Getting Started with Android BLE blog post

Android/BluetoothChat/.gitignore

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+*.iml
+.gradle
+/local.properties
+/.idea/caches
+/.idea/libraries
+/.idea/modules.xml
+/.idea/workspace.xml
+/.idea/navEditor.xml
+/.idea/assetWizardSettings.xml
+.DS_Store
+/build
+/captures
+.externalNativeBuild
+.cxx
+local.properties

Android/BluetoothChat/app/.gitignore

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+/build

Android/BluetoothChat/app/build.gradle

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+plugins {
+    id 'com.android.application'
+    id 'kotlin-android'
+}
+
+android {
+    compileSdkVersion 30
+    buildToolsVersion "30.0.3"
+
+    defaultConfig {
+        applicationId "ditto.live.bluetoothchat"
+        minSdkVersion 25
+        targetSdkVersion 30
+        versionCode 1
+        versionName "1.0"
+
+        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
+    }
+
+    buildTypes {
+        release {
+            minifyEnabled false
+            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
+        }
+    }
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_1_8
+        targetCompatibility JavaVersion.VERSION_1_8
+    }
+    kotlinOptions {
+        jvmTarget = '1.8'
+    }
+}
+
+dependencies {
+
+    implementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
+    implementation 'androidx.core:core-ktx:1.3.2'
+    implementation 'androidx.appcompat:appcompat:1.2.0'
+    implementation 'com.google.android.material:material:1.3.0'
+    implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
+    implementation 'androidx.legacy:legacy-support-v4:1.0.0'
+    testImplementation 'junit:junit:4.+'
+    androidTestImplementation 'androidx.test.ext:junit:1.1.2'
+    androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'
+
+    implementation 'androidx.fragment:fragment-ktx:1.2.5'
+    implementation 'com.github.bassaer:chatmessageview:2.0.1'
+    implementation 'de.hdodenhof:circleimageview:3.0.0'
+    implementation "androidx.swiperefreshlayout:swiperefreshlayout:1.0.0"
+    implementation 'androidx.lifecycle:lifecycle-viewmodel-ktx:2.2.0'
+}

Android/BluetoothChat/app/proguard-rules.pro

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+# Add project specific ProGuard rules here.
+# You can control the set of applied configuration files using the
+# proguardFiles setting in build.gradle.
+#
+# For more details, see
+#   http://developer.android.com/guide/developing/tools/proguard.html
+
+# If your project uses WebView with JS, uncomment the following
+# and specify the fully qualified class name to the JavaScript interface
+# class:
+#-keepclassmembers class fqcn.of.javascript.interface.for.webview {
+#   public *;
+#}
+
+# Uncomment this to preserve the line number information for
+# debugging stack traces.
+#-keepattributes SourceFile,LineNumberTable
+
+# If you keep the line number information, uncomment this to
+# hide the original source file name.
+#-renamesourcefileattribute SourceFile

Android/BluetoothChat/app/src/androidTest/java/ditto/live/bluetoothchat/ExampleInstrumentedTest.kt

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+package ditto.live.bluetoothchat
+
+import androidx.test.platform.app.InstrumentationRegistry
+import androidx.test.ext.junit.runners.AndroidJUnit4
+
+import org.junit.Test
+import org.junit.runner.RunWith
+
+import org.junit.Assert.*
+
+/**
+ * Instrumented test, which will execute on an Android device.
+ *
+ * See [testing documentation](http://d.android.com/tools/testing).
+ */
+@RunWith(AndroidJUnit4::class)
+class ExampleInstrumentedTest {
+    @Test
+    fun useAppContext() {
+        // Context of the app under test.
+        val appContext = InstrumentationRegistry.getInstrumentation().targetContext
+        assertEquals("ditto.live.bluetoothchat", appContext.packageName)
+    }
+}

Android/BluetoothChat/app/src/main/AndroidManifest.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+    package="ditto.live.bluetoothchat">
+
+    <uses-permission android:name="android.permission.BLUETOOTH"/>
+    <uses-permission android:name="android.permission.BLUETOOTH_ADMIN"/>
+    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
+    <uses-feature android:name="android.hardware.bluetooth_le" android:required="true"/>
+
+    <application
+        android:allowBackup="true"
+        android:icon="@mipmap/ic_launcher"
+        android:label="@string/app_name"
+        android:roundIcon="@mipmap/ic_launcher_round"
+        android:supportsRtl="true"
+        android:theme="@style/Theme.BluetoothChat">
+        <activity android:name=".MainActivity">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+
+                <category android:name="android.intent.category.LAUNCHER" />
+            </intent-filter>
+        </activity>
+    </application>
+
+</manifest>

Android/BluetoothChat/app/src/main/java/ditto/live/bluetoothchat/BLEMessage.kt

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+package ditto.live.bluetoothchat
+
+abstract class BLEMessage(val text: String)
+class RemoteMessage(text: String) : BLEMessage(text)
+class LocalMessage(text: String) : BLEMessage(text)

Android/BluetoothChat/app/src/main/java/ditto/live/bluetoothchat/BluetoothConstants.kt

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+package ditto.live.bluetoothchat
+import java.util.*
+
+//App service UUID
+val chatDiscoveryServiceID = UUID.fromString("42332fe8-9915-11ea-bb37-0242ac130002")
+
+//Gatt service message characteric ID used
+val chatMessageCharacteristicID = UUID.fromString("43eb0d29-4188-4c84-b1e8-73231e02af95")
+
+//UUID to confirm device connection
+val confirmCharacteristicID = UUID.fromString("f0ab5a15-b003-4653-a248-73fd504c128f")

Android/BluetoothChat/app/src/main/java/ditto/live/bluetoothchat/BluetoothScanViewModel.kt

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+package ditto.live.bluetoothchat
+
+import android.app.Application
+import android.bluetooth.*
+import android.bluetooth.le.*
+import android.os.ParcelUuid
+import androidx.lifecycle.AndroidViewModel
+import androidx.lifecycle.LiveData
+import androidx.lifecycle.MutableLiveData
+
+class BluetoothScanViewModel(app: Application) : AndroidViewModel(app) {
+    //our variables that will be set and used for the callback of nearby discovered devices
+    private val _scanResults = MutableLiveData<MutableMap<String, BluetoothDevice>>()
+    val scanResults = _scanResults as LiveData<Map<String, BluetoothDevice>>
+
+    //get an instance of the local bluetooth adapter
+    private val adapter: BluetoothAdapter = BluetoothAdapter.getDefaultAdapter()
+    //scanner we will use to discover nearby devices using our UUID
+    private var scanner: BluetoothLeScanner? = null
+
+    private var scanCallback: DeviceScanCallback? = null
+    private val scanFilters: List<ScanFilter>
+    private val scanSettings: ScanSettings
+
+    init {
+        scanFilters = createFilters()
+        scanSettings = ScanSettings.Builder()
+                .setScanMode(ScanSettings.SCAN_MODE_LOW_POWER)
+                .build()
+        startScan()
+    }
+
+    override fun onCleared() {
+        super.onCleared()
+        scanner?.stopScan(scanCallback)
+        scanCallback = null
+    }
+
+    fun startScan() {
+        if (scanCallback == null) {
+            scanner = adapter.bluetoothLeScanner
+            scanCallback = DeviceScanCallback()
+            scanner?.startScan(scanFilters, scanSettings, scanCallback)
+        }
+    }
+
+    /**
+     * Use our unique UUID for filtering results for Bluetooth LE scans
+     */
+    private fun createFilters(): List<ScanFilter> {
+        val builder = ScanFilter.Builder()
+        builder.setServiceUuid(ParcelUuid(chatDiscoveryServiceID))
+        val filter = builder.build()
+        return listOf(filter)
+    }
+
+    /**
+     * A callback of device scanning
+     * Set our scan results for discovered devices
+     */
+    private inner class DeviceScanCallback : ScanCallback() {
+        override fun onBatchScanResults(results: List<ScanResult>) {
+            super.onBatchScanResults(results)
+            val res = mutableMapOf<String, BluetoothDevice>()
+            for (item in results) {
+                item.device?.let { device ->
+                    res[device.address] = device
+                }
+            }
+            _scanResults.value = res
+        }
+
+        override fun onScanResult(
+            callbackType: Int,
+            result: ScanResult
+        ) {
+            super.onScanResult(callbackType, result)
+            val res = mutableMapOf<String, BluetoothDevice>()
+            result.device?.let { device ->
+                res[device.address] = device
+            }
+            _scanResults.value = res
+        }
+    }
+}