问题
My son is writing a simple RPG game that has a number of non-player characters (aka NPC's). Each NPC has an associated "script" that controls its behaviour. We were going to use a mini custom script language to write these behaviours but I'm now wondering if this would be better done in C#5/Async.
Taking a really simple example, suppose one of the NPC's just walks between two points I'm thinking it would be nice to write something like this:
while (true)
{
await WalkTo(100,100);
await WalkTo(200,200);
}
The WalkTo method would be an async method that handles everything to do with walking between the two points and does this over a number of frames from the game loop. It's not a blocking method that can be off-loaded to a background thread.
And this is where I'm stuck... I haven't been able to find any examples using async/await in this manner, but it seems it would be perfect for it.
Ideas?
Here's some very rough pseudo code for what I'd like to do:
class NpcBase
{
// Called from game loop
public void onUpdate(double elapsedTime)
{
// Move the NPC
.
.
.
// Arrived at destination?
if (Arrived)
{
// How do I trigger that the task is finished?
_currentTask.MarkComplete();
}
}
// Async method called by NPC "script"
public async Task WalkTo(int x, int y)
{
// Store new target location
// return a task object that will be "triggered" when the walk is finished
_currentTask = <something??>
return _currentTask;
}
Task _currentTask;
}
回答1:
Okay, it sounds like one option would be to have a TaskCompletionSource for each frame of the game. You can then await the Task from WalkTo, and set the result in OnUpdate:
private TaskCompletionSource<double> currentFrameSource;
// Called from game loop
public void OnUpdate(double elapsedTime)
{
...
var previousFrameSource = currentFrameSource;
currentFrameSource = new TaskCompletionSource<double>();
// This will trigger all the continuations...
previousFrameSource.SetResult(elapsedTime);
}
// Async method called by NPC "script"
public async Task WalkTo(int x, int y)
{
// Store new target location
while (/* we're not there yet */)
{
double currentTime = await currentFrameSource.Task;
// Move
}
}
I'm not sure how efficient this will be, admittedly... but it should work.
回答2:
I think I've figured it out in a simple test program
Firstly, I've got a base class for the NPC's like this:
EDIT: Updated NpcBase to use TaskCompletionSource:
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;
}
}
}
For reference, here's the old version of NpcBase with custom IAsyncResult implementation instead of TaskCompletionSource:
// 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;
}
}
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().
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;
}
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.
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();
}
}
And it works, all seems to be running on the main UI thread... which is what I wanted.
Of course it needs to be fixed to handle cancelling of operations, exceptions etc... but the basic idea is there.
来源：https://stackoverflow.com/questions/14952689/using-c-sharp-5-async-to-wait-for-something-that-executes-over-a-number-of-game