Class Promise<T>

A Promise is used for operations that retrieve data asynchronously. Use this object to determine the status of the operation (i.e., whether it has completed), and the resulting data.

Inheritance

Object

Promise<T>

Namespace: UnityEngine.XR.ARSubsystems

Syntax

public abstract class Promise<T> : CustomYieldInstruction

Type Parameters

Name	Description
T	The type of information the asynchronous operation retrieves.

Remarks

Since Promise<T> derives from CustomYieldInstruction, you can yield return on a Promise in a coroutine. If you prefer not to use the Promise as a coroutine, you may manually check keepWaiting to determine if the operation has completed. Once the operation is complete, you can get the resulting value from result.

Examples

Example usage in a coroutine:

IEnumerator MyCoroutine()
{
    var promise = GetDataAsync();
    yield return promise;
    Debug.LogFormat("Operation complete. Result = {0}", promise.result);
}

Properties

keepWaiting

Will return true as long as the operation has not yet completed.

Declaration

public override bool keepWaiting { get; }

Property Value

Type	Description
Boolean

result

The result of the asynchronous operation. Not valid until keepWaiting returns false.

Declaration

public T result { get; }

Property Value

Type	Description
T

Methods

CreateResolvedPromise(T)

Creates a resolved promise, i.e., one that is already complete.

Declaration

public static Promise<T> CreateResolvedPromise(T result)

Parameters

Type	Name	Description
T	result	The result of the operation.

Returns

Type	Description
Promise<T>	A completed Promise<T>.

OnKeepWaiting()

Invoked whenever keepWaiting is queried. Implement this to perform per-frame updates.

Declaration

protected abstract void OnKeepWaiting()

Resolve(T)

The creator of the Promise<T> should call this when the asynchronous operation completes.

Declaration

protected void Resolve(T result)

Parameters

Type	Name	Description
T	result	The result of the asychronous operation.