This guide describes how to add a single Flutter screen to an existing Android app. A Flutter screen can be added as a normal, opaque screen, or as a see-through, translucent screen. Both options are described in this guide.

本指南讲述了如何在一个现有的 Android 应用中添加单个 Flutter 页面。 添加到应用中的单个 Flutter 页面可以是不透明的普通页面，也可以是透明的页面。 这两种页面的使用都会在本指南中提到。

Flutter provides FlutterActivity to display a Flutter experience within an Android app. Like any other Activity, FlutterActivity must be registered in your AndroidManifest.xml. Add the following XML to your AndroidManifest.xml file under your application tag:

Flutter 提供了 FlutterActivity，用于在 Android 应用内部展示一个 Flutter 的交互界面。 和其他的 Activity 一样，FlutterActivity 必须在项目的 AndroidManifest.xml 文件中注册。 将下边的 XML 代码添加到你的 AndroidManifest.xml 文件中的 application 标签内：

<activity
  android:name="io.flutter.embedding.android.FlutterActivity"
  android:theme="@style/LaunchTheme"
  android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
  android:hardwareAccelerated="true"
  android:windowSoftInputMode="adjustResize"
  />

The reference to @style/LaunchTheme can be replaced by any Android theme that want to apply to your FlutterActivity. The choice of theme dictates the colors applied to Android's system chrome, like Android's navigation bar, and to the background color of the FlutterActivity just before the Flutter UI renders itself for the first time.

上述代码中的 @style/LaunchTheme 可以替换为想要在你的 FlutterActivity 中使用的其他 Android 主题。 主题的选择决定 Android 系统展示框架所使用的颜色， 例如 Android 的导航栏，以及 Flutter UI 自身的第一次渲染前 FlutterActivity 的背景色。

With FlutterActivity registered in your manifest file, add code to launch FlutterActivity from whatever point in your app that you'd like. The following example shows FlutterActivity being launched from an OnClickListener.

在你的清单文件中注册了 FlutterActivity 之后， 根据需要，你可以在应用中的任意位置添加打开 FlutterActivity 的代码。 下边的代码展示了如何在 OnClickListener 的点击事件中打开 FlutterActivity。

:::note

Make sure to use the following import:

确保使用如下的语句导入：

import io.flutter.embedding.android.FlutterActivity;

:::

{% tabs "android-language" %} {% tab "Jetpack Compose" %}

MyButton(onClick = {
    startActivity(
        FlutterActivity.createDefaultIntent(this)
    )
})

@Composable
fun MyButton(onClick: () -> Unit) {
    Button(onClick = onClick) {
        Text("Launch Flutter!")
    }
}

{% endtab %} {% tab "Kotlin" %}

myButton.setOnClickListener {
  startActivity(
    FlutterActivity.createDefaultIntent(this)
  )
}

{% endtab %} {% tab "Java" %}

myButton.setOnClickListener(new OnClickListener() {
  @Override
  public void onClick(View v) {
    startActivity(
      FlutterActivity.createDefaultIntent(currentActivity)
    );
  }
});

{% endtab %} {% endtabs %}

The previous example assumes that your Dart entrypoint is called main(), and your initial Flutter route is '/'. The Dart entrypoint can't be changed using Intent, but the initial route can be changed using Intent. The following example demonstrates how to launch a FlutterActivity that initially renders a custom route in Flutter.

上述的例子假定了你的 Dart 代码入口是调用 main()，并且你的 Flutter 初始路由是 '/'。 Dart 代码入口不能通过 Intent 改变，但是初始路由可以通过 Intent 来修改。 下面的例子讲解了如何打开一个自定义 Flutter 初始路由的 FlutterActivity。

{% tabs "android-language" %} {% tab "Jetpack Compose" %}

MyButton(onClick = {
  startActivity(
    FlutterActivity
      .withNewEngine()
      .initialRoute("/my_route")
      .build(this)
  )
})

@Composable
fun MyButton(onClick: () -> Unit) {
    Button(onClick = onClick) {
        Text("Launch Flutter!")
    }
}

{% endtab %} {% tab "Kotlin" %}

myButton.setOnClickListener {
  startActivity(
    FlutterActivity
      .withNewEngine()
      .initialRoute("/my_route")
      .build(this)
  )
}

{% endtab %} {% tab "Java" %}

myButton.addOnClickListener(new OnClickListener() {
  @Override
  public void onClick(View v) {
    startActivity(
      FlutterActivity
        .withNewEngine()
        .initialRoute("/my_route")
        .build(currentActivity)
      );
  }
});

{% endtab %} {% endtabs %}

Replace "/my_route" with your desired initial route.

可以用你想要的初始路由替换掉 "/my_route"。

The use of the withNewEngine() factory method configures a FlutterActivity that internally create its own FlutterEngine instance. This comes with a non-trivial initialization time. The alternative approach is to instruct FlutterActivity to use a pre-warmed, cached FlutterEngine, which minimizes Flutter's initialization time. That approach is discussed next.

工厂方法 withNewEngine() 可以用于配置一个 FlutterActivity， 它会在内部创建一个属于自己的 FlutterEngine 实例，这会有一个明显的初始化时间。 另外一种可选的做法是让 FlutterActivity 使用一个预热且缓存的 FlutterEngine， 这可以最小化 Flutter 初始化的时间。 这种方式接下来会讨论到。

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 默认会创建它自己的 FlutterEngine。 每一个 FlutterEngine 会有一个明显的预热时间。 这意味着加载一个标准的 FlutterActivity 时， 在你的 Flutter 交互页面可见之前会有一个短暂的延迟。 想要最小化这个延迟时间，你可以在抵达你的 FlutterActivity 之前， 初始化一个 FlutterEngine，然后使用这个已经预热好的 FlutterEngine。

To pre-warm a FlutterEngine, find a reasonable location in your app to instantiate a FlutterEngine. The following example arbitrarily pre-warms a FlutterEngine in the Application class:

要预热一个 FlutterEngine， 可以在你的应用中找一个合理的地方实例化一个 FlutterEngine。 下面的这个例子是在 Application 类中预先初始化一个 FlutterEngine：

{% tabs "android-language" %} {% tab "Kotlin" %}

class MyApplication : Application() {
  lateinit var flutterEngine : FlutterEngine

  override fun onCreate() {
    super.onCreate()

    // Instantiate a FlutterEngine.
    flutterEngine = FlutterEngine(this)

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

    // Cache the FlutterEngine to be used by FlutterActivity.
    FlutterEngineCache
      .getInstance()
      .put("my_engine_id", flutterEngine)
  }
}

{% endtab %} {% tab "Java" %}

public class MyApplication extends Application {
  public FlutterEngine flutterEngine;
  
  @Override
  public void onCreate() {
    super.onCreate();
    // Instantiate a FlutterEngine.
    flutterEngine = new FlutterEngine(this);

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

    // Cache the FlutterEngine to be used by FlutterActivity.
    FlutterEngineCache
      .getInstance()
      .put("my_engine_id", flutterEngine);
  }
}

{% endtab %} {% endtabs %}

The ID passed to the FlutterEngineCache can be whatever you want. Make sure that you pass the same ID to any FlutterActivity or FlutterFragment that should use the cached FlutterEngine. Using FlutterActivity with a cached FlutterEngine is discussed next.

传给 FlutterEngineCache 的 ID 可以是你想要的任何名称。 确保 FlutterActivity 或 FlutterFragment 在使用缓存的 FlutterEngine 时，传递了同样的 ID。 基于缓存的 FlutterEngine 来使用 FlutterActivity 会在后续讨论到。

:::note

To warm up a FlutterEngine, you must execute a Dart entrypoint. Keep in mind that the moment executeDartEntrypoint() is invoked, your Dart entrypoint method begins executing. If your Dart entrypoint invokes runApp() to run a Flutter app, then your Flutter app behaves as if it were running in a window of zero size until this FlutterEngine is attached to a FlutterActivity, FlutterFragment, or FlutterView. Make sure that your app behaves appropriately between the time you warm it up and the time you display Flutter content.

要预热一个 FlutterEngine，你必须执行一个 Dart 入口。 切记当 executeDartEntrypoint() 方法调用时，你的 Dart 入口方法就会开始执行。 如果你的 Dart 入口调用了 runApp() 来运行一个 Flutter 应用， 那么你的 Flutter 应用会像是运行在一个大小为零的窗口中， 直至 FlutterEngine 附属到一个 FlutterActivity，FlutterFragment 或 FlutterView。 请确保你的应用在开始预热到你展示 Flutter 内容中间的这段时间里表现正常。

:::

With a pre-warmed, cached FlutterEngine, you now need to instruct your FlutterActivity to use the cached FlutterEngine instead of creating a new one. To accomplish this, use FlutterActivity's withCachedEngine() builder:

要使用预热且缓存的 FlutterEngine 时， 让你的 FlutterActivity 从缓存中获取 FlutterEngine，而不是创建一个新的。 可以使用 FlutterActivity 的 withCachedEngine() 方法来实现：

{% tabs "android-language" %} {% tab "Kotlin" %}

myButton.setOnClickListener {
  startActivity(
    FlutterActivity
      .withCachedEngine("my_engine_id")
      .build(this)
  )
}

{% endtab %} {% tab "Java" %}

myButton.addOnClickListener(new OnClickListener() {
  @Override
  public void onClick(View v) {
    startActivity(
      FlutterActivity
        .withCachedEngine("my_engine_id")
        .build(currentActivity)
      );
  }
});

{% endtab %} {% endtabs %}

When using the withCachedEngine() factory method, pass the same ID that you used when caching the desired FlutterEngine.

当使用 withCachedEngine() 方法时，传递你缓存对应 FlutterEngine 时用的相同 ID。

Now, when you launch FlutterActivity, there is significantly less delay in the display of Flutter content.

现在，当你加载 FlutterActivity 时，在展示 Flutter 内容前的延迟会明显降低。

:::note

When using a cached FlutterEngine, that FlutterEngine outlives any FlutterActivity or FlutterFragment that displays it. Keep in mind that Dart code begins executing as soon as you pre-warm the FlutterEngine, and continues executing after the destruction of your FlutterActivity/FlutterFragment. To stop executing and clear resources, obtain your FlutterEngine from the FlutterEngineCache and destroy the FlutterEngine with FlutterEngine.destroy().

当使用一个缓存的 FlutterEngine 时， FlutterEngine 会比展示它的 FlutterActivity 或 FlutterFragment 存活得更久。 切记，Dart 代码会在你预热 FlutterEngine 时就开始执行， 并且在你的 FlutterActivity 或 FlutterFragment 销毁后继续运行。 要停止代码运行和清理相关资源，可以从 FlutterEngineCache 中获取你的 FlutterEngine， 然后使用 FlutterEngine.destroy() 来销毁 FlutterEngine。

:::

:::note

Runtime performance isn't the only reason that you might pre-warm and cache a FlutterEngine. A pre-warmed FlutterEngine executes Dart code independent from a FlutterActivity, which allows such a FlutterEngine to be used to execute arbitrary Dart code at any moment. Non-UI application logic can be executed in a FlutterEngine, like networking and data caching, and in background behavior within a Service or elsewhere. When using a FlutterEngine to execute behavior in the background, be sure to adhere to all Android restrictions on background execution.

运行时的性能考量并不是你会预热和缓存一个 FlutterEngine 的唯一原因。 一个预热的 FlutterEngine 会独立于 FlutterActivity 执行 Dart 代码， 即一个 FlutterEngine 可以在任意时刻用于执行任意代码。 非 UI 的应用逻辑可以在 FlutterEngine 中执行， 例如网络请求和数据缓存，以及在 Service 中或其他地方的后台行为。 当使用 FlutterEngine 在后台执行任务时，确保满足 Android 对于后台执行的所有限制。

:::

:::note

Flutter's debug/release builds have drastically different performance characteristics. To evaluate the performance of Flutter, use a release build.

Flutter 的 debug 与 release 构建体现了完全不同的性能。 评估 Flutter 的性能表现时，请使用 release 构建版本。

:::

{% include docs/add-to-app/android-initial-route-cached-engine.md %}

Most full-screen Flutter experiences are opaque. However, some apps would like to deploy a Flutter screen that looks like a modal, for example, a dialog or bottom sheet. Flutter supports translucent FlutterActivitys out of the box.

大部分的全屏 Flutter 交互页面是不透明的。 但是，一些应用可能会发布一个类似模态框的 Flutter 页面， 例如，一个对话框或者底部工作表。 Flutter 默认支持透明的 FlutterActivity。

To make your FlutterActivity translucent, make the following changes to the regular process of creating and launching a FlutterActivity.

要将你的 FlutterActivity 设置为透明， 在创建和加载 FlutterActivity 的常规步骤中做如下的变更。

Android requires a special theme property for Activitys that render with a translucent background. Create or update an Android theme with the following property:

Android 需要一个特殊的主题属性来让 Activity 以一个透明的背景渲染。 使用如下属性来创建或者修改一个 Android 主题：

<style name="MyTheme" parent="@style/MyParentTheme">
  <item name="android:windowIsTranslucent">true</item>
</style>

Then, apply the translucent theme to your FlutterActivity.

然后，将透明主题应用到你的 FlutterActivity。

<activity
  android:name="io.flutter.embedding.android.FlutterActivity"
  android:theme="@style/MyTheme"
  android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
  android:hardwareAccelerated="true"
  android:windowSoftInputMode="adjustResize"
  />

Your FlutterActivity now supports translucency. Next, you need to launch your FlutterActivity with explicit transparency support.

现在你的 FlutterActivity 已经支持透明化。 下一步，你需要在打开 FlutterActivity 时显式启用透明模式。

To launch your FlutterActivity with a transparent background, pass the appropriate BackgroundMode to the IntentBuilder:

要打开透明背景的 FlutterActivity， 需要把对应的 BackgroundMode 传递给 IntentBuilder：

{% tabs "android-language" %} {% tab "Kotlin" %}

// Using a new FlutterEngine.
startActivity(
  FlutterActivity
    .withNewEngine()
    .backgroundMode(FlutterActivityLaunchConfigs.BackgroundMode.transparent)
    .build(this)
);

// Using a cached FlutterEngine.
startActivity(
  FlutterActivity
    .withCachedEngine("my_engine_id")
    .backgroundMode(FlutterActivityLaunchConfigs.BackgroundMode.transparent)
    .build(this)
);

{% endtab %} {% tab "Java" %}

// Using a new FlutterEngine.
startActivity(
  FlutterActivity
    .withNewEngine()
    .backgroundMode(FlutterActivityLaunchConfigs.BackgroundMode.transparent)
    .build(context)
);

// Using a cached FlutterEngine.
startActivity(
  FlutterActivity
    .withCachedEngine("my_engine_id")
    .backgroundMode(FlutterActivityLaunchConfigs.BackgroundMode.transparent)
    .build(context)
);

{% endtab %} {% endtabs %}

You now have a FlutterActivity with a transparent background.

现在你的 FlutterAcivity 的背景已经是透明的了。

:::note

Make sure that your Flutter content also includes a translucent background. If your Flutter UI paints a solid background color, then it still appears as though your FlutterActivity has an opaque background.

确保你的 Flutter 内容也有一个透明的背景。 如果你的 Flutter UI 绘制了一个特定的背景颜色， 那么你的 FlutterActivity 依旧看起来会是有一个不透明的背景。

:::