[pigeon] Add an initial example app (#3761)

This creates an initial example app covering Android (Kotlin), iOS and macOS (Swift), and Windows, showing integration of Pigeon into an app directly, without using a plugin. This serves as both a simple runnable example for clients, and as a future source for snippet extraction for documentation. It includes a simple integration test so that CI will ensure that it's actually working.

Since we can't demonstrate Java and Objective-C in the same application, we could consider adding a second example app covering those in the future.

Currently it shows only host API, and only a single trivial method, but we can expand over time as is useful for documentation.

Part of flutter/flutter#66511

.github/dependabot.yml

@@ -477,6 +477,25 @@ updates:
       - dependency-name: "*"
         update-types: ["version-update:semver-minor", "version-update:semver-patch"]
 
+  - package-ecosystem: "gradle"
+    directory: "/packages/pigeon/example/app/android/app"
+    commit-message:
+      prefix: "[pigeon]"
+    schedule:
+      interval: "weekly"
+    open-pull-requests-limit: 10
+    ignore:
+      - dependency-name: "com.android.tools.build:gradle"
+        update-types: ["version-update:semver-minor", "version-update:semver-patch"]
+      - dependency-name: "junit:junit"
+        update-types: ["version-update:semver-minor", "version-update:semver-patch"]
+      - dependency-name: "org.mockito:*"
+        update-types: ["version-update:semver-minor", "version-update:semver-patch"]
+      - dependency-name: "androidx.test:*"
+        update-types: ["version-update:semver-minor", "version-update:semver-patch"]
+      - dependency-name: "org.robolectric:*"
+        update-types: ["version-update:semver-minor", "version-update:semver-patch"]
+
   - package-ecosystem: "gradle"
     directory: "/packages/pigeon/platform_tests/test_plugin/android"
     commit-message:

packages/pigeon/CHANGELOG.md

@@ -1,3 +1,7 @@
+## NEXT
+
+* Adds an example application that uses Pigeon directly, rather than in a plugin.
+
 ## 9.2.4
 
 * [objc] Fixes a warning due to a C++-style function signature in the codec

packages/pigeon/example/app/.gitignore

@@ -0,0 +1,44 @@
+# Miscellaneous
+*.class
+*.log
+*.pyc
+*.swp
+.DS_Store
+.atom/
+.buildlog/
+.history
+.svn/
+migrate_working_dir/
+
+# IntelliJ related
+*.iml
+*.ipr
+*.iws
+.idea/
+
+# The .vscode folder contains launch configuration and tasks you configure in
+# VS Code which you may wish to be included in version control, so this line
+# is commented out by default.
+#.vscode/
+
+# Flutter/Dart/Pub related
+**/doc/api/
+**/ios/Flutter/.last_build_id
+.dart_tool/
+.flutter-plugins
+.flutter-plugins-dependencies
+.packages
+.pub-cache/
+.pub/
+/build/
+
+# Symbolication related
+app.*.symbols
+
+# Obfuscation related
+app.*.map.json
+
+# Android Studio will place build artifacts here
+/android/app/debug
+/android/app/profile
+/android/app/release

packages/pigeon/example/app/.metadata

@@ -0,0 +1,45 @@
+# 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.
+
+version:
+  revision: a8354ff165eda6174ae423dca3b65c10fa952f4c
+  channel: main
+
+project_type: app
+
+# Tracks metadata for the flutter migrate command
+migration:
+  platforms:
+    - platform: root
+      create_revision: a8354ff165eda6174ae423dca3b65c10fa952f4c
+      base_revision: a8354ff165eda6174ae423dca3b65c10fa952f4c
+    - platform: android
+      create_revision: a8354ff165eda6174ae423dca3b65c10fa952f4c
+      base_revision: a8354ff165eda6174ae423dca3b65c10fa952f4c
+    - platform: ios
+      create_revision: a8354ff165eda6174ae423dca3b65c10fa952f4c
+      base_revision: a8354ff165eda6174ae423dca3b65c10fa952f4c
+    - platform: linux
+      create_revision: a8354ff165eda6174ae423dca3b65c10fa952f4c
+      base_revision: a8354ff165eda6174ae423dca3b65c10fa952f4c
+    - platform: macos
+      create_revision: a8354ff165eda6174ae423dca3b65c10fa952f4c
+      base_revision: a8354ff165eda6174ae423dca3b65c10fa952f4c
+    - platform: web
+      create_revision: a8354ff165eda6174ae423dca3b65c10fa952f4c
+      base_revision: a8354ff165eda6174ae423dca3b65c10fa952f4c
+    - platform: windows
+      create_revision: a8354ff165eda6174ae423dca3b65c10fa952f4c
+      base_revision: a8354ff165eda6174ae423dca3b65c10fa952f4c
+
+  # User provided section
+
+  # List of Local paths (relative to this file) that should be
+  # ignored by the migrate tool.
+  #
+  # Files that are not part of the templates will be ignored by default.
+  unmanaged_files:
+    - 'lib/main.dart'
+    - 'ios/Runner.xcodeproj/project.pbxproj'

packages/pigeon/example/app/README.md

@@ -0,0 +1,9 @@
+# pigeon_example_app
+
+This demonstrates using Pigeon for platform communication directly in an
+application, rather than in a plugin.
+
+To update the generated code, run:
+```sh
+dart run pigeon --input pigeons/messages.dart
+```

packages/pigeon/example/app/android/.gitignore

@@ -0,0 +1,13 @@
+gradle-wrapper.jar
+/.gradle
+/captures/
+/gradlew
+/gradlew.bat
+/local.properties
+GeneratedPluginRegistrant.java
+
+# Remember to never publicly share your keystore.
+# See https://flutter.dev/docs/deployment/android#reference-the-keystore-from-the-app
+key.properties
+**/*.keystore
+**/*.jks

packages/pigeon/example/app/android/app/build.gradle

@@ -0,0 +1,72 @@
+def localProperties = new Properties()
+def localPropertiesFile = rootProject.file('local.properties')
+if (localPropertiesFile.exists()) {
+    localPropertiesFile.withReader('UTF-8') { reader ->
+        localProperties.load(reader)
+    }
+}
+
+def flutterRoot = localProperties.getProperty('flutter.sdk')
+if (flutterRoot == null) {
+    throw new GradleException("Flutter SDK not found. Define location with flutter.sdk in the local.properties file.")
+}
+
+def flutterVersionCode = localProperties.getProperty('flutter.versionCode')
+if (flutterVersionCode == null) {
+    flutterVersionCode = '1'
+}
+
+def flutterVersionName = localProperties.getProperty('flutter.versionName')
+if (flutterVersionName == null) {
+    flutterVersionName = '1.0'
+}
+
+apply plugin: 'com.android.application'
+apply plugin: 'kotlin-android'
+apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"
+
+android {
+    namespace "dev.flutter.pigeon_example_app"
+    compileSdkVersion flutter.compileSdkVersion
+    ndkVersion flutter.ndkVersion
+
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_1_8
+        targetCompatibility JavaVersion.VERSION_1_8
+    }
+
+    kotlinOptions {
+        jvmTarget = '1.8'
+    }
+
+    sourceSets {
+        main.java.srcDirs += 'src/main/kotlin'
+    }
+
+    defaultConfig {
+        // TODO: Specify your own unique Application ID (https://developer.android.com/studio/build/application-id.html).
+        applicationId "dev.flutter.pigeon_example_app"
+        // You can update the following values to match your application needs.
+        // For more information, see: https://docs.flutter.dev/deployment/android#reviewing-the-gradle-build-configuration.
+        minSdkVersion flutter.minSdkVersion
+        targetSdkVersion flutter.targetSdkVersion
+        versionCode flutterVersionCode.toInteger()
+        versionName flutterVersionName
+    }
+
+    buildTypes {
+        release {
+            // TODO: Add your own signing config for the release build.
+            // Signing with the debug keys for now, so `flutter run --release` works.
+            signingConfig signingConfigs.debug
+        }
+    }
+}
+
+flutter {
+    source '../..'
+}
+
+dependencies {
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
+}

packages/pigeon/example/app/android/app/src/debug/AndroidManifest.xml

@@ -0,0 +1,7 @@
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+    <!-- The INTERNET permission is required for development. Specifically,
+         the Flutter tool needs it to communicate with the running application
+         to allow setting breakpoints, to provide hot reload, etc.
+    -->
+    <uses-permission android:name="android.permission.INTERNET"/>
+</manifest>

packages/pigeon/example/app/android/app/src/main/AndroidManifest.xml

@@ -0,0 +1,33 @@
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+    <application
+        android:label="pigeon_example_app"
+        android:name="${applicationName}"
+        android:icon="@mipmap/ic_launcher">
+        <activity
+            android:name=".MainActivity"
+            android:exported="true"
+            android:launchMode="singleTop"
+            android:theme="@style/LaunchTheme"
+            android:configChanges="orientation|keyboardHidden|keyboard|screenSize|smallestScreenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
+            android:hardwareAccelerated="true"
+            android:windowSoftInputMode="adjustResize">
+            <!-- Specifies an Android theme to apply to this Activity as soon as
+                 the Android process has started. This theme is visible to the user
+                 while the Flutter UI initializes. After that, this theme continues
+                 to determine the Window background behind the Flutter UI. -->
+            <meta-data
+              android:name="io.flutter.embedding.android.NormalTheme"
+              android:resource="@style/NormalTheme"
+              />
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN"/>
+                <category android:name="android.intent.category.LAUNCHER"/>
+            </intent-filter>
+        </activity>
+        <!-- Don't delete the meta-data below.
+             This is used by the Flutter tool to generate GeneratedPluginRegistrant.java -->
+        <meta-data
+            android:name="flutterEmbedding"
+            android:value="2" />
+    </application>
+</manifest>

packages/pigeon/example/app/android/app/src/main/kotlin/dev/flutter/pigeon_example_app/MainActivity.kt

@@ -0,0 +1,25 @@
+// Copyright 2013 The Flutter Authors. 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.pigeon_example_app
+
+import ExampleHostApi
+import androidx.annotation.NonNull
+import io.flutter.embedding.android.FlutterActivity
+import io.flutter.embedding.engine.FlutterEngine
+
+private class PigeonApiImplementation: ExampleHostApi {
+    override fun getHostLanguage(): String {
+        return "Kotlin"
+    }
+}
+
+class MainActivity: FlutterActivity() {
+    override fun configureFlutterEngine(@NonNull flutterEngine: FlutterEngine) {
+        super.configureFlutterEngine(flutterEngine)
+
+        val api = PigeonApiImplementation()
+        ExampleHostApi.setUp(flutterEngine.dartExecutor.binaryMessenger, api);
+    }
+}

packages/pigeon/example/app/android/app/src/main/kotlin/dev/flutter/pigeon_example_app/Messages.g.kt

@@ -0,0 +1,77 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+// Autogenerated from Pigeon (v9.2.4), do not edit directly.
+// See also: https://pub.dev/packages/pigeon
+
+
+import android.util.Log
+import io.flutter.plugin.common.BasicMessageChannel
+import io.flutter.plugin.common.BinaryMessenger
+import io.flutter.plugin.common.MessageCodec
+import io.flutter.plugin.common.StandardMessageCodec
+import java.io.ByteArrayOutputStream
+import java.nio.ByteBuffer
+
+private fun wrapResult(result: Any?): List<Any?> {
+  return listOf(result)
+}
+
+private fun wrapError(exception: Throwable): List<Any?> {
+  if (exception is FlutterError) {
+    return listOf(
+      exception.code,
+      exception.message,
+      exception.details
+    )
+  } else {
+    return listOf(
+      exception.javaClass.simpleName,
+      exception.toString(),
+      "Cause: " + exception.cause + ", Stacktrace: " + Log.getStackTraceString(exception)
+    )
+  }
+}
+
+/**
+ * Error class for passing custom error details to Flutter via a thrown PlatformException.
+ * @property code The error code.
+ * @property message The error message.
+ * @property details The error details. Must be a datatype supported by the api codec.
+ */
+class FlutterError (
+  val code: String,
+  override val message: String? = null,
+  val details: Any? = null
+) : Throwable()
+/** Generated interface from Pigeon that represents a handler of messages from Flutter. */
+interface ExampleHostApi {
+  fun getHostLanguage(): String
+
+  companion object {
+    /** The codec used by ExampleHostApi. */
+    val codec: MessageCodec<Any?> by lazy {
+      StandardMessageCodec()
+    }
+    /** Sets up an instance of `ExampleHostApi` to handle messages through the `binaryMessenger`. */
+    @Suppress("UNCHECKED_CAST")
+    fun setUp(binaryMessenger: BinaryMessenger, api: ExampleHostApi?) {
+      run {
+        val channel = BasicMessageChannel<Any?>(binaryMessenger, "dev.flutter.pigeon.ExampleHostApi.getHostLanguage", codec)
+        if (api != null) {
+          channel.setMessageHandler { _, reply ->
+            var wrapped: List<Any?>
+            try {
+              wrapped = listOf<Any?>(api.getHostLanguage())
+            } catch (exception: Throwable) {
+              wrapped = wrapError(exception)
+            }
+            reply.reply(wrapped)
+          }
+        } else {
+          channel.setMessageHandler(null)
+        }
+      }
+    }
+  }
+}

packages/pigeon/example/app/android/app/src/main/res/drawable-v21/launch_background.xml

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Modify this file to customize your launch splash screen -->
+<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
+    <item android:drawable="?android:colorBackground" />
+
+    <!-- You can insert your own image assets here -->
+    <!-- <item>
+        <bitmap
+            android:gravity="center"
+            android:src="@mipmap/launch_image" />
+    </item> -->
+</layer-list>

packages/pigeon/example/app/android/app/src/main/res/drawable/launch_background.xml

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Modify this file to customize your launch splash screen -->
+<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
+    <item android:drawable="@android:color/white" />
+
+    <!-- You can insert your own image assets here -->
+    <!-- <item>
+        <bitmap
+            android:gravity="center"
+            android:src="@mipmap/launch_image" />
+    </item> -->
+</layer-list>