Hey guys I m trying to await a result of a callback from the

Question

Hey guys I m trying to await a result of a callback from the Amazon LWA sdk but it s a bit advanced and confusing for me This is their method ``` AuthorizationManager getToken context SCOPES tokenListener ``` I want to wait for it to get the result in the listener and then continue on with my code but I can t figure out if it s at all possible

streetsofboston · Answer

``` suspend fun getAuthManagerToken context Context scopes Scopes Token = suspendCoroutine cont gt AuthorizationManager getToken context scopes token gt cont resume token ```

Schadenfreude · Answer

The listener can return either a token or an error its type is `Listener lt AuthorizeResult AuthError gt `

streetsofboston · Answer

Is `AuthError` a `Throwable`

louiscad · Answer

< Schadenfreude> Then use `resumeWithException` when there s an error and if there s no `Throwable` use your own

Schadenfreude · Answer

< streetsofboston> yes it s a throwable

streetsofboston · Answer

``` suspend fun getAuthManagerToken context Context scopes Scopes Token = suspendCoroutine cont gt AuthorizationManager getToken context scopes token error gt if error = null resumeWithException error else cont resume token ```

streetsofboston · Answer

I assumed the type name s in my example I don t know their exact form

Schadenfreude · Answer

So thanks to < streetsofboston> I managed to figure it out here s the final solution ``` private suspend fun getAuthManagerToken context Context scopes Array lt Scope gt AuthorizeResult = suspendCoroutine cont gt AuthorizationManager getToken context scopes object Listener lt AuthorizeResult AuthError gt override fun onError authError AuthError cont resumeWithException authError override fun onSuccess authResult AuthorizeResult cont resume authResult ```

Sam · Answer

< Schadenfreude> < streetsofboston> Is there any reason not to use suspendCancellableCoroutine and cancel getToken when not needed anymore

streetsofboston · Answer

`suspendCancellableCoroutine` In the code sample of Daniel the `getAuthManagerToken` has no reason to cancel the suspended coroutine itself The outer scope that calls `getAuthManagerToken` still can cancel the suspended fun `suspendCancellableCoroutine` will just provide a `cont` to the implementation of `getAuthManagerToken` that now has an additional `cancel` function

Sam · Answer

Okay if getToken returns a cancellable call then it makes sense to use suspendCancellableCoroutine

Sam · Answer

that way the pending getToken request and its resources can be dropped early

streetsofboston · Answer

If a cancelation happens most of the time the outer scope that calls the function does the cancelation The `getAuthManager` doesn t need to worry about it in this case If the `getAuthManagerToken` itself needs to cancel it then it needs to call `suspendCancellableCoroutine` so that it has a `CancelableContinuation` not sure if I have the class name right instead of a plain `Continuation` and now it can call `cancel ` on it if necessary instead of calling `resumeWithException ` Cancelation is almost like `resumeWithException` because it cancels the suspending call but it is not fatal it has just canceled

pakoito · Answer

< louiscad> I thought resumeWithExceptions was only for crashing cases not for control flow

louiscad · Answer

< pakoito> It s to forward `Throwable`s back into the control flow from error exceptions callbacks