Add plugin for Android lifecycle in embedding (flutter#2168)

Author: amirh

packages/flutter_android_lifecycle/.gitignore

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+.DS_Store
+.dart_tool/
+
+.packages
+.pub/
+
+build/

packages/flutter_android_lifecycle/.metadata

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+# This file tracks properties of this Flutter project.
+# Used by Flutter tool to assess capabilities and perform upgrades etc.
+#
+# This file should be version controlled and should not be manually edited.
+
+version:
+  revision: 0e605cc4dd83137f785769dea5e8ae7da1afb361
+  channel: master
+
+project_type: plugin

packages/flutter_android_lifecycle/CHANGELOG.md

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+## 1.0.0
+
+* Introduces a `FlutterLifecycleAdapter`, which can be used by other plugins to obtain a `Lifecycle`
+  reference from a `FlutterPluginBinding`.

packages/flutter_android_lifecycle/LICENSE

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+// Copyright 2019 The Chromium Authors. All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//    * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//    * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//    * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

packages/flutter_android_lifecycle/README.md

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+# Flutter Android Lifecycle Plugin
+
+[![pub package](https://img.shields.io/pub/v/flutter_android_lifecycle.svg)](https://pub.dartlang.org/packages/flutter_android_lifecycle)
+
+A Flutter plugin for Android to allow other Flutter plugins to access an Android `Lifecycle` object
+in the plugin's binding.
+
+The purpose of having this plugin instead of exposing an Android `Lifecycle` object in the engine's
+Android embedding plugins API is to force plugins to have a pub constraint that signifies the
+major version of the Android `Lifecycle` API they expect.
+
+## Installation
+
+Add `flutter_android_lifecycle` as a [dependency in your pubspec.yaml file](https://flutter.io/using-packages/).
+
+## Example
+
+Use a `FlutterLifecycleAdapter` within another Flutter plugin's Android implementation, as shown
+below:
+
+```java
+import androidx.lifecycle.Lifecycle;
+import io.flutter.embedding.engine.FlutterEngine;
+import io.flutter.embedding.engine.plugins.FlutterPlugin;
+import io.flutter.embedding.engine.plugins.FlutterPlugin.FlutterPluginBinding;
+import io.flutter.embedding.engine.plugins.lifecycle.FlutterLifecycleAdapter;
+
+public class MyPlugin implements FlutterPlugin {
+  @Override
+  public void onAttachedToEngine(@NonNull FlutterPluginBinding binding) {
+    Lifecycle lifecycle = new FlutterLifecycleAdapter.getLifecycle(binding);
+    
+    // Use lifecycle as desired.
+  }
+  
+  //...
+}
+```
+
+[Feedback welcome](https://github.com/flutter/flutter/issues) and
+[Pull Requests](https://github.com/flutter/plugins/pulls) are most welcome!

packages/flutter_android_lifecycle/android/.gitignore

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+*.iml
+.gradle
+/local.properties
+/.idea/workspace.xml
+/.idea/libraries
+.DS_Store
+/build
+/captures

packages/flutter_android_lifecycle/android/build.gradle

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+group 'io.flutter.plugins.flutter_android_lifecycle'
+version '1.0'
+
+buildscript {
+    repositories {
+        google()
+        jcenter()
+    }
+
+    dependencies {
+        classpath 'com.android.tools.build:gradle:3.5.0'
+    }
+}
+
+rootProject.allprojects {
+    repositories {
+        google()
+        jcenter()
+    }
+}
+
+apply plugin: 'com.android.library'
+
+android {
+    compileSdkVersion 28
+
+    defaultConfig {
+        minSdkVersion 16
+        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
+    }
+    lintOptions {
+        disable 'InvalidPackage'
+    }
+
+    dependencies {
+        implementation "androidx.annotation:annotation:1.1.0"
+    }
+}
+
+// TODO(amirh): Remove this hack once androidx.lifecycle is included on stable. https://github.com/flutter/flutter/issues/42348
+afterEvaluate {
+    def containsEmbeddingDependencies = false
+    for (def configuration : configurations.all) {
+        for (def dependency : configuration.dependencies) {
+            if (dependency.group == 'io.flutter' &&
+                    dependency.name.startsWith('flutter_embedding') &&
+                    dependency.isTransitive())
+            {
+                containsEmbeddingDependencies = true
+                break
+            }
+        }
+    }
+    if (!containsEmbeddingDependencies) {
+        android {
+            dependencies {
+                def lifecycle_version = "2.1.0"
+                api "androidx.lifecycle:lifecycle-common-java8:$lifecycle_version"
+                api "androidx.lifecycle:lifecycle-runtime:$lifecycle_version"
+            }
+        }
+    }
+}

packages/flutter_android_lifecycle/android/gradle.properties

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+org.gradle.jvmargs=-Xmx1536M
+android.enableR8=true
+android.useAndroidX=true
+android.enableJetifier=true

packages/flutter_android_lifecycle/android/gradle/wrapper/gradle-wrapper.properties

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+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.10.2-all.zip

packages/flutter_android_lifecycle/android/settings.gradle

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+rootProject.name = 'flutter_android_lifecycle'