我花了几天时间试图弄清楚如何将 Flutter UI 添加到我现有的 Android 应用程序中。最大的挑战是让 MethodChannel 与从 MainActivity 调用的 FlutterActivity 一起工作。我知道这与这里提出的问题有点不同，但是当我搜索“Android FlutterActivity MethodChannel”时，返回了这篇文章。在浏览了很多关于如何做到这一点的资源之后，我终于在这里找到了我的解决方案：
https://github.com/flutter/samples/tree/master/add_to_app/android_using_plugin/app/src/main/java/dev/flutter/example/androidusingplugin
最初，在 Android Studio 中，打开现有应用程序后，我依次点击 File、New、New Module、Flutter Module。我收到一个错误，必须执行手动步骤。
我的目标是在 MainActivity - onCreate 中启动 FlutterActivity（在 flutter_module 中打开 main.dart），然后利用尽可能多的原生 Flutter 代码开发 Flutter“屏幕”，并使用 MethodChannel 进行有限的平台调用。在开发替代 Flutter 代码时，我将继续注释掉现有的 Android 代码。
这是最终对我有用的方法：
../App_Project/Android/Existing_Android_App/settings.gradle
include ':app'
setBinding(new Binding([gradle: this]))
evaluate(new File(settingsDir.parentFile, '../flutter_module/.android/include_flutter.groovy'))
include ':flutter_module’
project(':flutter_module’).projectDir = new File('../../flutter_module’)
rootProject.name=‘existing_android_app’
../App_Project/Android/Existing_Android_App/app/build.gradle
dependencies {
…
implementation project(':flutter')
}
../App_Project/Android/Existing_Android_App/app/src/main/AndroidManifest.xml
<activity
android:name="io.flutter.embedding.android.FlutterActivity"
android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
android:hardwareAccelerated="true"
android:windowSoftInputMode="adjustResize" />
../App_Project/Android/Existing_Android_App/app/src/main/java/com/existing_android_app/MainActivity.java
package com.existing_android_app;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import io.flutter.embedding.android.FlutterActivity;
import io.flutter.embedding.engine.FlutterEngine;
import io.flutter.embedding.engine.FlutterEngineCache;
import io.flutter.embedding.engine.dart.DartExecutor;
import io.flutter.plugin.common.MethodCall;
import io.flutter.plugin.common.MethodChannel;
public class MainActivity extends AppCompatActivity {
final String ENGINE_ID = "1";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
FlutterEngine flutterEngine = new FlutterEngine(this);
flutterEngine.getDartExecutor().executeDartEntrypoint(DartExecutor.DartEntrypoint.createDefault());
FlutterEngineCache.getInstance().put(ENGINE_ID, flutterEngine);
MethodChannel channel = new MethodChannel(flutterEngine.getDartExecutor(), "com.existing_android_app/myMethodChannel");
channel.setMethodCallHandler(
new MethodChannel.MethodCallHandler() {
@Override
public void onMethodCall(@NonNull MethodCall call, @NonNull MethodChannel.Result result) {
String url = call.argument("url");
if (call.method.equals("openBrowser")) {
openBrowser(url);
}
else {
result.notImplemented();
}
}
});
startActivity(FlutterActivity.withCachedEngine(ENGINE_ID).build(this));
}
void openBrowser(String url) {
Intent intent = new Intent(Intent.ACTION_VIEW);
intent.setData(Uri.parse(url));
this.startActivity(intent);
}
}
../App_Project/flutter_module/lib/home_page.dart
class AppHomePage extends StatefulWidget {
@override
_HomePageState createState() => _HomePageState();
}
class _HomePageState extends State<AppHomePage> {
static const platform = const MethodChannel(‘com.existing_android_app/myMethodChannel’);
Future<void> _openBrowser() async {
try {
final int result = await platform.invokeMethod('openBrowser', <String, String> { 'url': "http://bing.com” });
}
catch (e) {
print('***** _openBrowser error: ' + e.toString());
}
}
@override
Widget build(BuildContext context) {
return SafeArea(
child: Scaffold(
appBar: CustomAppBar(),
body: Column(
children: <Widget>[
RaisedButton(
label: Text('Search',
style: TextStyle(fontSize: 18.0),
),
onPressed: () { _openBrowser(); },
) // RaisedButton.icon
], // Widget
) // Column
) // Scaffold
); // SafeArea
}