Fix wrong alpha set on background drawable

Fixes: 250728240

When the Activity transition was stopped before
the background started fading in, the background
would be set to an alpha = 1. This was the wrong
value, it should have been 255.

Test: new test
Change-Id: Ia1026d17aa516db5d1faf0115f946ee64c15d710

core/java/android/app/EnterTransitionCoordinator.java

@@ -650,7 +650,7 @@ class EnterTransitionCoordinator extends ActivityTransitionCoordinator {
             if (decorView != null) {
                 Drawable drawable = decorView.getBackground();
                 if (drawable != null) {
-                    drawable.setAlpha(1);
+                    drawable.setAlpha(255);
                 }
             }
         }

core/tests/coretests/AndroidManifest.xml

@@ -1654,6 +1654,12 @@
             android:exported="true">
         </activity>
 
+        <activity android:name="android.app.activity.ActivityTransitionDrawableTest$TestActivity"
+                  android:exported="true"
+                  android:enabled="true"
+                  android:theme="@style/Theme">
+        </activity>
+
         <activity
             android:name="android.os.TestVrActivity"
             android:enableVrMode="com.android.frameworks.coretests/android.os.TestVrActivity$TestVrListenerService">

core/tests/coretests/src/android/app/activity/ActivityTransitionDrawableTest.java

@@ -0,0 +1,122 @@
+/*
+ * Copyright 2022 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.app.activity;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import android.app.Activity;
+import android.app.ActivityOptions;
+import android.content.Intent;
+import android.os.Bundle;
+import android.platform.test.annotations.Presubmit;
+import android.transition.Fade;
+import android.view.View;
+import android.view.Window;
+
+import androidx.test.filters.MediumTest;
+import androidx.test.rule.ActivityTestRule;
+import androidx.test.runner.AndroidJUnit4;
+
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import java.util.ArrayList;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Test for verifying Activity Transitions Drawable behavior
+ */
+@RunWith(AndroidJUnit4.class)
+@MediumTest
+@Presubmit
+public class ActivityTransitionDrawableTest {
+    private static final String LAUNCH_ON_START = "launch on start";
+
+    @Rule
+    public final ActivityTestRule<TestActivity> mActivityTestRule =
+            new ActivityTestRule<>(TestActivity.class, true);
+
+    @Test
+    public void stopTransitionDrawableAlphaRestored() throws Throwable {
+        mActivityTestRule.runOnUiThread(() -> {
+            Activity activity = mActivityTestRule.getActivity();
+            Intent intent = new Intent(activity, TestActivity.class);
+            intent.putExtra(LAUNCH_ON_START, true);
+            Bundle bundle = ActivityOptions.makeSceneTransitionAnimation(activity).toBundle();
+            activity.startActivity(intent, bundle);
+        });
+
+        assertThat(TestActivity.activityAdded.await(5, TimeUnit.SECONDS)).isTrue();
+        TestActivity topActivity = TestActivity.sInstances.get(2);
+        TestActivity middleActivity = TestActivity.sInstances.get(1);
+        assertThat(topActivity.startedLatch.await(5, TimeUnit.SECONDS)).isTrue();
+        assertThat(middleActivity.stoppedLatch.await(5, TimeUnit.SECONDS)).isTrue();
+        mActivityTestRule.runOnUiThread(() -> {
+            assertThat(middleActivity.getWindow().getDecorView().getBackground().getAlpha())
+                    .isEqualTo(255);
+        });
+    }
+
+    public static class TestActivity extends Activity {
+        public static final ArrayList<TestActivity> sInstances = new ArrayList<TestActivity>();
+        public static CountDownLatch activityAdded = new CountDownLatch(3);
+
+        private boolean mLaunchOnStart = false;
+        public CountDownLatch startedLatch = new CountDownLatch(1);
+        public CountDownLatch stoppedLatch = new CountDownLatch(1);
+
+        @Override
+        protected void onCreate(Bundle savedInstanceState) {
+            getWindow().requestFeature(Window.FEATURE_ACTIVITY_TRANSITIONS);
+            getWindow().setAllowEnterTransitionOverlap(false);
+            setContentView(new View(this));
+            Fade longFade = new Fade();
+            longFade.setDuration(2000);
+            getWindow().setEnterTransition(longFade);
+            getWindow().setExitTransition(longFade);
+            super.onCreate(savedInstanceState);
+            mLaunchOnStart = getIntent().getBooleanExtra(LAUNCH_ON_START, false);
+            sInstances.add(this);
+            activityAdded.countDown();
+        }
+
+        @Override
+        protected void onStart() {
+            super.onStart();
+            if (mLaunchOnStart) {
+                mLaunchOnStart = false;
+                Intent intent = new Intent(this, TestActivity.class);
+                startActivity(intent);
+            }
+            startedLatch.countDown();
+        }
+
+        @Override
+        protected void onStop() {
+            super.onStop();
+            stoppedLatch.countDown();
+        }
+
+        @Override
+        protected void onDestroy() {
+            super.onDestroy();
+            sInstances.remove(this);
+        }
+    }
+}