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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#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#58837
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79
shell/platform/android/io/flutter/embedding/android/MotionEventTracker.java
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package io.flutter.embedding.android; | ||
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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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