多个 Flutter 页面或视图

实验性

Experimental

目前在 Android 和 iOS 上，除了第一个 Flutter 实例以外，其他每一个实例的内存占用量大约为 180kB。

The current memory footprint for each additional Flutter instance beyond the first instance is ~180kB on Android and iOS.

随着 Flutter 2.0.0 正式版的发布，Flutter 实例之间将通过宿主平台的 平台通道（或 Pigeon）进行处理。若您对我们平台通信的里程碑感兴趣，或是有其他多个 Flutter 实例的问题，请查看 Issue 72009。

As of the 2.0.0 release, communication between Flutter instances is handled using platform channels (or Pigeon) through the host platform. To see our roadmap on communication, or other multiple-Flutters issues, see Issue 72009.

使用场景

Scenarios

在 Flutter 2.0.0 发布之前，FlutterEngine 的多个实例和相关的 UI 可以同时启动，但是每个实例都有明显的延迟和固定的内存占用。

Before Flutter 2.0.0, multiple instances of FlutterEngine and its associated UI could be launched, but each instance came with significant latency and fixed memory cost.

多个 Flutter 实例在以下场景有优势：

Multiple Flutter instances can be useful in the following scenarios:

• 集成了 Flutter 界面的应用，其位置并不在路由栈的叶子节点上，且其可能是混合路由栈，即 native -> Flutter -> native -> Flutter。

  An application where the integrated Flutter screen is not a leaf node of the navigation graph, and the navigation stack might be a hybrid mixture of native -> Flutter -> native -> Flutter.

• 多个 Flutter view 同时集成在同一个页面上，且同时显示。

  A screen where multiple partial screen Flutter views might be integrated and visible at once.

使用多个 Flutter 实例的优势在于，每一个实例互相独立，各自维护路由栈、UI 和应用状态。这简化了应用程序整体的状态保持考虑，并且进一步模块化。了解更多关于多个 Flutter 使用的动机和场景，请查看 flutter.cn/go/multiple-flutters。

The advantage of using multiple Flutter instances is that each instance is independent and maintains its own internal navigation stack, UI, and application states. This simplifies the overall application code’s responsibility for state keeping and improves modularity. More details on the scenarios motivating the usage of multiple Flutters can be found at flutter.dev/go/multiple-flutters.

Flutter 2.0.0 大幅减少了额外的 Flutter 引擎的内存占用，从 Android 上 约 19MB，iOS 上 约 13MB，降至 约 180kB。将固定成本减少了约 99% 后，您可以更自由地将多个 Flutter 集成至您的应用。

The 2.0.0 Flutter release drastically reduces the memory footprint of additional Flutter engines from ~19MB on Android and ~13MB on iOS, to ~180kB on Android and iOS. This ~99% fixed cost reduction allows the multiple Flutters pattern to be used more liberally in your add-to-app integration.

组件

Components

在 Android 和 iOS 上添加多个 Flutter 实例的主要 API 是基于新的 FlutterEngineGroup 类 (Android API, iOS API) 来创建 FlutterEngine 的，而不是通过以前的 FlutterEngine 构造。

The primary API for adding multiple Flutter instances on both Android and iOS is based on a new FlutterEngineGroup class (Android API, iOS API) to construct FlutterEngines, rather than the FlutterEngine constructors used previously.

尽管 FlutterEngine API 的用法简洁明了，但从 FlutterEngineGroup 生成的 FlutterEngine 具有常用共享资源（例如 GPU 上下文、字体度量和隔离线程的快照）的性能优势，从而加快首次渲染的速度、降低延迟并降低内存占用。

Whereas the FlutterEngine API was direct and easier to consume, the FlutterEngine spawned from the same FlutterEngineGroup have the performance advantage of sharing many of the common, reusable resources such as the GPU context, font metrics, and isolate group snapshot, leading to a faster initial rendering latency and lower memory footprint.

• 由 FlutterEngineGroup 生成的 FlutterEngine 可以用来关联 UI 相关的类，例如 FlutterActivity 或 FlutterViewController，与通常构造缓存的 FlutterEngine 类似。

  FlutterEngines spawned from FlutterEngineGroup can be used to connect to UI classes like FlutterActivity or FlutterViewController in the same way as normally constructed cached FlutterEngines.

• 第一个 FlutterEngineGroup 生成的 FlutterEngine 不需要持续保活，只要有 1 个可用的 FlutterEngine，就可以随时在各个 FlutterEngine 之间共享资源。

  The first FlutterEngine spawned from the FlutterEngineGroup doesn’t need to continue surviving in order for subsequent FlutterEngines to share resources as long as there’s at least 1 living FlutterEngine at all times.

• 通过 FlutterEngineGroup 生成的首个 FlutterEngine 与使用先前的构造方法构造的 FlutterEngine 有相同的性能特征。

  Creating the very first FlutterEngine from a FlutterEngineGroup has the same performance characteristics as constructing a FlutterEngine using the constructors did previously.

• 当所有由 FlutterEngineGroup 构造的 FlutterEngine 都被销毁后，下一个创建的 FlutterEngine 与首个创造的性能特征相同。

  When all FlutterEngines from a FlutterEngineGroup are destroyed, the next FlutterEngine created has the same performance characteristics as the very first engine.

• FlutterEngineGroup 本身不需要持续保活。将其销毁后，已生成的 FlutterEngine 不受影响，但无法继续在现有共享的基础上创建新引擎。

  The FlutterEngineGroup itself doesn’t need to live beyond all of the spawned engines. Destroying the FlutterEngineGroup doesn’t affect existing spawned FlutterEngines but does remove the ability to spawn additional FlutterEngines that share resources with existing spawned engines.

示例

Samples

您可以在 GitHub 仓库 上找到在 Android 和 iOS 上使用 FlutterEngineGroup 的示例。

You can find a sample demonstrating how to use FlutterEngineGroup on both Android and iOS on GitHub.