FlutterEngine

@interface FlutterEngine : NSObject

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).

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:.

  • 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

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

    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.

    projectOrNil

    The FlutterDartProject to run.

  • 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

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

    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.

    projectOrNil

    The FlutterDartProject to run.

    allowHeadlessExecution

    Whether or not to allow this instance to continue running after passing a nil FlutterViewController to -setViewController:.

  • Unavailable

    The default initializer is not available for this object. Callers must use -[FlutterEngine initWithName:project:].

    Declaration

    Objective-C

    - (instancetype)init;
  • Unavailable

    Undocumented

    Declaration

    Objective-C

    + (instancetype)new NS_UNAVAILABLE;
  • 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.

    Declaration

    Objective-C

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

    Parameters

    entrypoint

    The name of a top-level function from the same Dart library that contains the app’s main() function. If this is 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.

  • 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.

    Declaration

    Objective-C

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

    Parameters

    entrypoint

    The name of a top-level function from a Dart library. If 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. 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.

  • 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;
  • 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;
  • 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 (readwrite, nonatomic) FlutterViewController *viewController;
  • The FlutterMethodChannel used for localization related platform messages, such as setting the locale.

    Declaration

    Objective-C

    @property (readonly, nonatomic) int *localizationChannel;
  • The FlutterMethodChannel used for navigation related platform messages.

    Declaration

    Objective-C

    @property (readonly, nonatomic) int *navigationChannel;
  • The FlutterMethodChannel used for core platform messages, such as information about the screen orientation.

    Declaration

    Objective-C

    @property (readonly, nonatomic) int *platformChannel;
  • The FlutterMethodChannel used to communicate text input events to the Dart Isolate.

    Declaration

    Objective-C

    @property (readonly, nonatomic) int *textInputChannel;
  • The FlutterBasicMessageChannel used to communicate app lifecycle events to the Dart Isolate.

    Declaration

    Objective-C

    @property (readonly, nonatomic) int *lifecycleChannel;
  • The FlutterBasicMessageChannel used for communicating system events, such as memory pressure events.

    Declaration

    Objective-C

    @property (readonly, nonatomic) int *systemChannel;
  • The FlutterBasicMessageChannel used for communicating user settings such as clock format and text scale.

    Declaration

    Objective-C

    @property (readonly, nonatomic) int *settingsChannel;
  • 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 (readonly, nonatomic) NSURL *observatoryUrl;