// return async-value.(or you can use `UniTask`(no result), `UniTaskVoid`(fire and forget)).
return (asset as TextAsset)?.text ?? throw new InvalidOperationException("Asset not found");
}
```
`UniTask<T>`
---
UniTask feature rely on C# 7.0([task-like custom async method builder feature](https://github.com/dotnet/roslyn/blob/master/docs/features/task-types.md)) so required Unity version is after `Unity 2018.3`.
Why UniTask(custom task-like object) is required? Because Task is too heavy, not matched to Unity threading(single-thread). UniTask does not use thread and SynchronizationContext because almost Unity's asynchronous object is automaticaly dispatched by Unity's engine layer. It acquires more fast and more less allocation, completely integrated with Unity.
You can await `AsyncOperation`, `ResourceRequest`, `UnityWebRequestAsyncOperation`, `IEnumerator` and others when using `UniRx.Async`.
`UniTask.Delay`, `UniTask.Yield`, `UniTask.Timeout` that is frame-based timer operators(no uses thread so works on WebGL publish) driven by custom PlayerLoop(Unity 2018 experimental feature). In default, UniTask initialize automatically when application begin, but it is override all. If you want to append PlayerLoop, please call `PlayerLoopHelper.Initialize(ref yourCustomizedPlayerLoop)` manually.
> Before Unity 2019.3, Unity does not have `PlayerLooop.GetCurrentPlayerLoop` so you can't use with Unity ECS package in default. If you want to use with ECS and before Unity 2019.3, you can use this hack below.
var playerLoop = ScriptBehaviourUpdateOrder.CurrentPlayerLoop;
// Setup UniTask's PlayerLoop.
PlayerLoopHelper.Initialize(ref playerLoop);
```
`UniTask.WhenAll`, `UniTask.WhenAny` is like Task.WhenAll/WhenAny but return type is more useful.
`UniTask.ctor(Func<UniTask>)` is like the embeded [`AsyncLazy<T>`](https://blogs.msdn.microsoft.com/pfxteam/2011/01/15/asynclazyt/)
```csharp
public class SceneAssets
{
public readonly UniTask<Sprite> Front;
public readonly UniTask<Sprite> Background;
public readonly UniTask<Sprite> Effect;
public SceneAssets()
{
// ctor(Func) overload is AsyncLazy, initialized once when await.
// and after it, await returns zero-allocation value immediately.
Front = new UniTask<Sprite>(() => LoadAsSprite("foo"));
Background = new UniTask<Sprite>(() => LoadAsSprite("bar"));
Effect = new UniTask<Sprite>(() => LoadAsSprite("baz"));
}
async UniTask<Sprite> LoadAsSprite(string path)
{
var resource = await Resources.LoadAsync<Sprite>(path);
return (resource as Sprite);
}
}
```
If you want to convert callback to UniTask, you can use `UniTaskCompletionSource<T>` that is the lightweight edition of `TaskCompletionSource<T>`.
```csharp
public UniTask<int> WrapByUniTaskCompletionSource()
{
var utcs = new UniTaskCompletionSource<int>();
// when complete, call utcs.TrySetResult();
// when failed, call utcs.TrySetException();
// when cancel, call utcs.TrySetCanceled();
return utcs.Task; //return UniTask<int>
}
```
You can convert Task -> UniTask: `AsUniTask`, `UniTask` -> `UniTask<AsyncUnit>`: `AsAsyncUnitUniTask`(this is useful to use WhenAll/WhenAny), `UniTask<T>` -> `UniTask`: `AsUniTask`.
If you want to convert async to coroutine, you can use `UniTask.ToCoroutine`, this is useful to use only allow coroutine system.
Some UniTask factory methods have `CancellationToken cancellation = default(CancellationToken)` parameter. Andalso some async operation for unity have `ConfigureAwait(..., CancellationToken cancellation = default(CancellationToken))` extension methods.
You can pass `CancellationToken` to parameter by standard [`CancellationTokenSource`](https://docs.microsoft.com/en-us/dotnet/api/system.threading.cancellationtokensource).
When detect cancellation, all methods throws `OperationCanceledException` and propagate to upstream. `OperationCanceledException` is special exception, if not handled this exception, finally it is propagated to `UniTaskScheduler.UnobservedTaskException`.
Default behaviour of received unhandled exception is write log as warning. Log level can change by `UniTaskScheduler.UnobservedExceptionWriteLogType`. If you want to change custom beavhiour, set action to `UniTaskScheduler.UnobservedTaskException.`
If you want to cancel behaviour in async UniTask method, throws `OperationCanceledException` manually.
```csharp
public async UniTask<int> FooAsync()
{
await UniTask.Yield();
throw new OperationCanceledException();
}
```
If you handle exception but want to ignore(propagete to global cancellation handling), use exception filter.
```csharp
public async UniTask<int> BarAsync()
{
try
{
var x = await FooAsync();
return x * 2;
}
catch (Exception ex) when (!(ex is OperationCanceledException))
{
return -1;
}
}
```
throws/catch `OperationCanceledException` is slightly heavy, if you want to care performance, use `UniTask.SuppressCancellationThrow` to avoid OperationCanceledException throw. It returns `(bool IsCanceled, T Result)` instead of throw.
```csharp
var (isCanceled, _) = await UniTask.DelayFrame(10, cancellationToken: cts.Token).SuppressCancellationThrow();
if (isCanceled)
{
// ...
}
```
Note: Only suppress throws if you call it directly into the most source method.
Some async operation for unity have `ConfigureAwait(IProgress<float> progress = null, ...)` extension methods.
```csharp
var progress = Progress.Create<float>(x => Debug.Log(x));
var request = await UnityWebRequest.Get("http://google.co.jp")
.SendWebRequest()
.ConfigureAwait(progress: progress);
```
Should not use `new System.Progress<T>`, because it allocate every times. Use `UniRx.Async.Progress` instead. Progress factory has two methods, `Create` and `CreateOnlyValueChanged`. `CreateOnlyValueChanged` calls only when progress value changed. Should not use `new System.Progress<T>`, it allocate every times.
Implements interface is more better.
```csharp
public class Foo : MonoBehaviour, IProgress<float>
{
public void Report(float value)
{
UnityEngine.Debug.Log(value);
}
public async UniTaskVoid WebRequest()
{
var request = await UnityWebRequest.Get("http://google.co.jp")
* Enable StackTrace(Toggle) - Capture StackTrace when task is started. Performance impact: high.
For debug use, enable tracking and capture stacktrace is useful but it it decline performance. Recommended usage is enable both to find task leak, and when done, finally disable both.
Reusable Promises
---
Some UniTask factory can reuse to reduce allocation. The list is `Yield`, `Delay`, `DelayFrame`, `WaitUntil`, `WaitWhile`, `WaitUntilValueChanged`.
`async void` is standard C# system so does not run on UniTask systems. It is better not to use. `async UniTaskVoid` is lightweight version of `async UniTask` because it does not have awaitable completion. If you don't require to await it(fire and forget), use `UniTaskVoid` is better. Unfortunately to dismiss warning, require to using with `Forget()`.
For Unit Testing
---
Unity's `[UnityTest]` attribute can test coroutine(IEnumerator) but can not test async. `UniTask.ToCoroutine` bridges async/await to coroutine so you can test async method.
```csharp
[UnityTest]
public IEnumerator DelayIgnore() => UniTask.ToCoroutine(async () =>
