Do not allow to select non-selectable items via mouse.

Bug: 28101625
Change-Id: I9f6cd4e259f7860bbc6c74c4d24c43e2c3ba1047

packages/DocumentsUI/src/com/android/documentsui/dirlist/MultiSelectManager.java

@@ -1268,6 +1268,11 @@ public final class MultiSelectManager {
             notifySelectionChanged();
         }
 
+        @Override
+        public boolean onBeforeItemStateChange(String id, boolean nextState) {
+            return notifyBeforeItemStateChange(id, nextState);
+        }
+
         private class ViewScroller implements Runnable {
             /**
              * The number of milliseconds of scrolling at which scroll speed continues to increase.
@@ -1655,7 +1660,9 @@ public final class MultiSelectManager {
                         if (id != null) {
                             // The adapter inserts items for UI layout purposes that aren't associated
                             // with files.  Those will have a null model ID.  Don't select them.
-                            mSelection.add(id);
+                            if (canSelect(id)) {
+                                mSelection.add(id);
+                            }
                         }
                         if (isPossiblePositionNearestOrigin(column, columnStartIndex, columnEndIndex,
                                 row, rowStartIndex, rowEndIndex)) {
@@ -1668,6 +1675,21 @@ public final class MultiSelectManager {
             }
         }
 
+        /**
+         * @return True if the item is selectable.
+         */
+        private boolean canSelect(String id) {
+            // TODO: Simplify the logic, so the check whether we can select is done in one place.
+            // Consider injecting FragmentTuner, or move the checks from MultiSelectManager to
+            // Selection.
+            for (OnSelectionChangedListener listener : mOnSelectionChangedListeners) {
+                if (!listener.onBeforeItemStateChange(id, true)) {
+                    return false;
+                }
+            }
+            return true;
+        }
+
         /**
          * @return Returns true if the position is the nearest to the origin, or, in the case of the
          *     lower-right corner, whether it is possible that the position is the nearest to the
@@ -1700,6 +1722,7 @@ public final class MultiSelectManager {
          */
         static interface OnSelectionChangedListener {
             public void onSelectionChanged(Set<String> updatedSelection);
+            public boolean onBeforeItemStateChange(String id, boolean nextState);
         }
 
         void addOnSelectionChangedListener(OnSelectionChangedListener listener) {

packages/DocumentsUI/tests/src/com/android/documentsui/dirlist/MultiSelectManager_GridModelTest.java

@@ -76,6 +76,11 @@ public class MultiSelectManager_GridModelTest extends AndroidTestCase {
                     public void onSelectionChanged(Set<String> updatedSelection) {
                         lastSelection = updatedSelection;
                     }
+
+                    @Override
+                    public boolean onBeforeItemStateChange(String id, boolean nextState) {
+                        return true;
+                    }
                 });
     }