Adds data transfer to Add2App samples, using caching on Android (#146)

experimental/add_to_app/android_fullscreen/app/src/main/AndroidManifest.xml

@@ -3,7 +3,7 @@
     package="dev.flutter.example.androidfullscreen">
 
     <application
-        android:name="io.flutter.app.FlutterApplication"
+        android:name=".MyApplication"
         android:allowBackup="true"
         android:icon="@mipmap/ic_launcher"
         android:label="@string/app_name"

experimental/add_to_app/android_fullscreen/app/src/main/java/dev/flutter/example/androidfullscreen/MainActivity.kt

@@ -6,18 +6,32 @@ package dev.flutter.example.androidfullscreen
 
 import android.os.Bundle
 import android.widget.Button
+import android.widget.TextView
 import androidx.appcompat.app.AppCompatActivity
 import io.flutter.embedding.android.FlutterActivity
 
 class MainActivity : AppCompatActivity() {
+    private var counterLabel: TextView? = null
 
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
         setContentView(R.layout.activity_main)
 
+        counterLabel = findViewById(R.id.counter_label)
+
         val button = findViewById<Button>(R.id.launch_button)
+
         button.setOnClickListener {
-            startActivity(FlutterActivity.createDefaultIntent(this))
+            val intent = FlutterActivity
+                .withCachedEngine(ENGINE_ID)
+                .build(this)
+            startActivity(intent)
         }
     }
+
+    override fun onResume() {
+        super.onResume()
+        val app = application as MyApplication
+        counterLabel?.text = "Current count: ${app.count}"
+    }
 }

experimental/add_to_app/android_fullscreen/app/src/main/java/dev/flutter/example/androidfullscreen/MyApplication.kt

@@ -0,0 +1,55 @@
+// Copyright 2019 The Flutter team. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package dev.flutter.example.androidfullscreen
+
+import android.app.Application
+import io.flutter.embedding.engine.FlutterEngine
+import io.flutter.embedding.engine.FlutterEngineCache
+import io.flutter.embedding.engine.dart.DartExecutor
+import io.flutter.plugin.common.MethodChannel
+import io.flutter.view.FlutterMain
+
+const val ENGINE_ID = "1"
+
+class MyApplication : Application() {
+    var count = 0
+
+    private var channel: MethodChannel? = null
+
+    override fun onCreate() {
+        super.onCreate()
+
+        FlutterMain.startInitialization(this)
+        FlutterMain.ensureInitializationComplete(this, null)
+
+        val flutterEngine = FlutterEngine(this)
+        flutterEngine
+            .dartExecutor
+            .executeDartEntrypoint(
+                DartExecutor.DartEntrypoint.createDefault()
+            )
+
+        FlutterEngineCache.getInstance().put(ENGINE_ID, flutterEngine)
+
+        channel = MethodChannel(flutterEngine.dartExecutor, "dev.flutter.example/counter")
+
+        channel?.setMethodCallHandler { call, _ ->
+            when (call.method) {
+                "incrementCounter" -> {
+                    count++
+                    reportCounter()
+                }
+                "requestCounter" -> {
+                    print("requestCounter")
+                    reportCounter()
+                }
+            }
+        }
+    }
+
+    private fun reportCounter() {
+        channel?.invokeMethod("reportCounter", count)
+    }
+}

experimental/add_to_app/android_fullscreen/app/src/main/res/layout/activity_main.xml

@@ -14,6 +14,18 @@
         app:layout_constraintBottom_toBottomOf="parent"
         app:layout_constraintLeft_toLeftOf="parent"
         app:layout_constraintRight_toRightOf="parent"
-        app:layout_constraintTop_toTopOf="parent" />
+        app:layout_constraintTop_toTopOf="parent"
+        tools:ignore="HardcodedText" />
+
+    <TextView
+        android:id="@+id/counter_label"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginBottom="32dp"
+        android:text="Current counter: 0"
+        app:layout_constraintBottom_toTopOf="@+id/launch_button"
+        app:layout_constraintLeft_toLeftOf="parent"
+        app:layout_constraintRight_toRightOf="parent"
+        tools:ignore="HardcodedText" />
 
 </androidx.constraintlayout.widget.ConstraintLayout>