Ensure the layer drawable callback is set when loading from theme

Previously we would skip setting the changing configurations and callback
if the drawable had been loaded post-inflation from a theme attribute.

Bug: 30756548
Change-Id: Ia5457723ae8a62506a7562299d3fe78ec21f8030

graphics/java/android/graphics/drawable/LayerDrawable.java

@@ -269,7 +269,8 @@ public class LayerDrawable extends Drawable implements Drawable.Callback {
 
             // If the layer doesn't have a drawable or unresolved theme
             // attribute for a drawable, attempt to parse one from the child
-            // element.
+            // element. If multiple child elements exist, we'll only use the
+            // first one.
             if (layer.mDrawable == null && (layer.mThemeAttrs == null ||
                     layer.mThemeAttrs[R.styleable.LayerDrawableItem_drawable] == 0)) {
                 while ((type = parser.next()) == XmlPullParser.TEXT) {
@@ -279,13 +280,12 @@ public class LayerDrawable extends Drawable implements Drawable.Callback {
                             + ": <item> tag requires a 'drawable' attribute or "
                             + "child tag defining a drawable");
                 }
-                layer.mDrawable = Drawable.createFromXmlInner(r, parser, attrs, theme);
-            }
 
-            if (layer.mDrawable != null) {
+                // We found a child drawable. Take ownership.
+                layer.mDrawable = Drawable.createFromXmlInner(r, parser, attrs, theme);
+                layer.mDrawable.setCallback(this);
                 state.mChildrenChangingConfigurations |=
                         layer.mDrawable.getChangingConfigurations();
-                layer.mDrawable.setCallback(this);
             }
 
             addLayer(layer);
@@ -387,7 +387,19 @@ public class LayerDrawable extends Drawable implements Drawable.Callback {
 
         final Drawable dr = a.getDrawable(R.styleable.LayerDrawableItem_drawable);
         if (dr != null) {
+            if (layer.mDrawable != null) {
+                // It's possible that a drawable was already set, in which case
+                // we should clear the callback. We may have also integrated the
+                // drawable's changing configurations, but we don't have enough
+                // information to revert that change.
+                layer.mDrawable.setCallback(null);
+            }
+
+            // Take ownership of the new drawable.
             layer.mDrawable = dr;
+            layer.mDrawable.setCallback(this);
+            state.mChildrenChangingConfigurations |=
+                    layer.mDrawable.getChangingConfigurations();
         }
     }