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[Fireperf][AASA] FirstDrawDoneListener (#4041)
* WIP * handler * handle bug prior to api 26 * tests * copyright * improve tests * comment fix * improve tests * comment * backport View.isAttachedToWindow() * improved registerForNextDraw_delaysAddingListenerForAPIsBelow26 * remove LayoutChangeListener * add check to mmake sure OnAttachStateChangeListener removes itself * mcreate helper isAliveAndAttached * improve test with Robolectric ShadowLooper
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‎firebase-perf/src/main/java/com/google/firebase/perf/util/FirstDrawDoneListener.java

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// Copyright 2022 Google LLC
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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//
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// You may obtain a copy of the License at
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package com.google.firebase.perf.util;
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import android.os.Build;
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import android.os.Handler;
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import android.os.Looper;
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import android.view.View;
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import android.view.ViewTreeObserver;
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import androidx.annotation.RequiresApi;
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import java.util.concurrent.atomic.AtomicReference;
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/**
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* OnDrawListener that unregisters itself and invokes callback when the next draw is done. This API
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* 16+ implementation is an approximation of the initial display time. {@link
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* android.view.Choreographer#postFrameCallback} is an Android API that provides a simpler and more
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* accurate initial display time, but it was bugged before API 30, hence we use this backported
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* implementation.
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*/
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@RequiresApi(Build.VERSION_CODES.JELLY_BEAN)
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public class FirstDrawDoneListener implements ViewTreeObserver.OnDrawListener {
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private final Handler mainThreadHandler = new Handler(Looper.getMainLooper());
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private final AtomicReference<View> viewReference;
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private final Runnable callback;
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/** Registers a post-draw callback for the next draw of a view. */
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public static void registerForNextDraw(View view, Runnable drawDoneCallback) {
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final FirstDrawDoneListener listener = new FirstDrawDoneListener(view, drawDoneCallback);
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// Handle bug prior to API 26 where OnDrawListener from the floating ViewTreeObserver is not
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// merged into the real ViewTreeObserver.
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// https://android.googlesource.com/platform/frameworks/base/+/9f8ec54244a5e0343b9748db3329733f259604f3
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if (Build.VERSION.SDK_INT < 26 && !isAliveAndAttached(view)) {
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view.addOnAttachStateChangeListener(
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new View.OnAttachStateChangeListener() {
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@Override
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public void onViewAttachedToWindow(View view) {
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view.getViewTreeObserver().addOnDrawListener(listener);
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view.removeOnAttachStateChangeListener(this);
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}
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@Override
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public void onViewDetachedFromWindow(View view) {
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view.removeOnAttachStateChangeListener(this);
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}
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});
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} else {
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view.getViewTreeObserver().addOnDrawListener(listener);
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}
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}
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private FirstDrawDoneListener(View view, Runnable callback) {
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this.viewReference = new AtomicReference<>(view);
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this.callback = callback;
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}
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@Override
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public void onDraw() {
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// Set viewReference to null so any onDraw past the first is a no-op
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View view = viewReference.getAndSet(null);
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if (view == null) {
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return;
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}
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// OnDrawListeners cannot be removed within onDraw, so we remove it with a
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// GlobalLayoutListener
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view.getViewTreeObserver()
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.addOnGlobalLayoutListener(() -> view.getViewTreeObserver().removeOnDrawListener(this));
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mainThreadHandler.postAtFrontOfQueue(callback);
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}
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/**
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* Helper to avoid <a
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* href="https://android.googlesource.com/platform/frameworks/base/+/9f8ec54244a5e0343b9748db3329733f259604f3">bug
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* prior to API 26</a>, where the floating ViewTreeObserver's OnDrawListeners are not merged into
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* the real ViewTreeObserver during attach.
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*
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* @return true if the View is already attached and the ViewTreeObserver is not a floating
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* placeholder.
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*/
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private static boolean isAliveAndAttached(View view) {
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return view.getViewTreeObserver().isAlive() && isAttachedToWindow(view);
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}
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/** Backport {@link View#isAttachedToWindow()} which is API 19+ only. */
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private static boolean isAttachedToWindow(View view) {
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if (Build.VERSION.SDK_INT >= 19) {
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return view.isAttachedToWindow();
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}
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return view.getWindowToken() != null;
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}
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}

‎firebase-perf/src/test/java/com/google/firebase/perf/util/FirstDrawDoneListenerTest.java

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// Copyright 2022 Google LLC
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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//
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// You may obtain a copy of the License at
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package com.google.firebase.perf.util;
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import static com.google.common.truth.Truth.assertThat;
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import static org.mockito.Mockito.inOrder;
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import static org.mockito.Mockito.mock;
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import static org.mockito.Mockito.never;
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import static org.mockito.Mockito.times;
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import static org.mockito.Mockito.verify;
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import static org.robolectric.Shadows.shadowOf;
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import android.os.Build;
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import android.os.Handler;
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import android.os.Looper;
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import android.view.View;
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import android.view.ViewTreeObserver;
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import android.view.ViewTreeObserver.OnDrawListener;
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import androidx.test.core.app.ApplicationProvider;
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import java.lang.reflect.Field;
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import java.util.ArrayList;
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import java.util.List;
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import java.util.concurrent.CopyOnWriteArrayList;
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import org.junit.Before;
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import org.junit.Test;
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import org.junit.runner.RunWith;
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import org.mockito.InOrder;
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import org.robolectric.RobolectricTestRunner;
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import org.robolectric.annotation.Config;
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import org.robolectric.annotation.LooperMode;
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/** Unit tests for {@link FirstDrawDoneListener}. */
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@RunWith(RobolectricTestRunner.class)
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@LooperMode(LooperMode.Mode.PAUSED)
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public class FirstDrawDoneListenerTest {
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private View testView;
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@Before
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public void setUp() {
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testView = new View(ApplicationProvider.getApplicationContext());
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}
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@Test
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@Config(sdk = 25)
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public void registerForNextDraw_delaysAddingListenerForAPIsBelow26()
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throws NoSuchFieldException, IllegalAccessException, ClassNotFoundException {
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ArrayList<OnDrawListener> mOnDrawListeners =
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initViewTreeObserverWithListener(testView.getViewTreeObserver());
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assertThat(mOnDrawListeners.size()).isEqualTo(0);
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// OnDrawListener is not registered, it is delayed for later
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FirstDrawDoneListener.registerForNextDraw(testView, () -> {});
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assertThat(mOnDrawListeners.size()).isEqualTo(0);
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// Register listener after the view is attached to a window
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List<View.OnAttachStateChangeListener> attachListeners = dispatchAttachedToWindow(testView);
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assertThat(mOnDrawListeners.size()).isEqualTo(1);
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assertThat(mOnDrawListeners.get(0)).isInstanceOf(FirstDrawDoneListener.class);
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assertThat(attachListeners).isEmpty();
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}
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@Test
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@Config(sdk = 26)
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public void registerForNextDraw_directlyAddsListenerForApi26AndAbove()
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throws NoSuchFieldException, IllegalAccessException {
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ArrayList<OnDrawListener> mOnDrawListeners =
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initViewTreeObserverWithListener(testView.getViewTreeObserver());
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assertThat(mOnDrawListeners.size()).isEqualTo(0);
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// Immediately register an OnDrawListener to ViewTreeObserver
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FirstDrawDoneListener.registerForNextDraw(testView, () -> {});
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assertThat(mOnDrawListeners.size()).isEqualTo(1);
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assertThat(mOnDrawListeners.get(0)).isInstanceOf(FirstDrawDoneListener.class);
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}
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@Test
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@Config(sdk = 26)
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public void onDraw_postsCallbackToFrontOfQueue() {
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Handler handler = new Handler(Looper.getMainLooper());
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Runnable drawDoneCallback = mock(Runnable.class);
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Runnable otherCallback = mock(Runnable.class);
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InOrder inOrder = inOrder(drawDoneCallback, otherCallback);
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FirstDrawDoneListener.registerForNextDraw(testView, drawDoneCallback);
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handler.post(otherCallback); // 3rd in queue
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handler.postAtFrontOfQueue(otherCallback); // 2nd in queue
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testView.getViewTreeObserver().dispatchOnDraw(); // 1st in queue
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verify(drawDoneCallback, never()).run();
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verify(otherCallback, never()).run();
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// Execute all posted tasks
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shadowOf(Looper.getMainLooper()).idle();
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inOrder.verify(drawDoneCallback, times(1)).run();
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inOrder.verify(otherCallback, times(2)).run();
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inOrder.verifyNoMoreInteractions();
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}
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@Test
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@Config(sdk = 26)
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public void onDraw_unregistersItself_inLayoutChangeListener()
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throws NoSuchFieldException, IllegalAccessException {
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ArrayList<OnDrawListener> mOnDrawListeners =
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initViewTreeObserverWithListener(testView.getViewTreeObserver());
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FirstDrawDoneListener.registerForNextDraw(testView, () -> {});
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assertThat(mOnDrawListeners.size()).isEqualTo(1);
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// Does not remove OnDrawListener before onDraw, even if OnGlobalLayout is triggered
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testView.getViewTreeObserver().dispatchOnGlobalLayout();
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assertThat(mOnDrawListeners.size()).isEqualTo(1);
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// Removes OnDrawListener in the next OnGlobalLayout after onDraw
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testView.getViewTreeObserver().dispatchOnDraw();
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testView.getViewTreeObserver().dispatchOnGlobalLayout();
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assertThat(mOnDrawListeners.size()).isEqualTo(0);
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}
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/**
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* Returns ViewTreeObserver.mOnDrawListeners field through reflection. Since reflections are
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* employed, prefer to be used in tests with fixed API level using @Config(sdk = X).
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*
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* @param vto ViewTreeObserver instance to initialize and return the mOnDrawListeners from
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*/
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private static ArrayList<OnDrawListener> initViewTreeObserverWithListener(ViewTreeObserver vto)
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throws NoSuchFieldException, IllegalAccessException {
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// Adding a listener forces ViewTreeObserver.mOnDrawListeners to be initialized and non-null.
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OnDrawListener placeHolder = () -> {};
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vto.addOnDrawListener(placeHolder);
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vto.removeOnDrawListener(placeHolder);
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// Obtain mOnDrawListeners field through reflection
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Field mOnDrawListeners =
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android.view.ViewTreeObserver.class.getDeclaredField("mOnDrawListeners");
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mOnDrawListeners.setAccessible(true);
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ArrayList<OnDrawListener> listeners = (ArrayList<OnDrawListener>) mOnDrawListeners.get(vto);
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assertThat(listeners).isNotNull();
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assertThat(listeners.size()).isEqualTo(0);
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return listeners;
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}
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/**
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* Simulates {@link View}'s dispatchAttachedToWindow() on API 25 using reflection.
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*
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* <p>This only simulates the part where dispatchAttachedToWindow() notifies the list of {@link
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* View.OnAttachStateChangeListener}.
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*
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* @param view the view in which we are simulating dispatchAttachedToWindow().
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* @return list of {@link View.OnAttachStateChangeListener} from the input {@link View}
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*/
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private static List<View.OnAttachStateChangeListener> dispatchAttachedToWindow(View view)
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throws ClassNotFoundException, NoSuchFieldException, IllegalAccessException {
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assert Build.VERSION.SDK_INT == 25;
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Class<?> listenerInfo = Class.forName("android.view.View$ListenerInfo");
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Field mListenerInfo = View.class.getDeclaredField("mListenerInfo");
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mListenerInfo.setAccessible(true);
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Object li = mListenerInfo.get(view);
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assertThat(li).isNotNull();
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Field mOnAttachStateChangeListeners =
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listenerInfo.getDeclaredField("mOnAttachStateChangeListeners");
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mOnAttachStateChangeListeners.setAccessible(true);
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CopyOnWriteArrayList<View.OnAttachStateChangeListener> listeners =
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(CopyOnWriteArrayList<View.OnAttachStateChangeListener>)
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mOnAttachStateChangeListeners.get(li);
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assertThat(listeners).isNotNull();
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assertThat(listeners).isNotEmpty();
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for (View.OnAttachStateChangeListener listener : listeners) {
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listener.onViewAttachedToWindow(view);
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}
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return listeners;
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}
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}

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