ContextAware.kt
/*
* Copyright 2020 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package androidx.activity.contextaware
import android.content.Context
import kotlinx.coroutines.suspendCancellableCoroutine
/**
* A `ContextAware` class is associated with a [Context] sometime after
* the class is instantiated. By adding a [OnContextAvailableListener], you can
* receive a callback for that event.
*
* Classes implementing [ContextAware] are strongly recommended to also implement
* [androidx.lifecycle.LifecycleOwner] for providing a more general purpose API for
* listening for creation and destruction events.
*
* @see ContextAwareHelper
*/
interface ContextAware {
/**
* Get the [Context] if it is currently available. If this returns
* `null`, you can use [addOnContextAvailableListener] to receive
* a callback for when it available.
*
* @return the Context if it is currently available.
*/
fun peekAvailableContext(): Context?
/**
* Add a new [OnContextAvailableListener] for receiving a callback for when
* this class is associated with a [android.content.Context].
*
* Listeners are triggered in the order they are added when added before the Context is
* available. Listeners added after the context has been made available will have the Context
* synchronously delivered to them as part of this call.
*
* @param listener The listener that should be added.
* @see removeOnContextAvailableListener
*/
fun addOnContextAvailableListener(listener: OnContextAvailableListener)
/**
* Remove a [OnContextAvailableListener] previously added via
* [addOnContextAvailableListener].
*
* @param listener The listener that should be removed.
* @see addOnContextAvailableListener
*/
fun removeOnContextAvailableListener(listener: OnContextAvailableListener)
}
/**
* Run [onContextAvailable] when the [Context] becomes available and
* resume with the result.
*
* If the [Context] is already available, [onContextAvailable] will be
* synchronously called on the current coroutine context. Otherwise,
* [onContextAvailable] will be called on the UI thread immediately when
* the Context becomes available.
*/
suspend inline fun <R> ContextAware.withContextAvailable(
crossinline onContextAvailable: (@JvmSuppressWildcards Context) -> @JvmSuppressWildcards R
): @JvmSuppressWildcards R {
val availableContext = peekAvailableContext()
return if (availableContext != null) {
onContextAvailable(availableContext)
} else {
suspendCancellableCoroutine { co ->
val listener = object : OnContextAvailableListener {
override fun onContextAvailable(context: Context) {
co.resumeWith(runCatching { onContextAvailable(context) })
}
}
addOnContextAvailableListener(listener)
co.invokeOnCancellation {
removeOnContextAvailableListener(listener)
}
}
}
}