Package io.flutter.embedding.engine.systemchannels

Class SettingsChannel.ConfigurationQueue

java.lang.Object

io.flutter.embedding.engine.systemchannels.SettingsChannel.ConfigurationQueue

Enclosing class:

SettingsChannel

public static class SettingsChannel.ConfigurationQueue
extends Object

A FIFO queue that maintains generations of configurations that are potentially used by the Flutter application.

Platform configurations needed by the Flutter app (for example, text scale factor) are retrived on the platform thread, serialized and sent to the Flutter application running on the Flutter UI thread. However, configurations exposed as functions that take parameters are typically not serializable. To allow the Flutter app to access these configurations, one possible solution is to create dart bindings that allow the Flutter framework to invoke these functions via JNI synchronously. To ensure the serialized configuration and these functions represent the same set of configurations at any given time, a "generation" id is used in these synchronous calls, to keep them consistent with the serialized configuration that the Flutter app most recently received and is currently using.

A unique generation identifier is generated by the SettingsChannel and associated with a configuration when it sends a serialized configuration to the Flutter framework. This queue keeps different generations of configurations that could be used by the Flutter framework, and cleans up old configurations that the Flutter framework no longer uses. When the Flutter framework invokes a function to access the configuration with a generation identifier, this queue finds the configuration with that identifier and also cleans up configurations that are no longer needed.

This mechanism is only needed because TypedValue#applyDimension does not take the current text scale factor as an input. Once the AndroidX API that allows us to query the scaled font size with a pure function is available, we can scrap this class and make the implementation much simpler.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	SettingsChannel.ConfigurationQueue.SentConfiguration

Constructor Summary

Constructors

Constructor	Description
ConfigurationQueue()

Method Summary

Modifier and Type	Method	Description
BasicMessageChannel.Reply	enqueueConfiguration(SettingsChannel.ConfigurationQueue.SentConfiguration config)	Adds the most recently sent SettingsChannel.ConfigurationQueue.SentConfiguration to the queue.
SettingsChannel.ConfigurationQueue.SentConfiguration	getConfiguration(int configGeneration)	Returns the SettingsChannel.ConfigurationQueue.SentConfiguration associated with the given configGeneration, and removes configurations older than the returned configurations from the queue as they are no longer needed.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ConfigurationQueue

public ConfigurationQueue()

Method Detail

getConfiguration

public SettingsChannel.ConfigurationQueue.SentConfiguration getConfiguration(int configGeneration)

Returns the SettingsChannel.ConfigurationQueue.SentConfiguration associated with the given configGeneration, and removes configurations older than the returned configurations from the queue as they are no longer needed.

enqueueConfiguration

@UiThread
@Nullable
public BasicMessageChannel.Reply enqueueConfiguration(SettingsChannel.ConfigurationQueue.SentConfiguration config)

Adds the most recently sent SettingsChannel.ConfigurationQueue.SentConfiguration to the queue.

Returns:

a BasicMessageChannel.Reply whose reply method must be called when the embedder receives the reply for the sent configuration, to properly clean up older configurations in the queue.