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/*
* Copyright (C) 2019 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 com.android.example.livedatabuilder.util
import androidx.lifecycle.LiveData
import androidx.lifecycle.Observer
import java.util.concurrent.CountDownLatch
import java.util.concurrent.TimeUnit
import java.util.concurrent.TimeoutException
/**
* Gets the value of a [LiveData] or waits for it to have one, with a timeout.
*
* Use this extension from host-side (JVM) tests. It's recommended to use it alongside
* `InstantTaskExecutorRule` or a similar mechanism to execute tasks synchronously.
*/
fun <T> LiveData<T>.getOrAwaitValue(
time: Long = 2,
timeUnit: TimeUnit = TimeUnit.SECONDS,
afterObserve: () -> Unit = {}
): T {
var data: T? = null
val latch = CountDownLatch(1)
val observer = object : Observer<T> {
override fun onChanged(o: T?) {
data = o
latch.countDown()
this@getOrAwaitValue.removeObserver(this)
}
}
this.observeForever(observer)
afterObserve.invoke()
// Don't wait indefinitely if the LiveData is not set.
if (!latch.await(time, timeUnit)) {
this.removeObserver(observer)
throw TimeoutException("LiveData value was never set.")
}
@Suppress("UNCHECKED_CAST")
return data as T
}
/**
* Observes a [LiveData] until the `block` is done executing.
*/
fun <T> LiveData<T>.observeForTesting(block: () -> Unit) {
val observer = Observer<T> { }
try {
observeForever(observer)
block()
} finally {
removeObserver(observer)
}
}
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