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Track motion events for reuse post gesture disambiguation (flutter#19484
) This change makes it so that we track all the motion events encountered by `FlutterView` and all of its subviews in the `MotionEventTracker` class, indexed by a unique `MotionEventId`. This identifier is then passed to the Flutter framework as seen in flutter/flutter#60930. Once the gestures take part in gesture disambiguation and are sent back to the engine, we look-up the original motion event using the `MotionEventId` and dispatch it to the platform. Bug: flutter/flutter#58837
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79 changes: 79 additions & 0 deletions
79
shell/platform/android/io/flutter/embedding/android/MotionEventTracker.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,79 @@ | ||
| package io.flutter.embedding.android; | ||
|
|
||
| import android.util.LongSparseArray; | ||
| import android.view.MotionEvent; | ||
| import androidx.annotation.Nullable; | ||
| import java.util.PriorityQueue; | ||
| import java.util.concurrent.atomic.AtomicLong; | ||
|
|
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| /** Tracks the motion events received by the FlutterView. */ | ||
| public final class MotionEventTracker { | ||
|
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| /** Represents a unique identifier corresponding to a motion event. */ | ||
| public static class MotionEventId { | ||
| private static final AtomicLong ID_COUNTER = new AtomicLong(0); | ||
| private final long id; | ||
|
|
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| private MotionEventId(long id) { | ||
| this.id = id; | ||
| } | ||
|
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| public static MotionEventId from(long id) { | ||
| return new MotionEventId(id); | ||
| } | ||
|
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| public static MotionEventId createUnique() { | ||
| return MotionEventId.from(ID_COUNTER.incrementAndGet()); | ||
| } | ||
|
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| public long getId() { | ||
| return id; | ||
| } | ||
| } | ||
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| private final LongSparseArray<MotionEvent> eventById; | ||
| private final PriorityQueue<Long> unusedEvents; | ||
| private static MotionEventTracker INSTANCE; | ||
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| public static MotionEventTracker getInstance() { | ||
| if (INSTANCE == null) { | ||
| INSTANCE = new MotionEventTracker(); | ||
| } | ||
| return INSTANCE; | ||
| } | ||
|
|
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| private MotionEventTracker() { | ||
| eventById = new LongSparseArray<>(); | ||
| unusedEvents = new PriorityQueue<>(); | ||
| } | ||
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| /** Tracks the event and returns a unique MotionEventId identifying the event. */ | ||
| public MotionEventId track(MotionEvent event) { | ||
| MotionEventId eventId = MotionEventId.createUnique(); | ||
| eventById.put(eventId.id, event); | ||
| unusedEvents.add(eventId.id); | ||
| return eventId; | ||
| } | ||
|
|
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| /** | ||
| * Returns the MotionEvent corresponding to the eventId while discarding all the motion events | ||
| * that occured prior to the event represented by the eventId. Returns null if this event was | ||
| * popped or discarded. | ||
| */ | ||
| @Nullable | ||
| public MotionEvent pop(MotionEventId eventId) { | ||
| // remove all the older events. | ||
| while (!unusedEvents.isEmpty() && unusedEvents.peek() < eventId.id) { | ||
| eventById.remove(unusedEvents.poll()); | ||
| } | ||
|
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| // remove the current event from the heap if it exists. | ||
| if (!unusedEvents.isEmpty() && unusedEvents.peek() == eventId.id) { | ||
| unusedEvents.poll(); | ||
| } | ||
|
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| MotionEvent event = eventById.get(eventId.id); | ||
| eventById.remove(eventId.id); | ||
| return event; | ||
| } | ||
| } |
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