How do I use the state object passed to a system.threading.timer?

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Hi,

I am a little confused by the System.Threading.Timer class. The following code compiles and runs fine:

C#

using System;
using System.Threading;

namespace ConsoleApplication1
{
	public class Repeater
	{
		public Repeater( Action<object> callback, object state )
		{
			// Timer takes a TimerCallback delegate, but this constructor takes an Action<object>.  I have
			// read the easiest way to 'cast' a delegate is using lambdas.  Like this:
			TimerCallback tcb = ( s ) => callback( s );

			// So now I can construct my Timer.
			_timer = new Timer( tcb, state, 0, 5000 );
		}

		private Timer _timer = null;
	}

	public class Program
	{
		static void Main( string[] args )
		{
			Action<object> callback = MyFunction;
			Repeater repeater = new Repeater( callback, _count );

			Console.ReadKey();
		}

		private static void MyFunction( object state )
		{
			Console.WriteLine( $"event...{(int)state}" );
		}

		private static int _count = 42;
	}
}

Every 5 seconds, it prints out "event...42".

When I read the MSDN documentation on Timer (Timer Constructor (TimerCallback, Object, Int64, Int64) (System.Threading)), it says that the state parameter is: "An object containing information to be used by the callback method." This implies I can somehow pass information into the callback function each time it is called. So, in my example above, I could find a way to get the callback to print out 42...43...44... etc.

Is there any way to do this, or is the state parameter usable only as a way to specify some kind of initial state for the callback delegate (as I have done here, by effectively saying, "Start counting from 42")?

Kind wishes ~ Patrick

What I have tried:

The code example given. I just can't work out how to write anything that does "more" than what I am doing already.

Posted 5-Apr-16 5:05am

Patrick Skelton

Updated 5-Apr-16 5:26am

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Patrick Skelton · Accepted Answer · 2016-04-05T05:26:00

I am not sure if it is the only or best solution, but the following code achieves what I was looking to do. Basically, all I have done is changed the "dumb" integer _count variable to a class, which means it is passed by reference and it can maintain its own internal state, like this:

C#

using System;
using System.Threading;

namespace ConsoleApplication1
{
	public class Repeater
	{
		public Repeater( Action<object> callback, object state )
		{
			// Time takes a TimerCallback delegate, but this constructor takes an Action<object>.  I have
			// read the easiest way to 'cast' a delegate is using lambdas.  Like this:
			TimerCallback tcb = ( s ) => callback( s );

			// So now I can construct my Timer.
			_timer = new Timer( tcb, state, 0, 5000 );
		}

		private Timer _timer = null;
	}

	public class Counter
	{
		public int Count { get; set; }
	}

	public class Program
	{
		static void Main( string[] args )
		{
			Counter counter = new Counter();
			Action<object> callback = MyFunction;
			Repeater repeater = new Repeater( callback, counter );

			Console.ReadKey();
		}

		private static void MyFunction( object state )
		{
			Counter counter = state as Counter;
			Console.WriteLine( $"event...{counter.Count}" );
			counter.Count = counter.Count + 1;
		}
	}
}

This seems to work. I would still appreciate any comments though.