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Juan Sebastian Martinez
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Adding a LavaBeatsViewModel
This encapsulates the business logic of playin the haptics beat effect as well as handling the graphical visualization triggers and logic
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  • samples/user-interface/haptics/src/main/java/com/example/platform/ui/haptics/lavabeats

‎samples/user-interface/haptics/src/main/java/com/example/platform/ui/haptics/lavabeats/LavaBeatsViewModel.kt‎

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/*
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* Copyright 2026 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* https://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.example.platform.ui.haptics.lavabeats
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import android.annotation.SuppressLint
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import android.app.Application
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import android.os.Build
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import android.os.Vibrator
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import android.os.vibrator.VibratorFrequencyProfile
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import androidx.annotation.RequiresApi
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import androidx.compose.runtime.State
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import androidx.compose.runtime.derivedStateOf
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import androidx.compose.runtime.mutableFloatStateOf
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import androidx.compose.runtime.mutableStateListOf
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import androidx.compose.runtime.mutableStateOf
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import androidx.core.content.ContextCompat
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import androidx.lifecycle.ViewModel
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import androidx.lifecycle.ViewModelProvider
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import androidx.lifecycle.viewModelScope
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import com.example.platform.ui.haptics.R
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import kotlin.time.Duration.Companion.milliseconds
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import kotlin.time.TimeSource
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import kotlinx.coroutines.Job
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import kotlinx.coroutines.delay
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import kotlinx.coroutines.launch
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/**
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* The view model that encapsulates business logic to modify the parameters of the haptic beat
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* effect, play the effect, and control the corresponding visualization.
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*/
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class LavaBeatsViewModel(
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val messageToUser: String,
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val supportsHapticBeatEffect: Boolean,
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private val vibrator: Vibrator,
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) : ViewModel() {
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// Haptic beat effect state variables
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val beatParameters = mutableStateListOf<BeatParameter>()
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// This is safely used by checks on supportsBeatHapticEffect
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@RequiresApi(Build.VERSION_CODES.BAKLAVA)
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private val vibratorFrequencyProfile: VibratorFrequencyProfile? = vibrator.frequencyProfile
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// This is safely checked by supportsBeatHapticEffect
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@SuppressLint("NewApi")
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private val vibratorFrequencyRange: ClosedFloatingPointRange<Float>? =
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if (supportsHapticBeatEffect) {
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vibratorFrequencyProfile?.let { it.minFrequencyHz..it.maxFrequencyHz }
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} else {
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null
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}
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// This is safely checked by supportsBeatHapticEffect
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@SuppressLint("NewApi")
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private val beatEffect = derivedStateOf {
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if (supportsHapticBeatEffect) {
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LavaBeatsHapticHelper.createEnvelopeBeatEffect(beatParameters = beatParameters)
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} else {
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null
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}
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}
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val beatTimingParams = derivedStateOf {
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beatEffect.value?.timingParams ?: BeatEffectTimingParams.Empty
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}
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// UI state control variables
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private val _isVibrating = mutableStateOf(false)
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val isVibrating: State<Boolean> = _isVibrating
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private val _showVisualization = mutableStateOf(true)
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val showVisualization: State<Boolean> = _showVisualization
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private val _showSettings = mutableStateOf(false)
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val showSettings: State<Boolean> = _showSettings
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// Visualization pulsing effect variables
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private val timeSource = TimeSource.Monotonic
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private val _pulseTime = mutableFloatStateOf(0f)
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val pulseTime: State<Float> = _pulseTime
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private var pulseTimeJob: Job? = null
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init {
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setDefaultParameters()
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updateFrequencyRanges()
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}
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fun setDefaultParameters() {
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beatParameters.clear()
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beatParameters.addAll(DEFAULT_PARAMETERS)
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}
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fun updateFrequencyRanges() {
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if (vibratorFrequencyRange != null) {
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beatParameters.forEachIndexed { i, parameter ->
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if (parameter.isFrequencyType) {
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val value = parameter.value.coerceIn(vibratorFrequencyRange)
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val newParameter = parameter.copy(value = value, range = vibratorFrequencyRange)
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beatParameters[i] = newParameter
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}
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}
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}
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}
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fun onToggleShowSettings() {
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_showSettings.value = !_showSettings.value
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}
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fun onToggleVisualization() {
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if (supportsHapticBeatEffect) {
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_showVisualization.value = !_showVisualization.value
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}
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}
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fun onSettingChanged(key: Int, settingValue: Float) {
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val range = beatParameters[key].range
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beatParameters[key] = beatParameters[key].copy(value = settingValue.coerceIn(range))
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}
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fun playHaptics() {
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if (Build.VERSION.SDK_INT < Build.VERSION_CODES.S) return
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beatEffect.value?.let {
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viewModelScope.launch {
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beginPulseTime()
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vibrator.vibrate(it.vibrationEffect)
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_isVibrating.value = true
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delay(it.totalDurationEstimateMillis.toLong().milliseconds)
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_isVibrating.value = false
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endPulseTime()
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}
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}
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}
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private fun beginPulseTime() {
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pulseTimeJob = viewModelScope.launch {
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val beginTime = timeSource.markNow()
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while (true) {
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val time = beginTime.elapsedNow().inWholeMilliseconds
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_pulseTime.floatValue = time / 1_000f
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delay(10L.milliseconds)
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}
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}
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}
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private fun endPulseTime() {
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pulseTimeJob?.cancel()
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pulseTimeJob = null
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_pulseTime.floatValue = 0f
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}
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companion object {
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private val DEFAULT_PARAMETERS =
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listOf(
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BeatParameter(
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description = "First pulse starting frequency (Hz)",
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value = 70f,
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isFrequencyType = true,
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),
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BeatParameter(
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description = "First pulse end frequency (Hz)",
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value = 90f,
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isFrequencyType = true,
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),
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BeatParameter(
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description = "First pulse duration (ms)",
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value = 16f,
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range = 1f..500f,
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),
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BeatParameter(description = "First pulse amplitude", value = 0.4f, range = 0f..1f),
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BeatParameter(
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description = "Second pulse frequency (Hz)",
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value = 80f,
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isFrequencyType = true,
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),
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BeatParameter(description = "Second pulse amplitude", value = 0.5f, range = 0f..1f),
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BeatParameter(
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description = "First to second pulse delay (ms)",
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value = 280f,
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range = 1f..500f,
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),
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BeatParameter(
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description = "Beats per minute",
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value = 60f,
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range = 1f..120f,
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steps = 1,
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),
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BeatParameter(
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description = "Number of beats",
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value = 5f,
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range = 1f..7f,
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steps = 5,
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),
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)
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fun provideFactory(application: Application): ViewModelProvider.Factory =
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object : ViewModelProvider.Factory {
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@Suppress("UNCHECKED_CAST")
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override fun <T : ViewModel> create(modelClass: Class<T>): T {
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val vibrator =
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ContextCompat.getSystemService(
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/*context = */ application,
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/*serviceClass = */ Vibrator::class.java,
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)!!
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var messageToUser: String
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var supportsHapticBeatEffect: Boolean
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if (
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Build.VERSION.SDK_INT >= Build.VERSION_CODES.BAKLAVA &&
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vibrator.areEnvelopeEffectsSupported()
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) {
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supportsHapticBeatEffect = true
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messageToUser = ""
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} else {
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supportsHapticBeatEffect = false
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messageToUser = application.getString(R.string.message_not_supported)
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}
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val viewModel =
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LavaBeatsViewModel(messageToUser, supportsHapticBeatEffect, vibrator)
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return viewModel as T
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}
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}
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}
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}

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