Fixed a RTL layouting bug with LinearLayout

When the RTL properties of a horizontal LinearLayout
changed, nobody enforced the view to be layouted anew,
even though its layout is dependent on the layout
direction. This could lead to stale layouts being
temporarily layouted the wrong way.

Bug: 20495301
Change-Id: I979c8d86ee711626b2901b65ebdf007c1eb1c0fa

core/java/android/util/LayoutDirection.java

@@ -26,6 +26,12 @@ public final class LayoutDirection {
     // No instantiation
     private LayoutDirection() {}
 
+    /**
+     * An undefined layout direction.
+     * @hide
+     */
+    public static final int UNDEFINED = -1;
+
     /**
      * Horizontal layout direction is from Left to Right.
      */

core/java/android/view/View.java

@@ -1871,6 +1871,12 @@ public class View implements Drawable.Callback, KeyEvent.Callback,
     @Retention(RetentionPolicy.SOURCE)
     public @interface ResolvedLayoutDir {}
 
+    /**
+     * A flag to indicate that the layout direction of this view has not been defined yet.
+     * @hide
+     */
+    public static final int LAYOUT_DIRECTION_UNDEFINED = LayoutDirection.UNDEFINED;
+
     /**
      * Horizontal layout direction of this view is from Left to Right.
      * Use with {@link #setLayoutDirection}.

core/java/android/widget/LinearLayout.java

@@ -185,6 +185,8 @@ public class LinearLayout extends ViewGroup {
     private int mShowDividers;
     private int mDividerPadding;
 
+    private int mLayoutDirection = View.LAYOUT_DIRECTION_UNDEFINED;
+
     public LinearLayout(Context context) {
         this(context, null);
     }
@@ -1567,6 +1569,17 @@ public class LinearLayout extends ViewGroup {
         }
     }
 
+    @Override
+    public void onRtlPropertiesChanged(@ResolvedLayoutDir int layoutDirection) {
+        super.onRtlPropertiesChanged(layoutDirection);
+        if (layoutDirection != mLayoutDirection) {
+            mLayoutDirection = layoutDirection;
+            if (mOrientation == HORIZONTAL) {
+                requestLayout();
+            }
+        }
+    }
+
     /**
      * Position the children during a layout pass if the orientation of this
      * LinearLayout is set to {@link #HORIZONTAL}.