differently and a lot of the gotchas that exist in 3.5 have been cleaned up.

For starters you can use auto generated properties:
public class TickArgs : EventArgs {
public DateTime Time {
set;
get;
}
}
You also do not need to instantiate the listening delegate:
public void Subscribe(Metronome m) {
m.Tick += HeardIt;
}

Here's how I would do it. First, note that I've made TickArgs sealed and immutable via readonly on the member variables. Second, I removed the TickHandler delegate and replaced with an EventHandler<TickArgs>. Thirdly, the Tick event itself is now private (renamed to _Tick) and accessed via a property. Lastly, the hook into the event in Listener uses a lambda expression (i.e. inline delegate) rather than an explicit method.
namespace Events3
{
using System;
// Args class.
public sealed class TickArgs : EventArgs
{
private readonly DateTime TimeNow;
public DateTime Time
{
get { return this.TimeNow; }
}
public TickArgs(DateTime TimeNow)
{
this.TimeNow = TimeNow;
}
}
// Producer class that generates events.
public sealed class Metronome
{
private event EventHandler<TickArgs> _Tick;
public event EventHandler<TickArgs> Tick
{
add { this._Tick += value; }
remove { this._Tick -= value; }
}
public void Start()
{
while (true)
{
System.Threading.Thread.Sleep(3000);
EventHandler<TickArgs> tick = this._Tick;
if (tick != null)
{
tick(this, new TickArgs(DateTime.Now));
}
}
}
}
// Consumer class that listens for events.
public sealed class Listener
{
public void Subscribe(Metronome m)
{
m.Tick += (sender, e) =>
{
System.Console.WriteLine("HEARD IT AT {0}", e.Time);
};
}
}
// Example.
public static class Test
{
static void Main()
{
Metronome m = new Metronome();
Listener l = new Listener();
l.Subscribe(m);
m.Start();
}
}
}

C# Threading Mechanism

Let's say I have an exposed interface as such:
interface IMyService
{
MyResult MyOperation();
}
This operation is synchronous and returns a value.
My implemented interface has to do the following:
Call an asynchronous method
Wait for event #1
Wait for event #2
This is due to a 3rd party COM object I am working with.
This code looks similar to the following
public MyResult MyOperation()
{
_myCOMObject.AsyncOperation();
//Here I need to wait for both events to fire before returning
}
private void MyEvent1()
{
//My Event 1 is fired in this handler
}
private void MyEvent2()
{
//My Event 2 is fired in this handler
}
My two events can happen in either order, it is quite random.
What is the proper threading mechanism I can use to synchronize this? I was using ManualResetEvent before I had to start waiting for the second event, and have not seen an easy way to use it for both events. These 2 events set variables that allow me to create the return value for MyOperation().
Any ideas on a good implementation for this? I have no control over the way the 3rd party object is implemented.

Two ManualResetEvents should do the trick for you. Just initialize them to false before you call the _myCOMObject.AsyncOperation(). Like this:
private ManualResetEvent event1;
private ManualResetEvent event2;
public MyResult MyOperation()
{
event1 = new ManualResetEvent(false);
event2 = new ManualResetEvent(false);
_myCOMObject.AsyncOperation();
WaitHandle.WaitAll(new WaitHandle[] { event1, event2 });
}
private void MyEvent1()
{
event1.Set();
}
private void MyEvent2()
{
event2.Set();
}
Edit
Thanks for the comments. I've changed the wait call to use WaitAll

My implementation example is as follows:
namespace ConsoleApplication1
{
class Program
{
private static WaitHandle[] waitHandles;
private static event EventHandler Evt1;
private static event EventHandler Evt2;
static void Main(string[] args)
{
waitHandles = new WaitHandle[]{
new ManualResetEvent(false),
new ManualResetEvent(false)
};
Evt1 += new EventHandler(Program_Evt1);
Evt2 += new EventHandler(Program_Evt2);
OnEvt1();
OnEvt2();
WaitHandle.WaitAll(waitHandles);
Console.WriteLine("Finished");
Console.ReadLine();
}
static void Program_Evt2(object sender, EventArgs e)
{
Thread.Sleep(2000);
((ManualResetEvent)waitHandles[0]).Set();
}
static void Program_Evt1(object sender, EventArgs e)
{
((ManualResetEvent)waitHandles[1]).Set();
}
static void OnEvt1()
{
if (Evt1 != null)
Evt1(null, EventArgs.Empty);
}
static void OnEvt2()
{
if (Evt2 != null)
Evt2(null, EventArgs.Empty);
}
}
}
I make it sleep for the purposes of this example and the WaitAll functionality
Cheers,
Andrew
P.S. another example would be using AsyncCallback, really quick and dirty example, but gives you more keys to open the door with :-) . Hope this helps!!
namespace ConsoleApplication1
{
class Program
{
private static WaitHandle[] waitHandles;
private static event EventHandler Evt1;
private static event EventHandler Evt2;
static void Main(string[] args)
{
waitHandles = new WaitHandle[]{
new ManualResetEvent(false),
new ManualResetEvent(false)
};
var callabck1 = new AsyncCallback(OnEvt1);
var callabck2 = new AsyncCallback(OnEvt2);
callabck1.Invoke(new ManualResetResult(null, (ManualResetEvent)waitHandles[0]));
callabck2.Invoke(new ManualResetResult(null, (ManualResetEvent)waitHandles[1]));
WaitHandle.WaitAll(waitHandles);
Console.WriteLine("Finished");
Console.ReadLine();
}
static void OnEvt1(IAsyncResult result)
{
Console.WriteLine("Setting1");
var handle = result.AsyncWaitHandle;
((ManualResetEvent)handle).Set();
}
static void OnEvt2(IAsyncResult result)
{
Thread.Sleep(2000);
Console.WriteLine("Setting2");
var handle = result.AsyncWaitHandle;
((ManualResetEvent)handle).Set();
}
}
public class ManualResetResult : IAsyncResult
{
private object _state;
private ManualResetEvent _handle;
public ManualResetResult(object state, ManualResetEvent handle)
{
_state = state;
_handle = handle;
}
#region IAsyncResult Members
public object AsyncState
{
get { return _state; }
}
public WaitHandle AsyncWaitHandle
{
get { return _handle; }
}
public bool CompletedSynchronously
{
get { throw new NotImplementedException(); }
}
public bool IsCompleted
{
get { throw new NotImplementedException(); }
}
#endregion
}
}

I am not sure I understood your question, but AutoResetEvent.WaitAll seems to solve your problem, if I got it right. It allows you to set more than one handler and it will only be released when all are set.
http://msdn.microsoft.com/en-us/library/z6w25xa6.aspx