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copied!<p>I think I've figured it out in a simple test program</p> <p>Firstly, I've got a base class for the NPC's like this:</p> <p>EDIT: Updated NpcBase to use TaskCompletionSource:</p> <pre><code>public class NpcBase { // Derived classes to call this when starting an async operation public Task BeginTask() { // Task already running? if (_tcs!= null) { throw new InvalidOperationException("busy"); } _tcs = new TaskCompletionSource<int>(); return _tcs.Task; } TaskCompletionSource<int> _tcs; // Derived class calls this when async operation complete public void EndTask() { if (_tcs != null) { var temp = _tcs; _tcs = null; temp.SetResult(0); } } // Is this NPC currently busy? public bool IsBusy { get { return _tcs != null; } } } </code></pre> <p>For reference, here's the old version of NpcBase with custom IAsyncResult implementation instead of TaskCompletionSource:</p> <pre><code>// DONT USE THIS, OLD VERSION FOR REFERENCE ONLY public class NpcBase { // Derived classes to call this when starting an async operation public Task BeginTask() { // Task already running? if (_result != null) { throw new InvalidOperationException("busy"); } // Create the async Task return Task.Factory.FromAsync( // begin method (ac, o) => { return _result = new Result(ac, o); }, // End method (r) => { }, // State object null ); } // Derived class calls this when async operation complete public void EndTask() { if (_result != null) { var temp = _result; _result = null; temp.Finish(); } } // Is this NPC currently busy? public bool IsBusy { get { return _result != null; } } // Result object for the current task private Result _result; // Simple AsyncResult class that stores the callback and the state object class Result : IAsyncResult { public Result(AsyncCallback callback, object AsyncState) { _callback = callback; _state = AsyncState; } private AsyncCallback _callback; private object _state; public object AsyncState { get { return _state; ; } } public System.Threading.WaitHandle AsyncWaitHandle { get { throw new NotImplementedException(); } } public bool CompletedSynchronously { get { return false; } } public bool IsCompleted { get { return _finished; } } public void Finish() { _finished = true; if (_callback != null) _callback(this); } bool _finished; } } </code></pre> <p>Next, I've got a simple "NPC" that moves in one dimension. When a moveTo operation starts it calls BeginTask in the NpcBase. When arrived at the destination, it calls EndTask().</p> <pre><code>public class NpcTest : NpcBase { public NpcTest() { _position = 0; _target = 0; } // Async operation to count public Task MoveTo(int newPosition) { // Store new target _target = newPosition; return BeginTask(); } public int Position { get { return _position; } } public void onFrame() { if (_position == _target) { EndTask(); } else if (_position < _target) { _position++; } else { _position--; } } private int _position; private int _target; } </code></pre> <p>And finally, a simple WinForms app to drive it. It consists of a button and two labels. Clicking the button starts both NPC and their position is displayed on the labels.</p> <pre><code>public partial class Form1 : Form { public Form1() { InitializeComponent(); } private void onButtonClick(object sender, EventArgs e) { RunNpc1(); RunNpc2(); } public async void RunNpc1() { while (true) { await _npc1.MoveTo(20); await _npc1.MoveTo(10); } } public async void RunNpc2() { while (true) { await _npc2.MoveTo(80); await _npc2.MoveTo(70); } } NpcTest _npc1 = new NpcTest(); NpcTest _npc2 = new NpcTest(); private void timer1_Tick(object sender, EventArgs e) { _npc1.onFrame(); _npc2.onFrame(); label1.Text = _npc1.Position.ToString(); label2.Text = _npc2.Position.ToString(); } } </code></pre> <p>And it works, all seems to be running on the main UI thread... which is what I wanted.</p> <p>Of course it needs to be fixed to handle cancelling of operations, exceptions etc... but the basic idea is there.</p>

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