Fix empty notif view flicker on keyguard

As the shade collapses, there is very slight gap between
when the shade collapses and status bar state changes to
KEYGUARD. During this gap, the empty notif view visibility
changes from VISIBLE->INVISIBLE->VISIBLE->GONE.

Ensure that the empty notif view alpha does not change
if the shade is collapsed.

Fixes: 333445519
Test: atest StackScrollAlgorithmTest
Flag: None
Change-Id: I16450015f13b5394e63f304d23f20e5e76da5d59

2 files changed, 23 insertions, 2 deletions

diff --git a/packages/SystemUI/src/com/android/systemui/statusbar/notification/stack/StackScrollAlgorithm.java b/packages/SystemUI/src/com/android/systemui/statusbar/notification/stack/StackScrollAlgorithm.java
index e980794d23dd..d0cebae40c5a 100644
--- a/packages/SystemUI/src/com/android/systemui/statusbar/notification/stack/StackScrollAlgorithm.java
+++ b/packages/SystemUI/src/com/android/systemui/statusbar/notification/stack/StackScrollAlgorithm.java
@@ -169,6 +169,14 @@ public class StackScrollAlgorithm {
                 }
             }
 
+            // On the final call to {@link #resetViewState}, the alpha is set back to 1f but
+            // ambientState.isExpansionChanging() is now false. This causes a flicker on the
+            // EmptyShadeView after the shade is collapsed. Make sure the empty shade view
+            // isn't visible unless the shade is expanded.
+            if (view instanceof EmptyShadeView && ambientState.getExpansionFraction() == 0f) {
+                viewState.setAlpha(0f);
+            }
+
             // For EmptyShadeView if on keyguard, we need to control the alpha to create
             // a nice transition when the user is dragging down the notification panel.
             if (view instanceof EmptyShadeView && ambientState.isOnKeyguard()) {
diff --git a/packages/SystemUI/tests/src/com/android/systemui/statusbar/notification/stack/StackScrollAlgorithmTest.kt b/packages/SystemUI/tests/src/com/android/systemui/statusbar/notification/stack/StackScrollAlgorithmTest.kt
index 82725d656bb9..a6fb7187ff5f 100644
--- a/packages/SystemUI/tests/src/com/android/systemui/statusbar/notification/stack/StackScrollAlgorithmTest.kt
+++ b/packages/SystemUI/tests/src/com/android/systemui/statusbar/notification/stack/StackScrollAlgorithmTest.kt
@@ -394,8 +394,20 @@ class StackScrollAlgorithmTest : SysuiTestCase() {
     }
 
     @Test
+    fun resetViewStates_shadeCollapsed_emptyShadeViewBecomesTransparent() {
+        ambientState.expansionFraction = 0f
+        stackScrollAlgorithm.initView(context)
+        hostView.removeAllViews()
+        hostView.addView(emptyShadeView)
+
+        stackScrollAlgorithm.resetViewStates(ambientState, /* speedBumpIndex= */ 0)
+
+        assertThat(emptyShadeView.viewState.alpha).isEqualTo(0f)
+    }
+
+    @Test
     fun resetViewStates_isOnKeyguard_emptyShadeViewBecomesOpaque() {
-        ambientState.setStatusBarState(StatusBarState.SHADE)
+        ambientState.setStatusBarState(StatusBarState.KEYGUARD)
         ambientState.fractionToShade = 0.25f
         stackScrollAlgorithm.initView(context)
         hostView.removeAllViews()
@@ -403,7 +415,8 @@ class StackScrollAlgorithmTest : SysuiTestCase() {
 
         stackScrollAlgorithm.resetViewStates(ambientState, /* speedBumpIndex= */ 0)
 
-        assertThat(emptyShadeView.viewState.alpha).isEqualTo(1f)
+        val expected = getContentAlpha(ambientState.fractionToShade)
+        assertThat(emptyShadeView.viewState.alpha).isEqualTo(expected)
     }
 
     @Test