LiveData.kt
/*
* Copyright 2018 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.lifecycle
import androidx.annotation.MainThread
/**
* Adds the given [onChanged] lambda as an observer within the lifespan of the given
* [owner] and returns a reference to observer.
* The events are dispatched on the main thread. If LiveData already has data
* set, it will be delivered to the onChanged.
*
* The observer will only receive events if the owner is in [Lifecycle.State.STARTED]
* or [Lifecycle.State.RESUMED] state (active).
*
* If the owner moves to the [Lifecycle.State.DESTROYED] state, the observer will
* automatically be removed.
*
* When data changes while the [owner] is not active, it will not receive any updates.
* If it becomes active again, it will receive the last available data automatically.
*
* LiveData keeps a strong reference to the observer and the owner as long as the
* given LifecycleOwner is not destroyed. When it is destroyed, LiveData removes references to
* the observer and the owner.
*
* If the given owner is already in [Lifecycle.State.DESTROYED] state, LiveData
* ignores the call.
*/
@MainThread inline fun <T> LiveData<T>.observe(
owner: LifecycleOwner,
crossinline onChanged: (T) -> Unit
): Observer<T> {
val wrappedObserver = Observer<T> { t -> onChanged.invoke(t) }
observe(owner, wrappedObserver)
return wrappedObserver
}