# FlutterEngine

Objective-C

    @interface FlutterEngine
        : NSObject <FlutterTextureRegistry, FlutterPluginRegistry>

Swift

    class FlutterEngine : NSObject, FlutterTextureRegistry, FlutterPluginRegistry

The FlutterEngine class coordinates a single instance of execution for a `FlutterDartProject`. It may have zero or one `FlutterViewController` at a time, which can be specified via `-setViewController:`. `FlutterViewController`‘s `initWithEngine` initializer will automatically call `-setViewController:` for itself.

A FlutterEngine can be created independently of a `FlutterViewController` for headless execution. It can also persist across the lifespan of multiple `FlutterViewController` instances to maintain state and/or asynchronous tasks (such as downloading a large file).

A FlutterEngine can also be used to prewarm the Dart execution environment and reduce the latency of showing the Flutter screen when a `FlutterViewController` is created and presented. See http://flutter.dev/docs/development/add-to-app/performance for more details on loading performance.

Alternatively, you can simply create a new `FlutterViewController` with only a `FlutterDartProject`. That `FlutterViewController` will internally manage its own instance of a FlutterEngine, but will not guarantee survival of the engine beyond the life of the ViewController.

A newly initialized FlutterEngine will not actually run a Dart Isolate until either `-runWithEntrypoint:` or `-runWithEntrypoint:libraryURI` is invoked. One of these methods must be invoked before calling `-setViewController:`.

- `-init`

  Default initializer for a FlutterEngine.

  Threads created by this FlutterEngine will appear as “FlutterEngine #” in Instruments. The prefix can be customized using `initWithName`.

  The engine will execute the project located in the bundle with the identifier “io.flutter.flutter.app” (the default for Flutter projects).

  A newly initialized engine will not run until either `-runWithEntrypoint:` or `-runWithEntrypoint:libraryURI:` is called.

  FlutterEngine created with this method will have allowHeadlessExecution set to `YES`. This means that the engine will continue to run regardless of whether a `FlutterViewController` is attached to it or not, until `-destroyContext:` is called or the process finishes.

  #### Declaration

  Objective-C

      - (nonnull instancetype)init;

  Swift

      convenience init()

- `-initWithName:`

  Initialize this FlutterEngine.

  The engine will execute the project located in the bundle with the identifier “io.flutter.flutter.app” (the default for Flutter projects).

  A newly initialized engine will not run until either `-runWithEntrypoint:` or `-runWithEntrypoint:libraryURI:` is called.

  FlutterEngine created with this method will have allowHeadlessExecution set to `YES`. This means that the engine will continue to run regardless of whether a `FlutterViewController` is attached to it or not, until `-destroyContext:` is called or the process finishes.

  #### Declaration

  Objective-C

      - (nonnull instancetype)initWithName:(nonnull NSString *)labelPrefix;

  Swift

      convenience init(name labelPrefix: String)

  #### Parameters

  `labelPrefix` | The label prefix used to identify threads for this instance. Should be unique across FlutterEngine instances, and is used in instrumentation to label the threads used by this FlutterEngine.

- `-initWithName:project:`

  Initialize this FlutterEngine with a `FlutterDartProject`.

  If the FlutterDartProject is not specified, the FlutterEngine will attempt to locate the project in a default location (the flutter_assets folder in the iOS application bundle).

  A newly initialized engine will not run the `FlutterDartProject` until either `-runWithEntrypoint:` or `-runWithEntrypoint:libraryURI:` is called.

  FlutterEngine created with this method will have allowHeadlessExecution set to `YES`. This means that the engine will continue to run regardless of whether a `FlutterViewController` is attached to it or not, until `-destroyContext:` is called or the process finishes.

  #### Declaration

  Objective-C

      - (nonnull instancetype)initWithName:(nonnull NSString *)labelPrefix
                                   project:(nullable FlutterDartProject *)project;

  Swift

      convenience init(name labelPrefix: String, project: FlutterDartProject?)

  #### Parameters

  `labelPrefix` | The label prefix used to identify threads for this instance. Should be unique across FlutterEngine instances, and is used in instrumentation to label the threads used by this FlutterEngine.
  `project` | The `FlutterDartProject` to run.

- `-initWithName:project:allowHeadlessExecution:`

  Initialize this FlutterEngine with a `FlutterDartProject`.

  If the FlutterDartProject is not specified, the FlutterEngine will attempt to locate the project in a default location (the flutter_assets folder in the iOS application bundle).

  A newly initialized engine will not run the `FlutterDartProject` until either `-runWithEntrypoint:` or `-runWithEntrypoint:libraryURI:` is called.

  #### Declaration

  Objective-C

      - (nonnull instancetype)initWithName:(nonnull NSString *)labelPrefix
                                   project:(nullable FlutterDartProject *)project
                    allowHeadlessExecution:(BOOL)allowHeadlessExecution;

  Swift

      convenience init(name labelPrefix: String, project: FlutterDartProject?, allowHeadlessExecution: Bool)

  #### Parameters

  `labelPrefix` | The label prefix used to identify threads for this instance. Should be unique across FlutterEngine instances, and is used in instrumentation to label the threads used by this FlutterEngine.
  `project` | The `FlutterDartProject` to run.
  `allowHeadlessExecution` | Whether or not to allow this instance to continue running after passing a nil `FlutterViewController` to `-setViewController:`.

- `-initWithName:project:allowHeadlessExecution:restorationEnabled:`

  Initialize this FlutterEngine with a `FlutterDartProject`.

  If the FlutterDartProject is not specified, the FlutterEngine will attempt to locate the project in a default location (the flutter_assets folder in the iOS application bundle).

  A newly initialized engine will not run the `FlutterDartProject` until either `-runWithEntrypoint:` or `-runWithEntrypoint:libraryURI:` is called.

  #### Declaration

  Objective-C

      - (nonnull instancetype)initWithName:(nonnull NSString *)labelPrefix
                                   project:(nullable FlutterDartProject *)project
                    allowHeadlessExecution:(BOOL)allowHeadlessExecution
                        restorationEnabled:(BOOL)restorationEnabled;

  Swift

      init(name labelPrefix: String, project: FlutterDartProject?, allowHeadlessExecution: Bool, restorationEnabled: Bool)

  #### Parameters

  `labelPrefix` | The label prefix used to identify threads for this instance. Should be unique across FlutterEngine instances, and is used in instrumentation to label the threads used by this FlutterEngine.
  `project` | The `FlutterDartProject` to run.
  `allowHeadlessExecution` | Whether or not to allow this instance to continue running after passing a nil `FlutterViewController` to `-setViewController:`.
  `restorationEnabled` | Whether state restoration is enabled. When true, the framework will wait for the attached view controller to provide restoration data.

- `-run`

  Runs a Dart program on an Isolate from the main Dart library (i.e. the library that contains `main()`), using `main()` as the entrypoint (the default for Flutter projects), and using “/” (the default route) as the initial route.

  The first call to this method will create a new Isolate. Subsequent calls will return immediately and have no effect.

  #### Declaration

  Objective-C

      - (BOOL)run;

  Swift

      func run() -> Bool

  #### Return Value

  YES if the call succeeds in creating and running a Flutter Engine instance; NO otherwise.

- `-runWithEntrypoint:`

  Runs a Dart program on an Isolate from the main Dart library (i.e. the library that contains `main()`), using “/” (the default route) as the initial route.

  The first call to this method will create a new Isolate. Subsequent calls will return immediately and have no effect.

  #### Declaration

  Objective-C

      - (BOOL)runWithEntrypoint:(nullable NSString *)entrypoint;

  Swift

      func run(withEntrypoint entrypoint: String?) -> Bool

  #### Parameters

  `entrypoint` | The name of a top-level function from the same Dart library that contains the app’s main() function. If this is FlutterDefaultDartEntrypoint (or nil) it will default to `main()`. If it is not the app’s main() function, that function must be decorated with `@pragma(vm:entry-point)` to ensure the method is not tree-shaken by the Dart compiler.

  #### Return Value

  YES if the call succeeds in creating and running a Flutter Engine instance; NO otherwise.

- `-runWithEntrypoint:initialRoute:`

  Runs a Dart program on an Isolate from the main Dart library (i.e. the library that contains `main()`).

  The first call to this method will create a new Isolate. Subsequent calls will return immediately and have no effect.

  #### Declaration

  Objective-C

      - (BOOL)runWithEntrypoint:(nullable NSString *)entrypoint
                   initialRoute:(nullable NSString *)initialRoute;

  Swift

      func run(withEntrypoint entrypoint: String?, initialRoute: String?) -> Bool

  #### Parameters

  `entrypoint` | The name of a top-level function from the same Dart library that contains the app’s main() function. If this is FlutterDefaultDartEntrypoint (or nil), it will default to `main()`. If it is not the app’s main() function, that function must be decorated with `@pragma(vm:entry-point)` to ensure the method is not tree-shaken by the Dart compiler.
  `initialRoute` | The name of the initial Flutter `Navigator` `Route` to load. If this is FlutterDefaultInitialRoute (or nil), it will default to the “/” route.

  #### Return Value

  YES if the call succeeds in creating and running a Flutter Engine instance; NO otherwise.

- `-runWithEntrypoint:libraryURI:`

  Runs a Dart program on an Isolate using the specified entrypoint and Dart library, which may not be the same as the library containing the Dart program’s `main()` function.

  The first call to this method will create a new Isolate. Subsequent calls will return immediately and have no effect.

  #### Declaration

  Objective-C

      - (BOOL)runWithEntrypoint:(nullable NSString *)entrypoint
                     libraryURI:(nullable NSString *)uri;

  Swift

      func run(withEntrypoint entrypoint: String?, libraryURI uri: String?) -> Bool

  #### Parameters

  `entrypoint` | The name of a top-level function from a Dart library. If this is FlutterDefaultDartEntrypoint (or nil); this will default to `main()`. If it is not the app’s main() function, that function must be decorated with `@pragma(vm:entry-point)` to ensure the method is not tree-shaken by the Dart compiler.
  `uri` | The URI of the Dart library which contains the entrypoint method (example “package:foo_package/main.dart”). If nil, this will default to the same library as the `main()` function in the Dart program.

  #### Return Value

  YES if the call succeeds in creating and running a Flutter Engine instance; NO otherwise.

- `-runWithEntrypoint:libraryURI:initialRoute:`

  Runs a Dart program on an Isolate using the specified entrypoint and Dart library, which may not be the same as the library containing the Dart program’s `main()` function.

  The first call to this method will create a new Isolate. Subsequent calls will return immediately and have no effect.

  #### Declaration

  Objective-C

      - (BOOL)runWithEntrypoint:(nullable NSString *)entrypoint
                     libraryURI:(nullable NSString *)libraryURI
                   initialRoute:(nullable NSString *)initialRoute;

  Swift

      func run(withEntrypoint entrypoint: String?, libraryURI: String?, initialRoute: String?) -> Bool

  #### Parameters

  `entrypoint` | The name of a top-level function from a Dart library. If this is FlutterDefaultDartEntrypoint (or nil); this will default to `main()`. If it is not the app’s main() function, that function must be decorated with `@pragma(vm:entry-point)` to ensure the method is not tree-shaken by the Dart compiler.
  `libraryURI` | The URI of the Dart library which contains the entrypoint method (example “package:foo_package/main.dart”). If nil, this will default to the same library as the `main()` function in the Dart program.
  `initialRoute` | The name of the initial Flutter `Navigator` `Route` to load. If this is FlutterDefaultInitialRoute (or nil), it will default to the “/” route.

  #### Return Value

  YES if the call succeeds in creating and running a Flutter Engine instance; NO otherwise.

- `-runWithEntrypoint:libraryURI:initialRoute:entrypointArgs:`

  Runs a Dart program on an Isolate using the specified entrypoint and Dart library, which may not be the same as the library containing the Dart program’s `main()` function.

  The first call to this method will create a new Isolate. Subsequent calls will return immediately and have no effect.

  #### Declaration

  Objective-C

      - (BOOL)runWithEntrypoint:(nullable NSString *)entrypoint
                     libraryURI:(nullable NSString *)libraryURI
                   initialRoute:(nullable NSString *)initialRoute
                 entrypointArgs:(nullable NSArray<NSString *> *)entrypointArgs;

  Swift

      func run(withEntrypoint entrypoint: String?, libraryURI: String?, initialRoute: String?, entrypointArgs: [String]?) -> Bool

  #### Parameters

  `entrypoint` | The name of a top-level function from a Dart library. If this is FlutterDefaultDartEntrypoint (or nil); this will default to `main()`. If it is not the app’s main() function, that function must be decorated with `@pragma(vm:entry-point)` to ensure the method is not tree-shaken by the Dart compiler.
  `libraryURI` | The URI of the Dart library which contains the entrypoint method (example “package:foo_package/main.dart”). If nil, this will default to the same library as the `main()` function in the Dart program.
  `initialRoute` | The name of the initial Flutter `Navigator` `Route` to load. If this is FlutterDefaultInitialRoute (or nil), it will default to the “/” route.
  `entrypointArgs` | Arguments passed as a list of string to Dart’s entrypoint function.

  #### Return Value

  YES if the call succeeds in creating and running a Flutter Engine instance; NO otherwise.

- `-destroyContext`

  Destroy running context for an engine.

  This method can be used to force the FlutterEngine object to release all resources. After sending this message, the object will be in an unusable state until it is deallocated. Accessing properties or sending messages to it will result in undefined behavior or runtime errors.

  #### Declaration

  Objective-C

      - (void)destroyContext;

  Swift

      func destroyContext()

- `-ensureSemanticsEnabled`

  Ensures that Flutter will generate a semantics tree.

  This is enabled by default if certain accessibility services are turned on by the user, or when using a Simulator. This method allows a user to turn semantics on when they would not ordinarily be generated and the performance overhead is not a concern, e.g. for UI testing. Note that semantics should never be programmatically turned off, as it would potentially disable accessibility services an end user has requested.

  This method must only be called after launching the engine via `-runWithEntrypoint:` or `-runWithEntryPoint:libraryURI`.

  Although this method returns synchronously, it does not guarantee that a semantics tree is actually available when the method returns. It synchronously ensures that the next frame the Flutter framework creates will have a semantics tree.

  You can subscribe to semantics updates via `NSNotificationCenter` by adding an observer for the name `FlutterSemanticsUpdateNotification`. The `object` parameter will be the `FlutterViewController` associated with the semantics update. This will asynchronously fire after a semantics tree has actually built (which may be some time after the frame has been rendered).

  #### Declaration

  Objective-C

      - (void)ensureSemanticsEnabled;

  Swift

      func ensureSemanticsEnabled()

- `viewController`

  Sets the `FlutterViewController` for this instance. The FlutterEngine must be running (e.g. a successful call to `-runWithEntrypoint:` or `-runWithEntrypoint:libraryURI`) before calling this method. Callers may pass nil to remove the viewController and have the engine run headless in the current process.

  A FlutterEngine can only have one `FlutterViewController` at a time. If there is already a `FlutterViewController` associated with this instance, this method will replace the engine’s current viewController with the newly specified one.

  Setting the viewController will signal the engine to start animations and drawing, and unsetting it will signal the engine to stop animations and drawing. However, neither will impact the state of the Dart program’s execution.

  #### Declaration

  Objective-C

      @property (nonatomic, weak) FlutterViewController *_Nullable viewController;

  Swift

      weak var viewController: FlutterViewController? { get set }

- `localizationChannel`

  The `FlutterMethodChannel` used for localization related platform messages, such as setting the locale.

  Can be nil after `destroyContext` is called.

  #### Declaration

  Objective-C

      @property (nonatomic, readonly, nullable) FlutterMethodChannel *localizationChannel;

  Swift

      var localizationChannel: FlutterMethodChannel? { get }

- `navigationChannel`

  The `FlutterMethodChannel` used for navigation related platform messages.

  Can be nil after `destroyContext` is called.

  See

  Navigation Channel

  See

  Navigator Widget

  #### Declaration

  Objective-C

      @property (nonatomic, readonly) FlutterMethodChannel *_Nonnull navigationChannel;

  Swift

      var navigationChannel: FlutterMethodChannel { get }

- `restorationChannel`

  The `FlutterMethodChannel` used for restoration related platform messages.

  Can be nil after `destroyContext` is called.

  See

  Restoration Channel

  #### Declaration

  Objective-C

      @property (nonatomic, readonly) FlutterMethodChannel *_Nonnull restorationChannel;

  Swift

      var restorationChannel: FlutterMethodChannel { get }

- `platformChannel`

  The `FlutterMethodChannel` used for core platform messages, such as information about the screen orientation.

  Can be nil after `destroyContext` is called.

  #### Declaration

  Objective-C

      @property (nonatomic, readonly) FlutterMethodChannel *_Nonnull platformChannel;

  Swift

      var platformChannel: FlutterMethodChannel { get }

- `textInputChannel`

  The `FlutterMethodChannel` used to communicate text input events to the Dart Isolate.

  Can be nil after `destroyContext` is called.

  See

  Text Input Channel

  #### Declaration

  Objective-C

      @property (nonatomic, readonly) FlutterMethodChannel *_Nonnull textInputChannel;

  Swift

      var textInputChannel: FlutterMethodChannel { get }

- `lifecycleChannel`

  The `FlutterBasicMessageChannel` used to communicate app lifecycle events to the Dart Isolate.

  Can be nil after `destroyContext` is called.

  See

  Lifecycle Channel

  #### Declaration

  Objective-C

      @property (nonatomic, readonly) FlutterBasicMessageChannel *_Nonnull lifecycleChannel;

  Swift

      var lifecycleChannel: FlutterBasicMessageChannel { get }

- `systemChannel`

  The `FlutterBasicMessageChannel` used for communicating system events, such as memory pressure events.

  Can be nil after `destroyContext` is called.

  See

  System Channel

  #### Declaration

  Objective-C

      @property (nonatomic, readonly) FlutterBasicMessageChannel *_Nonnull systemChannel;

  Swift

      var systemChannel: FlutterBasicMessageChannel { get }

- `settingsChannel`

  The `FlutterBasicMessageChannel` used for communicating user settings such as clock format and text scale.

  Can be nil after `destroyContext` is called.

  #### Declaration

  Objective-C

      @property (nonatomic, readonly) FlutterBasicMessageChannel *_Nonnull settingsChannel;

  Swift

      var settingsChannel: FlutterBasicMessageChannel { get }

- `keyEventChannel`

  The `FlutterBasicMessageChannel` used for communicating key events from physical keyboards

  Can be nil after `destroyContext` is called.

  #### Declaration

  Objective-C

      @property (nonatomic, readonly) FlutterBasicMessageChannel *_Nonnull keyEventChannel;

  Swift

      var keyEventChannel: FlutterBasicMessageChannel { get }

- `observatoryUrl`

  The `NSURL` of the observatory for the service isolate.

  This is only set in debug and profile runtime modes, and only after the observatory service is ready. In release mode or before the observatory has started, it returns `nil`.

  #### Declaration

  Objective-C

      @property (nonatomic, readonly, nullable) NSURL *observatoryUrl;

  Swift

      var observatoryUrl: URL? { get }

- `binaryMessenger`

  The `FlutterBinaryMessenger` associated with this FlutterEngine (used for communicating with channels).

  #### Declaration

  Objective-C

      @property (nonatomic, readonly) NSObject<FlutterBinaryMessenger> *_Nonnull binaryMessenger;

  Swift

      var binaryMessenger: FlutterBinaryMessenger { get }

- `isolateId`

  The UI Isolate ID of the engine.

  This property will be nil if the engine is not running.

  #### Declaration

  Objective-C

      @property (nonatomic, copy, readonly, nullable) NSString *isolateId;

  Swift

      var isolateId: String? { get }

- `isGpuDisabled`

  Whether or not GPU calls are allowed.

  Typically this is set when the app is backgrounded and foregrounded.

  #### Declaration

  Objective-C

      @property (nonatomic) BOOL isGpuDisabled;

  Swift

      var isGpuDisabled: Bool { get set }

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