Expressive (a)synchronous code using coroutines

As everyone knows, long-running operations in Android apps should never be executed on the main thread. With the goal of protecting developers from making mistakes, the Android ecosystem relies heavily on asynchronous APIs that can be found all over the framework and also in many third-party libraries. Although this might do the trick for simple apps and workflows, this becomes a problem as complexity grows in the codebase. In this talk, we'll explore how to leverage coroutines to convert asynchronous APIs into synchronous ones for the sake of expressiveness, readability and developer sanity.

Transcript

1. Expressive (a)synchronous code using coroutines Flávio Faria
2. fun makeAsyncCall() { val asyncApi = AsyncApi() asyncApi.doSomethingAsync { result -> // do something useful with result } }
3. fun makeAsyncCall() { val asyncApi = AsyncApi() asyncApi.doSomethingAsync { result -> runOnUiThread { // do something useful with result } } }
4. Why are APIs designed like this?
5. Why are APIs designed like this? Answer: to prevent blocking the main thread (mostly)
7. • Getting the user location
8. • Getting the user location • Playing media
9. • Getting the user location • Playing media • Managing Bluetooth devices
10. • Getting the user location • Playing media • Managing Bluetooth devices • Third-party service libraries
11. Bluetooth Low Energy API
12. GATT Server (device)
13. GATT Server (device) Service 1
14. GATT Server (device) Service 1 Characteristic 1 Characteristic 2
15. GATT Server (device) Service 1 Characteristic 1 Characteristic 2 Service 2 Characteristic 1 Characteristic 2 Characteristic 3
16. GATT Server (battery-powered device) Battery Service Battery Level … … … … …
18. 1. Scan for BLE devices
19. 1. Scan for BLE devices 2. Connect to a device
20. 1. Scan for BLE devices 2. Connect to a device 3. Discover services
21. 1. Scan for BLE devices 2. Connect to a device 3. Discover services 4. Retrieve characteristic value
22. private val adapter = BluetoothAdapter.getDefaultAdapter()
23. private val adapter = BluetoothAdapter.getDefaultAdapter() fun discoverDevice() { adapter.bluetoothLeScanner.startScan(scanCallback) }
24. private val adapter = BluetoothAdapter.getDefaultAdapter() fun discoverDevice() { adapter.bluetoothLeScanner.startScan(scanCallback) }
25. private val adapter = BluetoothAdapter.getDefaultAdapter() fun discoverDevice() { adapter.bluetoothLeScanner.startScan(scanCallback) } private val scanCallback = object : ScanCallback() { }
26. private val adapter = BluetoothAdapter.getDefaultAdapter() fun discoverDevice() { adapter.bluetoothLeScanner.startScan(scanCallback) } private val scanCallback = object : ScanCallback() { override fun onScanResult(callbackType: Int, result: ScanResult) { } }
27. private val adapter = BluetoothAdapter.getDefaultAdapter() fun discoverDevice() { adapter.bluetoothLeScanner.startScan(scanCallback) } private val scanCallback = object : ScanCallback() { override fun onScanResult(callbackType: Int, result: ScanResult) { if (result.device.name == "My Battery-Powered BLE device") { adapter.bluetoothLeScanner.stopScan(this) val gatt = result.device.connectGatt(context, false, gattCallback) } } }
28. private val adapter = BluetoothAdapter.getDefaultAdapter() fun discoverDevice() { adapter.bluetoothLeScanner.startScan(scanCallback) } private val scanCallback = object : ScanCallback() { override fun onScanResult(callbackType: Int, result: ScanResult) { if (result.device.name == "My Battery-Powered BLE device") { adapter.bluetoothLeScanner.stopScan(this) val gatt = result.device.connectGatt(context, false, gattCallback) } } }
29. private val gattCallback = object : BluetoothGattCallback() { }
30. private val gattCallback = object : BluetoothGattCallback() { override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) { } }
31. private val gattCallback = object : BluetoothGattCallback() { override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) { if (status == BluetoothGatt.GATT_SUCCESS && newState == BluetoothGatt.STATE_CONNECTED) { gatt.discoverServices() } } }
32. private val gattCallback = object : BluetoothGattCallback() { override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) { if (status == BluetoothGatt.GATT_SUCCESS && newState == BluetoothGatt.STATE_CONNECTED) { gatt.discoverServices() } } }
33. private val gattCallback = object : BluetoothGattCallback() { override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) { if (status == BluetoothGatt.GATT_SUCCESS && newState == BluetoothGatt.STATE_CONNECTED) { gatt.discoverServices() } } }
34. private val gattCallback = object : BluetoothGattCallback() { override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) {…} }
35. private val gattCallback = object : BluetoothGattCallback() { override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) {…} override fun onServicesDiscovered(gatt: BluetoothGatt, status: Int) { } }
36. private val gattCallback = object : BluetoothGattCallback() { override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) {…} override fun onServicesDiscovered(gatt: BluetoothGatt, status: Int) { if (status == BluetoothGatt.GATT_SUCCESS) { gatt.services .find { it.uuid == BATTERY_SERVICE_UUID } ?.characteristics ?.find { it.uuid == BATTERY_CHAR_UUID } ?.let { characteristic -> gatt.readCharacteristic(characteristic) } } } }
37. private val gattCallback = object : BluetoothGattCallback() { override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) {…} override fun onServicesDiscovered(gatt: BluetoothGatt, status: Int) { if (status == BluetoothGatt.GATT_SUCCESS) { gatt.services .find { it.uuid == BATTERY_SERVICE_UUID } ?.characteristics ?.find { it.uuid == BATTERY_CHAR_UUID } ?.let { characteristic -> gatt.readCharacteristic(characteristic) } } } }
38. private val gattCallback = object : BluetoothGattCallback() { override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) {…} override fun onServicesDiscovered(gatt: BluetoothGatt, status: Int) { if (status == BluetoothGatt.GATT_SUCCESS) { gatt.services .find { it.uuid == BATTERY_SERVICE_UUID } ?.characteristics ?.find { it.uuid == BATTERY_CHAR_UUID } ?.let { characteristic -> gatt.readCharacteristic(characteristic) } } } }
39. private val gattCallback = object : BluetoothGattCallback() { override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) {…} override fun onServicesDiscovered(gatt: BluetoothGatt, status: Int) {…} }
40. private val gattCallback = object : BluetoothGattCallback() { override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) {…} override fun onServicesDiscovered(gatt: BluetoothGatt, status: Int) {…} override fun onCharacteristicRead( gatt: BluetoothGatt, characteristic: BluetoothGattCharacteristic, status: Int ) { } }
41. private val gattCallback = object : BluetoothGattCallback() { override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) {…} override fun onServicesDiscovered(gatt: BluetoothGatt, status: Int) {…} override fun onCharacteristicRead( gatt: BluetoothGatt, characteristic: BluetoothGattCharacteristic, status: Int ) { if (status == BluetoothGatt.GATT_SUCCESS) { val batteryLevel = BigInteger(characteristic.value) Log.d("BLE", "Battery level: $batteryLevel”) } } }
52. • What thread are these requests running on?
53. • What thread are these requests running on? • What thread are these callbacks running on?
54. • What thread are these requests running on? • What thread are these callbacks running on? • Is all this thread switching really needed?
55. • What thread are these requests running on? • What thread are these callbacks running on? • Is all this thread switching really needed? • What if we're already on a background thread?
56. Async APIs aren’t nice
57. Async APIs aren’t nice Why?
59. • Make assumptions about the client's execution requirements
60. • Make assumptions about the client's execution requirements • Less expressive / complicated statement flow (goto)
61. • Make assumptions about the client's execution requirements • Less expressive / complicated statement flow (goto) • Couple business logic with execution logic
62. • Make assumptions about the client's execution requirements • Less expressive / complicated statement flow (goto) • Couple business logic with execution logic • Harder to mock
63. • Make assumptions about the client's execution requirements • Less expressive / complicated statement flow (goto) • Couple business logic with execution logic • Harder to mock • Harder to debug
64. • Make assumptions about the client's execution requirements • Less expressive / complicated statement flow (goto) • Couple business logic with execution logic • Harder to mock • Harder to debug • Harder to handle errors
65. • Make assumptions about the client's execution requirements • Less expressive / complicated statement flow (goto) • Couple business logic with execution logic • Harder to mock • Harder to debug • Harder to handle errors • Asynchronism is overly fine-grained
66. Fine-grained execution flow
74. Coarse-grained Execution Flow
80. Unsynchronizing the API
90. API implementation
91. class SuspendableBluetoothLeScanner(private val context: Context) { }
92. class SuspendableBluetoothLeScanner(private val context: Context) { suspend fun scan() = callbackFlow { } }
93. class SuspendableBluetoothLeScanner(private val context: Context) { suspend fun scan() = callbackFlow { val scanCallback = object : ScanCallback() { } } }
94. class SuspendableBluetoothLeScanner(private val context: Context) { suspend fun scan() = callbackFlow { val scanCallback = object : ScanCallback() { override fun onScanResult(callbackType: Int, result: ScanResult) { } } } }
95. class SuspendableBluetoothLeScanner(private val context: Context) { suspend fun scan() = callbackFlow { val scanCallback = object : ScanCallback() { override fun onScanResult(callbackType: Int, result: ScanResult) { if (!isClosedForSend) { offer(SuspendableBluetoothDevice(context, result.device)) } } } } }
96. class SuspendableBluetoothLeScanner(private val context: Context) { suspend fun scan() = callbackFlow { val scanCallback = object : ScanCallback() { override fun onScanResult(callbackType: Int, result: ScanResult) { if (!isClosedForSend) { offer(SuspendableBluetoothDevice(context, result.device)) } } } with(BluetoothAdapter.getDefaultAdapter().bluetoothLeScanner) { startScan(scanCallback) } } }
97. class SuspendableBluetoothLeScanner(private val context: Context) { suspend fun scan() = callbackFlow { val scanCallback = object : ScanCallback() { override fun onScanResult(callbackType: Int, result: ScanResult) { if (!isClosedForSend) { offer(SuspendableBluetoothDevice(context, result.device)) } } } with(BluetoothAdapter.getDefaultAdapter().bluetoothLeScanner) { startScan(scanCallback) awaitClose { stopScan(scanCallback) } } } }
98. sealed class GattEvent { class OnConnectionStateChange(val newState: Int) : GattEvent() class OnServicesDiscovered(val services: List<BluetoothGattService>) : GattEvent() class OnCharacteristicRead(val characteristic: BluetoothGattCharacteristic) : GattEvent() object Error : GattEvent() }
99. class CoroutineGattCallback : BluetoothGattCallback() { }
100. class CoroutineGattCallback : BluetoothGattCallback() { private val _eventsChannel = BroadcastChannel<GattEvent>(Channel.BUFFERED) }
101. class CoroutineGattCallback : BluetoothGattCallback() { private val _eventsChannel = BroadcastChannel<GattEvent>(Channel.BUFFERED) val eventsChannel: ReceiveChannel<GattEvent> get() = _eventsChannel.openSubscription() }
102. class CoroutineGattCallback : BluetoothGattCallback() { private val _eventsChannel = BroadcastChannel<GattEvent>(Channel.BUFFERED) val eventsChannel: ReceiveChannel<GattEvent> get() = _eventsChannel.openSubscription() override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) { } }
103. class CoroutineGattCallback : BluetoothGattCallback() { private val _eventsChannel = BroadcastChannel<GattEvent>(Channel.BUFFERED) val eventsChannel: ReceiveChannel<GattEvent> get() = _eventsChannel.openSubscription() override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) { if (status == BluetoothGatt.GATT_SUCCESS) { _eventsChannel.offer(GattEvent.OnConnectionStateChange(newState)) } else { _eventsChannel.offer(GattEvent.Error) } } }
104. class CoroutineGattCallback : BluetoothGattCallback() { private val _eventsChannel = BroadcastChannel<GattEvent>(Channel.BUFFERED) val eventsChannel: ReceiveChannel<GattEvent> get() = _eventsChannel.openSubscription() override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) { if (status == BluetoothGatt.GATT_SUCCESS) { _eventsChannel.offer(GattEvent.OnConnectionStateChange(newState)) } else { _eventsChannel.offer(GattEvent.Error) } } }
105. class CoroutineGattCallback : BluetoothGattCallback() { private val _eventsChannel = BroadcastChannel<GattEvent>(Channel.BUFFERED) val eventsChannel: ReceiveChannel<GattEvent> get() = _eventsChannel.openSubscription() override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) {…} }
106. class CoroutineGattCallback : BluetoothGattCallback() { private val _eventsChannel = BroadcastChannel<GattEvent>(Channel.BUFFERED) val eventsChannel: ReceiveChannel<GattEvent> get() = _eventsChannel.openSubscription() override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) {…} }
107. class CoroutineGattCallback : BluetoothGattCallback() { override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) {…} override fun onServicesDiscovered(gatt: BluetoothGatt, status: Int) { } }
108. class CoroutineGattCallback : BluetoothGattCallback() { override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) {…} override fun onServicesDiscovered(gatt: BluetoothGatt, status: Int) { if (status == BluetoothGatt.GATT_SUCCESS){ _eventsChannel.offer(GattEvent.OnServicesDiscovered(gatt.services)) } else { _eventsChannel.offer(GattEvent.Error) } } }
109. class CoroutineGattCallback : BluetoothGattCallback() { override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) {…} override fun onServicesDiscovered(gatt: BluetoothGatt, status: Int) { if (status == BluetoothGatt.GATT_SUCCESS){ _eventsChannel.offer(GattEvent.OnServicesDiscovered(gatt.services)) } else { _eventsChannel.offer(GattEvent.Error) } } }
110. class CoroutineGattCallback : BluetoothGattCallback() { override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) {…} override fun onServicesDiscovered(gatt: BluetoothGatt, status: Int) {…} }
111. class CoroutineGattCallback : BluetoothGattCallback() { override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) {…} override fun onServicesDiscovered(gatt: BluetoothGatt, status: Int) {…} override fun onCharacteristicRead( gatt: BluetoothGatt, characteristic: BluetoothGattCharacteristic, status: Int ) { } }
112. class CoroutineGattCallback : BluetoothGattCallback() { override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) {…} override fun onServicesDiscovered(gatt: BluetoothGatt, status: Int) {…} override fun onCharacteristicRead( gatt: BluetoothGatt, characteristic: BluetoothGattCharacteristic, status: Int ) { if (status == BluetoothGatt.GATT_SUCCESS) { _eventsChannel.offer(GattEvent.OnCharacteristicRead(characteristic)) } else { _eventsChannel.offer(GattEvent.Error) } } }
113. class SuspendableBluetoothDevice( private val context: Context, private val bluetoothDevice: BluetoothDevice ) { }
114. class SuspendableBluetoothDevice( private val context: Context, private val bluetoothDevice: BluetoothDevice ) { private var gatt: BluetoothGatt? = null private val callback = CoroutineGattCallback() }
115. class SuspendableBluetoothDevice( private val context: Context, private val bluetoothDevice: BluetoothDevice ) { private var gatt: BluetoothGatt? = null private val callback = CoroutineGattCallback() suspend fun connect(): Boolean { } }
116. suspend fun connect(): Boolean { }
117. suspend fun connect(): Boolean { with(callback.eventsChannel.consumeAsFlow()) { } }
118. suspend fun connect(): Boolean { with(callback.eventsChannel.consumeAsFlow()) { gatt = bluetoothDevice.connectGatt(context, false, callback) } }
119. suspend fun connect(): Boolean { with(callback.eventsChannel.consumeAsFlow()) { gatt = bluetoothDevice.connectGatt(context, false, callback) return map { when (it) { is GattEvent.OnConnectionStateChange -> it.newState == BluetoothGatt.STATE_CONNECTED is GattEvent.Error -> false else -> null } } } }
120. suspend fun connect(): Boolean { with(callback.eventsChannel.consumeAsFlow()) { gatt = bluetoothDevice.connectGatt(context, false, callback) return map { when (it) { is GattEvent.OnConnectionStateChange -> it.newState == BluetoothGatt.STATE_CONNECTED is GattEvent.Error -> false else -> null } }.filterNotNull() } }
121. suspend fun connect(): Boolean { with(callback.eventsChannel.consumeAsFlow()) { gatt = bluetoothDevice.connectGatt(context, false, callback) return map { when (it) { is GattEvent.OnConnectionStateChange -> it.newState == BluetoothGatt.STATE_CONNECTED is GattEvent.Error -> false else -> null } }.filterNotNull().first() } }
122. suspend fun connect(): Boolean { with(callback.eventsChannel.consumeAsFlow()) { gatt = bluetoothDevice.connectGatt(context, false, callback) return map { when (it) { is GattEvent.OnConnectionStateChange -> it.newState == BluetoothGatt.STATE_CONNECTED is GattEvent.Error -> false else -> null } }.filterNotNull().first() } }
123. suspend fun connect(): Boolean {…}
124. class SuspendableBluetoothDevice( private val context: Context, private val bluetoothDevice: BluetoothDevice ) { private var gatt: BluetoothGatt? = null private val callback = CoroutineGattCallback() suspend fun connect(): Boolean {…} }
125. class SuspendableBluetoothDevice( private val context: Context, private val bluetoothDevice: BluetoothDevice ) { private var gatt: BluetoothGatt? = null private val callback = CoroutineGattCallback() suspend fun connect(): Boolean {…} suspend fun discoverServices() = gatt?.let { } ?: emptyList() }
126. class SuspendableBluetoothDevice( private val context: Context, private val bluetoothDevice: BluetoothDevice ) { private var gatt: BluetoothGatt? = null private val callback = CoroutineGattCallback() suspend fun connect(): Boolean {…} suspend fun discoverServices() = gatt?.let { with(callback.eventsChannel.consumeAsFlow()) { it.discoverServices() filterIsInstance<GattEvent.OnServicesDiscovered>().first().services } } ?: emptyList() }
127. class SuspendableBluetoothDevice( private val context: Context, private val bluetoothDevice: BluetoothDevice ) { private var gatt: BluetoothGatt? = null private val callback = CoroutineGattCallback() suspend fun connect(): Boolean {…} suspend fun discoverServices() = gatt?.let { with(callback.eventsChannel.consumeAsFlow()) { it.discoverServices() filterIsInstance<GattEvent.OnServicesDiscovered>().first().services } } ?: emptyList() }
128. class SuspendableBluetoothDevice( private val context: Context, private val bluetoothDevice: BluetoothDevice ) { private var gatt: BluetoothGatt? = null private val callback = CoroutineGattCallback() suspend fun connect(): Boolean {…} suspend fun discoverServices() = gatt?.let {…} ?: emptyList() }
129. class SuspendableBluetoothDevice( private val context: Context, private val bluetoothDevice: BluetoothDevice ) { private var gatt: BluetoothGatt? = null private val callback = CoroutineGattCallback() suspend fun connect(): Boolean {…} suspend fun discoverServices() = gatt?.let {…} ?: emptyList() suspend fun readCharacteristic(characteristic: BluetoothGattCharacteristic) = gatt?.let { } }
130. suspend fun readCharacteristic(characteristic: BluetoothGattCharacteristic) = gatt?.let { }
131. suspend fun readCharacteristic(characteristic: BluetoothGattCharacteristic) = gatt?.let { with(callback.eventsChannel.consumeAsFlow()) { it.readCharacteristic(characteristic) filterIsInstance<GattEvent.OnCharacteristicRead>().first().characteristic } }
132. suspend fun readCharacteristic(characteristic: BluetoothGattCharacteristic) = gatt?.let { with(callback.eventsChannel.consumeAsFlow()) { it.readCharacteristic(characteristic) filterIsInstance<GattEvent.OnCharacteristicRead>().first().characteristic } }
133. suspend fun readCharacteristic(characteristic: BluetoothGattCharacteristic) = gatt?.let {…}
134. class SuspendableBluetoothDevice( private val context: Context, private val bluetoothDevice: BluetoothDevice ) { private var gatt: BluetoothGatt? = null private val callback = CoroutineGattCallback() suspend fun connect(): Boolean {…} suspend fun discoverServices() = gatt?.let {…} ?: emptyList() suspend fun readCharacteristic(characteristic: BluetoothGattCharacteristic) = gatt?.let {…} }
135. Final API
136. val bluetoothLeScanner = SuspendableBluetoothLeScanner(context)
137. val bluetoothLeScanner = SuspendableBluetoothLeScanner(context) val bluetoothDevice = bluetoothLeScanner.scan()
138. val bluetoothLeScanner = SuspendableBluetoothLeScanner(context) val bluetoothDevice = bluetoothLeScanner.scan().first()
139. val bluetoothLeScanner = SuspendableBluetoothLeScanner(context) val bluetoothDevice = bluetoothLeScanner.scan().first() with(bluetoothDevice) { if (connect()) { } }
140. val bluetoothLeScanner = SuspendableBluetoothLeScanner(context) val bluetoothDevice = bluetoothLeScanner.scan().first() with(bluetoothDevice) { if (connect()) { val services = discoverServices() } }
141. val bluetoothLeScanner = SuspendableBluetoothLeScanner(context) val bluetoothDevice = bluetoothLeScanner.scan().first() with(bluetoothDevice) { if (connect()) { val services = discoverServices() val batteryService = services.firstOrNull { it.uuid == BATTERY_SERVICE_UUID } } }
142. val bluetoothLeScanner = SuspendableBluetoothLeScanner(context) val bluetoothDevice = bluetoothLeScanner.scan().first() with(bluetoothDevice) { if (connect()) { val services = discoverServices() val batteryService = services.firstOrNull { it.uuid == BATTERY_SERVICE_UUID } batteryService?.characteristics?.firstOrNull { it.uuid == BATTERY_CHAR_UUID } } } }
143. val bluetoothLeScanner = SuspendableBluetoothLeScanner(context) val bluetoothDevice = bluetoothLeScanner.scan().first() with(bluetoothDevice) { if (connect()) { val services = discoverServices() val batteryService = services.firstOrNull { it.uuid == BATTERY_SERVICE_UUID } batteryService?.characteristics?.firstOrNull { it.uuid == BATTERY_CHAR_UUID }?.let { val batteryLevel = readCharacteristic(it)?.value Log.d("BLE", "Battery level: ${BigInteger(batteryLevel)}”) } } }
144. val bluetoothLeScanner = SuspendableBluetoothLeScanner(context) val bluetoothDevice = bluetoothLeScanner.scan().first() with(bluetoothDevice) { if (connect()) { val services = discoverServices() val batteryService = services.firstOrNull { it.uuid == BATTERY_SERVICE_UUID } batteryService?.characteristics?.firstOrNull { it.uuid == BATTERY_CHAR_UUID }?.let { val batteryLevel = readCharacteristic(it)?.value Log.d("BLE", "Battery level: ${BigInteger(batteryLevel)}”) } } else { Log.d("BLE", "Error connecting to device") } }
145. val bluetoothLeScanner = SuspendableBluetoothLeScanner(context) val bluetoothDevice = bluetoothLeScanner.scan().first() with(bluetoothDevice) { if (connect()) { val services = discoverServices() val batteryService = services.firstOrNull { it.uuid == BATTERY_SERVICE_UUID } batteryService?.characteristics?.firstOrNull { it.uuid == BATTERY_CHAR_UUID }?.let { val batteryLevel = readCharacteristic(it)?.value Log.d("BLE", "Battery level: ${BigInteger(batteryLevel)}”) } } else { Log.d("BLE", "Error connecting to device") } }
146. Takeaway
148. • Async APIs sometimes can be confusing and hard to follow
149. • Async APIs sometimes can be confusing and hard to follow • Avoid making assumptions about execution requirements
150. • Async APIs sometimes can be confusing and hard to follow • Avoid making assumptions about execution requirements • Code should be linear like a recipe for better expressiveness
151. • Async APIs sometimes can be confusing and hard to follow • Avoid making assumptions about execution requirements • Code should be linear like a recipe for better expressiveness • Coroutines can help clean up callback-heavy APIs
152. Thank you