[TopAppBar] Updated the handling of liftOnScrollColor not override android:background.

PiperOrigin-RevId: 547883467

Author: pekingme

lib/java/com/google/android/material/appbar/AppBarLayout.java

@@ -36,6 +36,7 @@
 import android.graphics.drawable.ColorDrawable;
 import android.graphics.drawable.ColorStateListDrawable;
 import android.graphics.drawable.Drawable;
+import android.graphics.drawable.LayerDrawable;
 import android.os.Build;
 import android.os.Build.VERSION;
 import android.os.Build.VERSION_CODES;
@@ -74,6 +75,7 @@
 import androidx.core.view.accessibility.AccessibilityViewCommand;
 import androidx.customview.view.AbsSavedState;
 import com.google.android.material.animation.AnimationUtils;
+import com.google.android.material.animation.ArgbEvaluatorCompat;
 import com.google.android.material.appbar.AppBarLayout.BaseBehavior.SavedState;
 import com.google.android.material.internal.ThemeEnforcement;
 import com.google.android.material.motion.MotionUtils;
@@ -271,7 +273,6 @@ public AppBarLayout(@NonNull Context context, @Nullable AttributeSet attrs, int
       } else {
         initializeLiftOnScrollWithElevation(context, materialShapeDrawable);
       }
-      ViewCompat.setBackground(this, materialShapeDrawable);
     }
 
     liftOnScrollColorDuration = MotionUtils.resolveThemeDuration(context,
@@ -337,19 +338,34 @@ private ColorStateList getBackgroundCSL() {
   }
 
   private void initializeLiftOnScrollWithColor(MaterialShapeDrawable background) {
-    background.setAlpha(lifted ? 255 : 0);
-    background.setFillColor(liftOnScrollColor);
-    liftOnScrollColorUpdateListener = valueAnimator -> {
-      float alpha = (float) valueAnimator.getAnimatedValue();
-      background.setAlpha((int) alpha);
+    MaterialShapeDrawable liftBackground = new MaterialShapeDrawable();
+    liftBackground.setFillColor(liftOnScrollColor);
+    liftBackground.setAlpha(lifted ? 255 : 0);
+    background.setAlpha(lifted ? 0 : 255);
+
+    liftOnScrollColorUpdateListener =
+        valueAnimator -> {
+          float liftAlpha = (float) valueAnimator.getAnimatedValue();
+          background.setAlpha((int) (255f - liftAlpha));
+          liftBackground.setAlpha((int) liftAlpha);
+
+          if (!liftOnScrollListeners.isEmpty()) {
+            int mixedColor =
+                ArgbEvaluatorCompat.getInstance()
+                    .evaluate(
+                        liftAlpha / 255f,
+                        background.getResolvedTintColor(),
+                        liftBackground.getResolvedTintColor());
+            for (LiftOnScrollListener liftOnScrollListener : liftOnScrollListeners) {
+              if (background.getFillColor() != null) {
+                liftOnScrollListener.onUpdate(0, mixedColor);
+              }
+            }
+          }
+        };
 
-      for (LiftOnScrollListener liftOnScrollListener : liftOnScrollListeners) {
-        if (background.getFillColor() != null) {
-          liftOnScrollListener.onUpdate(
-              0, background.getFillColor().withAlpha((int) alpha).getDefaultColor());
-        }
-      }
-    };
+    LayerDrawable layerBackground = new LayerDrawable(new Drawable[] {background, liftBackground});
+    ViewCompat.setBackground(this, layerBackground);
   }
 
   private void initializeLiftOnScrollWithElevation(
@@ -365,6 +381,7 @@ private void initializeLiftOnScrollWithElevation(
         liftOnScrollListener.onUpdate(elevation, background.getResolvedTintColor());
       }
     };
+    ViewCompat.setBackground(this, background);
   }
 
   /**
@@ -1003,7 +1020,7 @@ boolean setLiftedState(boolean lifted, boolean force) {
     if (force && this.lifted != lifted) {
       this.lifted = lifted;
       refreshDrawableState();
-      if (liftOnScroll && getBackground() instanceof MaterialShapeDrawable) {
+      if (liftOnScroll && isLiftOnScrollCompatibleBackground()) {
         if (liftOnScrollColor != null) {
           startLiftOnScrollColorAnimation(
               lifted ? 0 : 255, lifted ? 255 : 0);
@@ -1017,6 +1034,21 @@ boolean setLiftedState(boolean lifted, boolean force) {
     return false;
   }
 
+  private boolean isLiftOnScrollCompatibleBackground() {
+    if (getBackground() instanceof MaterialShapeDrawable) {
+      return true;
+    }
+    if (getBackground() instanceof LayerDrawable) {
+      LayerDrawable layerBackground = (LayerDrawable) getBackground();
+      if (layerBackground.getNumberOfLayers() == 2
+          && layerBackground.getDrawable(0) instanceof MaterialShapeDrawable
+          && layerBackground.getDrawable(1) instanceof MaterialShapeDrawable) {
+        return true;
+      }
+    }
+    return false;
+  }
+
   private void startLiftOnScrollColorAnimation(
       float fromValue, float toValue) {
     if (liftOnScrollColorAnimator != null) {

testing/java/com/google/android/material/testapp/res/layout/design_appbar_toolbar_liftonscroll_color.xml

@@ -26,6 +26,7 @@
     android:id="@+id/app_bar"
     android:layout_height="wrap_content"
     android:layout_width="match_parent"
+    android:background="@color/material_blue_grey_900"
     app:liftOnScroll="true"
     app:liftOnScrollColor="@color/material_blue_grey_950">
 

tests/javatests/com/google/android/material/appbar/AppBarWithToolbarTest.java

@@ -22,6 +22,7 @@
 import static org.junit.Assert.assertEquals;
 
 import android.graphics.Rect;
+import android.graphics.drawable.LayerDrawable;
 import android.view.View;
 import android.view.ViewGroup;
 import androidx.coordinatorlayout.widget.CoordinatorLayout;
@@ -394,7 +395,19 @@ public void testLiftOnScrollColor() throws Throwable {
     final int appbarHeight = mAppBar.getHeight();
     final int longSwipeAmount = 3 * appbarHeight / 2;
 
-    assertEquals(0, ((MaterialShapeDrawable) mAppBar.getBackground()).getAlpha());
+    LayerDrawable background = (LayerDrawable) mAppBar.getBackground();
+    MaterialShapeDrawable backgroundLayer = (MaterialShapeDrawable) background.getDrawable(0);
+    MaterialShapeDrawable liftLayer = (MaterialShapeDrawable) background.getDrawable(1);
+
+    assertEquals(
+        mAppBar.getResources().getColor(R.color.material_blue_grey_900),
+        backgroundLayer.getResolvedTintColor());
+    assertEquals(
+        mAppBar.getResources().getColor(R.color.material_blue_grey_950),
+        liftLayer.getResolvedTintColor());
+
+    assertEquals(255, backgroundLayer.getAlpha());
+    assertEquals(0, liftLayer.getAlpha());
 
     // Perform a swipe-up gesture across the horizontal center of the screen.
     performVerticalSwipeUpGesture(
@@ -403,9 +416,7 @@ public void testLiftOnScrollColor() throws Throwable {
         originalAppbarBottom + 3 * longSwipeAmount / 2,
         longSwipeAmount);
 
-    assertEquals(255, ((MaterialShapeDrawable) mAppBar.getBackground()).getAlpha());
-    assertEquals(
-        mAppBar.getResources().getColor(R.color.material_blue_grey_950),
-        ((MaterialShapeDrawable) mAppBar.getBackground()).getFillColor().getDefaultColor());
+    assertEquals(0, backgroundLayer.getAlpha());
+    assertEquals(255, liftLayer.getAlpha());
   }
 }