ios 跳转flutter页面 黑页 flutter开屏页

在上一篇中我介绍了Android和Flutter如何实现混合编译，我们这篇就要学习怎么实现Android页面打开一个Flutter页面。

建议使用FlutterBoost进行页面之间的跳转，本文仅用来学习官方的demo

老规矩，我们先要把官方教程摆出来 英文官网 Native Flutter页面路由跳转，官方思路是有两种：

• Adding a Flutter screen to an Android app （添加一个Flutter Screen,可以理解为Activity）
• Adding a Flutter Fragment to an Android app （添加一个Flutter Fragment）

1 准备工作，一定要看哈~

app的AndroidManifest.xml文件中增加以下代码:

<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"
            />

2 添加一个Flutter Screen

2.1不指定页面（有黑屏延迟,不建议采用）

startActivity(FlutterActivity.createDefaultIntent(currentActivity) );

2.2指定页面 （有黑屏延迟，不建议采用）

//这里的initialRoute就是指定要跳转的Flutter页面，你想跳转哪个就要先在Flutter里面注册，再在Native中使用
 Intent intent = FlutterActivity.withNewEngine().initialRoute("/my_route").build(this);

这两种方式是最简单的，同时也是性能最差的，从Native页面过渡到Flutter页面会出现短暂的黑屏延迟，非常影响体验感

为什么会出现黑屏延迟呢?

Every FlutterActivity creates its own FlutterEngine by default. Each FlutterEngine has a non-trivial warm-up time. This means that launching a standard FlutterActivity comes with a brief delay before your Flutter experience becomes visible. To minimize this delay, you can warm up a FlutterEngine before arriving at your FlutterActivity, and then you can use your pre-warmed FlutterEngine instead.

每一个FlutterActivity创建都对应一个FlutterEngine的创建，而FlutterEngine创建有自己的“预热”时间，这就意味着FlutterActivity页面可见之前需要等待FlutterEngine预热，所以此时屏幕是黑色的，等预热之后，页面才回变得可见。

于是乎降低这个黑屏延迟的方案就有了！——提前预热FlutterEngine

在哪里预热呢？这个要看你的逻辑而定了，下面是在Application中初始化的，仅供参考。

2.3不指定页面（黑屏延迟很短，可以使用）

public class NativeApplication extends Application {
    FlutterEngine flutterEngine;

    @Override
    public void onCreate() {
        super.onCreate();

        flutterEngine = new FlutterEngine(this);

        // Start executing Dart code to pre-warm the FlutterEngine.
        flutterEngine.getDartExecutor().executeDartEntrypoint(
                DartExecutor.DartEntrypoint.createDefault()
        );

        // Cache the FlutterEngine to be used by FlutterActivity.
        FlutterEngineCache
                .getInstance()
                .put("my_engine_id", flutterEngine);
    }
}
//页面跳转
 Intent intent = FlutterActivity.withCachedEngine("my_engine_id").build(this);

2.4指定页面（黑屏延迟很短，可以使用）

public class NativeApplication extends Application {
    FlutterEngine flutterEngine;

    @Override
    public void onCreate() {
        super.onCreate();

        super.onCreate();
        // Instantiate a FlutterEngine.
        flutterEngine = new FlutterEngine(this);
        // Configure an initial route.
        flutterEngine.getNavigationChannel().setInitialRoute("your/route/here");
        // Start executing Dart code to pre-warm the FlutterEngine.
        flutterEngine.getDartExecutor().executeDartEntrypoint(
                DartExecutor.DartEntrypoint.createDefault()
        );
        // Cache the FlutterEngine to be used by FlutterActivity or FlutterFragment.
        FlutterEngineCache
                .getInstance()
                .put("my_engine_id", flutterEngine);
    }
}

//页面跳转
 Intent intent = FlutterActivity.withCachedEngine("my_engine_id").build(this);

咸鱼开源的Flutter_Boost对这个启动做了优化，等后续我会持续更新的,这里先按照官方的文档学习

3 添加一个Flutter Fragment

英文官方文档在这里 Adding a Flutter Fragment to an Android app

public class SecondActivity extends FragmentActivity {
    private static final String TAG_FLUTTER_FRAGMENT = "flutter_fragment";
    private FlutterFragment flutterFragment;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);
        FragmentManager fragmentManager = getSupportFragmentManager();

        if (flutterFragment == null) {
            flutterFragment = FlutterFragment.createDefault();
            FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
            fragmentTransaction.add(R.id.container, flutterFragment).commit();
        }
    }
}

除此之外你还需要将Activity生命周期方法回调给FlutterFragment,这里就直接贴原文的代码了。

public class MyActivity extends FragmentActivity {
    @Override
    public void onPostResume() {
        super.onPostResume();
        flutterFragment.onPostResume();
    }

    @Override
    protected void onNewIntent(@NonNull Intent intent) {
        flutterFragment.onNewIntent(intent);
    }

    @Override
    public void onBackPressed() {
        flutterFragment.onBackPressed();
    }

    @Override
    public void onRequestPermissionsResult(
        int requestCode,
        @NonNull String[] permissions,
        @NonNull int[] grantResults
    ) {
        flutterFragment.onRequestPermissionsResult(
            requestCode,
            permissions,
            grantResults
        );
    }

    @Override
    public void onUserLeaveHint() {
        flutterFragment.onUserLeaveHint();
    }

    @Override
    public void onTrimMemory(int level) {
        super.onTrimMemory(level);
        flutterFragment.onTrimMemory(level);
    }
}

当然还是会出现短暂延迟，你也可以采取之前提到的“预热引擎”的方式，由于代码高度一致，这里不再展示了。